Integrated Design and Analysis of Diamond-coated Drills

Abstract

The objective of this paper is to investigate the drill geometry effects on the deposition residual stresses in diamond coated carbide drills, especially the interface stresses. The approaches include (1) solid modeling of diamond-coated two-flute twist drills using commercial computer-aided design (CAD) software, and (2) finite element analysis (FEA) to simulate residual stresses in a diamond-coated drill, which are generated during the deposition process due to the mismatched thermal expansion coefficients. It is noted that the residual stresses generated by deposition in diamondcoated drills can be significant, on the order of GPa. The modeling methodology is employed to design drills of different geometries. Further, to compare interface stresses around the cutting edge, 2D FEA is applied to simulate residual stresses of the drill cross-sections and the interface stress data at the drill cutting edge is transformed to quantitatively evaluate the drill geometry effects. The major results are summarized as follows. (1) The micro-level geometry such as the edge radius has the most dominant effects on the interface stresses by the deposition. (2) In particular, the radial normal stresses can become largely tensile, over 1.0 GPa, which may affect the coating adhesion integrity. (3) Changing the macro-level geometry such as the helix angle, point angle, and web-thickness will affect the wedge angle, 10 o to 20 o