Experimental Study On Ultrasonic Vibration Milling Of NiTi Shape Memory Alloy

NiTi shape memory alloy is widely used in biomedical,aerospace,automotive and other fields due to its excellent shape memory effect.As a common machining method,milling can achieve high precision and high efficiency processing.However,the work hardening during the milling process of NiTi alloy will seriously affect the shape memory effect of the material,thus affecting the service performance of the product.In order to achieve high-quality processing of the alloy and meet its assembly requirements,this paper takes Ni_50.8at%Ti shape memory alloy as the research object to explore the auxiliary effect of ultrasonic vibration in the milling process of the alloy.Ultrasonic vibration plane milling and helical milling experiments were carried out to analyze the influence of milling parameters on milling force,surface roughness and microhardness.The corresponding optimization models are established,and the genetic algorithm is used to optimize the milling parameters.The main research contents are as follows:（1）Effect of ultrasonic vibration on milling performance of NiTi shape memory alloy.The ultrasonic vibration milling test platform is established;by designing a single factor comparison test,the differences of milling force,surface roughness and work hardening under ordinary milling and ultrasonic milling are analyzed.Combined with the metallographic structure and phase transformation characteristics of the milling surface,the effect of ultrasonic vibration on reducing the influence of work hardening on shape memory effect was explored.（2）Ultrasonic vibration plane milling and helical milling experiments of NiTi shape memory alloy.The tool trajectory analysis of ultrasonic vibration plane milling and helical milling is carried out.Based on the influence of each parameter in the single factor test on the work hardening and the actual processing experience,the orthogonal test schemes of plane milling and spiral milling are designed respectively,and the ultrasonic vibration plane milling and spiral milling experiments of NiTi shape memory alloy are carried out.The influence of milling parameters on milling force,surface roughness and work hardening is studied.The significance of each factor was judged by range analysis.For plane milling,the regression models of milling force F_x,F_y,F_z,surface roughness and work hardening are established.For helical milling,the regression models of milling force F_x,F_z and work hardening are established.（3）Optimization of ultrasonic vibration milling parameters of NiTi shape memory alloy.Based on the corresponding mathematical regression models in plane milling and helical milling experiments,a multi-objective optimization model of plane milling is established with the objectives of milling force,surface roughness,work hardening and processing efficiency,and a multi-objective optimization model of helical milling is established with the objectives of milling force,work hardening and processing efficiency.Then,the genetic algorithm is used to optimize the spindle speed,feed per tooth,milling depth,milling width of plane milling,spindle speed,tangential feed per tooth,pitch and other parameters of helical milling with the minimum work hardening as the main objective,and the optimal milling parameters are obtained.