Machine Tools - 2015-16

MA NUFA CT URI NG ENGI NEE RI NG

MACHINE TOOLS

(2015-16) Dr. G. R. C. PRADEEP E-mail: [email protected] 1

MACHINE TOOLS INTRODUCTION: •

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The process of metal cutting in which chip is formed is effected by a relative movement b/w the work piece and the hard edge of the cutting tool. The relative motion is produced by a combination of rotary and translatory motion of either work piece (or) tool (or)

both. The relative motion present between Work and Tool in various Machine Tools.

Dr. G. R. C. PRADEEP

Relative Motion Work Tool La t h e R T Shaper, Planer T T Drilling Fixed R&T Milling T R Surface Grinding T R Cylindrical Grinding R & T R Machine Tool

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The motion responsible for the cutting action is known as the primary motion or cutting motion. The motion responsible for gradually feeding the uncut portion is termed as the secondary motion or feed motion. Depending on the nature of these relativ e motions, various types of surfaces can be produced. The line generated by the CUTTING MOTION is called the GENERATRIX and the line generated from the FEED MOTION is called the DIRECTRIX. Various geometries can be obtained depending on the shapes of the Generatrix and the Directrix and their relative directions. They are represented in the following figures: Dr. G. R. C. PRADEEP

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Generation of various surfaces Process S.No Generatrix (G) Directrix (D) Surface obtained ( a ) S t r a i g h t Li n e S t r a i g h t Li n e P l a i n S u r f a c e Tracing of G (b) Circular Straight Line Cylindrical Surface Tracing of G (c) Circular Straight Line Plain Surface (Lines) Envelope of G Surface of revolution Tracing of G (d) Plain Curve Circular Dr. G. R. C. PRADEEP

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LATHE – MAIN PARTS

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CARRIAGE ASSEMBLY

Video 1

TOOLPOST (1) COMPOUND SLIDE (2) SWIVEL PLATE (2B) HANDWHEELS (2A, 3B, 5A) CROSS-SLIDE (3) SADDLE (4) APRON (5) CARRIAGE FEED MECHANISM (5C) Dr. G. R. C. PRADEEP

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SPECIFICATIONS OF LATHE 1) Height of centers over bed  U.K. spec. 2) Maximum swing over bed  USA spec. 3) Maximum swing over carriage 4) Maximum swing over Gap 5) Maximum distance b/w centers 6) Length of bed 7) No. of speeds and feeds etc. Dr. G. R. C. PRADEEP

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EARLY LATHES

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EARLY LATHES

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EARLY LATHES

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EARLY LATHES

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TYPES OF LATHES 1) Bench lathe: It is a very small lathe mounted on separately prepared bench or cabinet and used for small, precision works.

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2) Speed lathe: They do not have pr ovision for power feed and have no gear box, carriage, lead screw etc. Two or three spindle speeds are available by cone pulley arrangement. They are used for wood turning, polishing, metal spinning etc Dr. G. R. C. PRADEEP

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3) Engine lathe: In olden days lathe was driven by a steam engine. Hence the name is still in existence even after modern lathes are provided with motor drive.

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4) Tool Room La the: It is nothing but the engine lathe equipped with some extra attachments for accurate and precision work like taper turning attachment, follower rest, collets, different types of chucks etc. The bed is relatively small.

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5) Capstan & Turret lathes: These are sem i automatic type machines very useful for mass production (small lot sizes). Less skill is required for operator and wide range of operations can be performed. They carry special mechanisms for indexing their tool heads. They are provided with a front tool post which can hold 4 turning related tools and rear tool post which can hold 2 to 4 turning related tools. The turrets can hold only drilling related tools. The turning tools used in the rear tool post are reverse tools with reverse geometry.

Video 2,3

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Turret Indexing Backward travel of turret

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Turret Indexing in Capstan and Turret Lathes

Just before indexing at the end of the return stroke, the locking pin is withdrawn by the lever which is lifted at its other end by gradually riding against the hinged wedge as shown. Further backward travel of the turret slide causes rotation of the free head by the indexing pin and lever as shown. Rotation of the turret head by exact angle is accomplished by insertion of the locking pin in the next hole of the six equi-spaced holes.

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Turret Lathe

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Turret Lathe Layout

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Capstan Lathe

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Capstan Lathe Layout

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TurretLathe Capstanlathe 1. Turret head (square (or) 1. Turret head (round (or) square hexagonal) is mounted on (or) hexagonal) is mounted on saddle auxiliary slide that moves on guide ways provided on saddle 2. The above arrangement gives 2. Less rigidity, vibrations occur, rigidity as forces are hence suitable for lighter and transferred to bed. Hence smaller jobs (up to 60mm) and capable of ha ndling heavy precision work.

jobs (up to 200mm) and severe cutting conditions. 3 Tool travel is along entire bed 3. Tool travel is limited because of length auxiliary slide traverse limitation. 4. Tool feeding is slow and 4. Tool feeding is fast and causes causes fatigue to operator less fatigue to operator hands. hands 5. No tail stock 5. No tail stock Dr. G. R. C. PRADEEP

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6) Automatic lathes: These are designed so that all the working and Job handling movements of the complete Manufacturing process for a job are done automatically. No participation of the operator is required during the operation. They fall in the category of heavy duty, high speed lathes employed in mass production(large lot sizes). Geneva mechanism is used for indexing the turret. Video Types of automatic lathe: 4,5,6,7 1) According to type of stock material  Bar automatics;  Chucking automatics 2) According to No. of spindles  Single spindle;  Multiple spindle 3) According to the directions of the axis of m/c spindles  Horizontal;  Vertical Dr. G. R. C. PRADEEP

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The general purpose single spindle automatic lathes are widely used for quantity or mass production (by machining) of high quality fasteners; bolts, screws, studs, bushings, pins, shafts, rollers, handles and similar small metallic parts from long bars or tubes of regular section and also often from separate small blanks. Unlike the semiautomatic lathes, single spindle automats are : used always for producing jobs of rod, tubular or ring type and •

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of relatively smaller size. run fully automatically, including bar feeding and tool indexing, and continuously over a long duration repeating the same machining cycle for each product provided with up to five radial tool slides which are moved by cams mounted on a cam shaft of relatively smaller size and power but have high er spindle speeds Dr. G. R. C. PRADEEP

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Swiss type automatic lathe The characteristics and applications of these single spindle automatic lathes are : In respect of application: Used for precision machining of thin slender rod or tubular jobs, like components of small clocks and wrist watches in mass production. •

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Job Diameter range – 2 to 12 mm; Length range – 3 to size 30 mm. Dimensional accuracy and surface finish – almost as good as provided by grinding In respect of configuration and operation: There is no tailstock or turret High spindle speed (2000 – 10,000 rpm) for small job diameter. •

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The headstock travels enabling axial feed of the bar stock against the cutting tools as shown The cutting tools (up to five in number including two on the rocker arm) are fed radially Drilling and threading tools, if required, are moved axially using swivelling device(s) The cylindrical blanks are prefinished by grinding and are moved through a carbide guide bush Video 8

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7) Special – purpose lathes: These are designed to perform certain specified operations only. Video Eg: Facing lathe, vertical lathe, crank shaft lathe 9,10,11,12

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WORK HOLDING DEVICES 1) Chucks ---a) 3 Jaw – Self centering, smaller in size, used for round cross sections b) 4 Jaw – Not self centering, medium in size, used for round, square, rectangular cross sections.

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c) Collets– Fixed size. They are air operated or hand operated. Used in – Tool Room lathes, Bar Automatic Lathes, Vertical Milling m/c to hold end mills.

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d) Pneumatic Chucks – In chucking Automatics Note: In bar automatics the component is parted of from the bar and in chucking automatics, the component is released from the chuck and another blank is loaded from the magazine. e) Magnetic – Used for ferrous metals in Lathe, Milling, Surface Grinding machines for light works and also where Distortion is not permitted infor aerospace components. f) Vacuum – Similar to above,like used non ferrous metals

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2) Face plate – Used for large size work pieces of round, square, rectangular, and also very complex geometries not possible in any other devices. Dr. G. R. C. PRADEEP

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3) Carriers, Catch plates or Carrier Dogs – Used for supporting shafts, mandrels for imparting rotation. They clamp around the work piece and allow the rotary motion of the machine's spindle to be transmitted to the work piece.They are used in Lathes and also Cylindrical grinding operations.

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4) Centers – For supporting the rotation a) Live centre – used with face plate b) Dead centre – used in tail stock

Live centre

NonRevolving Dead centre

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Revolving Dead centre (Used for high speeds and high clamping pressures) Email: [email protected]

5) Mandrel – Used to support the work pieces and also for holding hollow parts to meet concentricity requirements Live Centre

Work piece

Dead Centre Face Plate Mandrel Carrier Dog Dr. G. R. C. PRADEEP

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6) Steady rest – mounted on bed, used for long heavy jobs that deflect centrally by self weight. 7) Follower rest – mounted on carriage and moves with tool, used for long thin jobs that deflect laterally by cutting force.

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TOOL POST

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Tool Setting on Lathe 1. Setting the tool below the centre decreases the effective rake angle and increases the effective clearance angle. This increases the cutting forces. 2. Setting the tool above the centre increases the effective rake angle and decreases the effective clearance angle. This increases rubbing with flank surface. Effective Rake is the apparent Rake angle w.r.t tool and work position and not the actual rake angle provided on the tool.

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2) Dr. G. R. C. PRADEEP

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TOOL HOLDERS HSS Tool Holders

Brazed Carbide tip Tool Holders (Can be grinded)

Throw away Carbide Tip Tool holders (Can not be Grinded)

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Box Tool Holders – Used in turret lathes to apply heavy cuts & act as travelling steadies.

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OPERATIONS 1) Straight turning: Here the work rotating about lathe axis, tool is fed parallel to it, depth of cut is perpendicular to it, thus producing a straight cylindrical surface. Here Diameter is effected but Length is not effected. 2) Shoulder / Step turning:

L

ФD

Same as above except that diameter is reduced only up to certain length. Dr. G. R. C. PRADEEP

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3) Facing:- Here the tool is fed perpendicular to the lathe axis and depth of cut is parallel to the lathe axis and thus producing a flat surface. Here Length (in Shafts) / thickness (in plates) is effected, but Diameter is not effected. 4) Knurling:- Process of embossing a diamond shaped pattern on work surface which is used for gripping purpose. Video 13,14 Dr. G. R. C. PRADEEP

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5) Taper turning:- Operation of producing tapered surfaces. The following methods are used 1. Swiveling of compound rest – Any Angle, Any D1 D2 Corresponding Taper length. L

θ

D1 = Larger Dia D2 = Smaller Dia L = Taper length θ = Half Cone Angle 2θ= Included Angle / Full cone Angle Dr. G. R. C. PRADEEP

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2. Tailstock set over – Small Angle, Long Job

Distance

θ

d f

S = Set over Distance L = Total Length of Work Piece Dr. G. R. C. PRADEEP

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3) Form Tool – Any Angle, Short taper length

d, f

4) Combined Feeds – 45 0 Chamfers

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5) Taper turning attachment The cross slide is delinked (Movement of tool is similar to from the saddle and is combined feed) connected to the attachment fixed on the bed. As the carriage (saddle) moves longitudinally, the cross slide is moved the guide blockcrosswise which by moves along the guide bar preset at the desired taper angle. This action causes the cutting tool to move at an angle to the axis of the work piece to produce a taper. Dr. G. R. C. PRADEEP

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Video 15 49

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Video

6) Metal Spinning:- It is the operation of pressing and forming cup shaped components from sheet metal. Dr. G. R. C. PRADEEP

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7) Spring winding:- We can wind spring on lathe. Here coiled spring can be made by passing a wire around the mandrel which is rotated in a chuck. Dr. G. R. C. PRADEEP

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8) Miscellaneous Operations:Drilling, Boring, Milling, Grinding etc.

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9) Thread cutting:- There are different thread forms like V, Square, Acme, buttress etc. Here the tool has the shape of thread profile. Zero rake angle is used for form tools like threading tool, parting tool, grooving tool etc.

