DEFECTS IN SHEET METAL:
1. Earing or planer anisotropy:
Edges of drawn cups may be wavy due to varying properties in different directions, this phenomenon is called earing .
2. Wrinkling in flange:
Due to compressive buckling in circumferential direction
3. Wrinkling in wall:
When a wrinkled flange is drawn into the cup or if the clearance is very large, resulting in a large suspended region.
Because of high tensile stresses that cause thinning and failure of the metal in the cup wall .
4.Tearing can also occur in a drawing process if the die has a sharp corner radius.
5. Surface scratches:
Can be seen on the drawn part if the punch and die are not smooth or if the lubrication of the process is poor.
5. Spring back:
After plastic deformation there is an elastic recovery this recovery is called spring back
Thinning abruptly in narrow area
Extension of sheet surface along all directions
CAUSES OF DEFECTS
Less Blank holder pressure
Die cavity depth and radius
Friction between the blank, blank holder, punch and die cavity
Clearances between the blank, blank holder, punch and die cavity
Blank shape and thickness
Final part geometry
HOW TO AVOID DEFECTS IN DIE DESIGN
Forming limit diagram simulation
Draw ratio selection
Proper blank holding pressure
Provision of draw beads for helping flow of material