チタン合金(Ti-6Al-4V)の鋸歯状切りくず生成のFEMシミュレーション(第2報) : 鋸歯状切りくず生成機構と難削性

概要

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Using the finite element modelling proposed in the previous paper, orthogonal machining of titanium alloy Ti-6Al-4V is simulated. Chip formation and cutting forces calculated are in good agreement with experimental results. Chip temperature just ahead of tool rake face is higher than tool temperature because of low density, low thermal conductivity and high flow stress of titanium alloy. Almost all frictional energy dissipated on the rake face, 28 percentage of total cutting energy in this simulation, therefore, must flows into the tool. Such high energy share to tool is one of reason for the difficulties in machining this alloy. Normal and frictional stresses on the rake face calculated for titanium alloy are as high as those measured for nickel base superalloy Inconel 750,and about two and a half times as high as those measured for mild steel S45C. Variation of strain rate, stress, temperature, and strain-hardening and strain-softening regions during a chip segmentation of the serrated chip formation are obtained. It is concluded that low fracture strain of the alloy and formation of ductile crack, but not the thermally activated strain-softening, are the trigger for onset of the serrated chip formation, while the softening, which takes place between the tip of fully developed crack and cutting edge, gives high deformability to the chip to be semi-discontinuous.
1993-06-05