UNIT 4 - MECHANICAL WORKING OF METALS AND SHEET METAL OPERATIONS PDF

MANUFACTURING TECHNOLOGY MECHANICAL WORKING OF METALS  OVERVIEW  Metal Working Process  Hot Working  Sheet Metal Operations  Cold Working  Shearing Operations  Forging  Types of Shearing Dies  Typ...

MANUFACTURING TECHNOLOGY MECHANICAL WORKING OF METALS  OVERVIEW  Metal Working Process  Hot Working  Sheet Metal Operations  Cold Working  Shearing Operations  Forging  Types of Shearing Dies  Types/Defects  Forming Operations  Extrusion  Cutting Tools in Sheet metal  Types/Defects process  Rolling  Striking Tools in Sheet Metals,  Types of Rolling Riveting  Rolling Mills  Rolling Defects  Drawing/Types MANUFACTURING TECHNOLOGY Mechanical Working of Metals  In this method no machining process is carried out, but it is used to achieve optimum mechanical properties in the metal.  The wastage of material in metal working process is negligible or very small. But the production is very high compared to other process. METAL FORMING PROCESS  Large set of manufacturing processes in which the material is deformed plastically to take the shape of the die geometry. The tools used for such deformation are called die, punch etc. depending on the type of process. Types of Metal Working or Processing Methods  Mechanical processing Mechanical working is a process of shaping of  Hot working metals by plastic deformation. When a metal is subjected to external force beyond yield strength  Cold working but less than fracture strength of the metal, metal is deformed by slip or twin formation.  Thermal processing  Heat treatments  Annealing  Recovery, recrystallization and growth  Both of these are used to control properties of the final product MANUFACTURING TECHNOLOGY Hot Working: T > 0.5Tm  Mechanical working of a metal above the recrystallization temperature but below the melting point is known as hot working.  The temperature at which the complete recrystallization of a metal take place with in a specified time  The recrystallization temperature of metal will be about 30 to 40% of its melting temperature. Types  Forging  Rolling  Extrusion  Drawing Hot Working  Advantages  Force requirement is less  Refined grain structure  No stress formation  Quick and Economical  Suitable for all metals  Disadvantages  Poor surface finish  Less accuracy  Very high tooling and handling cost  Sheets and wires cannot be produced MANUFACTURING TECHNOLOGY Cold Working :T < 0.3Tm  Mechanical working of a metal below the recrystallization temperature (Room Temperature) is known as cold working.  Reduces the amount of plastic deformation that a material can undergo in subsequent processing and requires more power for further working Types  Drawing  Squeezing  Bending  MANUFACTURING TECHNOLOGY Cold Working  Advantages  Better surface finish  High dimensional accuracy  Sheets and wires can be produced  Suitable for Mass production  Disadvantages  Stress formation in metal very high  Close tolerances cannot be achieved  No Refined grain structure MANUFACTURING TECHNOLOGY Comparison of Hot and Cold Working S.No Hot Working Cold Working 1 Working above Working below recrystallization recrystallization temperature temperature 2 Formation of new crystals No crystal formation 3 Surface finish not good Good surface finish 4 No stress formation Internal Stress formation 5 No size limit Limited size STRAIN HARDENING  It is called cold-working because the plastic deformation must  Work-hardening or cold- occurs at a temperature low working is the process of making enough that atoms cannot a metal harder and stronger rearrange themselves. through plastic deformation.  When a metal is worked at higher temperatures (hot-working) the  When a metal is plastically dislocations can rearrange and deformed, dislocations move little strengthening is achieved. and additional dislocations are generated.  The more dislocations within a material, the more they will interact and become pinned or tangled.  This will result in a decrease in the mobility of the dislocations and a strengthening of the material. This type of strengthening is commonly called cold-working.  Annealing involves heating to a  Recovery: specified temperature and then  Softening of the metal occurs through cooling at a very slow and removal of primarily linear defects called dislocations and the internal controlled rate. stresses.  Heat treatments are used to alter the  Recovery occurs at the lower physical and mechanical temperature stage of all annealing properties of metal without processes and before the appearance of new strain-free grains. The grain size changing its shape. and shape do not change.  Soften a metal for cold working  Improve machinability  Recrystallization:  Enhance electrical conductivity  New strain-free grains nucleate and grow to replace those deformed by internal stresses.  Grain growth:  If annealing is allowed to continue once recrystallization has completed, then grain growth (the third stage) occurs.  In grain growth, the microstructure starts to coarsen and may cause the metal to lose a substantial part of its original strength. This can however be regained with hardening. MANUFACTURING TECHNOLOGY Forging  Forging is a process in which the work piece is shaped by compressive forces applied through various dies and tools. It is one of the oldest metalworking operations. Most forgings require a set of dies and a press or a forging hammer.  Unlike rolling operations, which generally produce continuous plates, sheets, strip, or various structural cross-sections, forging operations produce discrete parts.  