复杂薄壁零件激光快速成形过程的热力耦合场数值模拟

Thermo-mechanical Coupling Field Simulation of Complex Thin-wall Part Laser Rapid Prototype Process

研究直接激光成形过程中叶片温度场与热应力场的关系,改善成形质量。以空心叶片为例,根据激光测量仪测得的散点图,用圆弧逼近得到叶片的近似轮廓。利用有限元软件MSC.Marc建立Ti-6Al-4V(TC4)圆弧逼近的空心叶片的有限元模型,并对激光直接成形过程进行数值模拟,得到叶片在成形过程以及冷却过程中的温度场和热应力场。随着成形的进行,由于热量的积累,成形叶片的温度不断升高,已成形部位的热应力随着成形过程的热循环不断变化,小曲率半径处的热应力大,且热循环对热应力变化影响较小;在直接激光成形结束后,整体温度开始下降,各处的热应力都逐渐升高。通过分析温度场和热应力场的分布情况,得到不同曲率半径对温度场和热应力场的影响规律。基于模拟结果,总结的规律和试验经验,提出改善成形质量的有效方法。并利用激光直接成形技术,加工出模拟分析模型的实物零件,验证模拟和结论的正确性。

The research is focused on the relationship between the thermal field and thermal stress field during the process of the blade direct laser forming, so as to improve the forming quality. A hollow blade has been taken as example. According to the blade scatter-plot measured by the laser measurement instrument, the blade outline is approximated by a series of arc splines. Using finite element software MSC.Marc, a finite element model of arc approximation of the Ti-6A1-4V （TC4） hollow blade is established, and the hollow blade of laser direct forming is simulated to acquire the thermal field and thermal stress field in the forming and cooling process. During the forming process, the temperature of the forming hollow blade is increased and thermal stress of the already formed parts constantly changes with the thermal cycle due to the heat accumulation. And the part with a smaller curvature radius has a greater thermal stress which is affected by thermal cycle slightly. After the forming process, the reduction of the whole temperature leads to the thermal stress of every part rising gradually. Moreover, analyzing the distribution of the thermal field and thermal stress field, the correlation between the curvature radius and thermal field and thermal stress field can be obtained. The forming method of improving the quality is put forward based on the simulation result, summarized correlation, and experience. Finally, the real part just like the simulation model is worked out by utilizing the laser direct forming technology to verify the correctness of the simulation and summarized relationship.