Bending of Sheet and Plate

1. Bending of Sheet and Plate Bending is done to form flanges, etc. Also for giving stiffness to a sheet part

3. In bending outer fibers are in tension and inner fibers are in compression Strain is usually equal in magnitude But in effect e0 is larger than ei because of neutral axis shift to inner surface With R/T e0-ei=

4. Minimum Bend Radius We can see that as R/T decreases tensile strain at the outer surface increases. Radius �R� at which cracks appear on the outer surface is called �minimum bending radius� Min. bending radius is expressed in terms of T (2T, 3T, etc.)

6. True strain at outer fiber for cracking = true fracture strain in tension test. Spring back Elastic recovery after the removal of load. (Finite modulus of elasticity) Rods, sheets, bars, etc. Radius of bending increases when load is removed. Springback factor Ks.

7. Bend Allowance Since recovery depends on the stress level and modulus of elasticity �E� we can recalculate Ri/Rf.

8. Bendability can be improved Heating the area Applying hydrostatic pressure Reducing outer tensile strain by compressive force As R/T decreases, narrow sheets (smaller length of bend) crack at the edge and move towards center. Wide sheet crack at center. Rough edges can also cause reduction of bendability (stress raisers).

9. Operations Beading Flanging Hemming Roll Forming Tube Bending

12. Bead Forming

17. Spinning Conventional Spinning As large as 6m (20 ft) Shear Spinning Missile nose cones, rocket parts. Tube Spinning

23. Diffusion and Super plastic formation A �hot� research area Honeycomb material Deep Drawing Pure drawing Stretching ironing

24. Superplastic Forming Same fine grained alloys can elongate as much as 2000% E.g. Zn-Al, titanium can be formed into very complex shapes. High ductility, low strength Very strain rate sensitive Extremely slow forming 10-4 to 10-2 s Some times forming can take hours