Typical forged products are bolts and rivets, connecting rods, shafts for turbines, gears, hand tools, and structural components for machinery, aircraft, railroads and a variety of other transportation equipment. MANUFACTURING TECHNOLOGY Forging Forging Methods Open‑Die Forging  Compression of work part between two flat dies  Deformation operation reduces height and increases diameter of work  Common names include upsetting or upset forging Upset Forging  An upset forging operation to form a head on a bolt or similar hardware item  The cycle consists of:  (1) wire stock is fed to the stop,  (2) gripping dies close on the stock and the stop is retracted,  (3) punch moves forward,  (4) bottoms to form the head. Heading Examples of heading (upset forging) operations: (a) heading a nail using open dies, (b) round head formed by punch, (c) and (d) two common head styles for screws formed by die (e) carriage bolt head formed by punch and die. Upsetting and Heading  Forging process used to form heads on nails, bolts, and similar hardware products  More parts produced by upsetting than any other forging operation  Performed cold, warm, or hot on machines called headers or formers  Wire or bar stock is fed into machine, end is headed, then piece is cut to length  For bolts and screws, thread rolling is then used to form threads Open‑Die Forging with No Friction  If no friction occurs between work and die surfaces, then homogeneous deformation occurs, so that radial flow is uniform throughout work part height Homogeneous deformation of a cylindrical work part 1. start of process with work piece at its original length and diameter,  Open‑Die Forging with Friction  Friction between work and die surfaces constrains lateral flow of work, resulting in barreling effect  In hot open-die forging, effect is even more pronounced due to heat transfer at and near die surfaces, which cools the metal and increases its resistance to deformation Deformation of a cylindrical work part in open‑die forging, showing pronounced barreling (1) start of process, (2) partial deformation, (3) final shape. Impression‑Die Forging  Compression of work part by dies with inverse of desired part shape  Flash is formed by metal that flows beyond die cavity into small gap between die plates  Flash serves an important function:  As flash forms, friction resists continued metal flow into gap, constraining material to fill die cavity  In hot forging, metal flow is further restricted by cooling against die plates Impression‑Die Forging (1)just prior to initial contact with raw work piece, (2)partial compression, (3)final die closure, causing flash to form in gap between die plates. MANUFACTURING TECHNOLOGY Trimming After Impression-Die Forging  Trimming operation (shearing process) to remove the flash after impression‑die forging. MANUFACTURING TECHNOLOGY  Advantages of impression-die forging compared to machining from solid stock:  Higher production rates  Less waste of metal  Greater strength  Favorable grain orientation in the metal  Limitations:  Not capable of close tolerances  Machining often required to achieve accuracies and features needed MANUFACTURING TECHNOLOGY Flash less Forging  Compression of work in punch and die tooling whose cavity does not allow for flash  Starting work part volume must equal die cavity volume within very close tolerance  Process control more demanding than impression‑die forging  Best suited to part geometries that are simple and symmetrical  Often classified as a precision forging process Flash less Forging (1)just before initial contact with work piece, (2)partial compression, (3)final punch and die closure. MANUFACTURING TECHNOLOGY Forging Hammers (Drop Hammers)  Apply impact load against work part Two types  Gravity drop hammers - impact energy from falling weight of a heavy ram  Power drop hammers - accelerate the ram by pressurized air or steam  Disadvantage: impact energy transmitted through anvil into floor of building  Commonly used for impression-die forging MANUFACTURING TECHNOLOGY Drop Hammer Details Diagram showing details of a drop hammer for impression‑die forging. MANUFACTURING TECHNOLOGY Forging Presses  Apply gradual pressure to accomplish compression operation Types  Mechanical press - converts rotation of drive motor into linear motion of ram  Hydraulic press - hydraulic piston actuates ram  Screw press - screw mechanism drives ram MANUFACTURING TECHNOLOGY Mechanical press MANUFACTURING TECHNOLOGY Hydraulic press MANUFACTURING TECHNOLOGY Forging Defects  Fracture  Exhausted ductility  Inter-granular fracture  Barreling - Friction Solution  limited deformation per step  Process anneal between steps EXTRUSION PROCESS MANUFACTURING TECHNOLOGY Extrusion  A plastic deformation process in which metal is forced under pressure to flow through a single, or series of dies until the desired shape is produced.  Process is similar to squeezing toothpaste out of a toothpaste tube  In general, extrusion is used to produce long parts of uniform cross sections  Typical products made by extrusion are railings for sliding doors, tubing having carious cross-sections, structural and architectural shapes, door and windows frames.  Extrusion Ratio  ER= A o /A f  A o – cross-sectional area of the billet  A f - cross-sectional area of extruded product  Extrusion Force  F = A o K Ln (A o/A f)  K-extrusion constant  A o , A f billet and extruded product areas  Types  Direct Extrusion (Forward Extrusion)  Indirect Extrusion (Backward Extrusion)  Hydrostatic Extrusion  Impact Extrusion Factors Influencing the Extrusion Force  Friction  Material Properties  Reduction In Area  Speed  Temperature  Geometry Of The Die MANUFACTURING TECHNOLOGY Direct Extrusion  Billet is placed in a chamber and forced through a die opening by a hydraulically-driven ram or pressing stem.  