Gajra Gears Summer Training Report

REPORT

Industrial Training for

gajra gears dewas

IN PARTIAL FULFILLMENT OF INDUSTRIAL TRAINING

SUBMITTED BY

SUBMITTED TO

Manish Jain

R. B, Dutta

(Sch. No.111116040) B.Tech (Final Year) MANIT-Bhopal

factory manager gajra gears dewas

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Acknowledgem ent

Summer training is a golden opportunity for learning and selfdevelopment. I consider myself very lucky and honored to have so many wonderful people lead me through in completion of this project.

My grateful thanks to Mr. R. B. Dutta Sir who in spite of being extraordinarily busy with their duties, took time out to hear, guide and keep me on the correct path. I do not know where I would have been without him. A humble ‘Thank you’ Sir. I am also very thankful to Mr. K.K. Sinha, for his guidence in heat treatment plant.

Last but not the least there were so many who shared valuable information that helped in the successful completion of this project.

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CERTIFICATE This is to certify that the dissertation work entitled “Gear manufacturing processes” is a bonafide work carried out in partial fulfilment of the requirements for the award of Bachelor of Technology in MechanicalEngineering from Maulana Azad National Institute of Technology, Bhopal during the year 2011-2015.

Project Guide Mr R. B . Dutta

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ABOUT THE INDUSTRY INDUSTRY OVERVIEW The Gajra Group made its beginnings in 1950 with the formation of Elve Corporation. Originally trading in diesel engines and spares it then moved on to making Gears in 1962 with the set up of Gajra Gears. After establishing a name in automotive gears the group further added to its capabilities by setting up Gajra Differential Gears in 1991. With a modest beginning the group has over the years expanded its product range. The Gajra Group now offers transmission and differential gears, cutting tools and toolings (jigs, fixtures) that serve the purpose of manufacturing these gears, material handling pallets for the safe movement of these goods and machined castings and assemblies.

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Plant Layout

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Automotive Industry Global Position of Indian Automotive Industry: Automotive industry plays a pivotal role in country's rapid economic and industrial development. It caters to the requirement of equipment for basic industries like \ steel, non-ferrous metals, fertilizers, refineries, petrochemicals, shipping, textiles, plastics, glass, rubber, capital equipments, logistics, paper, cement, sugar, etc. It\ facilitates the improvement in various infrastructure facilities like power, rail and road transport. Due to its deep forward and backward linkages with almost

every segment of the economy, the industry has a strong and positive multiplier effect and thus propels progress of a nation. The automotive industry comprises of the automobile and the auto component sectors. It includes passenger cars; light, medium and heavy commercial vehicles; multi-utility vehicles such as jeeps, scooters, motor-cycles, three wheelers, tractors, etc; and auto components like engine parts, drive and transmission parts, suspension and braking parts, electrical, body and chassis parts; etc. In India, automotive is one of the largest industries showing impressive growth over the years and has been significantly making increasing contribution to overall industrial development in the country. Presently, India is fifth largest manufacturer of commercial vehicles as well as largest manufacturer of tractors. The sector has shown great advances in terms of development, spread, absorption of newer technologies and flexibility in the wake of changing business scenario. The Indian automotive industry has made rapid strides since delicensing and opening up of the sector in 1991. It has witnessed the entry of several new manufacturers with the state-of-art technology, thus replacing the monopoly of few manufacturers. The norms for foreign investment and import of technology have also been liberalised over the years for manufacture of vehicles. (Source: Website of Business Portal of India: Industry and Services: Automobile Industry) 6

Domestic Scenario Indian Economy: There was a significant slowdown in the growth rate in the second half of 2008-09, following the financial crisis that began in the industrialised nations in 2007 and spread to the real economy across the world. The growth rate of the gross domestic product (GDP) in 2008-09 was 6.7 per cent, with growth in the last two quarters hovering around 6 per cent. The real turnaround came in the second quarter of 2009-10 when the economy grew by 7.9 per cent. As per the advance estimates of GDP for 2009-10, released by the Central Statistical Organisation (CSO), the economy is expected to grow at 7.2 per cent in 2009-10, with the industrial and the service sectors growing at 8.2 and 8.7 per cent respectively. This recovery is impressive for at least three reasons. First, it has come about despite a decline of 0.2 per cent in agricultural output, which was the consequence of sub-normal monsoons. Second, it foreshadows renewed momentum in the manufacturing sector, which had seen continuous decline in the growth rate for almost eight quarters since 200708. Indeed, manufacturing growth has more than doubled from 3.2 per cent in 2008-09 to 8.9 per cent in 2009-10. Third, there has been a recovery in the growth rate of gross fixed capital formation, which had declined significantly in 2008-09 as per the revised National Accounts Statistics (NAS).

