Novel approach towards finite element analysis of residual stresses in electrical discharge machining process

The high temperature gradients generated in electrical discharge machining process by electric discharges result in residual stresses on the surface layers of electrodes. These residual stresses can lead to deficiencies in machined workpiece such as micro-cracks, reduction in strength and fatigue life, and possibly catastrophic failure. In the present research, a finite element model (FEM) has been developed to estimate the distribution of residual stress in the machined surface of workpiece through considering temperature-dependency of the physical properties of AISI H13 tool steel as workpiece and solid-state phase transformation. The data achieved by FE simulation have been validated using experiments handled by nano-indentation measurement on the side of cubic ED-machined workpiece. The results showed that the profile form of residual stress is independent from discharge energy; though with increase in pulse energy, the maximum of tensile residual stress and the depth where the maximum is observed slightly increase. Furthermore, the maximum calculated value for residual stress exceeds ultimate strength of AISI H13 tool steel, 1990 MPa, and reaches the amount of 2150 MPa for lowest pulse energy. The maximum residual stress measured by nano-indentation is 2040 which represents the slight deviation of 50 MPa or 2.5 % with the predicted values.