4 4 6 . 3 0 5 A M A N U F A C T U R I N G P R O C E S S E S

Chapter 6. Bulk Deformation Processes

Sung-Hoon Ahn

School of Mechanical and Aerospace Engineering Seoul National University 2 Classification of Deformation Processes

ƒ Temperature

ƒ Hot working(열간가공) T > 0.6Tm

ƒ Warm working(온간가공) T = 0.3 ~ 0.5Tm ƒ Cold working(냉간가공) T < 0.3Tm

ƒ Type of operation ƒ Primary working(1차가공) : solid piece of metal(금속괴) → slabs(슬래브), plates(후판), billets(빌랫). ƒ Secondary working(2차가공) : products from primary working(1차가공품) → bolts(볼트), sheet metal parts(금속판재품), wire(선재).

ƒ Size and shape of the workpiece ƒ Bulk deformation(부피성형가공) : thickness or cross section of the work- piece changes(forging(단조), rolling(압연), extrusion(압출), drawing(인발)). ƒ Sheet forming(판재성형가공) : generally shape changes, thickness changes are undesirable. 3 Forggg(ing (단조))( (1 )

Bellows / Blower(풀무)

Anvil(모루) 4 Forggg(ing (단조))( (2 )

ƒ Plastic deformation of the workpiece is carried out by compressive forces.

ƒ Crankshafts, connecting rods, turbine disks, gg,ears, wheels, bolt heads, hand tools, etc.

ƒ The recrystallization temperature(재결정온도)formetals: T /Tm ~ 0.5

ƒ Basic categories of forging ƒ Open die(자유단조) ƒ Impression die(형단조) ƒ Closed die(폐쇄단조) 5 Open-die forggg(ing (자유단조)

ƒ Reducing the height of workpiece between two flat dies by compressing it.

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 6 Forces and work of deformation

Reduction in height h − h = 0 1 ×100% h0 h − h ⎛ h ⎞ 0 1 ⎜ 0 ⎟ e1 = , ε1 = ln⎜ ⎟ h0 ⎝ h1 ⎠

v v Relative velocity e&1 = − , ε&1 = − bhlbetween the plates h0 h1 A h F = YA , A = 0 0 1 1 h σ ε 1 ε1 σ Work = volume d , = Kε n ∫0

F = Yf A1, Work = (volume)(Y )(ε1) ε 1 ε n K dε Kε n Y = ∫0 = 1 ε1 n +1

Ref. (Yf : Flow stress, Y : Average flow stress) S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 7 Methods of analysis - Slab method (1)

Horizontal forces :( σ x + dσ x )h + 2μσ ydx −σ xh = 0 σ 2μσ d + y dx = 0 ⓐ x h UiUsing ditdistorti on-energy criteri on f or pl ane st rai n σ 2 : Average flow stress y −σ x = Y = Y′ σ 3 ⓑ Ref. d y = dσ x S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 8 Methods of analysis - Slab method (2)

ⓐ & ⓑ give 2μσ dσ + y dx = 0 σ y h

d y 2μ O.D.E −2μx / h = − dx ⎯⎯⎯→ σ y = Ce σ y σ h

Boundary conditions : x = a, x = 0 ⎯⎯→ σ y = Y ' at the edges of the specimen μ C = Y 'e2 a / h 2μ (a−x)/ h p = σ y = Y'e σ 2μ (a−x)/ h x = σ y −Y '= Y '[e −1] ⎛ μa ⎞ pav ≈ Y '⎜1+ ⎟ : Average pressure ⎝ h ⎠

F = ( pav )(2a)(width) : Forging force 9 Methods of analysis - Slab method (3)

Rectangular Specimen Die pressure

Question : What should be the shape before deformation to make a rectangular part? Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 10 Methods of analysis - others

ƒ Slip-line analysis(미끄럼선 해석) ƒ Upper-bound technique(상계해법) ƒ Finite element method(유한요소법)

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 11 Impression-die/closed-die forggg(ing(형단조)(1 )

