PRESS TOOLS-Shearing Theory


SHEARING THEORY

Shearing Theory Shearing is the method of cutting sheets or strips without forming chip.The material is stressed i a section which lies parallel to the forces applied.The forces are applied by means of shearing blades or punch and die.
Critical stages of shearing Stage1:Plastic deformation The force applied by the punch on the stock - material tends to deform it into the die opening .When the elastic limit is exceeded by further application of force.
- the material is forced into the die oopening in the form of an embossed pad on the lower face of the material .
-A corresponding depresion is formed onn the upper face.
This stage impacts a radius on the upper edge of the pening in the strip and on the lower edge f the punched cut material (which may e blank or slug)
Stage 2:
Penetration As the load is further increased ,the punch will penetrate the aterial to a certain depth.An equally thick portion of the metal is forced into the dies.This impacts a bright polished finish (cut band) on both the strip and the blank or the slug.on optimum cutting conditions,the cut band will be 1/3rd the sheet thicness.
Stage 3:
Fracture I n this stage,fracture starts from both upper and lower cutting edgesAs the punch travels further,these fractures will extend towards each other and meet to cause complete separation.This stage impacts a dull fractured edge.


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