Modelling of hard part machining Eu-Gene Ng a , David K. Aspinwall b,* a School of Manufacturing and Mechanical Engineering, University of Birmingham, Edgbaston B15 2TT, UK b School of Manufacturing and Mechanical Engineering, Interdisciplinary Research Centre (IRC) in Materials for High Performance Applications, University of Birmingham, Edgbaston B15 2TT, UK Abstract The paper initially reviews the use of finite element modelling (FEM) to determine orthogonal machining performance. Over the last decade, the development and use of FEM to evaluate the effect of tool coatings, cutting environment and chip formation on cutting forces and temperatures, etc., has increased dramatically. The different chip separation criteria and FEM software used by various researchers are detailed. An FE model is presented using ABAQUS/Explicit TM to simulate continuous and segmental chip formation when machining AISI H13 tool/die steel heat treated to 49 HRC with polycrystalline cubic boron nitride (PCBN) tools. The work utilised the shear failure criteria and element deletion/adaptive remeshing modules found in ABAQUS/Explicit. The assignment of tool/chip interface friction was dependent on the magnitude of the direct stress acting on the rake face of the tool. Experimental data involving chip morphology and cutting forces were used to validate the model. The temperature generated in the shear zone was higher with the segmented chip (up to 700 8C) than with the continuous chip (up to 250 8C), for the same machining parameters. # 2002 Published by Elsevier Science B.V. Keywords: Modelling; Hard part machining; Finite element modelling 1. Introduction In the early 1970s Okushima and Kakino [1] and Tay et al. [2] pioneered the use of finite element modelling (FEM) to simulate the orthogonal machining process. The main advantage of using FEM compared to other empirical mod- els is its ability to represent workpiece material properties as a function of temperature, stress and strain rate. Similarly, the tool/chip interface can be idealised with sticking and sliding friction conditions. Tay et al. used the Eulerian formulation technique which is still being used by a number of current researchers [3–5]. Here, the finite element grid is spatially fixed and the material flows through it. Such an approach is usually used to study the steady state cutting process, without the need to simulate the lengthy transition from incipient to steady state cutting conditions, or the use of chip separation criteria [6]. The major benefit of using Eulerian formulation is fewer elements are required to specify the chip and workpiece, thereby reducing the com- putation time. The disadvantage of using such an approach is that experimental work must be carried out in order to ascertain the chip geometry and shear angle. Furthermore only continuous chip formation can be modelled. With the development of faster processors with larger memory in the late 1980s, model limitations and computa- tional difficulties have to some extent been overcome, consequently the use of an updated Lagrangian formulation has increased. The principal advantages of this approach are that the tool can be simulated from some initial state to steady state cutting and the chip geometry together with workpiece residual stress can be predicted. Here, the ele- ments are attached to the workpiece material and chip separation criteria identified in order to allow the chip to break free from the workpiece. Various researchers have proposed different chip separation criteria for FEM simula- tion in machining, which are either classified as physical or geometric. The former includes strain energy density [7], effective plastic strain [8] and stress, while geometric cri- teria relate to the distance between the overlapping nodes and the tool tip. Hunag and Black [9] investigated the effect of using both types of criteria in their model. Neither type had a substantial effect on chip geometry, distribution of shear stress, effective stress or effective plastic strain in the chip and in the machined surface. However, the magnitude designated for these criteria did have a major effect on mesh distortion, together with the value of maximum shear stress, and the effective stress in the machined surface. Journal of Materials Processing Technology 127 (2002) 222–229 * Corresponding author. Tel.: þ44-121-414-4196; fax: þ44-121-414-3958. E-mail address: d.aspinwall@bham.ac.uk (D.K. Aspinwall). 0924-0136/02/$ – see front matter # 2002 Published by Elsevier Science B.V. PII:S0924-0136(02)00146-2