Study On Micromachining Technology Of Thermal-mechanical Effect On Engineering Ceramics

With the progress of science and technology,micro-electromechanical systems(MEMS)has been developing rapidly,especially in recent years,MEMS device needs to grow with each passing day.As the representative of insulating and very hard brittle material,engineering ceramics have characteristics of non-conducting,high temperature resistance,corrosion resistance,high hardness and so on,they are more and more widely used in MEMS.Especially for the high temperature,strong corrosion,strong vibration and other harsh working environment,engineering ceramic materials can be fully used to satisfy the working requirements.However,as the representative of the engineering ceramics,Al2O3 ceramics have high melting point,high hardness and brittleness,it is very difficult for them to carry out micromachining.At present,the non-traditional micromachining such as ultrasonic machining,abrasive water-jet machining,electrochemical discharge machining and laser beam machining have been used in engineering ceramics.However,in order to get better process efficiency and process quality,electrochemical discharge grinding machining and picosecond laser machining engineering ceramics were deeply studied in this thesis,and compared their process results through analyzing influences of thermal-mechanical effect.The main research contents were as follows:1.The mechanism of electrochemical discharge grinding machining engineering ceramics was studied.The forming process of gas film on tool electrode surface was mainly analyzed.The material was removed mainly through thermal erosion of spark and chemical corrosion,and the temperature distribution model of spark discharge was established.Combining the principle of electrochemical discharge machining with the principle of diamond abrasive grinding engineering ceramics,the following process was studied: engineering ceramics were softened by high temperature of spark discharge and then plastic grinding was carried out by diamond abrasive.2.The experimental device of electrochemical discharge grinding machining was constructed,and experiments of micro-hole drilling were carried out on the Al2O3 ceramics.Single variable control method was adopted.The laws of supply voltage or process frequency and micro-hole morphology,micro-hole depth,micro-hole entrance diameter,process efficiency were studied.The results indicated that process efficiency increased and extreme micro-hole depth increased with increasing of supply voltage or decreasing of process frequency.It also resulted in increasing of micro-hole entrance diameter and worse micro-hole surface morphology.3.The experiments of micro-hole machining were carried out by picosecond laser equipment on the Al2O3 ceramics.The mechanism of picosecond laser machining Al2O3 ceramics was studied.Then,the experimental device was introduced,and the experiments of micro-hole drilling were carried out by changing scanning path of laser,output power of laser,repetition frequency of laser,scanning speed and scanning times.The laws of above process parameters and micro-hole morphology,micro-hole entrance diameter,process depth were studied.Moreover,BP neural network and genetic algorithm were applied to optimizing above process parameters,and the best process parameters were obtained quickly and accurately.4.The micro-hole characteristics of electrochemical discharge grinding machining and picosecond laser machining were compared,which included micro-hole entrance morphology,roughness of micro-hole interior wall,shape precision of micro-hole and process residue around micro-hole.Because of different effects of thermal-mechanical effect,the micro-hole entrance roundness of picosecond laser machining was better,the micro-hole of electrochemical discharge grinding machining had smooth interior,on taper and no impurity.5.Electrochemical discharge grinding machining has advantages of simple device,low process cost and good process flexibility,picosecond laser machining technology has advantages of high process efficiency,simple operation and good process flexibility.They belong to the non-traditional micromachining technology,which can be used to process hard and brittle materials such as engineering ceramics and have broad application prospect.