Study On Bottom Profiles Of Micro-holes Machined By Micro USM

Minimization of industrial products is the important trend in the21th century. Micro actuators, micro component parts and micro optical devices fabricated by micro electromechanical system (MEMS) technology have been widely used in biomedicine, aviation, aerospace, new energy and so on. The key to produce minimized products is micro machining technique, such as micro electrical discharge machining (EDM), laser machining and micro ultrasonic machining (USM). Hard and brittle materials such as single crystal silicon and ceramics have excellent performances, namely, high hardness and strength, high temperature resistance, good corrosion and wear resistance. Therefore these materials have a great potential for wide use. Due to high hardness, these materials cannot be machined by traditional mechanical machining methods such as drilling and milling, resulting in bad quality and low efficiency. Micro USM is suitable to machine these hard and brittle materials.It was found that bottom profiles of micro holes machined by micro USM can be convex or concave under different machining parameters. This paper is aimed to explain this phenomenon.In micro USM, material is removed using a tool to impact abrasive particles into the workpiece, chipping material away from the workpiece. Workpiece material removal only occurs where abrasive particles exist. Therefore, different distributions of abrasive particles result in different bottom profiles of machined surfaces. Based on two-phase (solid and liquid) flow, forces acted on abrasive particles during machining is analyzed. After the calculation of radial velocity of abrasive slurry in the machining zone based on the assumption of incompressibility of slurry, the movement differential equation of abrasive particles is obtained. Simulation results show that abrasive particles move to the center during vibration. The abrasive particles move faster toward the center in the case of larger ultrasonic amplitude or bigger abrasive particles, resulting in concave bottom shape of micro hole. When small particles are used or the vibration amplitude is small, the bottom profile of machined surface shows convex. Experimental results match the theoretical analysis well.All experiments in this study were conducted using the self developed numerical control program.