Dies are machined to the desired cross-section Friction increases the extrusion force MANUFACTURING TECHNOLOGY Direct Extrusion Schematic illustration of direct extrusion process MANUFACTURING TECHNOLOGY Direct Extrusion Hollow and Semi Hollow section is formed using a mandrel  MANUFACTURING TECHNOLOGY Indirect Extrusion  Metal is forced to flow through the die in an opposite direction to the ram’s motion.  Lower extrusion force as the work billet metal is not moving relative to the container wall. Limitations  Lower rigidity of hollow ram  Difficulty in supporting extruded product as it exits die direct extrusion to produce (a) a solid cross section and (b) a hollow cross sectio MANUFACTURING TECHNOLOGY Indirect Extrusion Schematic illustration of indirect extrusion process MANUFACTURING TECHNOLOGY Process Variables in Direct & Indirect Extrusion  The die angle   Reduction in cross-section A f  Extrusion speed  Billet temperature,  Extrusion pressure. MANUFACTURING TECHNOLOGY Tube Extrusion  Accomplished by forcing the stock through the sides of the mandrel placed between dies Tube or Pipe MANUFACTURING TECHNOLOGY Hydrostatic Extrusion  The pressure required for extrusion is supplied through and incompressible fluid medium surrounding the billet  Usually carried at room temperature, typically using vegetable oils as the fluid  Brittle materials are extruded generally by this method  It increases ductility of the material  It has complex nature of the tooling MANUFACTURING TECHNOLOGY Hydrostatic Extrusion Schematic illustration Hydrostatic Extrusion process Impact Extrusion  Similar to indirect extrusion  Punch descends rapidly on the blank, which is extruded backward Schematic illustration of the impact-extrusion process. The extruded parts are stripped by the use of a stripper plate, because they tend to MANUFACTURING TECHNOLOGY Hot extrusion  prior heating of billet to above its recrystallization temperature Cold extrusion  prior heating of billet to below its recrystallization temperature Advantages  Wide variety of shapes  High production rates  Improved microstructure and physical properties  Close tolerances are possible  Economical  Design flexibility Limitation  part cross section must be uniform throughout length  MANUFACTURING TECHNOLOGY Extrusion Die Features (a) Definition of die angle in direct extrusion; (b) effect of die angle on ram force. MANUFACTURING TECHNOLOGY Extrusion Defects a. Centre-burst: internal crack due to excessive tensile stress at the center possibly because of high die angle, low extrusion ratio. b. Piping: sink hole at the end of billet under direct extrusion. c. Surface cracking: High part temperature due to low extrusion speed and high strain rates. ROLLING OPERATION MANUFACTURING TECHNOLOGY Rolling  Deformation process in which work thickness is reduced by compressive forces exerted by two opposing rolls The rolling process (specifically, flat rolling) Rolling:  Initial breaking down of an ingot (or a continuously cast slab) is done by hot rolling.  A cast structure includes coarse and non-uniform grains. This structure is usually brittle and may contain porosities.  Hot rolling converts the cast structure to a wrought structure.  This structure has finer grains and enhanced ductility, both resulting from the breaking up of brittle grain boundaries and the closing up of internal defects, especially porosity.  The product of the first hot rolling operation is called bloom or slab.  A Bloom usually has a square cross-section, at least 150 mm (6in) on the side; Blooms are processed further, by shape rolling, into structural shapes, such as I-beams and railroad rails.  A Slab is usually rectangular in cross section. Slabs are rolled into planes and sheet.  Billets are usually square, with a cross-sectional area smaller than blooms; they are later rolled into various shapes, such as round rods and bars, by the use of shaped rolls.  Hot-rolled round rods are used as the starting material for rod and wire drawing. They are called wire rods. Rolling  One of the primary first process to convert raw material into finished product.  Starting material (Ingots) are rolled into blooms, billets, or slabs by feeding material through successive pairs of rolls.  Bloom - square or rectangular cross section with a thickness greater than 6” and a width no greater than 2x’s the thickness  Billets - square or circular cross section - - smaller than a bloom  Slabs - rectangular in shape (width is greater than 2x’s the thickness), slabs are rolled into plate, sheet, and strips. MANUFACTURING TECHNOLOGY Rolling Rolled Products Made of Steel  Some of the steel products made in a rolling mill. MANUFACTURING TECHNOLOGY Rotating rolls perform two main functions:  Pull the work into the gap between them by friction between work part and rolls  Simultaneously squeeze the work to reduce its cross section  MANUFACTURING TECHNOLOGY Types of Rolling  Based on work piece geometry :  Flat rolling - used to reduce thickness of a rectangular cross section  Shape rolling - square cross section is formed into a shape such as an I‑beam  Based on work temperature :  Hot Rolling – most common due to the large amount of deformation required  Cold rolling – produces finished sheet and plate stock Flat Rolling  Heated metal is passed between rotating rolls to reduce the cross-section.  