Development of new drilling force models for improving drill point geometries

A comprehensive method for predicting the torque and thrust force in drilling mild steel with arbitrarily designed drill points is established. The main objective of this study is to show the influence of drill point geometry and the interference of chip ejection on drilling forces in order to improve drill point design.; In this research, new drilling force models are developed. Both drilling torque and thrust force are functions of the following variables: the dynamic rake angle ({dollar}gamma{dollar}oe), effective inclination angle ({dollar}lambda{dollar}se), dynamic cutting velocity (Ve), length of cutting edge (a{dollar}sb{lcub}rm w{rcub}{dollar}), uncut chip thickness (a{dollar}sb{lcub}rm c{rcub}{dollar}), chip flow angle ({dollar}eta{dollar}), and cutting ratio (r). On the basis of the empirical cutting force models from the end turning tests together with the effects of the interference of chip flows related to different elementary edges, the prediction of the torque and thrust force for an arbitrarily designed drill can be carried out by integrating differential cutting forces induced by all elementary cutting edges.; Comparing the predicted values with and without interference, the simulation results show that the interference of chip ejection can contribute about 30% to 50% of the free cutting forces. The experimental results agree well with the calculations using different drilling conditions and a broad variety of drill point geometries. The measured and predicted values show a good agreement with the average errors within {dollar}pm{dollar}15% for the torque model and from {dollar}-{dollar}19% to 12% for the thrust model.; In order to facilitate the improvement of drill point geometry, new drilling force models incorporating a Computer-Aided-Drill-Analysis (CADA) method were developed for the evaluation of drill performance in this thesis. In addition, the appropriate grinding methods including a drill grinding kinematic model and drill grinding conditions for grinding MFDs with a CNC drill grinder were developed and experimental verification was achieved.; Experimental results show that the modified MFD when compared with the typical MFD can improve drill performance significantly. Specifically, the improvements include: (1) reducing the penetration time by 34.4%, (2) reducing thrust force by 22.2% and torque by 29.3%, and (3) increasing tool life by 140%.