ORIGINAL ARTICLE Novel approach towards finite element analysis of residual stresses in electrical discharge machining process Mohammadreza Shabgard 1 & Soleyman Seydi 1 & Mirsadegh Seyedzavvar 1 Received: 4 February 2013 /Accepted: 29 June 2015 /Published online: 11 July 2015 # Springer-Verlag London 2015 Abstract The high temperature gradients generated in elec- trical discharge machining process by electric discharges re- sult 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 exper- iments 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 ulti- mate 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. Keywords Electrical discharge machining (EDM) . Finite element modeling (FEM) . Nano-indentation . Residual stresses . Solid-state phase transformation 1 Introduction Electric discharge machining (EDM) is a thermal process where thermal energy is generated in a discharge channel, called plasma channel. Extremely high temperature resulted from the transient heat flux, induces thermal and consequently residual stresses within the surface layers of the workpiece. These residual stresses can lead to defects in the machined workpiece such as micro-cracks, decrease in strength and fa- tigue life, and possibly catastrophic failure. Thus, it is of par- amount importance to develop methods of predicting the set- tings of machining in which the level of residual stresses ex- ceeds over the permissible values [1, 2]. Phase transformation from solid to liquid as well as liquid to vapor occurs during the heating cycle of every discharge. Part of the transformed material is removed but the rest re- solidifies on the surface of the workpiece. This re-solidified layer is usually called the white layer, as it is not easily etch- able. Below the re-solidified white layer lies a second layer that does not melt but is still affected by heat. For steels, during the cool-down cycle, solid-state transformations occur in this heat-affected zone because the highest temperature reaches beyond the austenite transformation temperature [3]. Mamalis et al. [4] with some micro-hardness and micrograph measurements have shown that most of the heat-affected zone transforms to martensite. A lot of efforts have been made to introduce numerical models for EDM process in order to predict temperature dis- tribution during each electric discharge and thereafter estimate the profile and size of crater formed by every single discharge, the material removal rate (MRR), and the tool wear rate (TWR). In the late 80s, DiBitonto et al. [5, 6] developed a model based on point heat source for cathode erosion of EDM process and disk-shaped heat source with Gaussian dis- tribution of heat flux for anode erosion, and compared them * Mohammadreza Shabgard mrshabgard@tabrizu.ac.ir 1 Department of Manufacture, Faculty of Mechanical Engineering, University of Tabriz, Tabriz, Iran Int J Adv Manuf Technol (2016) 82:1805–1814 DOI 10.1007/s00170-015-7510-7