TWIST DRILL DEFORMATION AND OPTIMUM DRILL GEOMETRY

Drilling is one of the most important and fundamental machining operat ions. A high level of accuracy is required in drilling operations, esp ecially with the advent of automation. Since a drill bit has a very co mplicated structure and plunges inside the work material during drilli ng, the drill deflection cannot be measured practically. However, it c an be evaluated through the finite element method. An appropriate univ ersal model for twist drills has been developed using 20-node isoparam etric elements. The model is based on the basic parameters of the dril l bit and automatic mesh generation is possible for any size of drill. Using this model the drill bit has been statically analyzed and the d rill deformations, namely radial, angular and axial, were arrived at. The results are discussed in this paper. Further the drill bit has bee n analyzed for its optimum geometry. The optimum values of helix angle , chisel angle, point angle and drill margin have been suggested. The effect of feed rate and work material hardness on the three drill defo rmations has also been analyzed and presented in this paper.