Optimum selection of variable punch-die clearance to improve tool life in blanking non-symmetric shapes

• This study aims at improving punch life in blanking (piercing) by selecting variable punch-die clearance.
• Based on ‘least punch stress’ criterion, guidelines for (geometry dependent) variable punch-die clearance was developed using Finite Element Analysis.
• Experimental tests show that variable punch-die clearance gives almost three times longer punch life than uniform clearance.

Punch-die clearance is a well-known parameter affecting both tool life and edge quality of parts in blanking and piercing. Selecting the optimum or best punch-die clearance can give a significantly longer tool life by minimizing tool wear. Previous studies have shown the effect of punch-die clearance on various sheet materials and thicknesses during blanking of round parts while non-round geometries are more commonly found in industrial applications. Therefore, in this study, the effect of part geometry is considered to select the ‘best’ punch-die clearance to minimize tool wear. In blanking non-round geometries, the punch and die undergo non-uniform wear, with higher wear observed in areas with sharp radii and abrupt changes in geometry. In the present study, the effect of punch-die clearance on punch stress for blanking various shapes is investigated using Finite Element (FE) analysis. The punch-die clearance that gives the lowest value of the punch stress for the different part geometries is identified. A method is developed to select a geometry dependent variable punch-die clearance to obtain more uniform wear on the punch, thereby increasing the punch and die life.