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Majority of screws are right handed threads. They are tightened by clock wise rotation. When cut on lathe, tool advances from right to left. Screws with left handed threads are used in exceptional cases. They are tightened by counter clock wise rotation. When cut on lathe, tool advances from left to right. Spindle rotation is same for both operations but lead screw rotation is opposite. Left hand threads are used on lathe spindles, left hand pedal of bicycle, connections on the acetylene Cylinders (to avoid wrong connections), left-hand grinding wheel on a bench Helix grinder, in Turnbuckles in combination with right handed threads to adjust the tensions in Left Hand Right Hand cables, tie rods etc. Thread Thread Dr. G. R. C. PRADEEP

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Tapered threads are used for water (or) Gas pipes and plumbing supplies, which require a water tight (or) air tight connection. Tapered threads Single produce a wedging action and hence produces a pressure tight joint. Double Thread Terminology: Lead – The distance moved by screw or nut in one revolution. Pitch (P) – The distance between two successive peaks or valleys. Lead = P for single start thread Triple Lead = 2P for double start threads (It has two start points) Lead = 3P for triple start threads (It has three start points) Dr. G. R. C. PRADEEP

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V threads are the standard threads used on most threaded fasteners and are by far the most common. Due to its profile, the square thread is more difficult to machine than a V thread and is only used where strength and wear resistance make it worthwhile. The Acme and Buttress threads are easier to machine. The Buttress thread can be used only where the applied loading is always in one direction. It is sometimes used in bench vices. The Lead screw in lathe in combination with split nut uses an Acme thread which can apply load in both directions. Lathe spindle and lead screw must be in same relative position for each cut. A Thread-chasing dial is attached to carriage for this purpose. It will take care of engagement of thread at the same starting point for every cut. Dr. G. R. C. PRADEEP

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Thread-Chasing dial

Half Nut / Split Nut

Video 17,18,19

Video 17,18,19 Dr. G. R. C. PRADEEP

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Feed Rod is provided in medium to big size lathes and is engaged for other lathe operations except threading and operates by rack and pinion mechanism operated by change gears and other gears in apron. Dr. G. R. C. PRADEEP

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Video 20

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Back Gear “Back gear" is a gear mounted at the back of the headstock and allows the chuck to rotate slowly with greatly-increased turning power. Screw cutting also requires slow speeds. With a back gear fitted, the lathe not only becomes capable of cutting threads but can also tackle heavy-duty drilling, big-hole boring and large-diameter turning and facing; in other words, it is possible to use it to the very limits of its capacity and strength.

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TIME ESTIMATION 1) Machining Time = T = Length of cut / (feed x rpm) = L / (f x N) min f = feed in mm/rev 2) Cutting speed= V = πDN / 1000 m/min D = Starting diameter of work in mm,

N = RPM of work

Note: Some times D is taken as mean diameter also. 3) Combining above two formulae we can write, T = πDL / 1000fV

min

3) Feed per minute, fm = f x N mm/min 4) Depth of cut = d = (Di – Df) / 2 Di = Initial dia, Df = Final dia 5) Power or Work done = F x V

N-m/min

F = Cutting Force = k x d x f; Dr. G. R. C. PRADEEP

k = material constant 62

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6) Total Time for Threading = Time per cut x No. of cuts Time per cut = L / (p x N) [For Single Start Thread] p = Pitch = 1 / No. of threads per unit length L = Length of W.P + Approach Length + Over Travel 7) Time for Drilling =

πDL / 1000fV

L = Depth of hole, D = Dia of drill 8) Time for Boring = πDL / 1000fV L = Depth to be bored, D = Starting Dia of hole 9) Time for facing = L / (f x N) L = Radius of W.P 10) MRR = 1000Vfd mm3/min

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Gear Train Calculation for Thread cutting: 1) Transformation ratio = Gear Ratio = Lead of Work piece / Lead of Lead screw = Speed of Lead screw / Speed of Work piece (Spindle) These relations are true for threads cut in metric or inches units. All lathes are generally provided with set of change gears having teeth from 20 to 120 with a variation of 5 teeth. (20, 25, 30, 35, 40, etc). In addition the set has gear with 127 teeth called translating gear. For a simple Gear train, Gear Ratio = No. of teeth on Driver Gear (On Spindle) / No. of teeth on Driven Gear (On Lead Screw)

The number of teeth on intermediate gear has no effect on the gear ratio. Dr. G. R. C. PRADEEP

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For a Compound Gear train, Gear Ratio = (a/b) x (c/d) a, b, c, d = Teeth of respective gears

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SHAPER INTRODUCTION: The shaper is a reciprocating type of machine tool intended primarily to produce flat surfaces. These surfaces may be horizontal, vertical or inclined. Here the cutting tool is given a reciprocating motion, and after every cutting stroke, the work is fed (during return stroke) to provide an uncut layer for machining. Here cutting is not continuous and hence the machining is known as Intermittent cutting operation. This is used for initial rough machining. The cutting tool is a single point tool similar to lathe. Dr. G. R. C. PRADEEP

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Video 3,4 Dr. G. R. C. PRADEEP

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Bull Gear used in shaper to reduce the speed of rotation obtained from motor

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TYPES 1. According to the type of mechanisms used for giving reciprocating motion to the ram. a) Crank Shaper: Crank and Slotted lever mechanism is used to change rotary motion of the driving gear called bull gear.

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Stroke length = P1P2 = 2AP (CB/AC)

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b) Geared Shaper: Rack and pinion mechanism is used. Geared shapers hav e a reversible electric motor or any mechanical mechanism which quickly returns the ram, in readiness for another cut.

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c) Hydraulic Shaper: By hydraulic power i.e. oil with high pressure is pumped into a cylinder with piston.

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Advantages 1) The cutting speed is constant almost throughout the stroke unlike the other shapers where the speed changes continuously. 2) Power available remains constant through out hence it is possible to utilize the full cutting capacity of the tool. 3) The ram stroke reverses quickly with out any shock as the oil on either side of the piston provides a cushioning effect hence vibrations are minimum. Inertia of moving parts is relatively small. 4) The range and number cutting speeds possible are relatively large and control is simple. 5) More strokes per minute can be obtained by consuming less time for the cutting and return strokes at a given cutting speed. Dr. G. R. C. PRADEEP

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2. According to the position and travel of ram. a) Horizontal shaper: Reciprocates in a horizontal axis. b) Vertical shaper: Reciprocates in a vertical axis. It has a round table that c an rotate and also can be fed longitudinally and cross wise. Also the ram can be reciprocated at an angle up to 100 from the vertical position enabling machining inclined surfaces.

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c) Traveling head shaper: The ram moves cross wise for feed during reciprocation. Used for heavy jobs where table feed is not possible.

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3. According to the type of design of the table: a) Standard Shaper: Table has only 2 movements, to give feed. b) Universal shaper: In addition to t he 2 movements, the table can be swiveled about a horizontal axis parallel to the ram ways and the upper portion of the table can be tilted about a second horizontal axis ┴ to the first axis. Dr. G. R. C. PRADEEP

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SPECIFICATIONS AND OPERATIONS SPECIFICATIONS: 1) The max. Length of stroke or cut 2) Table size 3) Return time to cutting time ratio. 4) Number of speeds and feeds. 5) Floor space required 6) Weight of machine etc OPERATIONS ON HORIZONTAL SHAPERS: 1) Machining Horizontal, Vertical, Angular surfaces 2) Cutting Slots, Grooves, Key ways, Splines, Gears etc (External Only) OPERATIONS ON VERTICAL SHAPERS: Similar to Slotters. Dr. G. R. C. PRADEEP

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TIME ESTIMATION (1) Cutting speed V = NL(1+m)/1000 m/min (This theoretical formula is used in calculations) L = Length of cutting stroke in mm m = Ratio of return time to cutting time N = No. of double strokes per min = RPM of bull gear Note: 1. In actual practice, the cutting speed changes during the cutting stroke in the crank type and geared type shapers. Hence the average cutting speed is expressed as: Vavg = V / 2 = NL(1+m) / 2 x 1000 2. The stopping point of cutting stroke in hydraulic shapers can vary depending on the resistance offered to cutting by the work material. Dr. G. R. C. PRADEEP

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(2) Time required by cutting stroke = L / 1000V (3) Return stroke time = m x cutting stroke time= mL/ 1000V (4) No. of double strokes required to complete the job = W / f W = Width of W.P. f = feed in mm (or) mm/Cutting stroke (or) mm/double stroke (5) Total time taken for one complete cut = LW(1+m)/1000fV (6) Metal Removal Rate (MRR) = 1000Vfd mm3 / min, where d = depth of cut in mm (7) Power consumed = K x MRR hp where K = constant for calculating horse power consumed (8) Theoretical peak to valley height = Rt = 0.5 f / tan θ mm Where 2 θ = Angle b/w the two cutting edges in the single point tool f /2 Rt Dr. G. R. C. PRADEEP

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θ

SLOTTER INTRODUCTION: This operates almost on the same principle as that of a shaper. Slotter was invented before shaper. Here the ram reciprocates in a vertical axis. There is no quick return and the mechanism used for ram is Crank and connecting rod mechanism. The slotter is provided with a rotary table that can moved andand cross wise. The slotter is be us ed for longitudinally making regular irregular surfaces both internal and external and also for handling complex work pieces. Slotter is more robust compared to vertical shaper. Video 1,2 Dr. G. R. C. PRADEEP

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TYPES 1) Puncher slotter: A heavy, rigid machine, for removing large amount of metal from large forgings and castings. The length of stroke is very large (1.8 - 2m).

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2) Precision slotter: It is a lighter machine and is operated at high speeds. Used for accurate finish, using light cuts.

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SPECIFICATIONS AND OPERATIONS SPECIFICATION: 1. Length of stroke 2. Diameter of table 3. Amount of cross and longitudinal travel of the table 4. No. of speeds and feeds 5. Floor space required 6. Net weight of the machine etc. OPERATIONS: 1) Machining slots, keyways, grooves of various shapes, both internal and external, Internal machining of blind holes, machining of dies, punches etc. 2) Machining flat surfaces, Cylindrical surfaces, Cams, internal and external gears. Dr. G. R. C. PRADEEP

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PLANER INTRODUCTION: The planer like shaper is a m/c tool primarily intended to produce plane and flat surfaces by a single point cutting tool. A planer is very large compared to shaper. In a planer the work which is supported on the table reciprocates past the stationary cutting tool and feed is given by the lateral movement of the tool.

Video 5,6

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TYPES 1)Double housing planer (or) standard planer: Has two vertical housings connected by a cast iron member on top. Table is mounted on the bed and can reciprocate. The Cross rail can move up and down on the vertical housings and one or two tool heads provided can travel cross wise for tool feed across the cross rail.

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2) Open side planer: Only one side housing and the cross rail is suspended as cantilever. Used for very wide Jobs.

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3) Divided Table Planer: Also called Tandem Planer. This type of planer has two tables on the bed which may be reciprocated separately together. This type of design saves much of the idle time while setting large no. of identical pieces on the machine. CROSS RAIL

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TABLES

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4) Pit planer: It is a massive construction. The table is stationary, the column carrying the cross rail reciprocates on massiv e horizontal rails mounted on both sides of the table. Suitable for very large works.

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5) Edge or plate planer: This is specially intended for squaring and beveling the edges of steel plates used for different pressure vessels and ship building works.

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SPECIFICATIONS AND OPERATIONS SPECIFICATIONS: 1.The size of the largest rectangular solid that can reciprocate under the tool. 2. No. of speeds and feeds available, 3. Floor space reqd. 4. Net wt. of machine etc. OPERATIONS: (1) Planning flat horizontal, vertical, angular surfaces (2) Slots and grooves.

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DRILLING INTRODUCTION: A drilling machine was primarily designed to originate a hole, but it can also perform a No. of similar o perations. In a drilling machine holes may be dri lled quickly and at low cost. The hole is generated by the rotating edge of a cutting tool known as the drill which exerts large force on the work clamped on the table. The cutting motion is provided by rotating the drill and feeding is done by giving rectilinear motion to the drill in the axial direction. Here the dr ill used has two cutting edges called lips. Dr. G. R. C. PRADEEP

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Video 1

TYPES (1) Portable drilling machine: This type of D.M. can be operated with ease anywhere in the work shop and is use d for drilling holes in work pieces in any position which cannot be drilled in a standard D.M. The entire D.M. including the motor is compact and small in size. The max. size of the drill that can accommodate is not more than 12 to 18 mm.

