Deep drawing and redrawing

Dr. Dinesh Kumar

PIE, NITJSR

Deep drawing• Deep drawing or cup drawing is

a process of forming hollow shaped components from flat pieces of sheet metal of from already drawn components.

• Examples: kitchen wares, boxes of various shapes, car bodies, domestic gas cylinder, etc.

Retaining metal in draw dies

With rigid blank holder

With spring pressure pad

Metal Flow during deep drawing

Factors affecting the metal flow during deep drawing• Radius on punch

• Draw radius on die

• Friction

• Material to be drawn

• Percentage reduction

• Drawing speed

• Die clearence

Factors affecting…… :Radius on punch• Punch corner radius=(4-10)thickness of sheet

• For single draw: Punch corner radius=as per the product design

• For multiple draws: Punch corner radius reduces after each draw

Factors affecting…… :Draw radius on die

• Draw radius on die=4*sheet thickness

• Too large radius will tend to release the sheet by the blank holder very soon thus the wrinkling may take place

• Too small radius will tend to thinning and tearing the sheet at the corners

• Friction plays an important role

• Too less friction: wrinkling

• Large friction: thinning and tearing of the sheet

Factors affecting…… :Friction

Factors affecting…… :Material to be drawn

• Large ductile material should be avoided

Factors affecting…… :Percentage reduction

h/d ratio Number of draws

Up to 0.7 1

0.7-1.5 2

1.5-3 3

3-7 4

• Low carbon steel:9-15m/min

• Non ferrous sheet: 45-60m/min

• Harder and less ductile material: low speed

Factors affecting…… :Drawing Speed

Factors affecting…… :Die Clearence

Blank Size (D) Calculation

Drawing Force

Blank Holding Force