Module 1

1. Die Design Fundamentals by J. R. Paquin, Industrial Press 2. Techniques of Press Working Sheet Metal by D F Eary and E

A Reed 3. Press Tools Design and Construction by P H Joshi, S Chand Publishing 4. Tool Design by C. Donaldson and V C Goold, TMH 5. Production Engineering by P. C. Sharma, S Chand Publishing 6. Metal working ASM Handbook

Contents Introduction Classification of Press working operations Advantages and Disadvantages of using press tools Applications of press working operations Theory of shearing in press working Optimum clearance Construction of shearing die Functions of different elements in press tool Methods of feeding strip/coil

Module1 Introduction to Press working

Introduction Manufacturing is the process of converting raw material into finished

product by value addition. Classification of manufacturing processes Primary-Basic shape and size 

Casting, Forming, Sheet Metal Operations and Powder Metallurgy

Secondary –Exact shape and size with considering tolerances 

Machining and Welding

Tertiary- Surface finishing 

Grinding, Honing and Lapping

All these comes under formative, subtractive and additive mfg. Mild steel, copper and brass are the chief materials used in press work

operations. The greatest production is from steel strip or sheet metal. Brass ( 70% Cu and 30% Zn) is used for press work operations extensively for deep-drawing operations.

Contd….. Press working is defined as chip less manufacturing process by which

components are made from sheet metals. Press working is a method of mass production involving the cold working of metals , usually in the form of thin sheets or strips. Press working make use of large forces by press tools for a short time interval which results in cutting or shaping the sheet metal. Press working is one of the extensively employed methods of fabricating parts of intricate shapes with thin walls. Press worked parts does not require any machining process. Cheapest and fastest method to complete manufacturing of components. Press working does not involve heating of the parts but we can get close tolerances and high surface finish can be obtained on the part. Press working forces are set up, guided and controlled in a machine referred to as PRESS.

Figure. Shearing operation

Figure. Shearing operation

Classification of Press working Operations

Cutting operations: Shearing - Separating material into two parts Blanking - Removing material to use for parts Punching - Removing material as scrap Slotting  Perforating  Notching  Nibbling  Lancing  Slitting  Parting  Cutoff  Trimming  Shaving 

Forming operations: Rolling and Forging Bending Drawing Extrusion

Cutting operations Blanking: Blanking is the operation of cutting a flat shape from sheet metal. The item punched out is known as the "blank“. Punching or Piercing: It is a cutting operation by which different holes openings are made in sheet metal. Punching is like blanking aside from that in punching, the gap is the fancied item.

Fine blanking It is a finishing operation in which shearing is done with small

clearances – about 1% - and close tolerances in order to achieve dimensional accuracy. It is a single step finishing operation. Square and smooth edges are produced applying clamping force on the blank. This prevents distortion of the sheet during operation

Notching: This is cutting operation by which metal pieces are cut from the

edge of the sheet , strip or blank.  Perforating: This is a procedure by which numerous gaps are little and near one another are cut in a level sheet metal. Trimming: This operation contains of cutting undesirable excess of material from the outskirts of a formerly framed segment.  Shaving: The edge of a blanked part are generally rough, uneven and non square. Precise measurements of the part are acquired by removing a thin segment of metal along the edges.  Slitting: It alludes to the operation of making incomplete gaps in a work piece.  Lancing: This is a cutting operation in which a gap is mostly cut and afterward one side is twisted down to frame a kind of tab. Since no metal is really evacuated and there will be no scrap.  Nibbling: The operation , which is utilized for just little amounts of segments, is intended for removing level parts from sheet metal. The level parts from easy to complex shapes.

 A typical punching operation is one in which a cylindrical punch tool pierces

the sheet metal, forming a single hole.  Piercing - The typical punching operation, in which a cylindrical punch pierces a hole into the sheet.

Slotting - A punching operation that forms rectangular holes in the

sheet. Sometimes described as piercing despite the different shape.

Perforating - Punching a close arrangement of a large number of

holes in a single operation.

Notching - Punching the edge of a sheet, forming a notch in the shape

of a portion of the punch.

Nibbling - Punching a series of small overlapping slits or holes

along a path to cutout a larger contoured shape. This eliminates the need for a custom punch and die but will require secondary operations to improve the accuracy and finish of the feature.