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(2) Sensitive D.M. It is a small machine designed for drilling small holes at high speed in light and small jobs. The base of the machine may be mounted on a bench or on the floor. There is no arrangement for the automatic feed of the drill spindle. High speed and hand feed are necessary for drilling small holes. As the operator can sense the progress of the drill it is called S.D.M. Drills size is 1.5 to 15.5 mm can be used in this machine. Super sensitive D.M. are designed to drill holes as small as 0.35 mm and can be rotated at a speed of 20,000 rpm or above. Dr. G. R. C. PRADEEP

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(3) Upright D.M.: This is designed for handling medium sized W.P. It is similar to a S.D.M. but is heavier and l arger t han S .D.M. and i s supplied with power feed arrangement. a) Round Column Section (or) Pillar D.M.: It consists of round column and a round table. The table can be moved up and down on the column for accommodating W.P. of different heights. The table may be rotated 360o about its own centre. The max. size of the hole that can be drilled is not more than 50mm. Dr. G. R. C. PRADEEP

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(b) Box Column Section Upright D.M.: The upright D.M. with box column section has a square table fitted on the slides at the front face of the machine column. Heavy box column gives the machine strength and rigidity. The table is raised or lowered by an elevating screw that gives additional support to the table. Heavier W.P. and holes more than 50 mm dia can be drilled by it. Dr. G. R. C. PRADEEP

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(4) Radial D.M: It is intended for drilling medium to large and heavy W.P. It consists of a heavy, round vertical column mounted on a large base. The column supports a radial arm which can be raised and lowered to accommodate work pieces of difference heights The arm may be swung around to any position over the work bed. The drill head containing mechanism for rotating and feeding the drill is mounted on the radia l arm and can be moved horizontally on the guide ways and clamped at any desired position. This can be further classified as 

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(a) Plain RDM.:- It has the movements explained above.

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(b) Semi Universal RDM:- In addition to the above 3 movements, the drill head can be swung about a horizontal axis to the arm. This 4 th movement of the drill head permits drilling hole at an angle to the H.P. other than normal position.

(c) Universal RDM:- In addition to the above 4 movements the drill head may be rotated on a horizontal axis. All these 5 movements enable it to drill on a W.P. at any angle and in any plane. Dr. G. R. C. PRADEEP

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(5) Gang D.M.: When a No. of single spindle D.M. columns are placed side by si de on a common base and have a common, work table, the machine is known as G.D.M. In a G.D.M. 4 to 6 spindles may be mounted side by side. The speed and feed of spindles are controlled independently. This type of machine is specially adapted for production work. A series of operations may be performed on the work by simply shifting the work from one position to the other on the work table each. Spindle may be set up properly with difference tools for different operations. Video 2, 3 Dr. G. R. C. PRADEEP

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(6) Multiple spindle D.M.: The function of the multiple spindle D.M. is to drill a No. of holes in a piece of work simultaneously and to reproduce the same pattern of holes in a No. of identical pieces in a mass production work such machines have several spindles driven by a single motor and all the spindles holding drills are fed into the work. Simultaneously. Feeding motion is usually obtained by raising the work table. But the feeding motion may also be secured by lowering the drill heads. The spindles are so constructed that their centre distance may be adjusted in any position as required by various jobs within the capacity of the drill head. For this purpose, the drill spindles are connected to the main drive by universal joints. The spindles are connected by a number of planetary gears so that even different size drills can be loaded. Dr. G. R. C. PRADEEP

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Video 4,5

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7) Deep Hole Drilling machine: Special machine and drills are required for drilling deep holes in rifle barrels, long spindles, oil holes in crank shafts, long shafts etc. The machine is operated at high speed and low feed. A long job is usually supported at several points to prevent any deflection. The work is usually rotated while the drill is fed into the work. This helps in feeding the drill in a st. path. The machine may be Horizontal type (or) Vertical type. The drill is withdrawn automatically each time when it penetrates in to the work to a depth equal to its d ia. This process permits the chip to clear out from the work. Video 6,7,8

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There are different types of deep hole drilling processes and are categorized by how the cutting coolant flushes heat and chips from the cutting face. They are: Gun drilling - The cutting tool is a straight fluted solid rod that has a hole bored down the center. Coolant is pumped through a hole in the inside of the drill. It flows back outside the drill, through the flute, bringing the chips with it. Drilling size (dia) is 3-50 mm. Dr. G. R. C. PRADEEP

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BTA (Boring and Trepanning Association) - The cutting tool is a tube. Coolant is pumped around the outside of the cutting tool at heavy pressure and carries chips out through the center of the tube. Very high penetration rates can be achieved with this system along with good surface finish. Depth to Diameter ratio is highest. Because tubes

have minimum sizes, this is only an acceptable technology for holes of diameter over 15 mm and up to 600 mm. Dr. G. R. C. PRADEEP

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Examples of Deep Hole Drilling

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Specifications 1. Max. size of drill that the machine can operate, 2. Max. spindle travel 3. Table diameter / size 4. Morse taper No. of the drill spindle 5. No. of spindle speeds and feeds available. 6. Floor space required 7. Net wt. of the machine

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TERMINOLOGY Drills are manufactured as: 1. Straight shank drills (up to ϕ 13.5 mm) 2. Taper shank Drills (ϕ 14.0 mm onwards)

Tang Shank Neck

Body

Tip Dr. G. R. C. PRADEEP

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Drilling M/c Spindle

Drill Chuck with Chuck key Morse taper is provided on all drilling accessories, inside drilling machine spindle, lathe tail stock, lathe turret, and lathe centres

Drift Dr. G. R. C. PRADEEP

Sleeve 114

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DRILL GEOMETRY Lip angle/ Tip Angle/ Point Angle

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Land / Margin: It maintains the alignment of the drill so that hole is straight and to the right (correct) size.

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Helix angle: Angle formed b/w a plane containing drill axis and the leading edge of land. Based on the value of the angle the drills can be classified as 1) Slow spiral series: 12 o to 22 o - Used for brass, bronze, CI that produce broken chips (brittle materials). They provide less lifting power, but are stronger, used for shallow holes. Also used in horizontal applications where drill is not rotating. 2) Regular spiral series: 28 o to 32o - most widely used 3) Fast/High spiral series: 34 o to 38 o – Used for softer ferrous and non-ferrous materials producing long string like chips (ductile materials). They provide great lifting power, but are weak, used for deep holes. Dr. G. R. C. PRADEEP

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Lip angle: Angle formed b/w the cutting edges (lips). Smaller point angles results in lower effective rake. Effect of change in effective rake is negligible on drill performance. Smaller the point angle, longer the lip length. Smaller point angles generate wider and thin chips. Higher point angles generate narrow and thick chips. Higher point angle increases the cutting efficiency of the drill because most materials are cut efficiently in the form of thick chips. Longer lip lengths reduce load per unit length of the lip and helps in resisting the wear caused by abrasive action during machining of metals like C.I.

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1) M.S.



1180 (< 180 HB)

2) Steel



1180 (180 - 280 HB)

3) Steel



1350 - 140o (280 – 380 HB)

4) Grey C.I.



900 (< 180 HB)

5) Grey C.I.



1180 (180 - 280 HB)

6) Chilled C.I.



1350 – 1400 (> 350 HB)

7) Aluminum 8) Copper



0



1180 118

9) Bronze



1180

10)Brass



1110

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Clearance / Lip relief Angle: Angle formed b/w flank and a plane normal to drill axis at the tip of the drill. Large angles (80–120) are used for ductile matls. to compensate elastic recovery. Small angles (6 0–80) are used for brittle matls.

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OPERATIONS 1) Drilling – Process of making hole in solid body. 2) Boring – Enlarging a hole completely with an adjustable tool with only one cutting edge. 3) Counter boring - Enlarging one end of the hole to form a square shoulder with srcinal hole to avoid projections in assemblies. 4) Counter sinking - Making a cone shaped enlargement to provide a recess for a screw head.

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5) Reaming – Sizing and finishing a small unhardened hole. a) Straight flute reamer is used for through holes in materials that do not form chips like C.I, Bronze, Brass. They form fine powder that will fall by gravity. b) Left hand spiral flute reamer is used for through holes in other b) c) materials and is very effective as a) they push the chips out of the through hole. c) Right hand spiral flute reamer Manual Reamer & Wrench is used for blind holes as they pull M/c Reamers the chips out of them. Chucking (M/c) Reamer Dr. G. R. C. PRADEEP

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d) Rose reamers are primarily used for roughing prior to final reaming. The cylindrical part of the reamer has no cutting edges, but merely grooves cut for the full length of the reamer body, providing a way for the chips to escape and a channel for lubricant to reach the cutting edges. To prevent binding they have a slight back taper. The cutting edges at the end 0

are ground to a 45 bevel.

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e) Shell reamers are similar to cutting portion of a chucking reamer. They are supplied without a shank and has a hole through the center. A arbor is used in conjunction with the shell reamer, the slots in the reamer engage lugs on the arbor for driving power.

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6) Lapping – Sizing and finishing a hole already hardened. 7)Tapping–Process of making internal threads in small holes.

Machine Tap with holder Manual Tap 8) Spot facing – Process of smoothing and squaring the surface around the hole or seat for a nut (or) head of a screw for burr removal.

Spot facing tools with pilot Dr. G. R. C. PRADEEP

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Burr formation during drilling

Dr. G. R. C. PRADEEP

Centre Drill used for making a centre impression on surface for locating the drill point, locating the lathe & Grinding centres. 127

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9) Trepanning – Operation of producing a hole by removing metal along the circumference of a hollow cutting tool. Used for producing large holes in plates.

Video 9,10,11 Dr. G. R. C. PRADEEP

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TIME ESTIMATION 1) Cutting speed, V=

πDN / 1000 m/min

2) Machining Time, T = L / (f x N) = L / fm L = L1 + L2 + L3 + L4 (Some times L= L 1 + 0.5D) L1 = Depth of hole L2 = Approach length L = Length of tip 3

= 0.5D / tanθ = 0.29D (For 2 θ = 1180)

(where, 2θ = Lip angle) L4 = Over Travel 3) Depth of cut, d = D / 2 4) MRR = πD2fN / 4 = πD2fm / 4 Dr. G. R. C. PRADEEP

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MILLING INTRODUCTION: A milling machine is a machine tool that removes metal as the work is fed against a rotating multi point cutter. The cutter rotates at a high speed, and because of the multiple cutting edges it removes the metal at a very fast rate. The first milling machine came into existence in about 1770 and was of French srcin. Dr. G. R. C. PRADEEP

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TYPES 1. Column & knee type: Most commonly used for general shop work. The ta ble is mounted on the kn ee casting, which in-turn is mounted on the vertical slides of the main column. The knee is vertically adjustable on the column, so that the table can be moved up and down to accommodate work of various heights. The table can be moved longitudinally and cross wise on the knee casting. Classification of this type is based on methods of supplying power to the table, diff. movement of the table and diff. axis of rotation of the main spindle.

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(a) Hand milling machine  Feeding is done by hand and used for light and simple operations like slots, grooves, keyways. This is available in both horizontal & vertical models Table movements are as above.

