Machining using a diamond-coated cutting tool: finite element simulations and experiments
Chemical vapor deposition (CVD) diamond-coated tools have the advantage of a low cost and flexibility in fabrications when compared with sintered polycrystalline diamond (PCD) tools in machining lightweight high-strength materials. However, coating-substrate interface delaminations remain a major technical barrier. Further, the complex effects of the tool geometry and the deposition residual stress, as well the machining conditions on the tool performance, have hindered the industrial applications of CVD diamond-coated tools. The objectives of this research are: (1) to develop finite element (FE) models of cutting simulations including deposition residual stresses for investigating tool edge radius effects on diamond-coated tool stress evolutions from depositions to machining; (2) to study diamond-coated tool performance in machining Al-Si alloys and Al-matrix composites with various cutting conditions; (3) to implement a cohesive zone interface in a diamond-coated tool for two-dimensional (2D) cutting simulations. The research methods include: (1) coupled thermo-mechanical finite element modeling of cutting simulations, including the deposition residual stress, for tool performance evaluations and tool stress evolutions; (2) machining of A390 alloy and A359/SiC-20p composite workpieces with a force sensor and tool wear evaluations at different conditions; and (3) incorporating a traction-separation law as the interface behavior in the FE cutting simulations for coating delamination analysis. The major findings are summarized as follows: (1) In gentle cutting, deposition residual stresses remain dominant, but change noticeably at a large uncut chip thickness. (2) 2D FE results of the cutting simulation are compared with the machining experiments. The difference between simulations and experiments is acceptable. (3) Increasing the edge radius will increase cutting forces; however, this increasing rate decreases at a higher feed. The combined effects of the tool geometry and cutting conditions result in complex wear behavior of diamond-coated tools. (4) The cutting simulations incorporating a cohesive-zone interface in a diamond-coated cutting tool demonstrate that the interface fracture energy is the major cause of coating delaminations. Furthermore, a larger uncut chip thickness tends to result in coating delaminations.