增材-微锻造加工工艺应力场数值模拟研究

激光熔丝增材制造过程中，材料快热快冷的特点使熔覆层产生不利于表面强度的残余应力，而增材-微锻加工工艺可提高增材制件的加工质量，改善增材制件微观组织及力学性能缺陷.以TC4为研究对象，通过超声微锻造工具头与熔池保持一定的相对距离做进给运动，对材料表面进行高频次冲击与滚压，使熔覆层表面得到改善和强化.对增材-微锻加工工艺进行顺序热结构耦合数值模拟研究，分析加工过程中熔覆层应力场变化情况.研究表明:对尚未冷却的增材熔覆层表面进行超声微锻造，熔覆层由于热源加载产生的残余拉应力转化为较为有益的残余压应力，降低了熔覆层表层缺陷发生的概率.不同的超声振幅、进给速度以及锻造温度参数对残余压应力及法向变形量有较大影响.

Numerical Simulation Study of Stress Fields in the Additive Manufacturing and Micro-forging Process

In the laser fuse additive manufacturing process， the residual stress of the cladding layer is disadvantageous to the surface strength because of the rapid heating and cooling of the material， and the additive manufacturing-micro-forging processing technology can improve the processing quality of laser fuse additives， mechanical properties and microstructures. TC4 is taken as the research object， and the material surface is improved and strengthened by high frequency impact and rolling on the surface of the cladding layer through the feeding movement of the ultrasonic micro-forging tool head and molten pool at a certain relative distance. A model is established to conduct the numerical simulation study on the sequential thermal structure coupling of the additive and micro-forging process， and analyze the variation of the stress field of the cladding layer during the processing. The results show that the residual tensile stress of the cladding layer due to heat source loading is transformed into beneficial residual compressive stress by ultrasonic micro-forging on the surface of the uncooled cladding layer， and the probability of surface defects is reduced. The parameters of ultrasonic amplitude， feed rate and forging temperature have great influence on the residual compressive stress and normal deformation.