Side view of flat rolling, indicating before and after thicknesses, work velocities, angle of contact with rolls, and other features. Shape Rolling  Work is deformed into a contoured cross section rather than flat (rectangular)  Accomplished by passing work through rolls that have the reverse of desired shape  Products include:  Construction shapes such as I‑beams, L‑beams, and U‑channels  Rails for railroad tracks  Round and square bars and rods MANUFACTURING TECHNOLOGY Shape Rolling MANUFACTURING TECHNOLOGY Thread Rolling Bulk deformation process used to form threads on cylindrical parts by rolling them between two dies  Important commercial process for mass producing bolts and screws  Performed by cold working in thread rolling machines  Advantages over thread cutting (machining):  Higher production rates  Better material utilization  Stronger threads and better fatigue resistance due to work hardening MANUFACTURING TECHNOLOGY  Thread rolling with flat dies (1) start of cycle (2) end of cycle MANUFACTURING TECHNOLOGY Thread Rolling MANUFACTURING TECHNOLOGY Rolling Mills  Equipment is massive and expensive  Rolling mill configurations:  Two-high – two opposing rolls  Three-high – work passes through rolls in both directions  Four-high – backing rolls support smaller work rolls  Cluster mill – multiple backing rolls on smaller rolls  Tandem rolling mill – sequence of two-high mills MANUFACTURING TECHNOLOGY Two-High Rolling. a -2‑high rolling mill. MANUFACTURING TECHNOLOGY Three-High Rolling. b -3‑high rolling mill. MANUFACTURING TECHNOLOGY Four-High Rolling. b -4‑high rolling mill. MANUFACTURING TECHNOLOGY Cluster Mill d -Cluster mill. MANUFACTURING TECHNOLOGY Tandem Rolling Mill A series of rolling stands in sequence e –Tandem Rolling mill. MANUFACTURING TECHNOLOGY Rolling Defects  (a) Waviness  Improper roller speeds  (b) Zipper cracks  Too much rolling in center  (c) Edge cracks  Too much rolling on outside  (d) Alligatoring  Too much induced tensile stress in the part, or defects DRAWING  Drawing is an operation in which the cross-section of solid rod, wire or tubing is reduced or changed in shape by pulling it through a die.  Drawn rods are used for shafts, spindles, and small pistons and as the raw material for fasteners such as rivets, bolts, screws.  Drawing also improves strength and hardness when these properties are to be developed by cold work and not by subsequent heat treatment. MANUFACTURING TECHNOLOGY Drawing Types  Wire Drawing  Cross‑section of a bar, rod, or wire is reduced by pulling it through a die opening  Similar to extrusion except work is pulled through die in drawing (it is pushed through in extrusion)  Although drawing applies tensile stress, compression also plays a significant role since metal is squeezed as it passes through die opening r = area reduction in drawing; Ao = original area of work; Af = final work Ao  A f r Drawing of wire. Ao MANUFACTURING TECHNOLOGY  Wire drawing machines consisting of multiple draw dies (typically 4 to 12) separated by accumulating drums  Each drum (capstan) provides proper force to draw wire stock through upstream die  Each die provides a small reduction, so desired total reduction is achieved by the series  Annealing sometimes required between dies to relieve work hardening Continuous drawing of wire MANUFACTURING TECHNOLOGY Area Reduction in wire Drawing  Change in size of work is usually given by area reduction Ao  A f r Ao  where r = area reduction in drawing; Ao = original area of work; and Af = final work Die Materials  Commonly used materials are Tool Steels and Carbides  Diamond dies are used for fine wire.  For improved wear resistance, steel dies may be chromium plated, and carbide dies may be coated with titanium nitride  For Hot drawing, cast-steel dies are used MANUFACTURING TECHNOLOGY Bar or Rod Drawing  Accomplished as a single‑draft operation ‑ the stock is pulled through one die opening  Beginning stock has large diameter and is a straight cylinder  Requires a batch type operation Hydraulically operated draw bench for drawing metal bars MANUFACTURING TECHNOLOGY Tube Drawing  Accomplished by pulling the stock through the sides of the mandrel placed between dies  MANUFACTURING TECHNOLOGY Wire Drawing vs. Bar Drawing  Difference between bar drawing and wire drawing is stock size  Bar drawing - large diameter bar and rod stock  Wire drawing - small diameter stock - wire sizes down to 0.03 mm (0.001 in.) are possible  Although the mechanics are the same, the methods, equipment, and even terminology are different Preparation of Work for Drawing  Annealing – to increase ductility of stock  Cleaning - to prevent damage to work surface and draw die  Pointing – to reduce diameter of starting end to allow insertion through draw die Features of a Draw Die  Entry region - funnels lubricant into the die to prevent scoring of work and die  Approach - cone‑shaped region where drawing occurs  Bearing surface - determines final stock size  Back relief - exit zone - provided with a back relief angle (half‑angle) of about 30  Die materials: tool steels or cemented carbides MANUFACTURING TECHNOLOGY SHEET METAL FORMING PROCESSES MANUFACTURING TECHNOLOGY Introduction to Sheet Metal  Metal is formed into thin and flat pieces. It is one of the fundamental forms used in metalworking, and can be cut and bent into a variety of different shapes.  Countless everyday objects are constructed by this process. Thicknesses can vary significantly,  extremely thin sheets are considered as foil or leaf,  sheets thicker than 6 mm (0.25 in) are considered as plate.  MANUFACTURING TECHNOLOGY Sheet Metal Processing  The raw material for sheet metal manufacturing processes is the output of the rolling process.  Typically, sheets of metal are sold as flat, rectangular sheets of standard size.  If the sheets are thin and very long, they may be in the form of rolls. Therefore the first step in any sheet metal process is to cut the correct shape and sized blank from larger sheet.  