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(b) Plain milling machine  This is a horizontal type milling m/c. This is more r igid and sturdy, for heavy work, can be fed by hand or be power. Table can fed as above. Video 1,2

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(c)Universal milling machine  This is also a horizontal type milling m/c. In addition to 3 movements in plain milling machine the table has a fourth movement i.e. it is fed at an angle to milling cutter. This enable it to perform helical milling. This machine can produce spur, spiral, bevel gears, twist drills, reamers, milling cutters etc. Dr. G. R. C. PRADEEP

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(d)Omniversal milling machine  This is a horizontal type milling m/c. The extra fifth movement is the table can be tilted in vertical plane providing a swivelby arrangement at the knee. This enables milling in any plane. Taper spiral groves in reamers, bevel gears etc can be done. Dr. G. R. C. PRADEEP

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(e) Vertical milling machine Here the position of the spindle is vertical and ┴ to the work table. The spindle head is clamped to the vertical column and can be swiveled at an angle . Also the spindle be adjusted up /head down can relative to work. The table movements are same as plain milling machine. Video 3,4 Dr. G. R. C. PRADEEP

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2. Plano Miller: It resembles a planer. It is having multiple spindle heads both in vertical and horizontal planes. It has a cross rail which can be raised or lowered along with cutters. of work surfacesHence can beno.machined simultaneously, thereby reducing production time. In a plano miller, the table has

Video 5

feed movement instead of reciprocation. Hence the table movement here is much slower than planning machine. Dr. G. R. C. PRADEEP

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3. Rotary table Machine  A modification of vertical milling machine adopted for machining flat surfaces. A No. of work pieces can be mounted on a circular table which rotates about vertical axis. The face milling cutters can be mounted spindles on andtwo can(or) be more set vertical at diff. heights relative to work so that when one cutter is roughing the other is finishing them. Continuous loading and unloading of work pieces can be done by the operator while milling is in progress. Dr. G. R. C. PRADEEP

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4.Planetary milling machine: Here the work is held stationary while the revolving cutter / cutters move in a planetary path to

Video 6,7

finish a cylindrical surface on the work either internally / externally / simultaneously. This machine is particularly adopted for milling internal / external threads of different pitches. Dr. G. R. C. PRADEEP

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5. Pantograph milling machine  It can duplicate a job by using a pantograph mechanism which permits the size o the work piece reproduced to be smaller than, equal to or greater than the size of a template or model used for this purpose. A pantograph is a mechanism that is generally constructed of fou r bars or links joined in the fo rm of parallelogram. Pantograph machines are available in 2D or 3D models. 2-D areare used forfor engraving or other designs, 3-Dmodels models used copyingletters any shape and contour of the work piece. The tracing stylus is moved manually on the contour of the model to be duplicated and the milling cutter mounted on the spindle moves in a similar path on the work piece, reproducing the shape of the model. Dr. G. R. C. PRADEEP

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Video 8

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SPECIFICATIONS 1. The maximum length of longitudinal, cross and verti cal travel of the table. 2. No. of spindle speeds, 3. No. of table speeds and feeds 4. Floor space required 5. Net weight required 6. Spindle nose taper (for vertical milling machine spindle) and taper on horizontal milling machine arbors

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MILLING GEOMETRY Peripheral cutter: As the cutting edges are arranged radially on the periphery the rake angle is called radial rake which is the cutting edges angle w.r.t to the periphery of the cutter. +ve radial rake gives better performance in peripheral milling. Face cutter: Two rake angles are defined here.

(a) Radial rake is the cutting insert’s angle w.r.t the periphery of the cutter (b) Axial rake is the cutting insert’s angle w.r.t the central axis of the cutter. Axial Rake has significant effect on axial force and thrust applied to the spindle. Radial rake has major effect on tangential and radial forces. +ve axial rake, - ve radial rake gives best performance. Dr. G. R. C. PRADEEP

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PERIPHERAL CUTTER

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FACE CUTTER

Side View

Bottom View Dr. G. R. C. PRADEEP

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METHODS OF MILLING 1. Peripheral Milling: It is the operation performed by a milling cutter to produce a machined surface parallel to the axis of rotation of the cutter. Here the cutting force is not uniform throughout the length of cut by each tooth. Due to this reason, a shock is developed in the mechanism of the machine that leads to a vibration. The quality of surface generated and the shape of the chip formed is dependent upon the rotation of the cutter relative to the direction of feed movement of the work. According to the relative movement between the tool and work, the peripheral milling is classified into two types:

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(a) Up milling / Conventional milling: The metal is removed by the cutter which is rotated against the travel of the W.P. The thickness of the chip is min. at the beginning of cut max. when the cut terminates. The cutting force is directed up wards and this tends to lift the work from the fixtures. This is used for roughing operations. The chips accumulate at the cutting zone, and may over be withcarried the cutter, spoiling the work surface. It generates a poor finish. Cutting force and power are more. Dr. G. R. C. PRADEEP

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(b) Down milling/ Climb milling: The metal is removed by the cutter which is rotated in the same direction of travel of the W.P. The thickness of the chip is max. when the tooth begins its cut and it reduces to the min. when the tooth leave the work. The cutting force is directed down wards and this tends seat the work firmly in the work holding devices. Hence fixture design is easier. This operation cannot be used on old machine as the ba ck lash error present in the scr ew elements that ma y cause vibration and dam ages the work surface considerably. Hence this operation should be performed on rigid machines provided with back last eliminator. This is used for finishing operations. The chips are also disposed off easily and do not interfere with the cutting. This results in improved surface finish. Cutting force and power are less. Dr. G. R. C. PRADEEP

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BACKLASH ELIMINATOR: This eliminates the backlash (play) between nut and table lead screw. Two independent nuts are mounted on lead screw. The nuts engage common crown gear which meshes with rack. The axial movement of rack is controlled by the backlash eliminator, engaging a knob on front of saddle. Turning the knob forces the nuts to move along lead screw in opposite directions. Dr. G. R. C. PRADEEP

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2. Face Milling: This is performed to produce a flat machined surface to the axis of rotation of the cutter. In this operation both up milling and down milling may be considered to be performed simultaneously on the work surface. When the cutter rotates through half of the revolution the direction of movement of the cutter tooth is opposite to the direction of feed and the condition reverse when the cutterisrotates through other half chip thickness min. at the beginning andofatrevolution. the end of The the cut, and it is max. when the work passes through the centre line of cutter. The surface generated in face milling is characterized by the tooth circular marks of the cutter. Face milling gives superior finish than peripheral milling.

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Draw Bolt Spindle

Cutter Holder Spindle Nose Taper

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3. End Milling: It is a combination of peripheral and face milling operations. The cutter has cutting edges both on the end face and on the periphery. The cutting characteristics may be of peripheral or face milling type according to the particular cutter surface used. When end cutting edges are only used to remove metal, the direction of rotation of the cutter and direction of helix of the cutter should be same. When cutting edges are used,ofthe of rotationperipheral of the cutter and direction of helix the direction cutter must be opposite to each other.

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Draw Bolt Collet Holder

Collet Wrench Collet

End Mill

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TAPER USED IN MILLING MACHINES American Standard Taper of 3.5” per foot is made standard taper in all milling machines built in U.S. Brown and Sharpe Taper of 0.5” per foot is also widely used on collets, arbors of horizontal machines, inside of vertical machine spindles and on grinding machine spindles. This is used in European and Asian Countries Dr. G. R. C. PRADEEP

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OPERATIONS 1. Plain Milling: Producing plain, flat horizontal surface. This is called slab milling if performed with a peripheral cutter and called face Milling if a face milling cutter is used.

2. Side Milling: Producing flat vertical surface on the side of a work piece by using side milling cutter.

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3. Straddle Milling: Producing flat vertical surfaces on both sides of the work piece by us ing two side milling cutter mounted on the same arbor. The distance between the two cutter can be adjusted by using spacing collars. Video 9

4. Gang Milling: Machining several surfaces simultaneously using a No. of cutters of same or diff. diameters mounted on the arbor of the machine, used widely for repetitive work

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5. Form Milling: Producing irregular contours using form cutters like concave, convex or any other shape. Convex Cutter Concave Milling Convex Milling Concave Cutter 6. End milling: Producing flat surfaces which may be vertical, horizontal or at an angle in reference t o the table surface like slots, grooves, key ways, steps etc. A vertical milling machine is most suitable for end milling. Dr. G. R. C. PRADEEP

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7. Saw milling: Producing narrow slots or grooves using saw milling cutter. It can also be performed for complete parting off operation.

8. Gear cutting: By using form re lieved cutter having the same profile of the tooth space of the gear. 9. Helical Milling: Producing helical flutes or grooves around the periphery of a cylindrical or conical work piece. 10. Cam Milling: Producing cams by using universal dividing head and a vertical milling attachment. Note: 8, 9, 10, above can be done in indexing. Dr. G. R. C. PRADEEP

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INDEXING It is the operation of dividing the periphery of a piece of work into any No. of equal parts. This is adopted for producing hexagonal and square headed bolts cutting splines on shafts, flutes in milling cutters, drills, taps and reamers, cutting of Gears, cams etc. Indexing is accomplished by using a special attachment known as dividing head or Index head. They are of 3 types  1) Plain / Simple dividing head 2) Universal Dividing head 3) Optical Dividing head Using these dividing heads, the work can be set in vertical, horizontal or in in clined positions re lative to the table surface. There are several methods of indexing. The choice of any one method depends upon the No. of divisions required and the type of dividing head used. Dr. G. R. C. PRADEEP

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PLAIN / SIMPLE INDEXING HEAD

UNIVERSAL INDEXING HEAD

OPTICAL INDEXING HEAD

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METHODS OF INDEXING 1) Direct Indexing: Also called rapid indexing, is used making small No. of d ivisions. This can be performed in both plain and universal dividing head. The spindle and index crank are connected by bevel gears. The required No. of divisions on the work is obtained by means of the rapid index plate generally fitted to the front end of the spindle nose. The plate has 24 equally spaced holes, into any one of which a spring loaded in is pushed to lock the spindle with the frame. While indexing, the pin is first taken out and then the spindle is rotated by hand, and after the required position is reached, it is again locked by pin. when the plate is turned throughout the required part o a revolution, the dividing head spindle and the work are also turned through the same part of the revolution. Dr. G. R. C. PRADEEP

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With a rapid index plate having 24 holes, it is possible to divided the work into equal divisions of all factors of 24 i.e. 2,3,4,6,8,12,24 Video 10

Rule: No. of holes to be moved

=

No. of holes in the direct index plate No. of divisions required

Q) Find out the index movement required to mill a hexagonal bolt by direct indexing. Ans. No. of holes to be moved = 24/6 = 4 After machining one side of the bolt the index plate will have to be moved by 4 holes for 5 times to machining the remaining 5 faces of the bolt. Dr. G. R. C. PRADEEP

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2) Simple Indexing: Also called plain indexing, is more accurate and suitable for numbers beyond the range of rapid indexing. The bevel gears are replaced by a worm and worm wheel. The shaft carrying the crank has a single threaded worm and it meshes with the worm wheel on spindle having 40 teeth. 40 turns of crank are necessary to rotate the spindle thro' one revolution, i.e one complete turn of the index crank will cause the worm wheel to make 1/40 of a revolution. For indexing fractions of a turn, various index plates are used. Dr. G. R. C. PRADEEP

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Rule: Index crank movement = 40/N, where N = No. of divisions required. If the crank movement obtained from the formula is a whole No. the index crank should be rotated equal to the whole No. derived. If the crank movement obtained from the above formula is a whole No. and a fraction then, the numerator and denominator of the fraction are multiplied by a suitable common No. which will make the denominator of the fraction equal to No. of holes in the index plate. The new numerator now stands for the No. of holes to be moved by index crank in the hole circle derived from denominator, in addition to the complete turns of crank. Eg: Index plates- 12, 14, 16, 18, 21 hole circles etc. Dr. G. R. C. PRADEEP

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Q) Set the dividing head to mill 30 teeth on a spur wheel blank. Use 21 hole index plate. Video Ans.

