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Fundamentals Of Metal Forming

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Published in: Mechanical
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Explains about the Basic concepts of Metal Forming Process.

Vinoth / Chennai

4 years of teaching experience

Qualification: B.Tech/B.E. (Sri Manakulavinayagar Engineering College - 2017)

Teaches: Biology, English, Mathematics, Physics, EVS, B.Tech Tuition, Mechanical, Spoken English, C / C++

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  1. sesseooJd Ouymoqnuevq
  2. IntrÖdÜcti h) Deformation processes have been designed to exploit the plasticity of engineering materials Plasticity is the ability of a material to flow as a solid without deterioration of properties Deformation processes require a large amount of force Processes include bulk flow, simple shearing, or compound bending www.fppt.info
  3. (1) Simple uniaxial Triaxial tension tension (7) Biaxial compression (4 (2) Biaxialtension (8) Biaxial compression, tension (3) (9) Triaxial compression Biaxial tension, compression (10) Pure shear (5) Biaxialtension and compression (11) Simple shearwith triaxial compression (6) Uniaxial compression (12) Biaxial shearwith triaxial compression www.fppt.info
  4. Classification of Some Forming Operations Process Rolling Forging Ext rusion Shear spinning Schematic Diagram State of Stress in NIain Part During Form in 12 www.fppt.info
  5. FormingOperaUons Tube spinning Swaging or kneading Deep drawing V.äre and tuEc drawing St retc hi ng Straight Fending Contoured Ranging (a) (a) Convex (a) Concave In flange of blank, 5 In wall of cup. i At Eend- 2 and 7 At outer flange. 6 At kend- 2 and 7 At outer flange- 1 At Ecnd- 2 and 7 www.fppt.info
  6. Forming Prodésgeqgnæpende tv,q$ Variables Forming processes consist of independent and dependent variables Independent variables are the aspects of the processes that the engineer or operator has direct control — Starting material — Starting geometry of the workpiece — Tool or die geometry — Lubrication — Starting temperature — Speed of operation — Amount of deformation www.fppt.info
  7. Dependent variables are those that are determined by the independent variable selection — Force or power requirements — Material properties of the product — Exit or final temperature — Surface finish and precision — Nature of the material flow www.fppt.info
  8. Independent-DepénfåenURe[aiipnships004 Independent variables- control is direct and immediate Dependent variables- control is entirely indirect — Determined by the process — If a dependent variable needs to be controlled, the designer must select the proper independent variable that changes the dependent variable www.fppt.info
  9. Information on the interdependence Of independent and dependent variables Independent variables Starting material Starting geometry Tool geometry Lubrication can be learned in three Links -Experience- -Experiment- -Modeling- Dependent variables Force or power requirements Product properties Exit temperature Surface finish Dimensional precision Material flow details ways — Experience — Experiment — Process modeling Starting temperature Speed of deformation Amount of deformation Figure Schematic representation of a metalforming system showing independent variables, dependent variables, and the various means of linking the two. www.fppt.info
  10. Process:MpdeUng Simulations are created using finite element modeling , Models predict how a material will can respond to a rolling process, fill a forging die, flow through an extrusion die, or solidify in a casting Heat treatments can be simulation Costly trial and error development cycles can be eliminated www.fppt.info
  11. Material being deformed must characterized — Strength or resistance for deformation — Conditions at different temperatures — Formability limits — Reaction to lubricants Speed of deformation and its effects Speed-sensitive materials- more energy is required to produce the same results www.fppt.info
  12. Und ér Friction and-Lübtica Metalworking Conditiofis are required to deform High forces and pressures a material For some processes, 50% of the energy is spent in overcoming friction Changes in lubrication can alter material flow, create or eliminate defects, alter surface finish and dimensional precision, and modify product properties Production rates, tool design, tool wear, and process optimization depend on the ability to determine and control friction www.fppt.info
