SiCp/Al Milling Mechanism And Surface Quality Under Ultrasonic Excitation

Being light and hard,aluminum matrix composite(SiCp/AL)has been widely used in aerospace,electronics,military and so on.However,the matrix and the reinforced phase in the composite have different physical properties,the material tends to be cut unequally with large cutting force,resulting in poor surface quality.Such deficiencies have greatly restricted its further application and development.Although these shortcomings have been improved to some extent by applying vibration cutting,researches on vibration milling are relatively less than vibration turning and grinding.In this paper,we have realized the ultrasonic vibration milling of the SiCp/AL material by applying ultrasonic excitation to the workpiece.On this basis,the milling mechanism of SiCp/AL composite under ultrasonic excitation and the surface quality of the machined materials have been systematically studied,which will provide theoretical and technical supports for the ultrasonic milling of SiCp/AL material.For the sake of convenience,all the so-called ultrasonic milling refers to the milling method under ultrasonic vibration of the workpiece,unless otherwise stated in this paper.The main contents of the paper are as follows:(1)the kinematic analysis of ultrasonic milling;(2)the establishment of the experimental milling system with ultrasonic vibration;(3)the modeling and factor analysis of SiCp/AL ultrasonic milling force;(4)the study on the effects of ultrasonic vibration on the crack propagation of materials;(5)the study on the surface quality of SiCp/AL by ultrasonic milling.Based on the kinematic analysis of workpiece during ultrasonic milling,we have studied the characteristics of separation speed,separation feed,and impact of ultrasonic milling.By stimulating the movement trajectory of ultrasonic milling under different milling parameters and amplitude,we have analyzed the relationship between these characteristics and the motion trajectory.It is concluded that when the speed characteristic of ultrasonic vibration milling is M<1,and the feed characteristic is f_z<2A,is odd,segregated ultrasonic vibration milling can be achieved with larger kinetic energy than that of ordinary milling.In this research,we have processed the workpiece by ultrasonic vibration machining in the feed direction using the constructed experimental ultrasonic vibration system.Through experiments,we compared and analyzed the wear conditions of Poly crystalline diamond(PCD)cutter and YG cutter after milling SiCp/AL composite,and finally determined to use the PCD cutter in the research.By analyzing the ultrasonic vibration milling of SiCp/AL,we conclude that the milling force is mainly composed of the chip forming force,the SiC fracture force,the ultrasonic impact force and the friction force.The mathematical model of the ultrasonic milling force of SiCp/AL has been established.We have specified the influences of different milling parameters and ultrasonic amplitude on milling force,and verified through experiments the correctness of the mathematical model.The research shows that rational configuration of milling speed,feed per tooth and ultrasonic amplitude can effectively reduce the milling force.Based on the theoretical study of material fracture toughness under nonlocal theory,the effects of ultrasonic vibration on the crack initiation and propagation have been analyzed from the perspectives of microscopic mechanics and energy.Also,the surface micro-structures of SiCp/AL composite processed respectively by ultrasonic milling and ordinary milling have been compared through experiments.It is concluded that the equivalent hardness of the material is reduced and the fracture toughness is increased in the process of ultrasonic processing,which demonstrates from the perspective of microcosmic material that ultrasonic milling force is less than ordinary milling force,and that the subsurface of the workpiece has better surface density and smoothness when processed by ultrasonic milling than by ordinary milling.Through systematically studying the surface roughness of groove bottom and groove sides after ultrasonic vibration milling,we have found that ultrasonic vertical milling has a negative influence on the roughness of the bottom slot surface,but a positive one on that of the side groove surface.It is concluded through multivariate experiments and variance analysis that the roughness of the machined surface formed by the cutting edge depends on the combined effect of the spindle speed,feed per tooth,ultrasonic amplitude and other factors in the process of ultrasonic vibration assisted milling.Thus,ideal surface roughness values can be achieved by reasonably selecting various parameter combinations.The macro and micro morphologies of the materials in ultrasonic vibration milling and ordinary milling have been compared and analyzed.It can be concluded that changes in tip trajectory lead to the scale shapes at the surface of groove bottom under ultrasonic vibration,and the ironing frequency and area in the cutting area increases with the vibration of workpiece.The prediction model of the surface roughness at the groove bottom and the groove sides has been established for ultrasonic vibration milling of SiCp/AL composite,which has been theoretically and experimentally verified respectively.It is concluded that the model can qualitatively analyze the trend of surface roughness,which is of practical guiding significance for predicting and estimating the roughness of the material.