Lancing - Creating a partial cut in the sheet, so that no material is

removed. The material is left attached to be bent and form a shape, such as a tab, vent, or louver.

Slitting - Cutting straight lines in the sheet. No scrap material is

produced.

Parting - Separating a part from the remaining sheet, by

punching away the material between parts.

Cutoff - Separating a part from the remaining sheet, without

producing any scrap. The punch will produce a cut line that may be straight, angled, or curved.

Trimming - Punching away excess material from the perimeter of a

part, such as trimming the flange from a drawn cup.

Shaving - Shearing away minimal material from the edges of a feature

or part, using a small die clearance. Used to improve accuracy or finish. Tolerances of ±0.001 inches are possible.

Forming Operations Bending: In this the material in the form of flat sheet or strip is

uniformly strained from a linear axis which lies in the neutral plane and perpendicular to the length wise direction of the sheet or metal. Rolling: Raw material is compressed between two rotating rollers such that the thickness of material can be reduced Forging: In this process raw material is compressed between the two dies such that stresses induced is greater than yield and less than ultimate. The forces applied to get the required shape and size of the component. Drawing: This is a process of forming a flat work piece into a hollow shape by means of a punch which cause the blank into a die cavity. Extrusion: Under the operation, the metal is caused to flow to all portions of a die cavity under the action of comprehensive forces.

Bending operation: while bending, the metal is stressed in both

tension and compression at the two sides of the neutral axis beyond the elastic limit but below the ultimate strength of the material.

Drawing operation: The drawing is the operation of production of cup

shaped parts from flat sheet metal blanks by bending and plastic flow of the metal. The operation is also known as cupping.

Benefits and limitations Advantages  No wastage of the material  Grain orientation is possible, because of this material changing from isotropic

to anisotropic.  Presses can produce components at fairly fast rates  Mass production  Unit cost of labor for operating the press is fairly low.  In some cases we can get excellent surface finish and close dimensional accuracy.

Disadvantages  Because of work hardening metal is less deformable due to its higher

resistance.  Force and energy required is high  In most cases we can produce prismatic components except forging.  Internal residual stresses developed will be high i.e dimensions of the component unstable

Applications  Mechanical /Machine components  Automotive  Medical  Construction  Aerospace  Oil and gas industries

Mechanical /Machine components

Automotive • Vintage Car Restoration • Roll Cage Fabrication • Custom Car Modification

Construction Stainless steel water fountain • Automatic metal gates • Aluminum enclosures • Metal concrete forms • Metal partitions with or without intricate designs • Custom floor tread plates • Intricately designed floor and ceiling panels • Lattice worked walls • Sculptures

Oil and gas •   Adapter plate •   Specialized pipes used for extraction •   Custom metal louvers used on site •   Storage tanks used in the interim stage between extraction and processing •   Variety of dampers like heavy duty, motorized, butterfly, and more

Medical •   Customized hospital beds •   HVAC systems •   Intricate instruments used during surgeries •   Sterilization cases for the orthopedic industry •   Physical therapy equipment •   Robotic blood sorting systems •   Custom medical carts

Aerospace industry •   Components for the hardness •   Large enclosures for the main body of an aircraft •   Components for the chassis •   Different types of bezels •   EMI & RFI assemblies •   Optical sensors •   Other structural components

Theory of Shearing  Shearing is the method of cutting sheets or strips without forming chip. The material is stressed in a section which lies parallel to the forces applied. The forces are applied by means of shearing blades or punch and die.  Critical stages of shearing  Stage1: Plastic deformation  The force applied by the punch on the stock - material tends to deform it into the die opening .When the elastic limit is exceeded by further application of force. - The material is forced into the die opening in the form of an embossed pad on the lower face of the material .A corresponding depression is formed on the upper face. This stage impacts a radius on the upper edge of the penning in the strip and on the lower edge if the punched cut material . Stage 2:Penetration  As the load is further increased ,the punch will penetrate the material to a certain depth. An equally thick portion of the metal is forced into the dies. This impacts a bright polished finish (cut band) on both the strip and the blank or the slug. on optimum cutting conditions, the cut band will be 1/3rd the sheet thickness.  Stage 3:Fracture  I n this stage, fracture starts from both upper and lower cutting edges, As the punch travels further, these fractures will extend towards each other and meet to cause complete separation. This stage impacts a dull fractured edge.

