Sheet Metal Forming Processes

Chapt 16

Shearing• Process that involves cutting sheet

metal by subjecting it to shear stresses, usually between a punch and a die.

Blank: removed from a large sheet or coil - part made from blank

Shearing terms

• Punching (piercing): sheared slug is discarded.

• Blanking: slug is the part, the rest is

discarded.

Shearing Operations

1. Die Cutting – consists of:

• Perforating- punching holes.• Parting- shearing sheet into two or more

pieces.• Notching-removing pieces or shapes

from edge.• Lancing- leaving a tab without removing

the material.

2. Fine Blanking

• v shaped notch locks sheet, less distortion.• Burrs (clearance, ductility, dull tool edges).

3. Slitting

• Driven• powered blades

• Pull-through• Strip pulled through idling blades

4. Steel Rules

• thin strip of metal is bent and held on its edge on a flat base.

• die is pressed against the sheet to cut parts (cookie cutter).

5. Nibbling

• successive punched holes

Bending

• One of the most common forming operations, used for producing parts and to impart stiffness.

• After bending, outer fibers of the material are under tension while the inner fibers are in compression.

Bending• Process Variables

• minimum bend radius• Smallest radius allowed before cracks on outer

surface

Bending Radius

• The bending radius is measured to the inner surface of the bend and it is normally expressed in terms of material thickness. (2T, 3T, etc.)

Springback: elastic recovery

• Compensation

• Over bending

• Bottoming

• Stretch bending

• Elevated temps

Bending Operations using press brake

• Beading• edge of sheet metal is bent into die cavity

• Flanging• bending of edges

• Hemming– edge folded over itself

Roll Forming

– Metal bent by series of rolls

Tube Bending and Forming

• pack inside of tube with sand to prevent buckling and folding.

• flexible mandrels

Bulging

• Flexible plug inserted inside part and compressed

Stretch forming

• Sheet clamped and stretched over die or form block• Aircraft wing skins and auto door panels

Rubber Forming

• Also called hydroforming• one die is replaced with a rubber or

polyurethane pad.• Pressure supplied by fluid

Spinning

• axisymmetric parts over a mandrel with tools or rollers.

Other Methods

Peen Forming - shot peening – leaves dimples

Explosive Forming

Magnetic-Pulse Forming – • energy stored in a capacitor is discharged

rapidly through a magnetic coil which surrounds a tubular work piece which is placed over solid plug

• Opposing magnetic fields forms thin work piece over solid plug

• Used to collapse thin wall tubes over rods, cables, plugs, compression crimp auto oil filter canisters