Spiral point drill temperature and stress in high-throughput drilling of titanium

The spatial and temporal distributions of the temperature and stress of a 9.92 mm diameter spiral point drill are studied in high-throughput drilling of Ti-6Al-4V with 384mm(3)/S material removal rate (MRR). A finite element thermal model using the inverse heat transfer method is applied to find the heat partition on the tool-chip contact area and convection heat transfer coefficient of cutting fluid. The thermal model is validated by comparing experimentally measured and numerically predicted drill temperature with good agreement. Thermo-mechanical finite element analysis is applied to solve the drill stress distribution. Modeling results confirm that the supply of cutting fluid is important to reduce the temperature across the drill cutting and chisel edges. At 183 m/min peripheral cutting speed, 0.05 mm/rev feed and 10.2 mm depth of drilling, the drill peak temperature is reduced from 1210 degrees C in dry drilling to 651 degrees C with cutting fluid supplied through the drill body. Under the same MRR, 61 m/min peripheral cutting speed and 0.15 mm/rev feed, the analysis shows that the drill peak temperature is reduced to 472 degrees C. The temperature induced thermal stress combined with the mechanical stress caused by cutting forces is analyzed to predict the location of drill failure. Applying the modified Mohr failure criterion, the drill cutting and chisel edges are found to be prone to failure in dry and wet drilling conditions, respectively. This study demonstrates the effectiveness of drill thermal and stress modeling for drilling process parameter selection and drill design improvement. (c) 2007 Elsevier Ltd. All rights reserved.