FORMING DEFECTS IN SHEET METALS


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

  • Punch speed

HOW TO AVOID DEFECTS IN DIE DESIGN

  • Forming analysis

  • Forming limit diagram simulation

  • Draw ratio selection

  • Proper blank holding pressure

  • Provision of draw beads for helping flow of material

#sheetmetal

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