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GEAR A gear is a rotating machine part having cut teeth, or cogs, which mesh with another toothed part in order to transmit torque. Two or more gears working in tandem are called a transmission and can produce a mechanical advantage through a gear ratio and thus may be considered a simple machine. Geared devices can change the speed, torque, and direction of a power source. The most common situation is for a gear to mesh with another gear; however, a gear can also mesh with a non-rotating toothed part, called a rack, thereby producing translation instead of rotation. The gears in a transmission are analogous to the wheels in a pulley. An advantage of gears is that the teeth of a gear prevent slipping. When two gears of unequal number of teeth are combined, a mechanical advantage is produced, with both the rotational speeds and the torques of the two gears differing in a simple relationship. In transmissions which offer multiple gear ratios, such as bicycles and cars, the term gear, as in first gear, refers to a gear ratio rather than an actual physical gear. The term is used to describe similar devices even when the gear ratio is continuous rather than discrete, or when the device does not actually contain any gears, as in a continuously variable transmission. Gears are mechanical components within machines and mechanical assemblies which transmit power and motion through successive engagement of their peripheral teeth. Gears perform certain key functions with machines and assemblies, including: •

Reversing rotational direction

• • •

Altering angular orientation of rotary motion Converting rotary to linear motion and vice-versa Altering speed and power transmission ratios 8

Gear design is based upon an involute curve form which imparts a rolling, rather than sliding action between engaging teeth. This rolling action provides a uniform rotary action that lowers both friction and wear of the gear teeth.

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TYPES OF GEARS SPUR GEARS Spur gears or straight-cut gears are the simplest type of gear. They consist of a cylinder or disk with the teeth projecting radially, and although they are not straight-sided in form, the edge of each tooth is

straight and aligned parallel to the axis of rotation. These gears can be meshed together correctly only if they are fitted to parallel shafts. HELICAL GEAR Helical or "dry fixed" gears offer a refinement over spur gears. The leading edges of the teeth are not parallel to the axis of rotation, but are set at an angle. Since the gear is curved, this angling causes the tooth shape to be a segment of a helix. Helical gears can be meshed in parallel or crossed orientations. The former refers to when the shafts are parallel to each other; this is the most common orientation. In the latter, the shafts are non-parallel, and in this configuration the gears are sometimes known as "skew gears". The angled teeth engage more gradually than do spur gear teeth, causing them to run more smoothly and quietly. With parallel helical gears, each pair of teeth first make contact at a single point at one side of the gear wheel; a moving curve of contact then grows gradually across the tooth face to a maximum then recedes until the teeth break contact at a single point on the opposite side. In spur gears, teeth

suddenly meet at a line contact across their entire width causing stress and noise. Spur gears make a characteristic whine at high speeds. Whereas spur gears are used for low speed applications and those situations where noise control is not 10

a problem, the use of helical gears is indicated when the application involves high speeds, large power transmission, or where noise abatement is important. The speed is considered to be high when the pitch line velocity exceeds 25 m/s. A disadvantage of helical gears is a resultant thrust along the axis of the gear, which needs to be accommodated by appropriate thrust bearings, and a greater degree of sliding friction between the meshing teeth, often addressed with additives in the lubricant.

For a 'crossed' or 'skew' configuration, the gears must have the same pressure angle and normal pitch; however, the helix angle and handedness can be different. The relationship between the two shafts is actually defined by the helix angle(s) of the two shafts and the handedness, as defined for gears of the same handedness for gears of opposite handedness Where is the helix angle of gear. The crossed configuration is less mechanically sound because there is only a point contact between the gears, whereas in the parallel configuration there is a line contact. Quite commonly, helical gears are used with the helix angle of one having the negative of the helix angle of the other; such a pair might also be referred to as having a right-handed helix and a left-handed helix of equal angles. The two equal but opposite angles add to zero: the angle between shafts is zero – that is, the shafts are parallel. Where the sum or the difference (as described in the equations above) is not zero the shafts are crossed. For shafts crossed at right angles, the helix angles are of the same hand because they must add to 90 degrees.

