Chapter 5 DRAWING Main contents: Deformation feature of drawing; Mechanic analysis of drawing; Problems arising in drawing; Drawing of cylindrical work-piece; Drawing of other revolving work; Drawing of boxes; Other drawing methods ; Assistant procedures of drawing.

Key points &Difficult point Problems arising in drawing; Drawing of cylindrical work-piece. Difficult parts: Mechanic analysis of drawing

New words deep drawing/深拉深, blank holder/压边圈, cylindrical/圆柱形的，cup/杯形件， conic /锥形的, box-shaped/盒形的，rectangular/矩形的 ironing drawing/变薄拉深,flange/凸缘, wrinkle/起皱 axisymmetric geometry/轴对称几何图形, die radius/凹模圆角半径, radial/径向的, punch corner radius/凸模圆角半径, redundant/多余的 longitudinal/纵向的，relative thickness of material/相对厚度， drawing ratio/拉深比， blank diameter/毛坯直径, number of successive draws/ 拉深次数， add for trimming/修边余量

§5.1 Deformation features of drawing Deep drawing is the process by which a punch is used to force sheet metal to flow between the surfaces of a punch and a die. A flat sheet is formed into a cylindrical-, conical-, or box-shaped part. 1. Types 2. Deformation feature 3. Stress and strain state

1. Types a)Pure drawing: without a reduction in the thickness b)Ironing drawing: with a reduction in the thickness

2. Deformation feature Grid method: Damage sites: bottom radius Thickness: upper becomes thicker lower becomes thinner Hardening: upper serious bottom light Changes in grid: bottom no change wall from sector to rectangle

3. Stress and strain state Four parts: deformation zone(the flange) D-d transition zone -2 die radius force transmitting zone-the wall transition zone-2 punch corner radius non-deforming zone-the bottom

§5.2 Mechanic analysis of drawing Stress analysis of deformation zone Stress distribution in deformation zone Varying law of maximum radial stress and maximum tangential stress Stress analysis of transmitting zone of wall

1. Stress analysis of deformation zone Equations of equilibrium Plastic condition Boundary condition when

2. Stress distribution in deformation zone Characteristic point: ,

3.Varying law of maximum radial stress and maximum tangential stress similar with hardening law 4. Stress analysis of transmitting zone of wall

§5.3 Problems arising in drawing Wrinkle Fracture Hardening

1. Wrinkle 1.1 Generate deformation zone 1.2 Affecting factors Relative thickness t/D0↑,wrinkle↓ Deformation degree m=d/D0↓,wrinkle ↑

1. Wrinkle 1.3 Preventing measures drawing ring(blank holder) taper die : make flange small reverse drawing

1. Wrinkle 1.4 Conditions of no wrinkles Flat die: t / D0≥(0.09~0.17)(1-m) Taper die: t / D0≥0.03(1-m)

2. Fracture 2.1 Stress analysis of cylindrical surface flange deformation resistance friction caused by drawing ring die radius friction resistance die radius bending resistance sum: efficient tension strength in the wall

2. Fracture 2.2 Condition of no fracture 2.3 Affecting factors 1) deformation degree: m↑fracture↓ 2) properties of materials: σb↑fracture↓ 3) size of parts : d , t ↑fracture↓ 4) radius of die and punch: rp ,rd↑frature↓ 5) lubrication: benefit and harmful

§5.4 Drawing of cylindrical work-piece 1. Blank 2. Drawing coefficient 3. Number of drawing 4. Drawing force and drawing power 5. Features of subsequent drawing 6. Determination of drawing die size 7. Homework

1. Blank Principle: constant surface area

2. Drawing coefficient 2.1 Definition and meaning m=d / D0 (or dn / dn-1) an index measuring deformation degree of drawing 2.2   Limit drawing coefficient [m] The maximum drawing coefficient where no wrinkle and no fracture occur. 2.3   Affecting factors Material: Die : Z↑Rd↑Rp↑,[m]↑ Drawing condition: blank holder, Hardening[m1]<[m2]<…<[mn]; lubrication

3. Number of drawing m<[m1] need more than one time drawing Examples n=log dn / m1D0 / log mn+1

4. Drawing force and drawing power 4.1   blank-holding force Q = A p 4.2   drawing force theoretical formula F=Aσρ empirical formula F=kπdtσb 4.3   choose press F = Fl + Q 4.4 drawing power

5. Features of subsequent drawing Inhomogeneous of blank thickness and mechanical properties ; Constant deformation zone ; Maximum drawing force occurs in later period ; Fracture occurs in the later period ; Wrinkle is not serious, because the subsequent drawing is more stable than the first drawing ; Drawing coefficient is large, because of hardening .

6. Determination of drawing die size 6.1   punch rp , dp ,(p93) die rd ,Dd , blank holder 6.2   clearance Z 6.3   structure of die and punch

Homework The workpiece shown in Fig.1 is made of 08 carbon steel sheet with the thickness of 2mm (1.5mm). Calculate the blank diameter before drawing, the number of operation, dimension of work piece after each operation, and the force need Judge whether a blank holder is needed and choose the press.

Homework Fig.1 Final workpiece

§5.5 Drawing of other revolving works Cylindrical works with flange Cylindrical works with steps Taper works Spherical works

1. Cylindrical works with flange 1.1 Blank(5 parts):constant surface area 1.2 Drawing coefficient relative flange diameter, relative height and relative radius. 1.3 Wide flange( ) features drawing principle drawing method calculation procedure 1.4 narrow flange

2. Cylindrical works with steps Drawing coefficient Number of drawing drawing methods for multi-drawing

3. Taper works 3.1 Blank: constant surface area 3.2 Deformation region: plane under flange, die radius, free surface between clearance 3.3 Drawing coefficient 3.4 The effect of the work-piece shape on the drawing process relative height(h/d2), relative taper top radius(d1/d2), relative thickness(t/d2)

4. Spherical works 4.1 deformation zone four parts: plane deformation zone under flange (curved surface) --drawing contact region rd free surface(varying) plastic deformation region(contact with the top of punch) --bulging 4.2 drawing coefficient 4.3 drawing methods

§5.6 Drawing of boxes square and rectangular boxes 1. Features of drawing deformation region and the stress state 2. Blank(shape and size) 3. Limited deformation degree of first drawing 4. Drawing of high box 5. Punch and die

§5.7 Other drawing methods 1.  Ironing 2.  Flexible die forming 3.  Locally-heated or locally-cooled drawing 4. Progressive drawing with sheet

§5.8 Assistant procedures of drawing Lubrication(position and function) Annealing(in process and stress-relief) Pickling(remove scale and dirts)