1. CHAPTER 6_PART II BULK DEFORMATION PROCESSES IN METALWORKING DPT 211 MANUFACTURING PROCESS 1

2. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e CONTENT 1.Rolling 2.Forging 3.Extrusion 4.Wire and Bar Drawing

3. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e BULK DEFORMATION Metal forming operations which cause significant shape change by deforming metal parts whose initial form is bulk rather than sheet  Starting forms:  Cylindrical bars and billets,  Rectangular billets and slabs, and similar shapes

4. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Importance of Bulk Deformation  Performed as cold, warm, and hot working operations  Little or no waste - some operations are near net shape or net shape processes  The parts require little or no subsequent machining

5. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Four Basic Bulk Deformation Processes 1.Rolling – slab or plate is squeezed between opposing rolls 2.Forging – work is squeezed and shaped between opposing dies 3.Extrusion – work is squeezed through a die opening, thereby taking the shape of the opening 4.Wire and bar drawing – diameter of wire or bar is reduced by pulling it through a die opening

6. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Deformation process in which work thickness is reduced by compressive forces exerted by two opposing rolls Figure 19.1 The rolling process (specifically, flat rolling). ROLLING

7. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e The Rolls Rotating rolls perform two main functions:  Pull the work into the gap between them by friction between workpart and rolls  Simultaneously squeeze the work to reduce its cross section

8. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Types of Rolling  Based on workpiece 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

9. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Flat-Rolling and Shape-Rolling Processes Figure 13.1 Schematic outline of various flat- rolling and shape-rolling processes. Source: After the American Iron and Steel Institute.

10. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Figure 19.2 Some of the steel products made in a rolling mill. Rolled Products Made of Steel

11. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Metal sizes in rolling  Slab: 50mm x 350mm to 300mm x 1800mm  Billet: 50mm x 50mm to 150mm x 150mm  Bloom: 150mm x 150mm to 400mm x 400mm  Plates: thickness of more than 6 mm and up to 300mm. Depend on applications  Sheets: thickness of less than 6 mm

12. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Figure 19.3 Side view of flat rolling, indicating before and after thicknesses, work velocities, angle of contact with rolls, and other features. Diagram of Flat Rolling

13. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Flat-Rolling Process Figure 13.2 (a) Schematic illustration of the flat-rolling process. (b) Friction forces acting on strip surfaces. (c) Roll force, F, and the torque, T, acting on the rolls. The width of the strip, w, usually increases during rolling, as shown later in Fig. 13.5.

14. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Flat Rolling Terminology Draft = amount of thickness reduction where d = draft; t o = starting thickness; and t f = final thickness

15. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Flat Rolling Terminology Reduction = draft expressed as a fraction of starting stock thickness: where r = reduction

16. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e  The true strain experienced by the work in rolling is based on before and after stock thicknesses. In equation form, є = In (t o / t f )  The true strain can be used to determine the average flow stress Y avg applied to the work material in flat rolling that is defined: Y avg = Kє n /(1+ n)where K is strength coefficient n is strain hardening exp  Contact length can be approximated by: L = √R (t o – t f )

17. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e  Roll force, F, is needed because the rolls apply the pressure on the material in order to reduce its thickness. This is, F = Y avg w L  Torque for each roll is: T = 0.5FL  The power required per roll can be estimated from the formula P = 2NFL where N is rotational speed of roller in rev/s N = 2R (R is roller radius in m)

18. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Example Calculation of Flat Rolling  Calculate the draft, contact length, average flow stress, roll force, torque, and power. Data given by: w = 300 mm, t o = 25 mm, R = 250 mm, t f = 22 mm, N = 50 rev/min, K = 275 MPa, n = 0.15.

19. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Solution  The draft attempted in this rolling operation is d = 25 – 22 = 3 mm  To compute rolling force, we need the contact length and the average flow stress. L = √250(25 – 22) = 27.4 mm = 0.00274  The average flow stress is determined from the true strain: є = In (25/22)= 0.128 Y avg = 275(0.128) 0.15 /(1+ 0.15) = 175.7 MPa  Rolling force is determined from, F = 175.7 MPa (300 mm )(27.4mm) = 1,444,069 N  Torque required to drive each roll is given by, T = 0.5(1,444,069)(27.4 x 10 -3 ) = 19,783 Nm  Power is obtained from, P = 2(50/60)(1,444,783)(27.4 x 10 -3 ) = 207,774 Nm/s @ W

20. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e where K = strength coefficient n = strain hardening exponent

21. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Figure 2.6 True stress- strain curves in tension at room temperature for various metals. The curves start at a finite level of stress: The elastic regions have too steep a slope to be shown in this figure, and thus each curve starts at the yield stress, Y, of the material

22. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e A rolling mill for hot flat rolling. The steel plate is seen as the glowing strip in lower left corner (photo courtesy of Bethlehem Steel).

23. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e 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

24. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Figure 19.5 Various configurations of rolling mills: (a) 2 ‑ high rolling mill. Two-High Rolling Mill

25. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Figure 19.5 Various configurations of rolling mills: (b) 3 ‑ high rolling mill. Three-High Rolling Mill

26. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Figure 19.5 Various configurations of rolling mills: (c) four ‑ high rolling mill. Four-High Rolling Mill

27. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Multiple backing rolls allow even smaller roll diameters Figure 19.5 Various configurations of rolling mills: (d) cluster mill Cluster Mill

28. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e A series of rolling stands in sequence Figure 19.5 Various configurations of rolling mills: (e) tandem rolling mill. Tandem Rolling Mill

29. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e FORGING Deformation process in which work is compressed between two dies  Oldest of the metal forming operations, dating from about 5000 B C  Components: engine crankshafts, connecting rods, gears, aircraft structural components, jet engine turbine parts  Also, basic metals industries use forging to establish basic form of large parts that are subsequently machined to final shape and size

30. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Classification of Forging Operations  Cold vs. hot forging:  Hot or warm forging – most common, due to the significant deformation and the need to reduce strength and increase ductility of work metal  Cold forging – advantage: increased strength that results from strain hardening

31. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Types of Forging Dies  Open ‑ die forging - work is compressed between two flat dies, allowing metal to flow laterally with minimum constraint  Impression ‑ die forging - die contains cavity or impression that is imparted to workpart  Metal flow is constrained so that flash is created  Flashless forging - workpart is completely constrained in die  No excess flash is created

32. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Figure 19.9 Three types of forging: (a) open ‑ die forging. Open-Die Forging

33. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Figure 19.10 Homogeneous deformation of a cylindrical workpart under ideal conditions in an open ‑ die forging operation: (1) start of process with workpiece at its original length and diameter, (2) partial compression, and (3) final size. Open-Die Forging with No Friction

34. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Figure 19.11 Actual deformation of a cylindrical workpart in open ‑ die forging, showing pronounced barreling: (1) start of process, (2) partial deformation, and (3) final shape. Open-Die Forging with Friction

35. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Figure 19.9 Three types of forging: (b) impression ‑ die forging. Impression-Die Forging

36. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Figure 19.14 Sequence in impression ‑ die forging: (1) just prior to initial contact with raw workpiece, (2) partial compression, and (3) final die closure, causing flash to form in gap between die plates. Impression-Die Forging

37. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Figure 19.9 Three types of forging (c) flashless forging. Flashless Forging

38. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Figure 19.17 Flashless forging: (1) just before initial contact with workpiece, (2) partial compression, and (3) final punch and die closure. Flashless Forging

39. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Forging Hammers (Drop Hammers) Apply impact load against workpart  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

40. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Figure 19.19 Drop forging hammer, fed by conveyor and heating units at the right of the scene (photo courtesy of Chambersburg Engineering Company).

41. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Figure 19.20 Diagram showing details of a drop hammer for impression ‑ die forging. Drop Hammer Details

42. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e EXTRUSION Compression forming process in which work metal is forced to flow through a die opening to produce a desired cross ‑ sectional shape  Process is similar to squeezing toothpaste out of a toothpaste tube  In general, extrusion is used to produce long parts of uniform cross sections

43. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Figure 19.30 Direct extrusion. Direct Extrusion

44. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Figure 19.31 (a) Direct extrusion to produce a hollow or semi ‑ hollow cross sections; (b) hollow and (c) semi ‑ hollow cross sections. Hollow and Semi-Hollow Shapes

45. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Extrusions and Products Made from Extrusions Figure 15.2 Extrusions and examples of products made by sectioning off extrusions. Source: Courtesy of Kaiser Aluminum.

46. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Figure 19.36 A complex extruded cross section for a heat sink (photo courtesy of Aluminum Company of America) Complex Cross Section

47. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Extrusion Presses  Either horizontal or vertical  Horizontal more common  Extrusion presses - usually hydraulically driven, which is especially suited to semi ‑ continuous direct extrusion of long sections  Mechanical drives - often used for cold extrusion of individual parts

48. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Pressure and other variables in direct extrusion Figure 3.16: Pressure and other variables in direct extrusion

49. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Analysis of Extrusion  The extrusion ratio or reduction ratio is defined: Extrusion ratio Cross sectional area of starting billet (mm 2 ) Final cross sectional area of extruded section

50. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Analysis of Extrusion (cont)  True strain in extrusion (no friction)  The pressure applied by the ram to compress the billet through the die opening (no friction)  Average flow stress during deformation K = strength coefficient n = strain hardening exponent

51. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Analysis of Extrusion (cont)  Johnson’s extrusion strain (friction exist) a and b are empirical constant for given die angle  The ram pressure to perform indirect extrusion  The ram pressure to perform direct extrusion  Ram force in indirect or direct extrusion

52. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e

53. Question 19.23  A cylindrical billet that is 100 mm and 50 mm in diameter is reduced by indirect extrusion to a 20 mm diameter. The Johnson’ s equation has a=0.8 and b=1.4. Given the strength coefficient and strain hardening exponent are 800 MPa and 0.13 respectively. Determine 1.Extrusion ratio 2.True strain 3.Extrusion strain 4.Ram pressure 5.Ram force

54. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Extrusion constant Figure 15.5 Extrusion constant k for various metals at different temperatures. Source: After P. Loewenstein

55. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e WIRE AND BAR 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

56. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Figure 19.40 Drawing of bar, rod, or wire. Wire and Bar Drawing

57. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Area Reduction in Drawing Change in size of work is usually given by area reduction: where r = area reduction in drawing; A o = original area of work; and A r = final work

58. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Drawing Practice and Products  Drawing practice:  Usually performed as cold working  Most frequently used for round cross sections  Products:  Wire: electrical wire; wire stock for fences, coat hangers, and shopping carts  Rod stock for nails, screws, rivets, and springs  Bar stock: metal bars for machining, forging, and other processes

59. ©2007 John Wiley & Sons, Inc. M P Groover, Fundamentals of Modern Manufacturing 3/e Figure 19.41 Hydraulically operated draw bench for drawing metal bars. Bar Drawing Bench