MANUFACTURING TECHNOLOGY Sheet Metal Working  Cutting and Forming operations are performed on relatively thin sheets of metal  Thickness of sheet metal = 0.4 mm to 6 mm  Thickness of plate stock > 6 mm  Operations are usually performed as cold working  Sheet metals process are characterized by high strength, good dimensional accuracy, better surface finish and relatively low cost. MANUFACTURING TECHNOLOGY Sheet Metal operations Introduction  Sheet metal forming is a grouping of many complementary processes that are used to form sheet metal parts.  One or more of these processes is used to take a flat sheet of ductile metal, and mechanically apply deformation forces that alter the shape of the material.  Before deciding on the processes, one should determine whether a particular sheet metal can be formed into the desired shape without failure.  The sheet metal operations done on a press may be grouped into two categories, cutting (shearing) operations and forming operations. MANUFACTURING Sheet Metal operations TECHNOLOGY MANUFACTURING Sheet Metal operations TECHNOLOGY  The art of sheet metal lies in the making of different shapes by adopting different operations. The major types of operations are given below  Shearing (Cutting)  Bending  Drawing  Squeezing  MANUFACTURING Sheet Metal operations TECHNOLOGY  Shearing (Shearing between Punch & Die)  Cutting to separate large sheets; or cut part perimeters or make holes in sheets  Bending  Straining sheet around a straight axis  Drawing  Forming of sheet into convex or concave shapes  Squeezing  Forming of sheet by gripping and pressing firmly – Coining & Embossing  MANUFACTURING Shearing (Cutting) TECHNOLOGY Shearing of sheet metal between two sharp cutting edges B. Punch begins to push into work, A. Just before the punch contacts work causing plastic deformation C. Punch compresses and penetrates into D. Fracture is initiated at the opposing work causing a smooth cut surface cutting edges which separates the sheet MANUFACTURING TECHNOLOGY Bending  Straining sheet metal around a straight axis to take a permanent bend Bending of sheet metal MANUFACTURING TECHNOLOGY  Metal on inside of neutral plane is compressed, while metal on outside of neutral plane is stretched Both compression and tensile elongation of the metal occur in bending MANUFACTURING TECHNOLOGY Types of Sheet metal Bending  V-bending- performed with a V - shaped die  Edge bending - performed with a wiping Die V-Bending  For low production  Performed on a press brake  V-dies are simple and inexpensive V-bending MANUFACTURING Edge Bending TECHNOLOGY  For high production  Pressure pad required  Dies are more complicated and costly Edge bending MANUFACTURING Stretching during Bending  TECHNOLOGY If bend radius is small relative to stock thickness, metal tends to stretch during bending, so that estimation of amount of stretching (final part length) is important. Bending Allowance A BA 2 R  K T  360 Where  BA = Bend allowance;  A = Bend angle;  R= Bend radius;  T = Stock thickness and K is factor to estimate stretching  If R < 2T, K = 0.33  If R = 2T, K = 0.50 MANUFACTURING TECHNOLOGY Bending Force Maximum bending force estimated as follows 2 K bf TS W T F Where D  F = Bending Force  TS = Tensile strength of sheet metal  W= Part width in direction of bend axis  D = Die opening dimension  T = Stock thickness and K is factor estimates bend force  For V-Bending- Kbf = 1.33  For Edge-Bending - Kbf = 0.33 or 0.50  MANUFACTURING Bending Force Calculation TECHNOLOGY Example -1  A sheet-metal part 3mm thick and 20mm long is bent to an included angle of 60o and a bend radius of 7.5mm in a V-die. The die opening is 15mm. The metal has tensile strength of 340 MPa. Compute the required force to bend the part. Solution Bending force Required 2 K bf TS W T F D 1.33 340 10 6 0.02 0.003 2 F 5426.4 N 0.015 The bending force required to bend the part is 5426.4 N MANUFACTURING Spring back in Bending TECHNOLOGY  Springback is the geometric change in the part at the end of the forming process, under the removal of forces.  Spring back = increase in included angle of bent part relative to included angle of forming tool after tool is removed Reason for spring back  When bending pressure is removed, elastic energy remains in bent part, causing it to recover partially toward its original shape  Spring back in bending shows itself as a decrease in bend angle and an increase in bend radius  MANUFACTURING Spring back TECHNOLOGY 1. During bending the work is forced to take the radius R b and include angle Ab of the bending tool (punch in v-bending) 2. After punch is removed the work springs back to radius R and angle A MANUFACTURING Spring back TECHNOLOGY  When a plate is bent, using a bending tool, the plate initially assumes the angle of the tool θ’. As the plate is removed from the tool, it springs back to an angle θ’b less than the tool angle.  The spring back, Sb defined as follows  MANUFACTURING Drawing TECHNOLOGY  Forming of sheet into convex or concave shapes  Sheet metal blank is positioned over die cavity and than punch pushed metal in to opening  Products – Beverage cans, automobile body parts and ammunition shells MANUFACTURING TECHNOLOGY Holding force of the Blank Where Sy is the Yield Tensile strength of the blank rp - Punch Radius or Die radius MANUFACTURING TECHNOLOGY Example-2  A cup drawing operation is performed in which the inside diameter is 80mm and the height is 50mm. The stock thickness is 3mm, and the starting diameter is 150mm. Punch and die radii = 4mm. The tensile strength of the material is 400Mpa and the yield strength is 180Mpa. Determine:  (i) Drawing ratio  (ii) Reduction  (iii) Drawing force  (iv) Blank holder force MANUFACTURING Solution TECHNOLOGY MANUFACTURING Blank Size Calculation TECHNOLOGY  For final dimensions of drawn shape to be correct, starting blank diameter Db must be correct.  