Optimum Cutting clearance and its effect on tolerances of press components

Cutting Clearance: Cutting clearance is the gap between a side of the punch and the corresponding side of the die opening when the punch is entered into the die opening. • Proper cutting clearance is necessary for the longer life of the tool. • Quality of the piece part also depends on proper cutting clearance. Misalignment between punch and Die The cutting characteristics also indicate whether the punch and die openings are in accurate alignment. Because of misalignment, clearance on one side increases and the other side decreases.

CLEARANCE In blanking operation , the die size is taken as the blank size and the punch is made smaller giving the necessary clearance between the die and the punch. Die size        = blank size  Punch size  = blank size - 2 x clearance  Clearance   = k . t .τ Where ‘τ’ is the shear stress permissible of material, t is the thickness of sheet metal stock, and k is a constant whose value may be taken as 0.003. In a Punching operation (piercing), the following equations hold. Punch size = blank size Die size      = blank size + 2 x clearance Clearance = k . t . τ

Clearance calculation:

The ideal clearance can be calculated by the following formula where C is a constant C=0.005 for very accurate component C=0.01 for normal components s=sheet thickness in mm T max=shear strength of the stock material in N/mm square  T max for some materials: Stainless steel=400N/mm square MS=400N/mm square Brass=200N/mm square  aluminum=100N/mm square Copper=250N/mm square

A typical die and punch set used for blanking operation , the sheet

metal used is called strip or stock.  The punch which is held in the punch holder is bolted to the press ram while die is bolted on the press table. During the working stroke, the punch penetrates the strip. On the return stroke of the press ram, the strip is lifted with the punch, but it is removed from the punch by the stripper plate. The clearance angle provided on the die depends on the material of stock, as well as its thickness.

Construction of shearing die

Functions of elements of press tool BASE PLATE  It is also called as die shoe or bolsters plate. Its main function is to provide a rigid foundation or base to the assembly. It assembles the fixed half of the tool. TOP PLATE  It is the top portion of the complete tool, which holds the top assembly or complete Tool through the punch holder. GUIDE PILLAR  These are cylindrical pins known as guide pins or guide pillars. These provide accurate alignment to the die set. The contacting surface of pillars and guide bushes have h7/h6 fit where as the press fitted portion of the bush with top plate have h7/j5 tolerance and are ground. One end of pillar press  fitted in the base plate with h7/p6 tolerance. The other portion, which is sufficient long, provides guide for top plate for easy sliding. GUIDE BUSH  These are mounted on the top plates, which provide smooth sliding contact between pillars and top plates.

DIE A complete tool consisting of a pair or a combination of pairs of mating members for producing work in presses. It includes well supporting and actuating part of the tool. It is a female part of a complete die. PUNCH It is a male member of a complete dies which mates or acts in conjunction with the female die to provide a desired effect upon the material being worked. PUNCH HOLDER It is a plate, which holds the punch. SHANK This is a projection from the upper shoe which enters the press slide flange recess and is clamped to the slide or press ram. PUNCH BACK PLATE It is a plate that supports the punch and is situated behind the punch holder plate. It avoids the dent marks that may produce during operation to the top plate. STRIPPER PLATE It is a plate solid or movable used to strip the work piece or part from the punch. It may or may not guide the stock.

STRIP GUIDE  In press tool the long pre-sheared stock strip to be fed through out the die surface. The strip guide combines the two metal strips or parallel blocks, which are screwed and doweled on the die surface in alignment with the die parameters. It acts as a gauge. It is one of the important elements of the progressive tools with fixed as well as floating stripper. SHEDDERS  It is used to expel the work piece from the die cavity. Shedder actuation may be achieved by  1. Pneumatic cylinder or cushion  2. Hydraulic cylinders or cushion  3. Rubber pads  4. Springs

PILOTS  Pilots are used to align the components accurately for secondary operation.