  13. Metalforming friction differs from the friction encountered in mechanical devices For light, elastic loads, friction is proportional to the applied pressure — p is the coefficient of friction At high pressures, friction Slope = Contact pressure, P is related to the strength Figure The effect of contact pressure on the frictional resistance between two surfaces. of the weaker material www.fppt.info
  14. Friction is resistance to sliding along an interface Resistance can be attributed to: — Abrasion — Adhesion Resistance is proportional to the strength of the weaker material and the contact area www.fppt.info
  15. Surface Détérlpfåtion Surface wear is related to friction Wear on the workpiece is not objectionable, but wear on the tooling is Tooling wear is economically costly and can impact dimensional precision Tolerance control can be lost Tool wear can impact the surface finish www.fppt.info
  16. Lubrication Key to success in many metalfornmng operations Primarily selected to reduce friction and tool wear, but may be used as a thermal barrier, coolant, or corrosion retardant Other factors — Ease of removal, lack of toxicity, odor, flammability, reactivity, temperature, velocity, wetting characteristics www.fppt.info
  17. Workpiece temperature can be one Of the most important process variables—I In general, an increase in temperature is related to a decrease in strength increase in ductility, and decrease in the rate of strain hardening Hot working Cold working Warm working www.fppt.info
  18. Hot Working Plastic deformation of metals at a above the recrystallization temperature Temperature varies greatly with material Recrystallization removes the effects of strain hardening Hot working may produce undesirable reactions from the metal and its surroundings www.fppt.info
  19. Structure and Property Hot Working The size of grains upon cooling is typically uniform Undesirable grain shapes can be common (such as columnar grains) Recrystallization is followed by: — grain growth — additional deformation and recrystallization — drop in temperature that will terminate diffusion and freeze the recrystallized structure www.fppt.info
  20. I-lot Work; Engineering properties can be improved through reorienting inclusion impurities During plastic deformation, impurities tend to flow along with the base metal or fraction into rows of fragments Figure Cross section of a 4-in.-diameter case copper bar polished and etched to show the as-cast grain structure. Figure Flow structure of a hot-forged gear blank. Note how flow is parallel to all critical surfaces. (Courtesy of Bethlehem Steel Corporation, Bethlehem, PA.) www.fppt.info
  21. Temperature Varia0tiOnseirp Hot WorkingDC)4 Success or failure of a hot deformation process often depends on the ability to control temperatures Over 90% of the energy imparted to a deforming workpiece is converted to heat Nonuniform temperatures may be produced and may result in cracking Thin sections cool faster than thick sections (b) Figure Schematic comparison of the grain flow in a machined thread (a) and a rolled thread (b). The rolling operation further deforms the axial structure produced by the previous wire- or rod-forming operations, while machining simply cuts through it. www.fppt.info
  22. Col&Wprking Plastic deformation below the recrystallization temperature Advantages as compared to hot working -No heating required — Better surface finish — Superior dimensional control — Better reproducibility — Strength, fatigue, and wear are improved — Directional properties can be imparted — Contamination is minimized www.fppt.info
  23. O Disadvantages.tCold Working» Higher forces are required to initiate and complete the deformation Heavier and more powerful equipment and stronger tooling are required Less ductility is available Metal surfaces must be clean and scale-free Intermediate anneals may be i red Imparted directional properties can be detrimental Undesirable residual stresses may be produced www.fppt.info
  24. Metal Properties-ahd Cold Workingm Two features that are significant in selecting a material for cold working are — Magnitude of the yield-point stress — Extent of the strain region from yield stress to fracture Springback should also be considered when selecting a material Increase in tensile strength due to work hardening. The high-carbon steel will also have more springback. True strain Low-carbon steel True strain High-carbon steel Figure Use of true stress-true strain diagram to assess the suitability of two metals for cold working. www.fppt.info
