Development and Validation of a Hybrid Model for the Prediction of Shape Deviations in dry Machining Processes

Abstract

Dry cutting operations offer economic and ecologic advantages over conventional machining. When machining conditions are pushed towards the regime of high performance cutting, the applicability of dry cutting is limited among others by the achievable geometric accuracy. In order to comply with increasing demands in machining precision and the necessity to expand the utilisation of dry cutting, a novel hybrid model has been developed exemplary for a face milling process. It enables a predictive minimisation of size and shape deviations in machining. The model takes into account deviations due to thermal expansion during the cutting operation and due to machining induced residual stresses which are especially important in the manufacturing of thin-walled high precision components. It is therefore based on two initially separated finite element sub-models. Sub-model 1 calculates the mechanic response of the workpiece loaded with a near surface residual stress field (source stresses) resulting from plastic deformations generated during the chip formation process. Sub-model 2 calculates the local thermal expansion of the workpiece during a three-dimensional simulation of a moving heat source.In this paper the focus lies on shape deviations resulting from thermo-elastic effects (sub-model 2). It covers a face milling process of plates made from normalized 42CrMo4. Transient three dimensional temperature fields are calculated in a FEM model of a moving surface heat source. The temperature fields are used to calculate the mechanical response of the workpiece which is coupled with a kinematic simulation of the tool movement to obtain the resulting surface shape. The results are validated against measured shape deviations for varying machining parameters. In the long term, the model will be applied to evaluate and identify optimal machining strategies.