Sheet-Metal Forming

Introduction• Sheet metal forming is a process that

materials undergo permanent deformation by cold forming to produce a variety of complex three dimensional shapes.

• The process is carried out in the plane of sheet by tensile forces with high ratio of surface area to thickness.

• Friction conditions at the tool-metal interface are very important and controlled by press conditions, lubrication, tool material and surface condition, and strip surface condition.

Classification of sheet metal parts (based on contour)

1) Singly curved parts2) Contoured flanged parts, i.e.,

parts with stretch flanges and shrink flanges.

3) Curved sections.4) Deep-recessed parts, i.e., cups

and boxes with either vertical or sloping walls.

5) Shallow-recessed parts, i.e., dish-shaped, beaded, embossed and corrugated parts.

Classification of sheet metal forming (based on operations)

1. Shearing2. Blanking3. Punching4. Bending5. Stamping6. Deep drawing7. Embossing8. Spinning9. Roll Forming

Forming machines

PressA press is a machine used for performing most of the cold working operations.1. Rigid Machine Frame2. Press Tools3. Ram4. Power Source and Mechanism5. Die Assy6. Press Accessories

Types of Press

1. Source of Power– Manual Press– Mechanical Press– Hydraulic Press– Pneumatic Press

Mechanical presses• energy stored in a flywheel

is transferred to the movable slide on the down stroke of the press.

• quick - acting , short stroke.

Hydraulic presses• slower - acting, longer

stroke.

2.Actions of presses According to number of slides, which can be operated independently of each other.

1) Single - action press- one slide- vertical direction

2) Double - action press- two slides- the second action is used to operated the hold-down, which prevents wrinkling in deep drawing.

3) Triple - action press- two actions above the die, one action below

3. Method of transmitting power to ram

1. Crank shaft and connecting rod system2. Cam3. Eccentric4. Toggle joint5. Knuckle joint6. Rack and Pinion7. Screw8. Gears

4. Position of the Ram1. Vertical2. Inclined

5. UseBlanking press, embossing press, Drawing press etc.

6. Design of Frame

7. Capacity or Size

Die Assembly

1. Die Block2. Die retainer & Die

shoe3. Stripper4. Punch5. Punch retainer &

Punch pad6. Pressure Plate7. Punch Holder8. Guide Pillars9. Stock Guide

Classification of Die

1. Single Operation Die1. Cutting Die2. Forming Die

2. Multi Operation Die1. Compound Die2. Progressive Die3. Transfer Die

Single Operation Die

Cutting Die

Forming Die

Single Operation Die

Multi Operation Die

Compound Die

Multi Operation Die

Progressive Die– Punches and dies are designed

so that successive stages in the forming of the part are carried out in the same die on each stroke of the press.

– The strip is fed from left to right.– The first punch is to make the

hole of the washer.– The washer is then blanked

from the strip.– The punch A is piercing the hole

for the next washer.

Theory of Shearing the Metal

Theory of Shearing the Metal

Theory of Shearing the Metal

Effect of Clearence

Bending Process

Bending Process

• A process by which a straight length is transformed into a curved length.

• Produce channels, drums, tanks.

Bending Operation

V-Die Bending

Punch Press Bends

Roll Forming

Roll Bending

Bending in sliding die machines

Press Brake Forming

• A single action press with a very long narrow bed.

• Used to form long, straight bends in pieces such as channels and corrugated sheets.

Press Brake Forming

• A single action press with a very long narrow bed.

• Used to form long, straight bends in pieces such as channels and corrugated sheets.

Beading

Method of Bending

(a) Three-roll bender:

(b) Wiper-type bender:

(c) Wrap forming:

Wiper-type bender:

Definition of terms used in bending

Spring Back

• Springback - the elastic recovery of the material after unloading of the tools

• To compensate with the unbending action of the springback, the metal should be slightly overbent.

Rubber Forming

Types of Stretch Forming

Shaving

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

- can be used to produce a smoother edge

Trimming