Effects of peripheral drilling moment on delamination using special drill bits

The delamination damage caused by the drilling thrust has been recognized as one of the major problems during drilling. Based on the earlier concentrated-load model proposed, the thrust force is the main cause to delaminate at the drill exit in workpiece. However, the central concentrated loading (twist drill) is considered a special case of the general condition also with circular loading (saw drill, candle stick drill and core drill). A comprehensive critical thrust force model considering the effects of the peripheral moment for saw drill, candle stick drill and core drill compared with twist drill is constructed in the present study. In this analysis, the critical thrust force associated with the effect of distributed peripheral moment causing the onset of delamination in use of special drills is predicted and discussed.