Study on micro-tribological contacts in cold forming: simulations and experimental results

The research presented in this paper is focused on the study of contact phenomena in cold forming operations, and is the development of a joint project between the University of Brescia and the WZL of the University of Aachen. The aim of the project is to study the contact phenomena, looking for an analytical description of the friction coefficient  as a function of the process parameters, piece and die roughness and material characteristics. The experimental tests were conducted with two elements, representing the die and the workpiece, forced into contact by means of a hydraulic device and sliding one over the other. From the simulative point of view a model of the problem was developed, considering the micro-geometry of the parts and the experimental results were used for its validation. The objective is to have a model suitable for representing the actual contact phenomenon so as to predict the behaviour of the parts in cold forming operations without conducting expensive experimental tests.Several parameters were varied during the tests evaluating their effects on the friction force. The factors investigated were: die material and roughness, piece material and roughness, contact pressure and sliding velocity.Since some peculiar behaviour and trends were identified in the experiments and simulations, further investigation into the parameter descriptions and the simulative model has been conducted, trying to furnish a more comprehensive model of the contact phenomena.