Solve Db by setting starting sheet metal blank volume = final product volume  To facilitate calculation, assume negligible thinning of part wall with diameter (d) and height (h) d h MANUFACTURING TECHNOLOGY The Size or Diameter of the blank is given by  Blank volume = Final product volume  D2/4 = d12/4 + d2h  D2 = d12 +4d2h  The Size or Diameter of the blank is 2 D  70  4 50 50 Example-3 Calculate the blank size of the given shell as shown in fig Blank size D = 122mm  Sheet metal Process in detail  Cutting (Shearing) Operations  In this operation, the work piece is stressed beyond its ultimate strength. The stresses caused in the metal by the applied forces will be shearing stresses. The cutting operations include  Punching (Piercing)  Blanking  Trimming  Notching  Perforating  Slitting  Lancing  Parting  Shaving  Fine blanking  MANUFACTURING TECHNOLOGY Shearing Operations  Punching (Piercing) It is a cutting operation by which various shaped holes are made in sheet metal. Punching is similar to blanking except that in punching, the hole is the desired product, the material punched out to form the hole being waste.  Blanking: Blanking is the operation of cutting a flat shape sheet metal. The article punched out is called the blank and is the required product of the operation. The hole and metal left behind is discarded as waste.  Notching: This is cutting operation by which metal pieces are cut from the edge of a sheet, strip or blank.  MANUFACTURING TECHNOLOGY Perforating: This is a process by which multiple holes which are very small and close together are cut in flat work material.  Slitting: It refers to the operation of making incomplete holes in a work piece.  Lancing: This is a cutting operation in which a hole is partially cut and then one side is bent down to form a sort of tab. Since no metal is actually removed, there will be no scrap. (Tab, Vent)  Parting: Parting involves cutting a sheet metal strip by a punch with two cutting edges that match the opposite sides of the blank.  MANUFACTURING The edge of blanked TECHNOLOGY Shaving: parts is generally rough, uneven and un-square. Accurate dimensions of the part are obtained by removing a thin strip of metal along the edges.  Fine blanking: Fine blanking is a operation used to blank sheet metal parts with close tolerances and smooth, straight edges in one step.  Trimming: This operation consists of cutting unwanted excess material from the periphery of previously formed components. MANUFACTURING TECHNOLOGY Shearing Operations  MANUFACTURING TECHNOLOGY Shearing Operations Schematic illustrations of shaving on a sheared edge. (a) Shaving a sheared edge. (b) Shearing and shaving, Fine blanking combined in one stroke. Shaving Trimming  MANUFACTURING Shearing Dies TECHNOLOGY  Because the formability of a sheared part can be influenced by the quality of its sheared edges, clearance control is important.  In practice, clearances usually range between 2% and 8% of the sheet’s thickness; generally, the thicker the sheet, the larger is the clearance (as much as 10%). However, the smaller the clearance, the better is the quality of the edge.  PUNCH AND DIE SHAPES As the surfaces of the punch and die are flat; the punch force builds up rapidly during shearing, because the entire thickness of the sheet is sheared at the same time.  However, the area being sheared at any moment can be controlled by beveling the punch and die surfaces, as shown in Figure. This geometry is particularly suitable for shearing thick blanks, because it reduces Examples the of the total use shearing of shear force. angles on punches and dies  TYPES OF SHEARING DIES  Progressive Dies:  Parts requiring multiple operations, such as punching, blanking and notching are made at high production rates in progressive dies.  The sheet metal is fed through a coil strip and a different operation is performed at the same station with each stroke of a series of punches.  Compound Dies:  Several operations on the same strip may be performed in one stroke with a compound die in one station.  These operations are usually limited to relatively simple shearing because they are slow and the dies are more expensive than those for individual shearing operations.  Transfer Dies (Combination Dies):  The sheet metal undergoes different operations at different stations, which are arranged along a straight line or a circular path.  After each operation, the part is transfer to the next operation for additional operations. MANUFACTURING Progressive Die TECHNOLOGY (a) Schematic illustration of making a washer in a progressive die. (b) Forming of the top piece of an aerosol spray can in a progressive die. MANUFACTURING  Compound Die TECHNOLOGY (a) (b) Schematic illustrations: (a) before and (b) after blanking a common washer in a compound die. Note the separate movements of the die (for blanking) and the punch (for punching the hole in the washer). MANUFACTURING  Transfer Dies TECHNOLOGY FORMING OPERATIONS MANUFACTURING Forming Operations TECHNOLOGY  In this operation, the stresses are below the ultimate strength of the metal.  In this operation, there is no cutting of the metal but only the contour of the work piece is changed to get the desired product. The forming operations include  Bending  Drawing  Squeezing  MANUFACTURING TECHNOLOGY Bending: In this operation, the material in the form of flat sheet or strip, is uniformly strained around a linear axis which lies in the neutral plane and perpendicular to the lengthwise direction of the sheet or metal  Drawing : This is a process of a forming a flat work piece into a hollow shape by means of a punch, which causes the blank to flow into die cavity.  