Prediction of micro drill break through thrust monitoring

With 50 HSS twist drills of 0.4 mm in diameter used as samples on a CNC high speed precise drilling machine, limit thrust values of micro drill breaks were examined while No.45 carbon steel was drilled. It is concluded from parameter evaluation and statistics that the limit thrust values obey the logarithm normal distribution law. The way of monitoring the threshold of thrust was also developed using the reliability theory. Experimental on-line monitoring was run at different reliable levels. When the reliable level selected was 0.999 and the drill utilization ratio was the same as that of in ordinary drills, the drill break ratio of 10 drills decreased from 30% to 0.