Basic Press Feeding Methods

• A press feed must meet three criteria to be successful. • First, it must be flexible in terms of setup. • Second, it must deliver the material with sufficient precision into the tool, • third, it must feed at the proper time. • The press feed must be flexible in its setup adjustment, to accommodate the full

range of material thicknesses and widths that may run in that press. • The feed line must deliver material with sufficient precision, not only moving the required amount of material into the die but also placing it precisely right to left and front to back, and squarely to the tool. • The feed line must index the material at the proper time, while maintaining the speed requirements of the stamping operation.

1. A feed must be flexible enough in its setup adjustment to accommodate the full range of applications that will be run on a press line with respect to feed length, material width and gauge, feed and pilot release timing, and die

2. The feed must deliver the material with sufficient precision into the tool.   It must not only move the desired amount of material into the tool, it must position it precisely in the die - front to back, side to side, and square with the tool.  Misalignment results in slippage and strip buckling, which cause material binding, misfeeding and short feeds.  Short feeding results in bad parts and broken dies. For this reason it is important that feeding equipment is installed on-center square to the tool and rigidly mounted.  Proper installation ensures that no movement can take place between the tool and the feed. 3. The feed device should deliver material at the proper pace so it keeps up with the speed of the operation.  The time that a feed actually has to deliver material is determined by the amount of time for one complete press or shear cycle, minus the time that the tooling is engaged, and minus the time required to detect a misfeed and stop the press. This means that the longer the die engagement, or the faster the speed of operation, the less time there is to feed. 

 As press feed technology continues to evolve, stampers are realizing  increased processing speeds,  improved processing flexibility,  easier setup,  better quality and reliability

The two basic feed types are roll feeds and gripper feeds  Roll feeds- use rollers to move the material into the tool  A roll feed can be powered either by a press or by its own self-contained drive system. Press-driven roll feeds  Press-driven roll feeds such as rack-and-pinion or cam feeds are always synchronized to the rotation of the press. These feeds always begin their motion at some predetermined point in the press cycle and finish it at another predetermined point, regardless of press speed or die engagement.

 Press-driven feeds exhibit a smooth motion called an s-curve move profile

instead of the trapezoidal move profile provided by most other feeds. With an s-curve motion profile, the rate of acceleration varies throughout the index, eliminating sharp transitions in velocity that can cause slippage.  Although the index speed must increase or decrease to keep pace with the press, the feed can draw as much power as it needs from the press to accomplish this, within the limitations of the mechanical coupling to the press.  Drawbacks to most press-driven feeds include  their difficulty of adjustment,  feed length limitations,  lack of inching capability, and  absence of controls interface. ……………Both types of press feeds can be powered by the press, by a selfcontained drive system (such as air- or hydraulic-powered), or by a servodrive system…………

Servo Driven Roll Feeds  Servo driven roll feeds have been used in press feeding.  The concept involves using a closed-loop positioning drive usually a servo but sometimes a stepper to control the index position of the feed rolls.  Servo driven roll feeds share many advantages with the press-driven variety, including  minimal space requirements,  low maintenance,  high speeds.  Servo-driven roll feeds are available in a variety of configurations, • feeder/straighteners, • conventional two- and four-roll units • unwinder/feeder/ straighteners, and zig-zag units.

 Gripper Feeds  employ gripping clamps and a linear motion to move the strip.

  They are available in a variety of sizes, from compact press-mounted units to

large cabinet-mounted models, which include pull-through straighteners.  Gripper feeds use a pair of clamps: the retainer, which remains stationary, and the gripper, which moves during the feed and return strokes. During the feed stroke, the retainer releases the strip as the gripper holds and moves it forward through the top half of the press cycle while the tool is open.  On the return stroke, the gripper releases the strip, and the retainer holds it while the gripper retracts from the press through the bottom half of the press cycle while the tool is closed. Since the return and feed strokes take about the same amount of time, gripper feeds are limited to a 180-degree feed window at the maximum operating speed.  The gripper's pulling force can be provided by air or hydraulic-powered cylinders, a hydraulic motor, a servomotor, or the press. The gripper usually is supported by guide bars or rails and is driven by cylinder rods, chains and sprockets or ball screws, or a mechanical linkage to the press.

 Press feeding methods are limited only by imagination.  Many important considerations in the purchase, setup, and operation

of this equipment will determine how productive it will be.  If the system is to work at maximum efficiency, each component must complement the others.