  25. Initial and Final Prdpertjes:in acold-WorkingJ Cpi-ö-éé-se 'Figure (Below) Stress- Quality of the starting material is important to the success or failure of the cold-working process The starting material should be clean and free of oxide or scale that might cause abrasion to the dies or rolls strain curve for a low- carbon steel showing the commonly observed yield- point runout; (Right) Luders bands or stretcher strains that form when this material is stretched to an amount less than the yield-point runout. 103 psi 50 30 20 10 0 Upper yield point Lower yield point Yield-point elongation or yield-point runout 1 2 3 Strain (% or in./in. 4 5 x 102) www.fppt.info
  26. Initial and Final Prdpertjes:in acold-WorkingJ Cpi-ö-éé-se 'Figure (Below) Stress- Quality of the starting material is important to the success or failure of the cold-working process The starting material should be clean and free of oxide or scale that might cause abrasion to the dies or rolls strain curve for a low- carbon steel showing the commonly observed yield- point runout; (Right) Luders bands or stretcher strains that form when this material is stretched to an amount less than the yield-point runout. 103 psi 50 40 // C 30 20 10 0 1 2 3 Strain (% or in./in. 4 5 x 102) www.fppt.info
  27. Initial and FihäFPjopOties in(azco$ Cold-working Process A quantitative measure of ' amount of cold work is needed in percent reduction in area: 0/0 Cold Work = R.A. { ( Ao - Af ) / Ao 100% This is also a logical measure of deformation imposed in drawing. www.fppt.info
  28. o Additional EffectS3Qf Cold Annealing heat may be treatments performed prior or at intermediate intervals to cold working Heat treatments allows additional cold working an deformation processes Cold working produces a structure where properties vary with direction, anisotropy 100 90 80 70 60 50 40 30 20 10 0 Tensile strength Yield strength % Elongation 100 90 80 70 60 50 30 20 10 100 o 20 40 60 80 Amount of cold work (%) Figure Mechanical properties of pure copper as a function of the amount of cold work (expressed in percent). www.fppt.info
  29. Deformations produced at temperatures intermediate to cold and hot worh!gg Advantages - Reduced loads on the tooling and equipment — Increased material ductility - Possible reduction in the number of anneals — Less scaling and decarburization — Better dimensional precision and smoother surfaces than hot working — Used for processes such as forging and extrusion www.fppt.info
  30. Isothermål%Forming Deformation that occurs under constant temperature Dies and tooling are heated to the same temperature as the workpiece Eliminates cracking from nonuniform surface temperatures Inert atmospheres may be used o 100 Ti-8Al-1 Mo-lv 50 1020 steel 1000 2000 A-286 alloy Steel 3000 Temperature, OF Figure Yield strength of various materials (as indicated by pressure required to forge a standard specimen) as a function of temperature. Materials with steep curves may require isothermal forming. (From "A Study of Forging Variables, " ML-TDR-64- 95, March 1964; courtesy of Battelle Columbus Laboratories, Columbus, OH.) www.fppt.info
  31. o opper is being reduced from a hot-rolled 3/82in.-diameter rod to a final diameter of 0.100 in. by wire drawing through a series of dies. The final wire should have a yield strength in excess of 50,000 psi and an elongation greater than 10%. Use Figure 15-8 to determine a desirable amount of final cold work. Compute the placement of the last intermediate anneal so that the final product has both the desired size and the desired properties. 0/0 Cold Work = R.A. = { ( - Af ) / Ao 1000/0 AO = (DO)2 It (DO)2/4 = (0.375)2/4 Af = (Df)2 (Df)2/4 = (0.1 ( AO - Af ) / AO = (0.375)2/4 - (0.1 )2/4 1/ (0.375)2/4 )/0.1416 = 92.9% > It means that one step in the wire drawing process is not feasible. www.fppt.info
  32. Additional EffectS@CgoldLWprking 100 90 80 70 60 50 40 30 20 10 Tensile strength Yield strength 0 ongatlon 20 40 60 Amount of cold work (%) 80 100 - (Copper) 90 80 70 60 s 50 c 40 30 20 10 100 www.fppt.info
  33. Additional EffectS@CgoldLWprking 100 90 80 70 60 50 40 30 20 10 Tensile strength Yield strength 0 ongatlon 20 40 60 Amount of cold work (%) 80 100 - (Copper) 90 80 70 60 s 50 c 40 30 20 10 100 www.fppt.info

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