DOUBLE HELICAL 11

Double helical gears, or herringbone gears, overcome the problem of axial thrust presented by "single" helical gears, by having two sets of teeth that are set in a V shape. A double helical gear can be thought of as two mirrored helical gears joined together. This arrangement cancels out the net axial thrust, since each half of the gear thrusts in the opposite direction resulting in a net axial force of zero. This arrangement can remove the need for thrust bearings. However, double helical gears are more difficult to manufacture due to their more complicated shape. For both possible rotational directions, there exist two possible arrangements for the oppositely-oriented helical gears or gear faces. One arrangement is stable, and the other is unstable. In a stable orientation, the helical gear faces are oriented so that each axial force is directed toward the centre of the gear. In an unstable orientation, both axial forces are directed away from the centre of the gear. In both arrangements, the total (or net) axial force on each gear is zero when the gears are aligned correctly. If the gears become misaligned in the axial direction, the unstable arrangement will generate a net force that may lead to disassembly of the gear train, while the stable arrangement generates a net corrective force. If the direction of rotation is reversed, the direction of the axial thrusts is also reversed, so a stable configuration becomes unstable, and vice versa. Stable double helical gears can be directly interchanged with spur gears without any need for different bearings.

BEVEL 12

A bevel gear is shaped like a right circular cone with most of its tip cut off. When two bevel gears mesh, their imaginary vertices must occupy the same point. Their shaft axes also intersect at this point, forming an arbitrary nonstraight angle between the shafts. The angle between the shafts can be anything except zero or 180 degrees. Bevel gears with equal numbers of teeth and shaft axes at 90 degrees are called mitre gears. SPIRAL BEVEL The teeth of a bevel gear may be straightcut as with spur gears, or they may be cut in a variety of other shapes. Spiral bevel gear teeth are curved along the tooth's length and set at an angle, analogously to the way helical gear teeth are set at an angle compared to spur gear teeth. Zerol bevel gears have teeth which are curved along their length, but not angled. Spiral bevel gears have the same advantages and disadvantages relative to their straight-cut cousins as helical gears do to spur gears. Straight bevel gears are generally used only at speeds below 5 m/s (1000 ft/min), or, for small gears, 1000 r.p.m.

HYPOID 13

Hypoid gears resemble spiral bevel gears except the shaft axes do not intersect. The pitch surfaces appear conical but, to compensate for the offset shaft, are in fact hyperboloids of revolution. Hypoid gears are almost always designed to operate with shafts at 90 degrees. Depending on which side the shaft is offset to, relative to the angling of the teeth, contact between hypoid gear teeth may be even smoother and more gradual than with spiral bevel gear teeth. Also, the pinion can be designed with fewer teeth than a spiral bevel pinion, with the result that gear ratios of 60:1 and higher are feasible using a single set of hypoid gears. This style of gear is most commonly found driving mechanical differentials; which are normally straight cut bevel gears; in motor vehicle axles. RACK & PINION A rack is a toothed bar or rod that can be thought of as a sector gear with an infinitely large radius of curvature. Torque can be converted to linear force by meshing a rack with a pinion: the pinion turns; the rack moves in a straight line. Such a mechanism is used in automobiles to convert the rotation of the steering wheel into the left-to-right motion of the tie rod(s). Racks also feature in the theory of gear geometry, where, for instance, the tooth shape of an interchangeable set of gears may be specified for the rack (infinite radius).

Gear Terminology There are several gear and gear-tooth dimensions and terms important to the understanding of gear production and finishing processes. These terms include: 14

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Base Circle: The diameter from which the involute tooth profile is developed.

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Pitch Circle: The imaginary rolling circle produced by the meshing gears during rotation. Also known as the Pitch Diameter.

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Line of Centers: Line connecting the Pitch Circle centers of mating gears.

• Pitch Point: The point of tangency of two gear Pitch Circles,

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through the Line of Centers. •

Line of Action: A line tangent to the Base Circles of mating gears, through the Pitch Point and thus the path of tooth contact.

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Pressure Angle: The angle formed between the Line of Action and a line tangent to the Pitch Point.

