Analytical and Experimental Studies of Drill Temperatures

This paper describes a model for calculating transient and steady-state drill temperatures for drills with arbitrary point geometries. The model is based on temperature solutions for a semi-infinite body and uses a transient analysis to partition heat between the drill, chip, and workpiece. A parametric model is used to characterize complex point geometries; heat source characteristics are modeled using empirical force equations from end turning tests. Temperature calculations are presented for several representative drill geometries and compared with temperatures measured by thermocouple methods. Two thermocouple methods were used: the standard welded thermocouple method, and a method in which an insulated wire was embedded in the workpiece, so that it would form a hot junction with the drill each time the drill cut through it. The agreement between calculated and measured temperatures is reasonable. Calculations indicate the helix and point angles have the greatest influence on drill temperatures. Increasing the helix angle increases the effective rake and thus reduces temperatures; the effect is relatively weak, however, for helix angles over 10 degrees. Increasing the point angle shortens the cutting edge and increases drill temperatures.