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 Pull-through powered blades 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