Determination of friction models for metallic die–workpiece interfaces

A two-parameter friction model is used which combines the Coulomb friction model and the friction factor yield stress model. The drawback of this two-parameter model is the complex nature of its calibration. In this paper a new technique is proposed to calibrate the model, which utilizes two testpiece geometries, namely the solid cylindrical compression testpiece and the ring compression testpiece. In addition, a mathematical model is required of the true stress–true strain behaviour of the material, so that finite deformation/finite element techniques can be used to accurately predict the compression behaviour of both testpieces. ombination of careful experimentation, carried out on aluminium alloy and copper testpieces, and of finite element analyses of the testpieces made using the two-parameter friction model, it has been shown that it is possible to derive the true stress–true strain curve for the workpiece materials; and, to calibrate the friction model. The geometrical changes of all testpieces, carefully measured throughout the tests, for a range of four different friction conditions, dry friction, lubricant, lead metal and nylon, have been predicted with good accuracy using the true stress–true strain constitutive models, the two-parameter friction model, and the finite-element analysis procedures. In this way, the proposed approach has been validated.