Characterization of galling during dry and lubricated punching of AA5754 sheet

Abstract

When sheets of aluminum alloys are pierced or trimmed, tool failure occurs by the transfer of material from the sheet to the surface of the tool. This phenomenon referred to as galling adversely affects sheared edge quality and increases energy consumption. An instrumented pneumatic press was designed and built to conduct shear–punch tests on 2 mm-thick AA5754-O sheets and to investigate the progression of galling to AISI M2 steel punching tools during dry and lubricated punching. The punching tests were performed using a clearance of 2.0% of the lower die diameter. Cumulative galling volumes were measured using a non-contact optical surface profilometer, and the rate of material transfer (the galling rate) was estimated for both dry and lubricated punching. The galling initially occurred at a high rate, and for dry punching, it was reduced to $74.6\times {10}^4\mu m^3/stroke$ between 20th and 125th strokes. Lubricating the aluminum sheet with an oil-based lubricant mitigated the material transfer, and the galling rate after the 20th stroke was reduced to $3.1\times {10}^4\mu m^3/stroke$. Punching force-displacement curves indicated a higher amount of energy expended to shear AA5754-O sheets in the dry punching compared to the lubricated punching that is suggested to be due to the higher galling resulting in higher friction forces at the interface.