11

Index crank movement = 40/30 = = = Thus for indexing, one complete turn and 7 holes in 21 hole circle of the index plate will have to be moved by the index crank, if 21 hole plate is selected. This can also be performed with 18 hole plate [ ] or 24 hole plate [ ] also. Dr. G. R. C. PRADEEP

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3) Compound indexing:- The indexing method is called compound due to the two separate movement of the index crank in two diff. hole circles of one (same) index plate to obtain a crank movement not obtainable by plain indexing. 4) Differential Indexing: The differential indexing may be considered as an automatic method (mechanization) of performing compound indexing. Here the Index crank is connected to milling machine feed rod through a set of gears to get continuous rotation for spindle for making helical grooves as shown. Video 12

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Setting of universal dividing head for spiral or helical grooves Dr. G. R. C. PRADEEP

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TIME ESTIMATION 1. Time required per cut = L / (f x N) = L / fm L = L1+ ATT L1=Length of W.P ; ATT = Added Table Travel 2. Total Milling time= Time per cut x No. of cuts(or) Indexing 3. Cutting speed, V = πDN / 1000; D = Cutter Diameter 4. Feed per tooth. ft = f / Z = fm / NZ, Z = No. of teeth 5. MRR = Wdfm ; d = depth of cut; W= Width of WP Calculation of ATT: Operations performed on the milling machines are done by peripheral cutters / slab cutters/ side and face cutters (Horizontal M/c) and face cutters or end mills (Vertical M/c). a) For Peripheral / Slab Cutters / Side and Face Cutters

∆ = Clearance at entry /exit Dr. G. R. C. PRADEEP

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General Case

FRONT VIEW

FRONT VIEW

ATT calculation neglecting clearance Dr. G. R. C. PRADEEP

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(v) Maximum uncut chip thickness =

(vi) Average uncut chip thickness = (vii) Peak to valley height for surface roughness = (viii) Effective no. of teeth cutting at same time = (ix) Mean Tangential Force =Fmt = K d fm W / πDN K = Material Constant (x) Mean Cutting Power = Fmt V Dr. G. R. C. PRADEEP

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b) For Face Cutters/End Mills i) Tool fully engaged, Roughing Pass – doesn’t require “Full Wipe”

General Case

Special Cases ii) Tool fully engaged, Finishing Pass – requires “Full Wiping ” (Single pass feed) iii) Tool not fully engaged with W 1. This is opposite in turning (i.e < 1). 4. Soft wheels are used for ha rd materials as th ey break easily to release worn out grains (High self sharpening capability). Hard wheels are used for soft materials as wear out is less and they retain the grains for more time. Dr. G. R. C. PRADEEP

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5. GRINDING RATIO: Grinding Ratio or G Ratio is the cubic mm of stock removed divided by the cubic mm of wheel lost. In conventional grinding it is 20:1 to 80:1 It is a measure of grinding production and reflects the amount of work a wheel can do during its useful life. As the wheel loses material it must be reset to maintain the required work piece size. 6. Al. oxide is the preferred abrasive compared to SiC to grind high tensile strength material like steel as Al. oxide is tougher than SiC. Also Al. oxide shows higher chemical inertness towards steel giving more wear resistance during grinding. •

• •

•

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Creep feed Grinding: It is different from conventional grinding. Here the entire depth of cut is completed in one pass only using very small feed rates (0.005 mm). High depth of cuts of order 1 to 30 mm with low speeds of 1 to 0.025 m/min are used. Cutting forces and power required are more. Open and soft wheels are used to accommodate large volume of chips generated. The cutting fluids are oil based due to low grinding speeds. This is mainly used for grinding work pieces made out of hard materials with deep slots or complex profiles and also for removing large amounts of material.Wheel wear rate is more. Dr. G. R. C. PRADEEP

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SUPER FINISHING PROCESSES The surface finish produced by various processes are: PROCESS: SURFACE FINISH (µm) : TYPE OF PROCESS Turning, boring :

0.05 to 25

: Machining Process

Milling

0.25 to 25

: Machining Process

:

Planning, shaping :

0.375 to 25

: Machining Process

Drilling

0.75 to 12.5

: Machining Process

:

Reaming, Broaching : 0.5 to 6.25

: Machining Process

Grinding

:

0.025 to 6.25

: Finishing Process

Honing

:

0.025 to 1.5 : Super Finishing Process

Lapping

:

0.013 to 0.75: Super Finishing Process

Burnishing

:

0.01 to 0.25 : Super Finishing Process

Polishing & Buffing: Dr. G. R. C. PRADEEP

: Super Finishing Process 197

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Honing This is used for finishing the inside surface of a hole. It can also be used for finishing external surfaces. Here abrasives are in the form of sti cks which are mounted on a mandrel which is given a reciprocating motion along the hole axis super imposed on a uniform rotary motion. The grit size is b/w 80 to 600 mesh size. Honing finds special application for cylinder bores as it produces a cross hatched pattern useful for lubrication. Special cutting fluids like sulphurised oils are used. Honing can also be used for finishing gears where tool is made in plastic or any bonding material impregnated with abrasives. Other examples include bearings, hydraulic cylinders, and gun barrels. Dr. G. R. C. PRADEEP

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Video 1

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Lapping A lap is generally made of material softer than work and has the same shape of the opposed mating part. Straight narrow grooves are cut at 90o on the lap surface and abrasive powder is sprinkled on the surface. A suitable fluid (carriers) is also applied like M/C oil, grease etc. Lapping is performed by hand or machines. To carry out the process, the lap is pressed against the work and moved back and forth over the surface in a figure-eight or other motion pattern, (unrepeated paths) subjecting all portions of the surface to the same action. C.I. is the mostly used lap material, other materials are soft steel Cu, Brass, hardwood etc. Abrasives are oxides of Al, Si, Cr and diamond etc. The grit size is b/w 120 to 1200 mesh size. This process has wide applications like gauges, measuring wires, m/c Spindles, threads, gears, lenses, bearing races etc. Dr. G. R. C. PRADEEP

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Video 2,3 Dr. G. R. C. PRADEEP

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Burnishing It consists of pressing hardened steel balls or rolls on to the surface of W.P. and also imparting feed motion to the same so that it causes plastic flow of minute irregularities like dents, projections etc. Eg: Burnishing of shafts. Shaft burnished on lathe Video 4

Hydraulic cylinders roller burnished on lathe Dr. G. R. C. PRADEEP

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Polishing Polishing is a finishing operation to improve the surface finish by means of a polishing wheel made of fabrics or leather and rotating at high speed. The abrasive grains are glued to the outside periphery of the polishing wheel. Polishing is used to remove scratches and burrs and to smoothen the rough surfaces. Polishing may be used to enhance and restore the looks of certain metal parts or object on cars and other vehicles, handrails, cookware, kitchenware, and architectural metal.

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Buffing Buffing is a finishing operation similar to polishing, in which abrasive grains are not glued to the wheel but are contained in a buffing compound that is pressed into the outside surface of the buffing wheel while it rotates. Buffing is used to provide attractive surfaces with high lustre. In applications such as pharmaceutical, dairy, and specialty plumbing, pipes are buffed to help prevent corrosion and to eliminate locations where bacteria or mold may reside. Buffing is also used in manufacture light reflectors.

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THREAD MANUFACTURING Threads are of prime importance to Engg. They are used as fasteners to transmit power / motion. The following are the methods of thread mfg. Casting Methods: Threads made by sand casting are rough and not used much, except some times in vices and rough machinery like construction equipment, mouth of glass bottles, spun cast iron pipes etc. Threads made by die casting are very accurate and of high finish. But as they can be made with low melting point non ferrous metals, they are not fit for repeated use and hence used in sewing machines, toys, type writers etc. Dr. G. R. C. PRADEEP

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Vide o - 1,2 Forming Methods: Thread Rolling is a cold working process in which a blank of dia. approximately equal to pitch dia (or) effective dia of reqd. thread is rolled between hardened steel rolling dies having the thread profile. This is the fastest method of producing threads at a rate of 200 to 1000 pieces / min. Being chip less forming there is lot of material saving. This is limited to external threads only (up to dia. 25 mm). This is widely used for mass production of fasteners like bolts, screws etc.

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Machining Methods: Thread cutting on lathe by a single point tool is a slow process but produces very accurate threads. Hence to increase Vide o - 3 productivity thread chasing has been developed with a little compromise on quality where a partly cut thread using a single point tool (one or two cuts) is finished by a multi point tool called thread chaser in one cut. Threads are cut in milling (internal & external) by a form cutter having the thread profile. It is more efficient and productive than lathe, when large amount of metal is to be removed. Special purpose machines are also available. Used for coarse threads, trapezoidal threads etc. Dr. G. R. C. PRADEEP

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Finishing Methods: Thread Grinding is used for producing very accurate threads. This is employed to cut threads on hardened materials, for which other methods are not possible. This is used to cut threads on taps, micro meter screws, lead screws, thread gauges, thread milling cutters etc. The principle of thread grinding is same as thread milling. A thread grinding m/c. grinding m/c.

is similar to that of a cylindrical

Miscellaneous Methods: Taps are used for cutting internal threads in small holes. Dies are used for cutting external threads on pipes and small parts. Dr. G. R. C. PRADEEP

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GEAR MANUFACTURING Gears are classified according to the shape of the tooth pair and disposition into Spur, Helical, Double Helical, Straight Bevel, Spiral Bevel, Hypoid Bevel, Worm and Spiral gears.

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Spur gears have their teeth parallel to the axis and are used for transmitting power between two parallel shafts. They have highest efficiency and excellent precision rating. They are used in high speed and high load application in all types of trains and a wide range of velocity ratios. Hence, they find wide applications right from clocks, household gadgets, motor cycles, automobiles, and railways to aircrafts. H elical gears to arethe used forHence parallel drives. Theytheir have teeth inclined axis. forshaft the same width, teeth are longer than spur gears and have higher load carrying capacity. They operate smoother and quieter than spur gears. Their precision rating is good. Their efficiency is slightly lower than spur gears. They are recommended for very high speeds and loads. Thus, these gears find wide applications in automotive gearboxes. Dr. G. R. C. PRADEEP

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Double helical or Herringbone gears used for transmitting power between two parallel shafts. They have opposing helical teeth and their load capacity is very high and are costly. Their applications are limited to high capacity reduction drives like that of cement mills and crushers. Rack is a segment of a gear of infinite diameter. The tooth can be spur or helical. This type of gearing is used for

converting rotary motion into translatory motion or vice versa.

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Straight bevel gears are used for transmitting power between intersecting shafts. They can operate under high speeds and high loads. Their precision rating is fair to good. Wide application of the straight bevel drives is in automotive differentials, right angle drives of blenders and conveyors. Spiral bevel gears are also used for transmitting power between intersecting shafts. The teeth contact length is more and they operate smoother than straight bevel gears. They have higher load capacity, but their efficiency is slightly lower. Usage is in automobile differentials. Hypoid bevel gears are also used for right angle drive in which the axes do not intersect. This permits the lowering of the pinion axis which is an added advantage in automobile drives. Their efficiency is lower than other two types of bevel gears. Usage is in current day automobile drives. Dr. G. R. C. PRADEEP

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Worm and worm gear pair consists of a worm, which is very similar to a screw and a worm gear, which is a helical gear. They are used in right-angle skew shafts. In these gears, the engagement occurs without any shock resulting in quieter operation. High reduction ratios are possible. Efficiency of these gears is low. Their precision rating is fair to good. The drives are very compact. Worm gearing finds wide

application in material handling etc. and transportation machinery, machine tools, automobiles Spiral gears are also known as crossed helical gears. They have high helix angle and transmit power between two nonintersecting non-parallel shafts. Their precision rating is poor. They are used for light load and low speed application such as instruments, sewing machine, textile machinery etc. Dr. G. R. C. PRADEEP

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The following are manufacturing methods. Casting Methods: Sand casting is used for large size gears used in farm machinery and Hand operated devices like cement mixer barrels, hoist gear box of dam gate lifting etc. The materials that can be sand cast are CI, cast steel, Bronzes, brass and ceramics.

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Die Casting is used for making large quantity of small gears used in lawn movers, instruments, cameras, toys etc. Materials used to manufacture die casted gears are zinc, aluminium and brass.

Centrifugal casting is used for making phosphor bronze (as it is resistant to sliding loads) worm wheel rims. Semi Centrifugal casting is used for making Gear blanks. Dr. G. R. C. PRADEEP

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Investment casting process is used for making complicated shapes economically. The process is useful if the gear is integral with some complicated shape that is very difficult to produce by machining. The process is used only if no other process is suitable since production cost is high. Tool steel, nitriding steel, monel, beryllium copper are the materials that can be investment casted for gears. Critical gear set Casting with pattern used in the surface-toWheel Gear used in air missile petroleum machinery system. Dr. G. R. C. PRADEEP

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Injection moulding is used for making light gears of thermo plastics and used in toys, projectors, Wind shield wipers, Xerox m/c, Washing m/c, Speedo meters, etc. The materials for injection molding components are Nylon, cellulose acetate, polystyrene, polyimide, phenolics.

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Video 1 Forming methods: Roll forming is the method where the gear blank is mounted on a shaft and is pressed in hard rolling dies. Both spur and helical gears can be made.

