Residual stress after EDM-FEM study and measurement results

During electro discharge machining (EDM) a characteristic residual stress profile is formed. The process is essentially thermal and leads to tensile residual stresses at the surface. The profile form is independent from the discharge energy. However, the profile depth, the maximum value of the tensile residual stresses and the depth where the maximum is observed are found to be energy dependent. The residual stress profile is characterised by an increase from a certain tensile value at the surface to a maximum underneath the surface, followed by a decrease until slightly compressive residual stresses are reached. In the present paper, a finite element model (FEM) based on an individual discharge was built to calculate the residual stresses originating from EDM with different discharge energies. The model uses axisymmetric elements and takes the temperature dependencies of thermo-mechanical material properties of the workpiece into account, considering stainless steel AISI 304. For each temperature elastic-perfectly plastic material behaviour was assumed. The calculated residual stress profiles are in good agreement with experimental results.