ƒ Impression-die forging : the workpiece acquires the shape of the die cavities ((pimpressions) while it is being upset between the closing dies. ƒ Flash(플래쉬) : significant role in the flow of material. ƒ Forces in impression-die forging : depending on its position, F=KpYfA. ƒ Land(랜드부) : controlling the forging load not to be excessive.

h ratio L

Plane strain

F = (K p )(Yf )(A)

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 12 Impression-die/closed-die forggg(ing(형단조)(2 )

ƒ Closed-die forging(폐쇄단조) : no flash is formed and the workpiece is completely surrounded by the dies. ƒ Precision forging(정밀단조), flashless forging(밀폐단조) : the part formed is close to the final dimensions, high forging load & capacity equipment needed. ƒ Isothermal forging(등온단조), hot-die forging(가열금형단조):thediesareheatedtothesame temperature as the hot blank.

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 13 Closed-die forggg(ing (폐쇄단조)

ƒ Orbital forging(궤도단조)

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 14 Miscellaneous forging operations (1)

ƒ Coining(코이닝) ƒ an example of closed-die forging ƒ minting of coins. ƒ Heading(헤딩)–Fig6.17 ƒ Piercing(천공) – Fig 6.18 ƒ Hubbing(허빙) ƒ Cogging(코깅) ƒ Fullering and edging(풀러링, 에징) ƒ Role forging(압연단조) ƒ Skew-rolling(강구전조작업)

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 15 Miscellaneous forging operations (2)

Cogging Roll forging(Cross rolling)

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 16 Miscellaneous forging operations (3)

Steel balls by skew-rolling

Steel balls by upsetting

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 17 Defects in forging (1)

ƒ Caused by the material flow patterns in the die cavity. ƒ Cold shut . ƒ Grain flow pattern, end grain. Buckling

Over sized billet

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 18 Defects in forging (2)

GGrainrain flowflow pattepatternrn (단류선 영향)

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 19 Die design (1) ƒ The most important rule in die design : the workpiece material flow in the direction of least resistance. ƒ Considerations ƒ Strength and ductility of the workpiece material. ƒ SiStrainrateand temperature. ƒ Frictional characteristics. ƒ Die distortion under high forging loads.

ƒ Die design parameters ƒ Flash clearance between the dies : 3% of the max. thickness. ƒ Length of the land : 5 times of the flash clearance. ƒ Proper radii for corners and fillets.

ƒ Die materials ƒ Tool and die steel(공구강및다이 Ref. 강) containing Cr, Ni, Mo and V. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 20 Die design (2)

ƒ Draft angles : Internal angles(7~10°) > External angles(3~5°)

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 21 Forging equipment

ƒ Hydraulic presses(유압프레스) ƒ Mechanical presses(기계프레스) ƒ Screw presses(나사프레스) : for parts requiring precision(turbine blades) and control of ram speed. ƒ H(Hammers(해머) : potentilial energy of theramis converted to kinet ic energy. ƒ Counterblow hammers(카운터블로해머)

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 22 Rollingg( (압연)

ƒ The process of reducing the thickness or changing the cross-section of a long workpiece by compressive forces applied through a set of rolls. ƒ Plate(후판):t≥6mm / sheet (박판): t≤ 6mm

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 23 Changes in the grain structure

WhtttWrought structure (단련 구조)

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 24 Mechanics of flat rolling

ƒ The velocity of strip must increase as it moves through the roll gap. ƒ Sliding occurs btbetween theroll and thestitrip due to the surface speed of the roll is constant. ƒ Neutral point or no slip point(중립점) ƒ LftLeft of neutltral poitint :workikpiece velitlocity roll velocity ƒ The frictional forces oppose each other at the neutral

point. (Ffriction_left > Ffriction_right) → yielding a net frictional force to the right.