Extrusion is used for small sized gears. After extrusion, a no. of gears can be parted from extruded rod of gear. Operations like piercing, hole upsetting are needed after parting and used in clocks, typewriters, toys etc. Aluminum, copper, naval brass, architect-ural bronze and phosphor bronze are the materials that are commonly extruded

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Forging has long been used in the manufacture of gears. Gear blanks can be produced by open-die forging, closed die forging and hot upset forging. Precision-forged gears requiring little or no finish machining are commonly used in the automotive, truck, off-highway, aerospace, railroad, agriculture, and material handling industries, as well as the energy and mining fields. Gears can be forged from low-alloy steel, brass, Al alloys, S.S, titanium, and some of the heat -resistant alloys. Although spur gears are the easiest to forge, helical and spiral-bevel gears can also be forged if their configurations permit ejection of the gear from the die cavity. Dr. G. R. C. PRADEEP

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Powder Metallurgy techniques also are used for making of balancer gears and oil pump gears in automotives, gear motors for household appliances, crane drives, motor driven window lift and seat adjustors, cluster gears, different types of gears that can be combined with built in keyways etc. Accuracy is similar to die-cast gears. Typically suited for small size gears. Economical for large lot sizes only. Sheet metal blanking is used for producing thin metallic gears form sheet metal to be used in wrist watches, toys, electricity & water meters, hand operated machine gears for slow speed mechanisms etc. Dr. G. R. C. PRADEEP

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Machining methods: a) Form cutter methods: They use a form tool having the shape of teeth space. Disadvantages are low productive, less accurate, high tooling cost as they need a change in tool if no. of teeth or pitch dia. is changed. Gear can be cut in shaper by a single point form tool. To increase productivity a shear speed process called shear speed gear shaper was developed which uses a ring of single point form tools arranged radially to cut all teeth simultaneously. This method is economical only for large qty production. Gear can be cut by mill ing using rotating form cutter. It is used for spur, helical, bevel and racks and has the same disadvantages. Gear cut by broaching are very accurate and used for large qty production but has same disadvantages except accuracy. Dr. G. R. C. PRADEEP

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b) Gear Generating method: The process is based on the principle that any two gears of same module will mesh together properly (module = pitch dia / no. of teet h). If one of the gears is made into a cutter by proper sharpening and it meshes with the gear blank, then the teeth on the blank are developed / generated by : a) The relative rolling and reciprocation motion of the cutter and the blankof(for and Shaping) b) Rotation hobPlaning and blank, feeding of hob and tilting of hob at the helix angle (for Hobbing). If the generating tool is a rack it is called Gear Planing. If the generating tool is a pinion, it is called Gear Shaping. If the generating tool is threaded and gashed (like worm) it is called hob, and the process is called Gear Hobbing. Dr. G. R. C. PRADEEP

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Gear planning is less accurate than other generating methods but more accurate than form cutting methods. Gear Hobbing is highly productive and highly accurate among all generation methods. Gear planning and Gear Hobbing are limited to external gears only. [(i) and (ii)] Gear Shaping can be used for both external and internal gears. [(iii) and (iv)] The major advantage of generating is that same cutter of particular module can cut gears of different no. teeth.

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GearPlaning

Gear Shaping Video 2

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Video 3

Gear Hobbing

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Finishing methods: Video –4 For smooth running, and good performance, the gears should be accurate. Common finishing methods that are employed after machining are: (a) For soft & unhardened gears → 1. Gear shaving: Shaving cutters perform minute cutting of flash or burr, correct profile errors, etc when meshed with machined gears.

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2. Gear burnishing: Gears are rolled under pressure with hardened gears to cause plastic flow of minute irregularities like dents, projections, cutter marks etc and also work hardens the surface creating beneficial compressive residual stresses. (b)For hard & hardened gears → 1. Grinding using form wheels

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2.Honing

3.Lapping

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JIGS AND FIXTURES Jig:- It is a device which holds and positions the work with the help of locating pins and clamps and locates (or) guides the cutting tool relative to the work. It is of lighter construction and is usually not fixed to the m/c. They are used for drilling and related operations like reaming, tapping, counter boring etc. Dr. G. R. C. PRADEEP

Locating pins: These are inserted in the body of Jigs and fixture to establish the desired relationship between work and jig or fixture. 229

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Fixture: It is a device which only holds and positions the works but does not itself locate (or) guide the cutting tool. It is of heavy

Machine Vice

construction is usually fixed and to the machine. They are used in turning, shaping, milling, grinding etc.

Dr. G. R. C. PRADEEP

Clamps: These are used to hold the work piece opposite to the action of cutting forces when ever fixtures are unable to do so. 230

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3-2-1 Principle of pin location

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Also called 6 - Point location principle. For anybody in free space there are 6 translatory moments and 6 rotary moments about x-y-z axis hence these 12 degrees of freedom (dof) are to be arrested for performing the machining operation. The figure shows how six pins can be used to arrest 9 dof. The pins A, B & C will not allow rotation about X & Y axis and also downward movement restricting 5 dof. The pins D & E will not arresting allow rotation about andallow also backward leftward moment 3 dof. The pin Z-axis F will not moment and hence arresting 1 more dof. To arrest the remaining 3 dof, 3 more pins will be required but this wi ll enclose the work completely and makes loading (or) unloading of work piece impossible. Thus to arrest these clamping devices are used. Dr. G. R. C. PRADEEP

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Other Principles of pin location: 1) Principle of minimum locating pins: The no. of locating pins used must be as min as possible. 2) Principle of extreme positions: The locating pins must be placed as far as possible from each other to achieve greatest degree of accuracy in location. 3) Principle of mutually ┴ planes: The work should be located such that the planes in which it is located are mutually ┴.

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Classification of locating pins 1) Locating pins: These are used when work pieces are having holes in them and are used for location purpose. a) Conical pins – Provide line contact and used for light jobs. Also can accommodate work pieces with varying hole sizes. b) Cylindrical / Round pins – Provide surface contact and used for heavy jobs. They can not accommodate work pieces with varying hole sizes. Provides uniform all around sliding clearance when work piece sits on it. Dr. G. R. C. PRADEEP

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c) Diamond pins – To be used in combination with round pins. They provide more lateral clearance and will take care of pitch distance variation in work pieces. Dr. G. R. C. PRADEEP

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2) Support pins: These are used when work pieces are not having holes in them.

a) b) a) Fixed Type – When work piece is having uniform dimensions. (Fixed Distance) b) Adjustable Type – When piece is having non-uniform dimensions. (Adjustable Distance) Dr. G. R. C. PRADEEP

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3) Jack Pins: – Used to accommodate different work pieces with different sizes and also in press tools for sheet metal location V-Locators: – Used for locating circular or semi-circular work pieces.

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Principles of clamping 1. The clamping pressure applied must counteract with the tool forces. 2. The clamping pressure should not deform the work piece. 3. The clamping should be simple, quick and foolproof. 4. The clamping pressure must be directed towards the point of support, otherwise the work may lift from the support. 5) Clamp should be arranged above the point of support. If not the clamping force may distort the work piece.

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TYPES OF CLAMPS 1. Light Clamping: a) Clamping Screws

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b) Hook Bolt Clamp

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2. Rigid Clamping – Lever type clamps: b) Swinging Latch Clamp

a) Bridge Clamp

c) Heel / Dog Clamp Dr. G. R. C. PRADEEP

d) Hinged Clamp 240

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3) Quick Clamping:

a) Quick Acting Nut WP

c) Cam operated clamp

b) C-Clamp Dr. G. R. C. PRADEEP

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Spherical Washers: They accommodate misalignment between clamp surface and clamping nut due to inclination of the strap. Thi s can be done by using a pair of spherical washers (male and female) instead of using a plain washer.

e

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Types of Drill Jigs 1)Template Jigs:- A template jig consists of a hardened template with holes in required position to gui de the drill. Here it is no t possible to vary the size of the drill.

2) Plate type jig:- It is similar to the above and is provided with Jig bushes instead of simple holes. Hence the same plate can be used for different size of the drill by replacing the jig bush provided the configuration of work piece is not changed. Dr. G. R. C. PRADEEP

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3) Box-type Jig :- This is used when holes are to be drilled in more than one plane.

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4) Swinging leaf Jig :- This will help easy loading and unloading of work piece.

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Note: Jigs can be made for drilling when large qty work pieces are required, otherwise it can be managed by marking and centre punching. But for drilling related operations like Reaming, Tapping, Counter boring etc, it is compulsory irrespective of qty of production. Types of fixtures: 1) Turning fixtures: Chucks, face plates, mandrels. 2) Shaper fixtures: M/c Vice 3) Milling fixtures: Milling m/c. vices, Setting blocks. 4) Surface grinding fixtures: Magnetic chucks (Ferrous metals), Vaccum chucks (Non-Ferrous metals) 5) Cylindrical grinding fixtures: Chucks, Face plates, Mandrels – (external grinding) Chucks, Face plates – (internal grinding) Dr. G. R. C. PRADEEP

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Setting Blocks – Used to set the work in relation to cutters for mass production Dr. G. R. C. PRADEEP

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Design principles common to jigs & Fixtures 1) The methods of location and clamping should be such that less time is consumed. 2) The jig / fixture must be as open as possible to enable the operator to remove the chips during operation. 3) Enough clearance must be provided to allow for variation in components sizes. 4) The Jig & fixture must be as rigid as possible. 5) Ejector devices must be used to force the work out of the Jig (or) fixture due to : a) Work piece is heavy b) Use of cutting fluids creates a film b/w surfaces which causes the work piece stick to the surface Dr. G. R. C. PRADEEP

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NON-TRADITIONAL M/C ING PROCESS Abrasive Jet Machining (AJM):

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This involves use of a high speed stream of abrasive particles (100 to 300m/s) carried by a high pressure (2 to 10 bar) gas (Co2,N2) / air on the work surface through a nozzle (ID = 0.2 to 1mm). The metal removal occurs through erosion caused by abrasive particles impacting the surface at high speed. The size and shape of the cut is controlled by moving the nozzle / work piece by cams, pantographs (or) other mechanisms. The abrasives generally used are Al O , SiC, 2 3 glass powder, etc. General Abrasive size is 10-50µm. Best cutting is achieved if size is b/w 15 µm to 20 µm. No zzle life for WC is 30hrs. Sapphire (Gem Stone) is 300 hrs. Mass flow rate of abrasives – 2 to 20 gm/min Flow rate of air / gas – 5 to 30 lit/min Stand-off Distance (SOD) or Nozzle tip distance – 0.5to5 mm Mixing ratio – Mass flow ratio of Abrasives to Gas / Air Dr. G. R. C. PRADEEP

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Applications: Producing different shapes/cavities in hard/brittle materials, fragile materials like Ag, Germanium, heat sensitive materials like glass, quartz, mica, silicon, Gallium, cleaning and polishing of plastics/Nylon/Teflon components, ceramics, deburring etc. Video 1

AWJM: Here a high jetofofsteel, waterAl, with abrasives can be used for cutting thickforce plates Metal Matrix Composites, Ceramic Matrix Composites, Fibre Reinforced Plastics etc. Video 2,3 WJM: Here a high force Jet of water can be used for cutting thin plates and foils of soft materials, paint removal, cleaning, cutting frozen meat, textile and leather industry. Dr. G. R. C. PRADEEP

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1. MRR = Volume of the material removed x (Mass flow rate of abrasives / Mass of abrasive grit) 2. Volume of material removed = 2πr3 / 3 r = radius of indentation = √(dg δ) dg = Diameter of abrasive particle δ = Depth of indentation 3. Mass of abrasive grit = πdg3ρg / 6 ρ = Density of abrasive particle 4. MRR gfor Brittle WP = MaVa3/2 / ρg1/4σw3/4 Va = Velocity of abrasive jet Ma = Mass flow rate of Abrasives σw = Flow strength of WP 5. MRR for Ductile WP = MaVa2 / 2σw 6. δ = Va dg √(ρg/6σw) Dr. G. R. C. PRADEEP

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Ultrasonic Machining (USM): Ultrasonic is vibratory wave of frequency > 16 KHz. Here a tool having the same shape of the cavity to be machined which is vibrating at 20 to 30 KHZ with amplitude between 0.01 to 0.06mm is pressed on to the work with a light force. An abrasive slurry is made to flow under pressure through tool – W.P. interface. This causes metal removal by abrasion. The tool is made of low carbon and other ductile metal alloys. Applications: Mainly used for brittle materials that have poor electrical conductivity and can not be machined by ECM/EDM. Machining of glass, ceramic, tungsten, gems, making tungsten carbide and diamond wire drawing dies, forging dies, extrusion dies etc. Dr. G. R. C. PRADEEP

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Video 4

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Chemical Machining (CHM): This is the stock removal process for producing desired shapes by removal of material by controlled chemical attack with acids/ alkalis (Etchant solution). Areas where material is not removed is protected by an etchant resistant material known as Maskant. a) Chemical Milling: Also called contour machining (or) etching is used for producing shapes by removing material from large surface areas. Application: Weight reduction by removing unwanted material from skin of Aeroplane, Rockets, Space crafts etc.

