SHEARING AND BENDING OF METALS

Sheet Metalworking

• Cutting and forming operations performed on relatively thin sheets of metal which are produced by rolling

• Thickness of sheet metal = 0.4 mm (1/64 in) to 6 mm (1/4 in)

• Thickness of plate stock > 6 mm• Operations usually performed as cold working

(except when the stock is thick or the metal is brittle then warm working is performed)

Sheet and Plate Metal Products

• Sheet and plate metal parts for consumer and industrial products such as:

• – Automobiles and trucks• – Airplanes• – Railway cars and locomotives• – Farm and construction equipment• – Small and large appliances• – Office furniture• – Computers and office equipment

Sheet Metal Processes

1. Cutting – Shearing to separate large sheets; or cut

part perimeters or make holes in sheets2. Bending – Straining sheet around a straight axis3. Drawing – Forming of sheet into convex or concave

shapes

Advantages of Sheet Metal Parts

• High strength• Good dimensional accuracy• Good surface finish• For large quantities, economical mass

production operations are available

Shearing operation• Several operations based on shearing performed Punching – sheared slug discardedBlanking – Slug is the part and the rest is scrap

Fig-16.4 -a

Sitting and Shaving Operations

• FIGURE 7.10 Sitting with rotary knives. This process is similar to opening cans.

FIGURE 7.11 Schematic illustrations of shaving on a sheared edge. (a) Shaving a sheared edge. (b) Shearing and shaving, combined in one stroke.

Shear Angles For Punches and Dies

• FIGURE 7.12 Examples of the use of shear angles on punches and dies.

Progressive Dies

FIGURE 7.13 (a) Schematic illustration of the making of a washer in a progressive die. (b) Forming of the top piece of an aerosol spray can in a progressive die. Note that the part is attached to the strip until the last operation is completed.

Tailor-Welded Blanks

• FIGURE 7.14 (a) Production of an outer side panel of a car body by laser welding and stamping. (b) Examples of laser welded and stamped automotive body components. Source: After M. Geiger and T. Nakagawa.

Cutting

Clearance in Sheet Metal Cutting

Clearance in Sheet Metal Cutting

Clearance in Sheet Metal Cutting

Angular Clearance

Cutting Forces

Cutting Forces

Progressive Dies

FIGURE 7.13 (a) Schematic illustration of the making of a washer in a progressive die. (b) Forming of the top piece of an aerosol spray can in a progressive die. Note that the part is attached to the strip until the last operation is completed.

Progressive Die Sets• Progressive die sets- two or

more sets of punches and dies mounted in tandem

• Transfer dies move individual parts from operation to operation within a single press

• Compound dies combine processes sequentially during a single stroke of the ram Figure 17-16 Progressive piercing and blanking die

for making a square washer. Note that the punches are of different length.

Compound dies :• Several operations on the same strip performed in one

stroke at one station with a compound dies

Fig 16.11 Schematic illustrations: (a) before and (b) after blanking a common washer in a compound die.note the separate movements of the die(or blanking) and the punch

Transfer dies• Sheet metal undergoes different operations at different stations

in a straight line or circular path.

Tool and Die Material :• Carbides are used for high production rates.

Allowance for Multiblank thru Die

• 1. Between Blanks with pitch .....................T min.• 2. Between Blanks diagonally ..................T min.• 3. Blank to the Edge of Material ........ 0.5 T min.

Springback is caused by the elastic recovery of the material upon unloading. The material tends to recover toward its originally flat shape. Overbend to compensate for springback