Sheet-Metal Forming Processes Pr ocess · PDF fileSheet-Metal Forming Processes ... Localized necking in a sheet-metal specimen under tension. (b) Determination of the angle of neck

Manufacturing Processes for Engineering Materials, 5th ed. Kalpakjian Schmid 2008, Pearson EducationISBN No. 0-13-227271-7
Sheet-Metal Forming Processes
TABLE 7.1 General characteristics of sheet-metal forming processes.
Process CharacteristicsRoll forming Long parts with constant complex cross-sections; good surface finish; high
production rates; high tooling costs.Stretch form-ing
Large parts with shallow contours; suitable for low-quantity production; highlabor costs; tooling and equipment costs depend on part size.
Drawing Shallow or deep parts with relatively simple shapes; high production rates;high tooling and equipment costs.
Stamping Includes a variety of operations, such as punching, blanking, embossing,bending, flanging, and coining; simple or complex shapes formed at highproduction rates; tooling and equipment costs can be high, but labor costsare low.
Rubber-padforming
Drawing and embossing of simple or complex shapes; sheet surface protectedby rubber membranes; flexibility of operation; low tooling costs.
Spinning Small or large axisymmetric parts; good surface finish; low tooling costs, butlabor costs can be high unless operations are automated.
Superplasticforming
Complex shapes, fine detail, and close tolerances; forming times are long,and hence production rates are low; parts not suitable for high-temperatureuse.
Peen forming Shallow contours on large sheets; flexibility of operation; equipment costscan be high; process is also used for straightening parts.
Explosiveforming
Very large sheets with relatively complex shapes, although usually axisym-metric; low tooling costs, but high labor costs; suitable for low-quantityproduction; long cycle times.
Magnetic-pulseforming
Shallow forming, bulging, and embossing operations on relatively low-strength sheets; most suitable for tubular shapes; high production rates;requires special tooling.

Localized Necking1
2
(a) (b) (c)
2 = 3
/2
1
2 ~110
Diffuse neck Localized neck
(d)
FIGURE 7.1 (a) Localized necking in a sheet-metal specimen under tension. (b) Determination of the angle of neck from the Mohr's circle for strain. (c) Schematic illustrations for diffuse and localized necking, respectively. (d) Localized necking in an aluminum strip in tension; note the double neck. Source: S. Kalpakjian.

Lueders Bands
(a)
Yield-pointelongation
Yielded metal
Lueder!s band
Unyielded metal
0 Strain
Str
ess
YupperYlower
(b) (c)
FIGURE 7.2 (a) Yield-point elongation and Lueders bands in tensile testing. (b) Lueder's bands in annealed low-carbon steel sheet. (c) Stretcher strains at the bottom of a steel can for common household products. Source: (b) Courtesy of Caterpillar Inc.

Stress-Corrosion Cracking
FIGURE 7.3 Stress-corrosion cracking in a deep-drawn brass part for a light fixture. The cracks have developed over a period of time. Brass and 300-series austenitic stainless steels are particularly susceptible to stress-corrosion cracking.

Shearing Process
Punch
Die
Sheet
A
B D
C
c
T
F
Punch
SlugSheet
Die
Penetration
Fracturesurface
Clearance
FIGURE 7.4 Schematic illustration of the shearing process with a punch and die, indicating important process variables.

Hole & Slug
(a)
Rollover depth
Penetration depth
Burnish depth
Fractureangle
Burr height
Fra
ctu
red
ep
th
Breakoutdimension
Sheetthickness
Burnishdimension
Flattened portionunder the punch
Burr heightDishing
Burr
Rough surface
Smooth surface(burnished)
Ideal slug
A C
B D
(b)
FIGURE 7.5 Characteristic features of (a) a punched hole and (b) the punched slug. Note that the slug has a different scale than the hole.