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Outside Circle: The outside diameter of gear. Also known as the Addendum Circle.

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Root Circle: The diameter of the gear at the tooth base. Also known as the Dedendum Circle.

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Addendum: The radial distance between the Pitch Circle and the Outside Circle of the gear.

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Dedendum: The radial distance between the Pitch Circle and the Root Circle.

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Tooth Thickness: The thickness of the gear tooth measured along the Pitch Circle.

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Circular Pitch: The length of the arc along the Pitch Circle between corresponding points of adjacent teeth.

 Face Width: The width of gear tooth measured axially. •

Tooth Face: The mating surface of a gear tooth between the Outside Circle and the Pitch Circle. 16

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Tooth Flank: The mating surface of a gear tooth measured between the Pitch Circle and the Root Circle.

Flow-chart showing gear manufacturing process

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Gear Manufacturing Introduction 18

Because of their capability for transmitting motion and power, gears are among the most important of all machine elements. Special attention is paid to gear manufacturing because of the specific requirements to the gears. The gear tooth flanks have a complex and precise shape with high requirements to the surface finish. Materials used to produce gears may include steel-which is the most common material, and various non-ferrous materials including plastics and composites. Manufacturing methods include: machining, forging, casting, stamping, powder-metallurgy techniques, and plastic injection molding. Of these, machining is the most common manufacturing method used. Gear machining is classified into two categories: 1. Gear Generating 2. Gear Form-Cutting Gear generating Gear generating involves gear cutting through the relative motion of a rotating cutting tool and the generating, or rotational, motion of the work piece. The two primary generating processes are hobbing and shaping.In gear generating, the tooth flanks are obtained (generated) as an outline of the subsequent positions of the cutter, which resembles in shape the mating gear in the gear pair HOBBING: Hobbing uses a helically fluted cutting tool called a hob. Both the hob and the work piece rotate as the hob is fed axially across the gear blank. Hobbing is limited to producing external gear teeth on spur and helical gears. Hobbing can be performed on a single gear blank, but also allows for stacking of multiple work pieces,

increasing production rates. Gear hobbing is a machining process in which gear teeth are progressively generated by a series of cuts with a helical cutting tool (hob). 19

All motions in hobbing are rotary, and the hob and gear blank rotate continuously as in two gears meshing until all teeth are cut. When bobbing a spur gear, the angle between the hob and gear blank axes is 90° minus the lead angle at the hob threads. For helical gears, the hob is set so that the helix angle of the hob is parallel with the tooth direction of the gear being cut. Additional movement along the tooth length is necessary in order to cut the whole tooth length: SHAPPING Shaping produces gears by rotating the work piece in contact with a reciprocating cutting tool. The cutter may be pinion shaped, a multi-tooth rack-shaped cutter, or a single-point cutting tool. This modification of the gear shaping process is defined as a process for generating gear teeth by a rotating and reciprocating pinion-shaped cutter. The cutter axis is parallel to the gear axis. The cutter rotates slowly in timed relationship with the gear blank at the same pitch-cycle velocity, with an axial primary reciprocating motion, to produce the gear teeth. A train of gears provides the required relative motion between the cutter shaft and the gear-blank shaft. Cutting may take place either at the downstroke or upstroke of the machine. Because the clearance required for cutter travel is small, gear shaping is suitable for gears that are located close to obstructing surfaces such as flanges. The tool is called gear cutter and resembles in shape the mating gear from the conjugate gear pair, the other gear

being the blank. Gear shaping is one of the most versatile of all gear cutting operations used to produce internal gears, external gears, and integral gear-pinion arrangements. 20

Advantages of gear shaping with pinion-shaped cutter are the high dimensional accuracy achieved and the not too expensive tool. The process is applied for finishing operation in all types of production rates

Generating action of a gearshaper cutter; (Bottom) series of photographs showing various stages in generating one tooth in a gear by means of a gear shaper, action taking place from right to left, corresponding to a diagram above. One tooth of the cutter was painted white.

Gear forming

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In gear form cutting, the cutting edge of the cutting tool has a shape identical with the shape of the space between the gear teeth. Two machining operations, milling and broaching can be employed to form cut gear teeth.

The principle of gear forming Form milling In form milling, the cutter called a form cutter travels axially along the length of the gear tooth at the appropriate depth to produce the gear tooth. After each tooth is cut, the cutter is withdrawn, the gear blank is rotated (indexed), and the cutter proceeds to cut another tooth. The process continues until all teeth are cut.

