Surface Quality Study On Ultrasonic Vibration Assisted Milling LY12 Aluminum Alloy

With the development of aeronautics, national defense and modern medical biotechnology, miniaturization equipments and micro-magnitude parts with high dimensional precision are needed, high shape precision and surface quality are required, so that traditional manufacturing technology is facing severe challenges. In order to solve these problems, researchers have done a lot of work in manufacturing technology, materials selection and processing parameters, among which ultrasonic vibration assisted milling is an effective method.Ultrasonic vibrator and power were purchased, workpiece and fixture were designed and made, and ultrasonic vibration experimental platform was set up. Ultrasonic vibration assisted milling LY12 aluminum alloy machining mechanism and surface quanlity were studied comprehensively. The kinematics of cutting edge in the ultrasonic vibration assisted machining process was analyzed. The condition of tool-chip periodicity separation was obtained through simulation, ultrasonic vibration amplitude was bigger than half of feed speed and ultrasonic vibration frequency was not integral multiple of the spindle rotating frequency.Based on experiments results and through analysis of variance and respond surface methodolody, the influence of machining parameters and their mutual interactions on surface roughness were analyzed systemically. Research results of bottom surface roughness show that ultrasonic vibration amplitude is the most influenced parameter, feed per tooth is the next, and spindle rotating speed is the last. Research results of slot side surface roughness show that spindle rotating speed is the most influenced parameter, ultrasonic vibration amplitude is the next, and feed per tooth is the last. Besides, the influences of parameters interaction are very important for surface roughness.Empirical models for surface roughness were built through exponential regression and polynomial regression methods, the significance of models and model coefficients were tested. Verification test results showed that surface roughness could be forecasted according to the empirical model and give a guide to parameter optimization.Single factor tests were carried out to analyze the influence of machining parameters on cutting force and temperature. Experimental results show a decrease of cutting force and cutting temperature in ultrasonic vibration assisted milling process, and the bigger the ultrasonic vibration amplitude, the more significant it decreased. As a result of high frequency vibration, the chips are easier to break up, and the cutting shear angle increases, which lead to cutting force decrease. The cutting tool surface contacts periodically with chip, which lead cutting temperature to decrease. It should be pointed out that too big ultrasonic vibration amplitude will lead to tool damage, which result in cutting force and the cutting temperature rise fast, tool life and surface quanlity become worse.Single factor test was carried out to investigate the influence of processing parameters on surface residual stresses. Research results showed the effect of spindle rotating speed and ultrasonic vibration amplitude to residual stress were obvious, but the feed per tooth was not obvious. The formation mechanism of residual stresses was analyzed from thermo-mechanical coupling. When milling speed vc<56.52/min, cutting forces are big while cutting temperature is low so that the residual stress caused by mechanical "burnishing" is dominant; When milling speed vc>56.52m/min, with the decrease of cutting forces and increase of cutting temperature, thermal load is a dominant factor affecting residual stress. Ultrasonic vibration can release surface residual stress, so that residual stress descrease in ultrasonic vibration assisted milling process.