Shearing Mechanics
(a) (b)
1. 2. 3.
Punch
Clearance, c
Die
12
0
12
0
14
0 (
HV
)
14
0
16
0
18
0
20
0
160
200
22
0 1
80
14
0
14
0
18
0
16
0
20
0
12
0
120
160
1
80
20
0
FIGURE 7.6 a) Effect of clearance, c, on the deformation zone in shearing. Note that, as clearance increases, the material tends to be pulled into the die, rather than being sheared. (b) Microhardness (HV) contours for a 6.4-mm (0.25-in.) thick AISI 1020 hot-rolled steel in the sheared region. Source: After H.P. Weaver and K.J. Weinmann.
Force
Penetration0
FIGURE 7.7 Typical punch force vs. penetration curve in shearing. The area under the curve is the work done in shearing. The shape of the curve depends on processing parameters and material properties.
Maximum punch force:
Fmax = 0.7(UTS)tL

Shearing Operations
(a) (b)
Discarded
Punching Blanking
Parting
Lancing
Perforating
Notching
Slitting
FIGURE 7.8 (a) Punching and blanking. (b) Examples of shearing operations on sheet metal.

Fine Blanking
(b)
(a)
Upper pressure pad
Blanking punch
Stinger (impingement ring)
Sheet metal
Punch
Slug
Sheet
Die
Upperpressurepad
Clearance
Fracturesurface
Lower pressure cushion
Blanking die
Lower pressure cushion
Support
FIGURE 7.9 (a) Comparison of sheared edges by conventional (left) and fine-blanking (right) techniques. (b) Schematic illustration of a setup for fine blanking. Source: Feintool International Holding.

Rotary Shearing
FIGURE 7.10 Slitting with rotary blades, a process similar to opening cans.
Drivencutter
Clearance
Ildingcutter
Workpiece

Shaving & Beveled Tooling
FIGURE 7.11 Schematic illustration of shaving on a sheared edge. (a) Shaving a sheared edge. (b) Shearing and shaving combined in one punch stroke.
(a) (b)
Shearededge
Sheet
Die
Sheet
DieClearance
FIGURE 7.12 Examples of the use of shear angles on punches and dies. Compare these designs with that for a common paper punch.
(a) (b) (c) (d)
Double-bevel shear Convex shear
Blankthickness
Shear angle
Punch
Die
Bevel shear
Punch
Die

Progressive Die
FIGURE 7.13 (a) Schematic illustration of producing a washer in a progressive die. (b) Forming of the top piece of a common aerosol spray can in a progressive die. Note that the part is attached to the strip until the last operation is completed.
(b)(a)
Ram
Blankingpunch
Pilot
Scrap
Die
Stop
Finishedwasher
Strip
Scrap
Strip
Stripper
Piercingpunch
Firstoperation
Slug
Part

Tailor-Welded Blanks
FIGURE 7.14 Examples of laser-welded and stamped automotive body components. Source: After M. Geiger and T. Nakagawa.
(a)
(b)
Blanking;laser cutting
Laser welding Stamping
g 60/60 (45/45)
m 20/20
Legend
Hot-galvanized alloy steel sheet. Zinc amount: 60/60 (45/45) g/m2.
Double-layered iron-zinc alloy electroplated steel sheet. Zinc amount 20/20 g/m2.
1 mm
1 mm
m 20/20
0.8 mmg 45/45
g 60/60
1 mmg 45/45
1 mmg 45/45
0.7 mm
1.5 mm
0.7 mm1.25 mm
Floor plate
2.0 mm
0.8 mm
Motor-compartmentside rail
0.7 mm0.7 mm
1.5 mm
Quarter inner with integratedshock-absorber support
Fender withintegrated reinforcement
Girder
1.5 mm
2.0 mm
Shock-absorbersupport
1.5 mm2.5 mm1.5 mm0.7 mm 0.7 mm

Bending & Minim Bend RadiusFIGURE 7.5 (a) Bendi

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Sheet-Metal Forming Processes Pr ocess · PDF fileSheet-Metal Forming Processes ... Localized necking in a sheet-metal specimen under tension. (b) Determination of the angle of neck