Squeezing: Under this operation, the metal is caused to flow to all portions of a die cavity under the action of compressive forces. MANUFACTURING TECHNOLOGY Types of Bending operations  MANUFACTURING TECHNOLOGY Bending operations V-bending Edge bending Roll bending Bending in 4-slide machine Air bending Coining  It is a cold working sizing operation. It is used for the production of metals and coins. The coining processes consists of die and punch. By using the punch and die, the impression and images are created on the metal.  The pressure involved in coining process is about 1600Mpa. The metal flows plastically and squeezed to the shape between the punch and die.  The metal is caused to flow in the direction of perpendicular force. The type of impression is formed by compressive force. The type of impression obtained on both sides will be different.  MANUFACTURING TECHNOLOGY Embossing  This is the process of making raised or projected design on the surface of the metal with its corresponding relief on the other side.  This operation includes drawing and bending.  It uses a die set which consists of die and punch with desired shape.  This operation requires less force compared with coining process. It is very useful for producing nameplates tags and designs on the metal.  DIFFERENCE BETWEEN  The COINING AND same design is created on EMBOSSING While in Coining both sides of work piece in operation, a different Embossing (One side design is created on each depressed and the other side side of work piece. raised). Force required for coining process is more than embossing process. Production of important articles such as medals, coins, tokens etc. MANUFACTURING Flanging TECHNOLOGY   Flanging is a process of bending the edges of sheet metals to 90o  Shrink flanging – subjected to compressive hoop stress.  Stretch flanging –subjected to tensile stresses  MANUFACTURING TECHNOLOGY Dimpling:  First hole is punched and expanded into a flange  Flanges can be produced by piercing with shaped punch  When bend angle < 90 degrees as in fitting conical ends its called flanging  MANUFACTURING Tube Forming or Bending TECHNOLOGY  Bending and forming tubes and other hollow sections require special tooling to avoid buckling and folding.  The oldest method of bending a tube or pipe is to pack the inside with loose particles, commonly used sand and bend the part in a suitable fixture.  This technique prevents the tube from buckling. After the tube has been bent, the sand is shaken out. Tubes can also be plugged with various flexible internal mandrels. MANUFACTURING Tube Forming TECHNOLOGY Methods of bending tubes. Internal mandrels, or the filling of tubes with particulate materials such as sand are often necessary to prevent collapse of the tubes during bending.Solid rods and structural shapes can also be bent by these techniques Stretch Forming  The sheet metal is clamped around its edges and stretched over a die or form block, which moves upward, downward or sideways, depending on the particular machine. Stretch forming is used primarily to make aircraft-wing skin panel, automobile door panels and window frames. Schematic illustration of a stretch-forming process. Aluminum skins for aircraft can be made by this process. Press break forming  Sheet metal or plate can be bent easily with simple fixtures using a press. Long and relatively narrow pieces are usually bent in a press break. This machine utilizes long dies in a mechanical or hydraulic press and is suitable for small production runs. The tooling is simple and adaptable to a wide variety of shapes. Schematic illustrations of various bending operations in a press brake Rubber Forming  One of the dies in a set is made of flexible material, such as a rubber or polyurethane membrane. Polyurethanes are used widely because of their resistance to abrasion, long fatigue life and resistance to damage by burrs or sharp edges of the sheet blank.  In bending and embossing sheet metal by the rubber forming method, as shown in the following Figure, the female die is replaced with a rubber pad. Parts can also be formed with laminated sheets of various nonmetallic material or coatings. Examples of the bending and the embossing of sheet metal with a metal punch and with a flexible pad serving as the female die. Beading  In beading, the edge of the sheet metal is bent into the cavity of a die. The bead gives stiffness to the part by increasing the moment on inertia of the edges. Also, it improves the appearance of the part and eliminates exposed sharp edges. (a) Bead forming with a single die. (b) Bead forming with two dies, in a press brake. Roll forming  For bending continuous lengths of sheet metal and for large production runs, roll forming is used. The metal strip is bent in stages by passing it through a series of rolls. Roll-forming process MANUFACTURING Stages in roll forming TECHNOLOGY Stages in roll forming of a sheet-metal door frame. In Stage 6, the rolls may be shaped as in A or B. Bulging  The basic forming process of bulging involves placing tabular, conical or curvilinear part into a split-female die and expanding it with, say, a polyurethane plug.  The punch is then retracted, the plug returns to its original shape and the part is removed by opening the dies. (a) Bulging of a tubular part with a flexible plug. Water pitchers can be made by this method. (b) Production of fittings for plumbing by expanding tubular blanks with internal pressure. The bottom of the piece is then punched out to produce a “T.” (c) Manufacturing of Bellows.  