Each cutter is designed to cut a range of tooth numbers. The precision of the form-cut tooth profile depends on the accuracy of the cutter and the machine and its stiffness.

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Dividing head (Left), and footstock Form cutters for finishing cutting (Left) and

for rough cuts (Right).

(Right) used to

index the gear blank in form milling.

In form milling, indexing of the gear blank is required to cut all the teeth. Indexing is the process of evenly dividing the circumference of a gear blank into equally spaced divisions. The index head of the indexing fixture is used for this purpose. The index fixture consists of an index head (also dividing head, gear cutting attachment) and footstock, which is similar to the tailstock of a lathe. The index head and footstock attach to the worktable of the milling machine. An index plate containing graduations is used to control the rotation of the index head spindle. Gear blanks are held between centers by the index head spindle and footstock. Work-pieces may also be held in a chuck mounted to the index head spindle or may be fitted directly into the taper spindle recess of some indexing fixtures. Broaching Broaching can also be used to produce gear teeth and is particularly applicable to internal teeth. The process is rapid and produces fine surface finish with high dimensional accuracy. However, because broaches are

expensive-and a separate broach is required for each size of gear-this method is suitable mainly for highquantity production.

Broaching the teeth of a gear segment by horizontal external broaching in one pass.

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Gear Finishing After manufacturing, gears require a number of finishing operations. Finishing operations include heat treatment and final dimensional and surface finishing. This finishing can be accomplished using:  Shaving  Grinding  Honing Shaving is performed with a cutter having the exact shape of the

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finished gear tooth. Only small amounts of material are removed by a rolling and reciprocating action. The process is fast but generally expensive due to the cost of machinery and tooling. Shaving is typically performed prior to heat treating. Grinding sometimes serves as an initial gear production process, but is most often employed for gear finishing. Grinding is classified as either form grinding or involutegeneration grinding. Form grinding uses wheels having the exact shape of the tooth spacing. The grinding wheels are either vitrifiedbond wheels, which require periodic re-dressing, or Cubic Boron Nitride (CBN) wheels, which can last hundreds of times longer than vitrified wheels without dressing. Involutegeneration grinding refers to a grinding wheel or wheels used to finish the gear tooth by axially rotating the workpiece while it is reciprocated in an angular direction, which in turn is determined by the type of gear being finished. This type of grinding is performed either intermittently or continuously. Intermittent grinding uses tooth profiles dressed on cup wheels, or on one or two single-rib wheels. Each tooth is ground individually, then the next is indexed to the wheel. Continuous grinding uses grinding wheels with the rack profile dressed helically on the outside diameter. Both the grinding wheel and the work turn in timed relationship for continuous finishing.

Honing involves the meshing of the gear teeth in a cross axis 27

relationship with a plastic, abrasive impregnated gear shaped tool. The tool traverses the tooth surface in a back and forth movement parallel to the workpiece axis. Honing polishes the gear tooth surface and can be used to correct minor errors in gear tooth geometry.

LAPPING Lapping is a machining process, in which two surfaces are rubbed together with an abrasive between them, by hand movement or by way of a machine. This can take two forms. The first type of lapping (traditionally called grinding), typically involves rubbing a brittle material such as glass against a surface such as iron or glass itself (also known as the "lap" or grinding tool) with an abrasive such as aluminum oxide, jeweller's rouge, optician's rouge, emery, silicon carbide, diamond, etc., in between them. This produces microscopic conchoidal fractures as the abrasive rolls about between the two surfaces and removes material from both. Lapping and polishing is a process by which material is precisely removed from a workpiece (or specimen) to produce a desired dimension, surface finish, or shape. The process of lapping and polishing materials has been applied to a wide range of materials and applications, ranging from metals, glasses, optics, semiconductors, and ceramics. Lapping and polishing techniques are beneficial due to the precision and control with which material can be removed. Surface finishes in the nanometer range can

also be produced using these

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techniques, which makes lapping and polishing an attractive method for materials processing. Lapping is the removal of material to produce a smooth, flat, unpolished surface. Lapping processes are used to produce dimensionally accurate specimens to high tolerances (generally less than 2.5 μm uniformity). The lapping plate will rotate at a low speed

(