Influence Of Edge Passivation And Cryogenic Treatment On The Reliability Of High Speed Steel Tap

Duo to the fierce competition and the pressure of a rising production cost and a trend towards automatic, energy-saving and unmanned manufucture, there is an increasing demand on stability of machining. But fracture happens during the cutting operation of the taps, which may cause poor dimensional accuracy, as well as deterioration of surface integrity of the workpiece, and even damage of CNC equipment if neglected. It had been widely confirmed in machinery industry that the HSS cutting tools for cryogenic treatment can improve its mechanical properties. Cutting tool edge passivation as a technology developed in recent decades can effectively reduce and eliminate the blade and burrs microscopic defects, cut down early wear of cutting tool machining stage, prolong the service life of cutting tools.In this research, HSS finished tap is taken as the sample. Super depth of field digital microscope and scanning electron microscope are conducted to measure failure types and the reasons. Based on stress-strength interference model, Order statistic model and system reliability model, a mathematical model on dynamic reliability are derived respectively by taking machining time and times of impact loading into account. At the same time, the constant stress accelerated life tests and Monte Carlo simulation method is used to achieve the reliability of taps coped with different technology. Use best linear unbiased estimate to analyze the data form the tests. The influence of cryogenic treatment and edge passivation are also been proved by force of comparison with torsional test of HSS material, torque measurement test when processing thread and constant stress accelerated life tests.The main work in this research is as follows:(1) Mathematical models on dynamic reliability of the high speed steel taps with different failure mode are derived from taking times of impact loading into account based on stress-strength interference, and the failure process of the system is analyzed.(2) Monte Carlo method is used to simulate the reliability of cascade system reliability model under random loading. The sample values of the critical fatigue stress and the stress distribution in the cutting head are acquired by Monte Carlo simulation which simplified calculation process.(3) The correctness of models is verified by the constant stress accelerated life tests. The influence of cryogenic treatment and edge passivation are also been proved by force of contrast...