Die cutting or shearing is a process used to cut stock without the use of burning or melting and without the formation of chips. This is a process that involves straight cutting blades of sheet metal (plates). Rods too can be cut using shearing. Trimming, roll sitting, piercing, and blanking are a few of the shearing-type operations.
In the process, a moving blade (punch) is used to push a work piece against the fixed blade (die).Clearance is a term used to define the separation between the two blades, and is measured at the point where the cutting takes place and perpendicular to the blade movement. The clearance between the two blades is kept from 5 to 40% of the thickness of the work piece. The material used in shearing experiences localized shear stresses between the die and the punch and forms two distinct sections on the sheared work piece; namely the plastic deformation and the fracture. Normal inhomogeneity in materials and inconsistencies in clearance can keep the shearing from being a uniform process.
The rough edge is caused by the fact that the fracture begins from the weakest point in the material and then moves on to the next weakest point until the entire work piece has been sheared. Clamping the top of the work piece with a die cushion can help reduce the roughness of the edge. Too much clearance can lead to heavy burring or roll-over and though the fracture zone can be completely eliminated above a certain pressure, the sheared edge might experience cracking and hardening.