1. Sheet Metal Forming Processes
Chapt 16

2. Shearing
Process that involves cutting sheet metal by subjecting it to shear stresses, usually between a punch and a die.

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

4. Shearing terms Punching (piercing): sheared slug is discarded.
Blanking: slug is the part, the rest is discarded.

5. Shearing Operations

6. 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.

7. 2. Fine Blanking v shaped notch locks sheet, less distortion.
Burrs (clearance, ductility, dull tool edges).

8. 3. Slitting Driven Pull-through powered blades
Strip pulled through idling blades

9. 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).

10. 5. Nibbling
successive punched holes

11. 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.

12. Bending Process Variables minimum bend radius
Smallest radius allowed before cracks on outer surface

13. 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.)

14. Springback: elastic recovery
Compensation
Over bending
Bottoming
Stretch bending
Elevated temps

15. Bending Operations using press brake
Beading
edge of sheet metal is bent into die cavity
Flanging
bending of edges
Hemming
edge folded over itself

16. Roll Forming
Metal bent by series of rolls

17. Tube Bending and Forming
pack inside of tube with sand to prevent buckling and folding.
flexible mandrels

18. Bulging
Flexible plug inserted inside part and compressed

19. Stretch forming Sheet clamped and stretched over die or form block
Aircraft wing skins and auto door panels

20. Rubber Forming Also called hydroforming
one die is replaced with a rubber or polyurethane pad.
Pressure supplied by fluid

21. Spinning
axisymmetric parts over a mandrel with tools or rollers.

22. Other Methods

23. Peen Forming - shot peening – leaves dimples

24. Explosive Forming

25. 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