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b) Chemical Blanking: Also called photo forming / photo etching where material is completely removed by chemical action. The maskant is sensitive to ultraviolet light which is applied on W.P. A negative is first developed having the contour from the photograph of an enlarged drawing of the complex profile. It is placed on the coated W.P. under vaccum pressure and then exposed to U.V. light. The U.V. light hardens the selective areas of resist which gets washed away in further developing, thus, exposing the areas to be machined. Etchant solution will now remove the material from W.P. Application: Printed circuit cards, intricate burr free stampings c) Chemical Engraving: Similar to above to create irregular shapes (narrow) on forgings, castings, extrusions etc. Dr. G. R. C. PRADEEP

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Video 5

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Electro – Chemical Machining (ECM): This is the process of metal removal by controlled dissolution of the anode of an electrolytic cell. The tool is cathode and work is anode. The tool advances towards the anode through the electrolyte and metal is removed from work through electrical action. The electrolyte is pumped at high pr. through the gap to conduct current and carry heat. MRR is independent of work hardness, Strength and thermal properties. MRR depends on Atomic weight and Valency. Electrolyte is so chosen that only anode is dissolved but no deposition takes place on cathode. The tool is made of Cu, Brass, Steel. Practically there is no tool wear. This process is used for machining any conducting material, complex profiles like turbine blades, nozzles, complex cavities in high strength materials, drilling holes, die sinking etc. Dr. G. R. C. PRADEEP

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Alloy machined Iron based Ni based Ti based Co-Cr-W-based WC based

Electrolyte Chloride Sol. In water (20% NaCl) HCl (or) mixture of brine & H2SO4 10% HF+ 10% HCl + 10% HNO 3 NaCl Strong alkaline solution

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FORMULAE: 1. Metal Removal Rate, Q = AI/ρZF cm3/sec A = Gram Atomic weight of the metallic ion I = Current (Amp), ρ = Density of the anode (g/cm3) Z = Valence of the cation, F = Faraday = 96500 Coulombs 2. Current density in the gap = J = K(V-∆V) / y = KV/y

∆V = Over voltage (extra voltage) required for ion transfer 1/K = Specific resistance of electrolyte in Ω- cm y = Inter electrode gap in cm, V = Supply voltage 3. Current passing through electrodes = I = J x S.A 4. Let % P in Alloy PQ = X%, % Q in AlloyPQ = (100-X)% ϵ = Gram equivalent weight of the metal = A/Z As 100 % of Alloy = X % of P + (100-X) % of Q Hence, 5. Electrode feed rate = (MRR / Surface area) cm/sec Dr. G. R. C. PRADEEP

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6. Electrolyte Flow rate = q (cm3/sec) = [I2 x (1/K) x y] / [4.187 x SA x

ρe x Cpe x (θB- θA)]

ρe = Density of electrolyte; C pe = Specific heat of electrolyte θB = Boiling temp of electrolyte; θA = Ambient temp 7. Velocity of flow of electrolyte = U = q / by (cm/sec) Cross section of electrode = SA = b x l U= [I2 x (1/K)] / [4.187 x SA x

ρe x Cpe x (θB- θA) x b]

Resistance of electrolyte, Re = (1/K) y / A If V = Applied Voltage, then V = I Re Also, U = [V2 x l] / [4.187 x (1/K) x y2 x ρe x Cpe x (θB-

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θA)]

Electro-chemical grinding (ECG): This is modification of ECM and Grinding. The grinding wheel is made cathode. The work is Anode. The electrolyte is carried past the work surface at high speed by ro tary action of grinding wheel. The electrolyte entrapped in small cavities of semi conductive oxide between projecting nonconducting abrasives form electrolytic cells. When these cells into causing contact with work the current flows from of wheelcome to work electro chemical decomposition work. Wheel will have shape of work. Metallic grinding wheels embedded with non- conductive abrasive particles such as aluminium oxide, diamond etc set in the conducting material like copper, brass, and nickel are used. Around 90% of the metal is removed by electrolysis action and only 10% is due to the abrasive action of grinding wheel. Dr. G. R. C. PRADEEP

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•

Video 6

Applications: Tungsten carbide inserts, Burr free sharpening of syringe needles, Super alloy turbine blades, Aerospace materials, Super alloys – Haste alloy, Inconel, Rene alloy etc. Dr. G. R. C. PRADEEP

263

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Electric Discharge Machining (EDM): Spark Erosion is metal removal process by an interrupted electric spark discharge between tool (cathode) and work (anode). A spark gap is maintain between tool and work. A dielectric is passed at the inte rface like Transformer Oil, Paraffin Oil, Kerosene, Lubricant Oil etc which have high flash point. Dielectrics is a fluid that does not conduct current under normal circumstances. In EDM it insulates, cools the electrode & W.P., conveys Spark, flushes the removed metal. At a suitable range of voltage the dielectric breaks down and electrons are emitted ionizing the gap, which creates compression shock waves developing a localized temp. of order 10000oC which melts a small amount of material. Dr. G. R. C. PRADEEP

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Tool should have High electrical and thermal conductivities and high density. Work should have low specific heat for better MRR. (It is the heat required to raise the temp of material by 1 0C). In EDM process, fine openings and deeper slots need to be avoided. Very fine surface finish values should not be specified. Application: Stamping tools, wire drawing and extrusion dies, forging dies, mould cavities, slots and ribs, collets, jet engine blade slots, mould cooling slots, die sinking etc.

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Video 7 Dr. G. R. C. PRADEEP

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Wire EDM is a variant in EDM process. It is a CNC machine. A part program is prepared according to the complex profile to be cut. Wire is a tool. Brass wire (60% Cu, 40% Zn) is used for quick cutting applications. Molybdenum wires are used for more accurate applications. Deionised water is the dielectric because it has low conductivity levels. Application: Wire EDM is used

in Aerospace, Medical,

Electronics andDie Semiconductor applications. It is mainly used for Tool & making industries, for cutting the hard Extrusion Dies, in making Fixtures, Gauges & Cams, Cutting of Gears, Strippers, Punches and Dies, Manufacturing hard Electrodes, Honey comb structures etc. Video 8

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•

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FORMULAE: Spark EDM: 1. MRR = 40 I / Tm1.23 (cm3/min) Where, I is the current amp, Tm is the melting temperature of work piece in 0C 2.Idle Time = RC ln [Vs / (Vs – Vc)] sec R = Charging resistance, C = Charging capacitance Vs = Supply Voltage or Open circuit voltage Vc = Charging Voltage 3. Average power Input = Total energy consumed per cycle / Cycle time 4.Total energy consumed per cycle (or) Spark Energy = 0.5CVc2 (J/cycle) Dr. G. R. C. PRADEEP

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5. On Time or Discharge Time = RmC ln [Vc / Vd] Vd = Discharge Voltage Rm = Machine Resistance 6. For RC type generator to get maximum power dissipation during charging Vc = Vs x 0.716 7. Cycle Time = Idle Time + Discharge Time Wire EDM: 7. MRR = (CSA of cut x Wire feed) mm3 /sec CSA of cut = Width of cut x thickness of WP Width of cut = Wire Diameter + Spark gap around wire

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Electron Beam Machining (EBM): This is metal removal process by high velocity focussed stream of electrons which heats, melts and vapourises metal at point of bombardment. A beam of electrons is emitted from the electrode gun (Tungsten or Tantalum filament) is directed electro magnetically (deflecting coils) on to the work. The gun is supplied with electric current from a high voltage source. into The kinetic high velocity electrons dc is converted thermalenergy energyofvaporizing the material. However hole made by this process will have taper of 20 – 40 when sheet thickness exceeds 0.1mm. Application: Fine gas orifices less than 0.002mm in space nuclear reactors, holes in injector nozzles in diesel engines, turbine blades for supersonic aero engines, contours in sheets, narrow slots etc. Dr. G. R. C. PRADEEP

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Video 9

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Laser Beam Machining (LBM) : Laser is electromagnetic radiation hence a laser beam is focused on the spot to be machined. The laser provides enough heat to melt and vapourise the metal. We can focus the laser on a spot 1/100 of a square mm in size. However taper is observed in the holes up to 1 0 – 20 when thickness exceeds 0.25 mm Application: Extremely small holes in hard materials (micro machining production), fuel filters, carburetor nozzles, Syringe needles, Jet engine blade cooling holes, Holes in lock nuts for safety wires etc.

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Video 10

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Plasma Arc Machining (PAM): When a flowing gas is heated to sufficiently high temperature to become partially ionized, it is known as plasma. The temperature is 11000oC to 30000oC. Gas like H2 / N2/ O2 is passed through a small chamber in which a high frequency spark (Arc) is maintained (Electrode is Copper electrode with tungsten tip and ceramic nozzle). This spark ionizes the gas atoms liberating large amounts of thermal energy which further vapourises the metal. Application: Profile cutting of S.S., Al. alloys, Tantalum, Zirconium and other very difficult to m/c materials. Dr. G. R. C. PRADEEP

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•

Video 11

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Ion Beam Machining (IBM): Here the process does not depend on heating of work to point of evaporation. It consists of an electron gun which discharges free electrons into a chamber filled with Argon gas. The gas is ionized by the electrons. The work piece is then bombarded with this ion-beam. The bombarding ions dislodge the su rface atoms of work by transferring the kinetic energy to them. Application: Micro Machining of computer parts, fine wire drawing dies, machining and polishing of optical components, preparation of materials for various investigations such as the thinning of samples for transmission electron microscopy or for structuring surfaces in the semi conductor industry etc. Dr. G. R. C. PRADEEP

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•

Video 12 Dr. G. R. C. PRADEEP

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Energy type

Mechanism of Energy source Process material removal

1) Mechanical Erosion

Mechanical/Fluid AJM, motion USM

2) Electro Chemical

Electric current

Ion displacement

ECM

3) Mechanical Plastic shear and Electric current ECG and Electro- ion displacement and mechanical chemical motion 4) Chemical

Corrosive reaction

Corrosive agent

CHM

5) Electro thermal

Fusion, Vaporization

Electric spark

EDM

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Energy type

Mechanism of Energy source Process material removal

6) Electro Thermal

Fusion, Vaporization

High electrons

speed EBM

7) Electro Thermal

Fusion, Vaporization

Powerful radiation

LBM

8) Electro Thermal

Fusion, Vaporization

Ionized substance PAM

9) Electro Thermal

Fusion

Ionized substance IBM

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Process

Surface Finish (µm)

Tolerance (mm)

USM

0.2– 1.6

AJM

0.3 – 2.3

± 0.002 to ± 0.005 0.0001

EDM

0.05 – 12.5

± 0.005 to ± 0.125 0.10

LBM

0.4 – 6.3

± 0.015 to ± 0.125 0.0001

EBM

25 – 35

± 0.3 to ± 0.4

ECM

0.2 – 1.5

± 0.005 to ± 0.25

PAM 2 –4

± 0.0125

MRR (cm3/ sec)

±0.125 Dr. G. R. C. PRADEEP

0.005

0.001 1.0 1.5

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NC, CNC, DNC, NC PART PROGRAMING Numerical control: An NC system consists of 3 basic components a) Program of Instructions: Detailed step by step directions which tells the machine tool what to do a nd is given by punched tape of paper / plastic. There are eight tracks. Two systems are used in preparation of tape. EIA system (Electronics Industry Association) follows Odd parity and stops the machine in event of finding even no. of holes. ISO system (International Organization for Standardization) follows even parity. Track 5 is used to punch extra hole to convert to odd (or) even system accordingly.

