The effect of process and material parameters on the coefficient of friction in the flat-die test

The effects of process and material parameters on the coefficient of friction in the flat-die test were examined. Low carbon steel, a hot-dip galvanized steel and ExtraGal™, another hot-dip galvanized steel were used in the tests. As the die surface roughness increased, the coefficient of friction increased most of the time. Under some conditions an optimum roughness was evident. The bare steel produced the highest coefficient of friction in the majority of the tests. The hot-dip galvanized steel and the ExtraGal™ alternated as the material that produced the lowest coefficient. The speed and load effects, found in other applications, have been confirmed, in general: the coefficient decreased for increases in load and speed in most cases. The contact rarely appeared to be starved of lubricants. In most instances the die made of the hardened tool steel created lower coefficients of friction than the cast iron dies. The results can be best understood in terms of micro-plasto-hydrodynamic lubrication, aided by the flow of the lubricants in micro-channels.