Sheet Metal Forming Processes

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 • powered blades • Pull-through • 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. Beading edge of sheet metal is bent into die cavity Flanging bending of edges Hemming edge folded over itself Bending Operations using press brake

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