3D-FE-Modelling of the Drilling Process – Prediction of Phase Transformations at the Surface Layer

Due to friction, plastic deformation and cutting, the drilling process leads to high mechanical and thermal loadings of drilling tool and workpiece. Distortion and modifications of the surface layer microstructure, especially rehardened zones, can be observed, whereby the experimental investigation of correlations between machining processes and resulting surface layers are very complicated and time consuming. This paper presents a numerical approach to predict machining induced phase transformations at the surface layer of drilled holes. Based on experimental results and 2D FE machining simulations, an abstract model representing the mechanical and thermal collective load of the drilling process has been developed in relation to the parameters cutting speed and feed rate. To predict phase transformations of the steel 42CrMo4 (AISI 4140) at the surface layer of drilled holes a 3D FE- model has been established using the commercial software ABAQUS. The kinetics of the phase transformations are implemented using specific user subroutines. The model calculates the process of austenization and the transformed volume fraction of the phases ferrite/perlite, bainite and martensite and also considers transformation plasticity and the resulting hardness of the microstructure. By simulating different combinations of cutting parameters, relations between drilling process and resulting surface layers of drilled holes have been studied. In addition the machining induced distortion of the workpiece can be calculated simultaneously. The simulation model has been verified by drilling experiments, thermal imaging and metallographic investigations. Predicting machining induced surface layer states, the functionality of future components can be improved.