II. BLANKING PROCESS
Blanking process can be considered to include series of phases in which sheet metal undergoes deformation and separation as seen in fig 2
Contact of punch
The punch first touches the fixed sheet .at impact a compressive stress rapidly builds on the punch and sends a shock wave through it
Elastic and plastic deformation
The punch penetrates into the sheet .first causing an elastic and then plastic deformation
Shearing and crack formation
When the stresses increase shearing occurs followed by fracture .fracture begins from both the punch end and die end of the sheet they usually meet and complete fracture of the material takes place
Breakthrough
If the sheet material has a high strength or is thick. A large force is required for blanking process. During fracture compressive forces are stored in the tool.