V −V Forward slip = f r Vr

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 25 Roll pressure distribution (1)

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 26 Roll pressure distribution (2)

σ (σ x + dσ x )(h + dh) − 2 pRdφ sinφ −σ xh ± 2μpRdφ cosφ = 0 h = h + 2R(1− cosφ) φ f d(σ xh)φ 2 = 2μpR(sinφ μ cosφ) h = hf + Rφ μ dφ m φ φ p h R −1 R d( xh) ln = ln 2 tan φ + lnC = 2 pR( m ) , (Q sin ≈ , cosφ ≈1) m d Yf′ R hf hf 2 h mμH p −σ x = Yf = Yf′ p = CY′ e 3 f R ′ d[( p −Yf )h] ⎛ ⎞ = 2 pR(φ m μ) R −1 R φ dφ H = 2 tan ⎜ φ ⎟ h ⎜ h ⎟ f ⎝ f ⎠ ⎡ ⎛ ⎞ ⎤ φd ⎜ p ⎟ φ ⎢Yf′ −1 h⎥ = 2 pR( m μ) R μH d ⎜ Y′ ⎟ i ⎢⎣ ⎝ f ⎠ ⎦⎥ In the entry zone :C = e φ hf d ⎛ p ⎞ ⎛ p ⎞ d φ ⎜ ⎟ ⎜ ⎟ h μ (Ho −H ) Yf′h + −1 Yf′h = 2 pR( μ) ′ ⎜ ′ ⎟ ⎜ ′ ⎟ m p = Yf e d ⎝ Yf ⎠ ⎝ Yf ⎠ d φ ho ⎛ ⎞ d ⎜ p ⎟ R d ⎜ Y′ ⎟ In the exit zone :C = ⎝ f ⎠ 2R φ h = ( m μ) f p /Yf′ h h μH p = Yf′ e hf 27 Neutral point / front and back tension

μ

Ho h e μ o = = eμ (Ho −2H n ) 2 H n hf e 1 ⎛ 1 h ⎞ H = ⎜ H − ln o ⎟ n ⎜ o ⎟ 2 ⎝ μ hf ⎠ h ⎛ h H ⎞ φ = f tan⎜ f ⋅ n ⎟ n ⎜ ⎟ R ⎝ R 2 ⎠

h μ (Ho −H ) Entry zone : p = (Yf′ −σ b ) e ho

h μH Exit zone: p = (Yf′ −σ f ) e hf Exmple 6.3 Back tension required to cause roll slip h f μHo pφ =0 = (Yf′ −σ b ) e ho ⎡ ⎛ h ⎞ ⎤ σ = Y′ ⎢1− ⎜ o ⎟(e−μHo )⎥ b f ⎜ h ⎟ ⎣⎢ ⎝ f ⎠ ⎦⎥ Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 28 Defects in rolling

ƒ Surface defects ƒ Structural defects ƒ Residual stresses ƒ In the case of small-diameter rolls or small reductions, plastic deformation occurs on the surfaces. → compressive stresses(surfaces), tiltensilest(blk)tresses(bulk). ƒ In the case of large-diameter rolls or high reduction, plastic deformation of the blkbulk isgreater than the surfaces. → tensile stresses(surfaces), compressive stresses(bulk)

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 29 Flat-rollingg( practice (평판 압연 작업)

ƒ Hot rolling : converts the coarse-grained, brittle and porous cast structure to wrought structure(finer grains and enhanced ductility).

ƒ Products of the first hot-rolling operation ƒ Bloom : square cross-section(정사각형), at least 150mm side, structural shapes by shape rolling(e.g. I-beam and railroad rails). ƒ Slab : rectangular in cross-section(직사각형), plates and sheet. ƒ Billet : square cross-section(정사각형) smaller than bloom, various shapes (e.g. round rods(환봉강) and bars)

ƒ Rolling equipment ƒ Small-diameter rolls are preferable, because the smaller the roll radius the lower the roll force. However, small rolls deflect under roll forces and have to be supported by other rolls. The cluster mill, or Sendzimir(다단압연기), is particularly suitable for cold rolling thin strips of high-strength metals. 30 Rolling equipment

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 31 Miscellaneous rolling operations (1)

ƒ Shape rolling(형상압연) : H-section part, I-Beam and channels. ƒ Ring rolling(링압연) :ringsfor rocket, turbines and gearwheel rims. ƒ Thread and gear rolling(나사 및 기어전조) : high production rates, great strength, improved fatigue life. ƒ Rotary tube piercing(회전천공) : hot-working process to make long, thick-walled seamless tubing.

