SHEARING 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

Shearing Operations: Punching, Blanking and Perforating

Punching: shearing process using a die and punch where the interior portion of the sheared sheet is to be discarded. Blanking: shearing process using a die and punch where the exterior portion of the shearing operation is to be discarded.Perforating: punching a number of holes in a sheetParting: shearing the sheet into two or more piecesNotching: removing pieces from the edges

Lancing: leaving a tab without removing any material

Slitting Operation

Slitting: a shearing operation carried out by a pair of circular cutting blades. Similar to the action of a can opener

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.

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

Quality of sheared edges

• Depends on process used• Edges can be rough, not square, and contain cracks, residual stresses, and a work-hardened layer• These are all detrimental to the ………………of the sheet• Quality can be improved by control of …………, tool and die design

Clearance in Sheet Metal Cutting

Clearance in Sheet Metal Cutting

Angular Clearance

Cutting Forces

Cutting Forces

Types of Piercing and Blanking• Shaving- finishing operation in

which a small amount of metal is sheared away from the edge of an already blanked part

• Cutoff- a punch and a die are used to separate a stamping or other product from a strip of stock

• Dinking- used to blank shapes from low-strength materials such as rubber, fiber, or cloth Figure 17-10 The dinking process.

Tools and Dies for Piercing and Blanking

• Basic components of a piercing and blanking die set are: punch, die, and stripper plate

• Punches and dies should be properly aligned so that a uniform clearance is maintained around the entire border

• Punches are normally made from low-distortion or air-hardenable tool steel

Figure 17-11 The basic components of piercing and blanking dies.

Blanking Operations

Figure 17-13 (Below) Typical die set having two alignment guideposts. (Courtesy of Danly IEM, Cleveland, OH.)

Die Tooling

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.

Sheet Metal Groups Allowances

Metal group a

1100S and 5052S aluminum alloys, all tempers

0.045

2024ST and 6061ST aluminum alloys; brass, soft cold rolled steel, soft stainless steel

0.060

Cold rolled steel, half hard; stainless steel, half hard and full hard

0.075