Assessment of hand-type hammer drill bits under percussive loading

Demir, Osman Koray
The task of a drill bit in percussive drilling is to transport the initial kinetic energy of the hammer to the workpiece in terms of stress waves. The efficiency of this transportation and the stresses that the drill bit is exposed to during the process is dependent on the nature of the stress waves. In hand-type hammer drilling, changing dimensions of the bit means changing conditions for the propagation and interaction of the stress waves. In this study, using finite element method, wave propagation and interaction in hand-type hammer drill bits is investigated with respect to drill bit dimensions. The main aim is to assess the effect of length and thickness on the efficiency and stress history of a hand-type drill bit. The results are evaluated in regard to workpiece hardness, which is a factor changing the effect of dimensions. In addition, chiseling test, which is used to prove bits under percussive loading, is carried out to detect differences between thin and thick drill bits, and the results are explained with the help of finite element simulations. Conclusions are drawn revealing the efficiency and stress history of drill bits under percussive loading with respect to thickness, length and workpiece hardness. Finally, it is seen that the real-life results of chiseling test are in agreement with the simulation results.