Fundamental Study On The Ultra-precision Machining Of Brittle Material And Construction Of Micro-cutting System

Brittle materials,such as ceramics,semiconductors and optical glasses,are widely used in various high-tech fields owing to their outstanding physical and chemical properties.They are made to components with high accuracy and surface quality.Because of the hard and brittle nature of these materials,it is easy to cause surface damage and tool wear due to material fracture in the mechanical processing.In order to obtain stable machining process and controllable surface quality,the cutting mechanism of brittle materials has become a research hotspot in ultra-precision machining.Molecular dynamics is one of the widely used simulation tools to study mechanism of nanometric cutting.However,the model scale is far smaller than that in practice.As a result,some important phenomena(ductile-brittle transition,material removal,tool wear,etc.)in processing have not been fully understood,which makes the theoretical guidance deficient.In addition,various assistant methods,such as surface modification,ultrasonic vibration cutting,etc.are proposed to improve the machinability.Nanometric machining of ion implanted materials(NiIM)is such a technology that reduces the surface brittleness by irradiating the workpiece using high energy ion beam.However,this method is faced with the problems of large dosage,long time and high cost,which makes it hard to use in production.For solving the issues mentioned above,the main topics in this work is as follows:1.Current molecular dynamics simulation model is modified,to significantly increase the cutting depth in the numerical simulation of nano-cutting on brittle material.Using the developed method,the micro-crack and sub-surface damage evolution in the cutting of monocrystalline silicon are observed and analyzed.The ductile-brittle transition depth got in simulation conform to the experimental result.2.A novel model of buried modified layer is proposed,which can improve the machinability and reduce the implantation dose and cost.The mechanism of crack propagation hindered by amorphous layer is revealed by molecular dynamics simulation,and experimental validation including lattice characterization and diamond turning is provided.3.A micro-cutting system is designed and built based on the analysis of the hardware selection and the processing scheme.Convenient evaluation of machinability and the machining of simple micro-structure array are achieved by this platform.