Simulation Model of Electrical Steel Piercing Simulation Model of Electrical Steel Piercing Sampsa V.A. Laakso 1 * , Arijussi Väänänen 2 , Sven Bossuyt 1 and Antero Arkkio 3 1 Department of Mechanical Engineering Aalto University Espoo, 02150, Finland 2 Department of Materials Science and Engineering Aalto University Espoo, 02150, Finland 3 Department of Electrical Engineering and Automation Aalto University Espoo, 02150, Finland ABSTRACT Electrical steel is used in electrical machinery for the active parts that form the magnetic circuits because the material has low iron loss and thus superior magnetizing properties. A typical electrical sheet has a thickness of 0.5 mm and is punched to a final shape with a piercing process. Piercing causes large deformations and residual stresses on the narrow zone of the cut surface. The deformations and stresses weaken the magnetic properties of electrical sheet and result in additional losses because the iron loss is increased after piercing [1]. This paper presents a simulation model of the piercing process to evaluate the deformations and stresses on the cut surface. The model is done with commercial FEM solver Deform. There has been an attempt to simulate the magneto- mechanical state of the punched surfaces but the piercing process itself was not simulated [2.] The electrical steel sheet investigated in this paper is isotropic electrical silicon steel M400-50A (EN 10106-96). 1. INTRODUCTION Non-oriented electrical steels like M400-50A are used commonly in rotating machines. M400-50A designation reads as M for magnetizing steel with maximum iron losses of 4 W/kg (400), 50 for 0.5 mm thickness and A for non- oriented grains. The iron losses in electrical steels can be divided in two main categories: hysteresis losses and dynamic losses. Dynamic losses can be further divided in classical losses and excess losses, which are significantly smaller than dynamic losses.[3] Piercing is typical manufacturing process for electrical steel sheet parts with good production output, relatively low production costs and consistent quality. However, the mechanical cutting of the sheet has been shown to increase the iron losses in electrical steel and therefore it is important to minimize the deformations caused by the tool, especially since International Electrotechnical Commission (IEC) standards have more strict limits regarding energy efficiency of electromechanical machines in the near future with IE5 class efficiency that is estimated to surpass the previous IE4 class (IEC 60034-30-1:2014) requirements by 20 % [4,5]. To address this issue, simulation model of the piercing process is developed to investigate the effect of different tool and process parameters on the mechanical state of the cut surface. FEM simulations of blanking have been done to predict edge quality, tool wear and forces, the effect of the process parameters, but the quantitative accuracy of the simulations is strongly dependent on the geometry modelling and tool properties like misalignment of the tool or tool deflections [6]. Ossart et al. in 2000 have developed a magneto-mechanistic model to describe the effect of plastic strain to the magnetic field and induction that have been shown to correlate well with measured data [2]. 2. MATERIALS AND METHODS In order to simulate the piercing process, a material model for M400-50A is required. Hollomon model [7] for strain hardening and Cockroft-Latham damage model [8] are selected to be used because the models are commonly used and not overly complex. Thermal softening and rate sensitivity are left out of scope in this study because their effect is assumed negligible in piercing process. Hollomon model:  =   Where  = stress,  = strain, K = yield stress equivalent, m = strain hardening exponent Cockroft-Latham model: =∫ ∗   Where * = maximum principal stress and C = critical value * Sampsa V.A. Laakso, DSc(Tech.): Tel.: +35840 70550 39; E-mail: sampsa.laakso@aalto.fi