Study On Theoretical Model Of Tool Wear In Ceramic Micro-milling

With the rapid development of micro-electromechanical technology,the application of small parts gradually expanded,simultaneously,the requirements of size and material of parts are getting higher and higher.Ceramic material has excellent physical and mechanical properties.Compared to other materials,it can be widely used where having special requirements.However,the strength and hardness of ceramic material after sintered are high,resulting in difficulties in processing.Pre-sintered ceramic body can be processing using simple mechanical cutting method with high efficiency.However,in the processing of pre-sintered ceramic body,the tool wear is very serious,especially in the three-dimensional micro-milling.This will cause a series of problems such as poor processing quality and low dimensional accuracy.At present,the tool wear problem of ceramic pre-sintered body micro-milling is still lack of relevant theoretical research.In this paper,many of pre-sintered alumina ceramic bodies with strength of about 7 MPa were prepared.On the basis of improving the original laboratory machine to improve the Z-axis accuracy,the theoretical model of tool wear in micro-milling of ceramic body was systematically studied.Application validation of the proposed model was carried out as well.According to the wear pattern of tool end face after machining and the analysis of the processing force,it was concluded that the low cycle fatigue of tool material resulted by repeated pressing and swiping of ceramic particles is the dominate factor casuing the tool wear.According to this,a theoretical model for predicting tool wear rate was established.Experiments under different parameters were carried out to verify the correctness of the model,including variable rotation speeds,variable milling speeds,variable layer thicknesses and variable tool sections.The results indicate that the tool wear rates calculated according to the theoretical model agree with the experimental results.According to the analyze of the relative errors,it was found that the detection error of the tool wear is the main reason leading to the difference between theoretical values and experimental results.According to the theoretical model,the sensitivities of the tool wear rate to the milling force of the semicircular section under different parameters was calculated.It was found that the rotation speed,the milling speed and the layer thickness have a great impact on the sensitivity.The sensitivities increase with the increase of the rotation speed,and decrease with the increase of the milling speed and the layer thickness.Model application experiments under different processing parameters were carried out.The results show that the cavity depth obtained by compensation processing according to thetheoretical model is very consistent with the target value.The absolute errors are less than2μm.The relative errors are less than 1%.To further verify the correctness of the model,the microstructures of step cylindrical,vertebral,concave ellipsoid and gear were successfully fabricated on pre-sintered alumina ceramic bodies.Through the calculation,the relative errors between the theoretical wear rates and the experimental wear rates are less than 10%.