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 32 Miscellaneous rolling operations (2)

ƒ Ring rolling

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 33 Miscellaneous rolling operations (3)

ƒ Thread and gear rolling

Grain flow lines ( 단류선)

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 34 Miscellaneous rolling operations (4)

ƒ Rotary tube piercing ƒ Thick-walled seamless tube.

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 35 Extrusion (압출)

Direct extrusion(직접압출) : high friction between billet Indirect extrusion(간접압출) : no friction between and wall billet and wall, die moves to the billet.

Impact extrusion(충격압출) : form of indirect extrusion, suitable for hollow shapes. Ref. Hydrostatic extrusion(정수압압출) : no friction S. Kalpakjian, "Manufacturing Processes for Engineering Materials", along the container walls. 3rd/4th ed. Addison Wesley 36 Mechanics of extrusion (1)

A Extrusion ratio, R = o Af ⎛ A ⎞ ⎛ L ⎞ ε = ln⎜ o ⎟ = ln⎜ f ⎟ = ln R 1 ⎜ ⎟ ⎜ ⎟ ⎝ Af ⎠ ⎝ Lo ⎠ Energy dissipated in plastic deformation per u = Yε1 unit volume Work = (Ao )(Lo )(u)

Work = FLo = pAo Lo ⎛ A ⎞ p = u = Y ln⎜ o ⎟ = (Y )(ln R) ⎜ ⎟ ⎝ Af ⎠

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 37 Mechanics of extrusion (2)

When friction is included

μ ⎛ tanα ⎞ cotα p = Y⎜1+ ⎟[(R) −1] ⎝ μ ⎠

Ptotal = Pplastic + Pfriction 2 Pttltotal = pVo (πD0 / 4) π 2 2 Pplastic = Vo ( D0 / 4)(Y )[ln(Do / D f ) ] 2 Pfriction = (Vo )(πD0 / 2)(Y / 2)ln(Do / D f )

2 p /Y = 3.41ln(Do / D f ) =1.7[ln(Do / D f ) ] p =1.7Y ln R π ⎛ D2 ⎞ ⎜ 0 ⎟ ( p friction )⎜ ⎟ = πDokL ⎝ 4 ⎠ 4L 2L p friction = k = Y Do Do Actual forces : p = Y (a + bln R) (Emperical formula) ⎛ 2L ⎞ p = Y⎜1.7ln R + ⎟ ⎝ Do ⎠ Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 38 Defects in extrusion

ƒ Surface cracking(표면균열) ƒ Too high extrusion temperature, friction, or extrusion speed. ƒ Periodic sticking of the extruded product along the die land. ƒ Extrusion defect(파이프결함) ƒ Surface oxides and impurities drawn toward the center of the billet. ƒ Reduced by modifying the flow pattern, machining the surface of the billet or using a dummy block. ƒ Internal cracking( 내부균열) : due to hydrostatic tensile stress at the center line.

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 39 Drawingg( (인발)

ƒ The cross-sectional area of a bar or tube is reduced by pulling it through a converging die. ƒ Rod and wire drawing are usually finishing process .

⎛ A ⎞ σ = Y ln⎜ o ⎟ d ⎜ ⎟ ⎝ Af ⎠ σ = Kε n Kε n Y = 1 n +1 ⎛ A ⎞ F = YA ln⎜ o ⎟ f ⎜ ⎟ ⎝ Af ⎠

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 40 Defects in drawing

ƒ Similar to defects in extrusion. ƒ Seams(솔기결함))g : longitudinal scratches or folds in the material.

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 41 Swaggg(ing (스웨이징))( (1 )

ƒ The metal flows in to the dies which appl y compressive force or impact to the metal at room temperature. ƒ Rotary swaging(회전 스웨이징) : a solid rod or a tube is reduced in diameter by reciprocating radial mov ement of dies. ƒ The Internal diameter and thickness or shape of the tube can be controlled with or without mandrels(맨드릴).

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 42 Swaggg(ing (스웨이징))( (2 )

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 43 Case study (Space shuttle)

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 44 Solid rocket casing

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley 45 Forging processes for solid rocket casing

Ref. S. Kalpakjian, "Manufacturing Processes for Engineering Materials", 3rd/4th ed. Addison Wesley