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 parts 2) 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) Shearing Blanking Punching Bending Stamping Deep drawing Embossing Spinning Roll Forming

Forming machines Press A press is a machine used for performing most of the cold working operations. Rigid Machine Frame Press Tools Ram Power Source and Mechanism Die Assy Press Accessories

Types of Press 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 Crank shaft and connecting rod system Cam Eccentric Toggle joint Knuckle joint Rack and Pinion Screw Gears

4. Position of the Ram Vertical Inclined 5. Use Blanking press, embossing press, Drawing press etc.

6. Design of Frame 7. Capacity or Size

Die Assembly Die Block Die retainer & Die shoe Stripper Punch Punch retainer & Punch pad Pressure Plate Punch Holder Guide Pillars Stock Guide

Classification of Die Single Operation Die Multi Operation Die Cutting Die Forming Die Multi Operation Die Compound Die Progressive Die 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 Three-roll bender: Wiper-type bender: 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 can be used to produce a smoother edge 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