OPTIMUM DESIGN OF THE MULTIFACET DRILL

A two-stage strategy has been used to design an optimum multifacet dri ll (MFD) for crankshaft drilling. In the first stage, a heuristic MFD was developed by adding an additional facet to the outer corner of the conventional split-point drill. Under accelerated life test condition s, this new drill can decrease thrust force by 21.0% and increase dril l life by 50% compared to a split-point drill. In the second stage, co mprehensive force models for predicting thrust and torque were modifie d and developed. Using the force models, point optimization was carrie d out to design the optimum MFD. This new MFD can further decrease the thrust by 21.3% over the heuristic MFD, and accelerated life tests ha ve shown a 25% further increase in drill life.