Wear Mechanism Of Diamond Tool Against Mold Steel In Diamond Turning Process By Molecular Dynamics

Mold steel has broad application prospects because of the excellent performance in the mold industry which is difficult to replace by other materials. For the machining of the steel mold, the main processing methods are traditional grinding, lapping and polishing processes. It is easy to produce large clamping error because of the multiple clamping required in the process. The entire machining process is time-consuming that should affect the processing efficiency. Therefore, the actual production process of mold steel is in urgent need of using ultra-precision machining technology to meet the requirements of accuracy and efficiency. Natural single crystal diamond is an ideal tool material for ultra-precision machining because of its excellent mechanical and physical properties. However, there is a serious tool wear when machining mold steel, so we cannot guarantee the processing quality and the precision of manufactured components. However the paucity of research on the mechanism of tool wear severely hinders the application of mold steel.Molecular dynamics could analyze the interaction between the tool and the workpiece atoms at the nanoscale processing areas, this paper make use of molecular dynamics to research the wear mechanism of diamond tool against mold steel in single point diamond turning process, the main contents and conclusions are as follows:(1) A modified embedded-atom method (MEAM) has taken into account to establish a simulation model of diamond tool cutting mold steel. According to the analysis results, iron atoms have unpaired d electrons, these iron atoms may connect with diamond carbon atoms through chemical bonds which are the driving force to the diamond removal and making diamond convert into graphite. Moreover, the atomic arrangement on (111) surface of both iron and diamond agreed with the vertical aligned principle so that the iron atoms could have a concentrated effect on the diamond. In the process of graphitization, atoms from cutting edge convert to graphite rather than all of the carbon atoms separated from the surface of diamond(2) An experiment of diamond tool wear is designed to validate the simulation conclusions. The experiment results showed that, it has undergone severe wear at low cutting speed and contact pressure, the tool is worn and diffused into the surface of workpiece in the cutting process, the carbon is detected by the way of iron compound.(3) Diamond and iron-based diamond melting model were established. The atomic arrangement of the case show that diamond atomic state during heating process, and the use of temperature-volume curve under different conditions to calculate the melting point of diamond, the result proved that the existence of iron can accelerate the diamond-graphite process and reduce the graphitization temperature.(4) In order to verify the applicability of the principle of vertical alignment in tool wear process, this paper calculate the graphite rate of diamond tool by coordination number changes. Tool wear deformation grow out of partial and extended outward, graphite phenomenon occurs over the expansion process, the maximum wear rate is (111) crystal plane; The higher cutting speed of processing conditions enable more energy of workpiece atoms focused on the chip part, which is contribute to get higher surface quality after processing; During the cutting process the workpiece atoms attached to the tool rake face formed "atomic film" is similar to Built-up edge, resulting in the variation of cutting thickness has little influence on tool wear.