Hydro forming Process  In hydro forming or fluid forming process, the pressure over the rubber membrane is controlled throughout the forming cycle, with maximum pressure reaching 100 MPa. This procedure allows close control of the part during forming to prevent wrinkling or tearing. Advantages: Low tooling cost Flexibility and ease of operation Low die wear No damage to the surface of the sheet and Capability to form complex shapes. The hydroform (or fluid forming) process. Note that, in contrast to the ordinary deep-drawing process, the pressure in the dome forces the cup walls against the punch. The cup travels with the punch; in this way, deep drawability is improved. Tube-Hydro forming Process  In tube hydro forming, steel or other metal tubing is formed in a die and pressurized by a fluid. This procedure can form simple tubes or it can form intricate hollow tubes as shown in the following Figure. Applications of tube-hydro formed parts include automotive exhaust and structural components. (a) Schematic illustration of the tube-hydroforming process. (b) Example of tube-hydroformed parts. Automotive exhaust and structural components, bicycle frames, and hydraulic and pneumatic fittings are produced through tube hydroforming. Explosive Forming Process  Explosive energy used as metal forming  Sheet-metal blank is clamped over a die  Assembly is immersed in a tank with water  Rapid conversion of explosive charge into gas generates a shock wave. The pressure of this wave is sufficient to form sheet metals. (a) explosive forming process. (b) confined method of explosive bulging of tubes.  MANUFACTURING TECHNOLOGY Deep Drawing Processes Deep Drawing  Drawing operation is the process of forming a flat piece of material (blank) into a hollow shape by means of a punch, which causes the blank to flow into the die-cavity.  Round sheet metal block is placed over a circular die opening and held in a place with blank holder & punch forces down into the die cavity. Wrinkling occurs at the edges.  Shallow drawing: depth of formed cup  D/2  Deep or moderate drawing: depth of formed cup > D/2 MANUFACTURING Deep Drawing TECHNOLOGY (a) deep-drawing process on a circular sheet-metal blank. The stripper ring facilitates the removal of the formed cup from the punch. (b) Process variables in deep drawing. Except for the punch force, F, all the parameters indicated in  MANUFACTURING TECHNOLOGY Examples of drawing operations (a) pure drawing and (b) pure stretching. The bead prevents the sheet metal from flowing freely into the die cavity. (c) Possibility of wrinkling in the unsupported region of a sheet in drawing.  MANUFACTURING TECHNOLOGY Ironing Process  If the thickness of the sheet as it enters the die cavity is more than the clearance between the punch and the die, the thickness will have to be reduced; this effect is known as ironing.  Ironing produces a cup with constant wall thickness thus, the smaller the clearance, the greater is the amount of ironing. Schematic illustration of the ironing process. Note that the cup wall is thinner than its bottom. All beverage cans without seams (known as two-piece cans) are ironed, generally in three steps, after being deep drawn into a cup. (Cans with separate tops and bottoms are known as three-piece cans.) Redrawing Operations  Containers or shells that are too difficult to draw in one operation are generally redrawn. In reverse redrawing, shown in following Figure, the metal is subjected to bending in the direction opposite to its original bending configuration.  This reversal in bending results in strain softening. This operation requires lower forces than direct redrawing and the material behaves in a more ductile manner. Reducing the diameter of drawn cups by redrawing operations: (a) conventional redrawing and (b) reverse redrawing. Small-diameter deep containers undergo many drawing and redrawing operations. MANUFACTURING TECHNOLOGY Metal-Forming Process for Aluminum Beverage Can MANUFACTURING TECHNOLOGY Steps in Manufacturing an Aluminium Can The metal-forming processes involved in manufacturing a two-piece aluminium beverage can MANUFACTURING TECHNOLOGY Aluminum Two-Piece Beverage Cans Aluminum two-piece beverage cans. Note the fine surface finish. MANUFACTURING Press for Sheet Metal TECHNOLOGY  Press selection for sheet metal forming operations depends on several factors:  Type of forming operation, and dies and tooling required  Size and shape of work pieces  Length of stroke of the slide, stroke per minute, speed and shut height (distance from the top of the bed to the bottom of the slide, with the stroke down)  Number of slides (single action, double action and triple action)  Maximum force required (press capacity, tonnage rating)  Type of controls  Die changing features  Safety features MANUFACTURING TYPES OF PRESS FRAMES TECHNOLOGY Schematic illustration of types of press frames for sheet- forming operations. Each type has its own characteristics of stiffness, capacity, and accessibility. MANUFACTURING TECHNOLOGY Sheet and Plate Metal Products  Sheet and plate metal parts for consumer and industrial products such as  Automobiles and trucks  Airplanes  Railway cars and locomotives  Farm and construction equipment  Small and large appliances  Office furniture  Computers and office equipment Advantages of Sheet Metal Parts  High strength  Good dimensional accuracy  Good surface finish  Relatively low cost  For large quantities, economical mass production operations are available Tools and Accessories  Marking and measuring tools Steel Rule  It is used to set out dimensions. Try Square  Try square is used for making and testing angles of 90degree Scriber  It used to scribe or mark lines on metal work pieces. Divider  This is used for marking circles, arcs, laying out perpendicular lines, bisecting lines, etc MANUFACTURING  Marking and measuring tools TECHNOLOGY MANUFACTURING TECHNOLOGY Straight snip Curved snip MANUFACTURING TECHNOLOGY Types of Mallets END