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Track No.: 1 to 4  Numerical values for dimensions, speeds etc. 5  Parity check – Check for errors in hole punching. 6 & 7  Alphabets – To identify various operations 8 End of block instruction b) Machine Control Unit



Which has 2 modules



(i) Datacircuits, processing unit circuits Consisting of a tape reader, reading decoding etc. (ii) Control loop unit  Consisting of position control loops, velocity control loops, coolant on / off, spindle on / off functions etc. c) Machine tool  Which performs the operation.

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Computer Numerical control: CNC is a NC system that utilizes a computer to perform the basic NC functions. NC systems are based on hard wired based controllers, where as CNC systems are based on soft wired based controllers. In a Hybrid CNC, the hardware components perform fns. like feed rate generation, circular interpolation etc. and the computer performs remaining control functions. In a straight CNC all the NC the functions are performed by computer. Direct Numerical Control: It is a manufacturing system in which No. of M/Cs are controlled by a computer through direct connection. The DNC computer provides instructions to each M/C/T on demand. DNC has a central computer, bulk memory to store NC part programs, telecommunication lines and M/C/T. Dr. G. R. C. PRADEEP

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Stepper motors: For operation of main spindle, AC or DC or servo motors are used. Servo motors have feedback sensors to give feed back to the controller. Stepper motors are used for rotary table control, tool (or) work positioning etc and are used without need for feedback system. In these motors the rotation of the shaft is divided into no. of parts known as “step”. Distances are converted to pulses and are fed to the stepper motor, and then the motor rotates the given angle. Eg: For 41 pulses, a 1.8 0 stepper motor (360/200) rotate precisely by (= 41 x 1.80) = 73.8 o ± 4% of step accuracy which is 0.07 o (0.04 x 1.8) Dr. G. R. C. PRADEEP

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BLU (Basic Length Unit): BLU represents the accuracy or resolution of the Machine Tool, which is defined as the minimum distance the machine tool slide can move. The units of measurement of coordinates can be given inches (or) mm in any NC system. But the values given in a programme are to be whole numbers (integers) only. Hence to represent the fractional dimensions, those values are divided by the resolution of the N.C. system. Eg; To represent a displacement of 1.115” in a NC M/C having resolution of 0.001”, it can be written as = 1.115 / 0.001 = 1115 BLU

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FORMULAE: 1.BLU = U x n x P x N U = Gear ratio, n = No .of starts of lead screw P = Pitch of lead screw, N = No. of revolutions/step 2. Speed of movement of table or m/c slide on lead screw = Distance travelled for one rotation / Time for one rotation 3. Frequency of pulses generated (Pulses /sec or Hz) = Speed ofmoved the table m/c =slide / Distance moved per pulse 4. Distance peror pulse BLU 5. 1 Pulse will cause rotation of stepper motor by 1 step 6. Any applied voltage will cause the table or m/c slide to move at a particular speed. If speed of movement has to be increased, voltage supplied has to be increased.

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Part programming Types of control systems: 1. Point – to - Point Control: In this system, the m/c. tool slide reaching a particular fixed coordinate point in the shortest possible path at rapid feed. This is suitable for drilling, tapping, reaming, punch presses, Jig boring etc. 2. Straight line control: This is an extension of point to point system, with a provision for machining along a st. line as in case of milling and turning operation at controlled or programmed feed rate. P 5

P1

P4

P3

P5

P4

P3 P3

P2 P1

(1) Dr. G. R. C. PRADEEP

P2

(2) 290

P1

(3)

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P2

3. Continuous path (or) contouring control: This system enables machining of profiles, contours and curved surfaces. The method by which continuous path system moves from one point to another point is called interpolation. Three types of interpolation are used – linear, circular and parabolic. Only few systems use parabolic interpolation. Linear interpolation enables machining along st. line including and circular enables machining circles taper and arcs. In linearinterpolation interpolation, the coordinates of the end point of line act as the beginning of next line. In circular interpolation also, the current point acts as the starting point and hence the end point of arc, arc radius etc. have to be mentioned.

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Methods of listing coordinates of points: (i) Absolute coordinate system: Here the coordinates of a point are always referred with reference to the same datum. Error correction is easy as any mistake made effects only that value. (ii) Incremental coordinate system: Here the coordinates of any point are calculated with reference to the previous point. Error correction is difficult as any mistake made effects all successive values also. 4

P4

3

POINT

+

P3

-

+

2 1 (0, 0)

P1

1

P2 2

3

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ABSOLUTE

INCREMENTAL

P1

(1,2)

(1,2)

P2

(2,2)

(1,0)

P3

(2,4)

(0,2)

P4

(1,3)

(-1,-1)

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Programming formats: Format is the method of writing the words in a bl ock of instruction. Three program formats are used. Fixed Block Format: Here the instructions are always given in the same sequence. All instructions must be given in every block, including those which remain unchanged from the preceding block. Tab Sequential Format: Here the instructions a block are always given in the same sequence as in case of fixed block format and each word is separated by the TAB character (>). If the word remaining same in succeeding block, the word need not be repeated but TAB (>) is required to maintain the sequence of words .

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Word address Format: Here each word is preceded and identified by its address letter. Here there is no fixed sequence. If word is unchanged, it need not be repeated in next blocks. Example: Fixed block format 00115.020.0200500EOB N X Y F S EOB 001 15.0 20.0 200 500 EOB 002 75.0 20.0 200 500 EOB TAB sequential format N X Y F S EOB 001 > 15.0 >20.0 >200 >500>EOB 002 > 75.0 >>>>EOB Word Address Format N001 X15.0 Y20.0 F200 S500 EOB N002 X75.0 EOB Dr. G. R. C. PRADEEP

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Writing a part program: The first instruction in any part program is to inform the control system about the various set-up conditions for the machining task to be taken up and should specify the following. 1. Block Number (Sequence number - N) 2. Coordinate value – absolute (or) incremental 3. Dimensional units – inches or metric 4. Tool Number ( T – word) 5. Spindle speed (S – Word) 6. Feed function (F – Word) – (mm/min or mm/rev) Each block is terminated by typing EOB character. Dr. G. R. C. PRADEEP

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Some codes: a) Preparatory function (or) operation code ‘G’  G00 - Point to point positioning, rapid traverse G01 - Linear interpolation G02 - Circular Interpolation C.W. G03 - Circular Interpolation C.C.W. G04 - Dwell G70 G71 G90 G91 G92

--

G94 G95 -

Dimensioning in in metric inch units Dimensioning units Absolute dimensions Incremental dimensions Zero preset [Presetting the srcin (changing the starting point) to any point other than (0,0)] Feed rate mm/ min Feed rate mm/rev Dr. G. R. C. PRADEEP

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b) Dimensional words  X,Y,Z 

Primary set of axes

c) Miscellaneous functions, M  M00



Program stop

M01



Optional stop

M02



End of program

M03 M04

 

Spindle C.W. Spindle C.C.W.

M05



Spindle OFF

M06



Tool change



Coolant ON



Coolant OFF

M07, M08 M09

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CANNED CYCLES / FIXED CYCLES: These are use for reducing length of part program so that the need to write repetitive instructions is avoided and less memory required. 1. Drill Cycle: (G81) When used the tool movements are (i) Rapid in X and / or Y to reach location (ii) Rapid in Z-axis to gauge height (iii) At a programmed feed in Z-axis to the depth (iv) Rapid retract to gauge height If used these 4 steps are automatically executed in same order every time G81 is used.

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2. Mill Cycle: (G78, G79) when used the table movements are (i) Rapid in X and / or Y to reach location (ii) Rapid in Z-axis to gauge height (iii) At a programmed feed in Z-axis to the depth (iv) Movement to remaining position if further programmed. G78 & G79 can be alternately used when moving in different planes for next cuts. 3. Cancel cycle: (G80) must be used to canc el the previous fixed cycle in the program to start another fixed cycle, in case of multiple operations. Dr. G. R. C. PRADEEP

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APT (Automatically Programmed Tools): The parts discussed previously are not so complex. They require less No. of instructions. However, most of the parts machined on NC M/C are more complex and hence the manual part programs become lengthy and very tedious in terms of defining parameters. Computer Aided Part Programming (CAPP) offers solution to these type of complex programs through programming languages like APT, ADAPT, AUTOMAP, EXAPT etc. The syntax rules of APT are very near to FORTRAN language. APT can be used to control up to 5 –axis. In APT it is ass umed that W.P. is stationary and tool does all the moving. The field length of each word is limited to 6 characters.

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Part Geometric definitions: Defining a point: Point is the smallest and basic element required to define a geometry. P1 (6,5,4)

(a) Cartesian coordinates P1 = POINT / 6,5,4

L1 P1

(b) By intersection of two lines

L1

P1 = POINT / INTOF, L1, L2 (c)

P1

By centre of circle P1 = POINT / CENTER, C1 Dr. G. R. C. PRADEEP

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C1

(2) (a)

Defining a Line: L1

P1

By joining two points

P2

L1 = LINE / P1, P2 (b)

By a point and parallel line

P1

L1 L2

L1 = LINE / P1, PARLEL, L2 (c)

By a point and a perpendicular line L1 = LINE / P1, PERPTO, L2

P1 L1 L2

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(d)

By a point and tangent to circle L1 = LINE / P1 , LEFT, TANTO, C1

C1

L1

C1

P1

L1 = LINE / P1, RIGHT, TANTO, C1

L1 P1

3)

DEFINING A CIRCLE:

C1 20

(a)

By centre point and radius

P1

C1 = CIRCLE / CENTER, P1, RADIUS, 20

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(b)

By Centre point and a point on circumference P2

C1 = CIRCLE / P1, P2 P1

(c)

Centre point and tangent line

C1 = CIRCLE / CENTER, P1, LEFT, TANTO, L1 P1

P1

C1 = CIRCLE / CENTER, P1, RIGHT, TANTO, L1 Dr. G. R. C. PRADEEP

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C1

4) (a)

DEFINING A PLANE: By 3 points PL = PLANE / P1, P2, P3

P3

P1 P2

(b) By a parallel plane which is at a distance PL1 Z = 30 PL2

PL2 = PLANE / PARLEL, PL1, ZLARGE, 30 Note: ZLARGE & ZSMALL can be used for telling the computer to use the largest (or) smallest values for Z. Dr. G. R. C. PRADEEP

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MISCELLANEOUS STATEMENTS: a) Spindle speed SPINDL / 2000, CLW SPINDL / 2000, CCLW SPINDL / OFF b) Feed Rate  MMPM – mm / min. FEDRAT / 2,MMPM FEDRAT / 0.1, MMPR  MMPR – mm / rev. c) Tool Change LOADTL /1 Note: LOADTL also unloads the previous tool and replaces it in the tool magazine. d) Tool definitions  CUTTER / 10 Cutter of dia 10 mm. Dr. G. R. C. PRADEEP

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e) Motion statement of Tool  (i) Initial position:  FROM / 6,5,4 Reference point  FROM / P1 Predefined point FROM / SETPT  Starting point

(or) (or)

(ii) Point to point motion : GOTO / P1 To position cutter above the required location. GODLTA / 0,0,10  Incremental instruction to move tool. Note: GODLTA is useful in drilling and related operations. iii) Contouring motion statements: GO/TO, L1, TO, C2  Tool moves touching surface of line L1 and moves towards circle C2 Dr. G. R. C. PRADEEP

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iv) Intermediate movement commands GOLFT  Leftward  Rightward GORGT GOFWD  Forward GOBACK  Backward BACK  Upward GOUP GODOWN  Downward

UP LFT

FWD

RGT DOWN

TO

These six commands are Used with one of the four ON Modifiers to define the surfaces. SURFACE TO  Just touching the surface PAST ON  On the surface PAST  Touching the surface on the far side TANTO  Used mostly for circles Dr. G. R. C. PRADEEP

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The surfaces defined are: (a) Drive surface (DS)



(b) Part surface (PS)



(c) Check surface (CS)

Guides the tool for producing desired shape of part. Guides the tool point (or) tool bottom Stops the tool indicating the end of motion.



CS

PS

DS Dr. G. R. C. PRADEEP

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Auxiliary and post processor statements: (a) MACHIN / UNIV

 For

(b) COOLNT / ON

 Coolant

COOLNT / OFF

defining name of machine. on

 Coolant off

(c)

FINI



Program is terminated

(d)

END



Shuts down the NC including the MCU

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