电弧增材制造钛合金成形工艺与过程控制

Titanium alloys are widely used in the fields of aerospace，navigation and energy engineering to fabricate large-scale integral components with complex geometry. The intrinsic properties of titanium alloys，such as low thermal conductivity and high chemical reactivity，result in a large buy-to-fly ratio in the fabrication of these components. This leads to remarkable time and production cost. Nowadays，additive manufacturing（AM）is causing a paradigm change in the manufacturing industry，and provides an alternative method for the fabrication of the large titanium components. To economically produce these large components，high deposition rates of kilograms per hour are necessary. Wire arc additive manufacturing（WAAM）is considered as one of the most promising AM technologies for the fabrication of large titanium components. The main advantages of WAAM are high deposition rate，high material utilization and low processing cost. However，the poor stability of the forming process，low surface quality and dimensional accuracy of the built parts are the major bottlenecks restricting the application of titanium components fabricated by WAAM. In order to promote the application of WAAMed titanium components，the research on the forming mechanism is the foundation，the optimization of process and equipment is the guarantee，and the monitoring and control of the process is the key. Therefore，WAAM technology based on different heat sources and their characteristics was discussed in this review. The commonly used heat sources of WAAM included gas metal arc welding，gas tungsten arc welding and plasma arc welding. The use of the auxiliary heat source to main a stable WAAM process was discussed as well. Then，the research and development of WAAM equipment and the application of WAAM titanium components were summarized. As WAAM technology moved toward higher deposition rate and heat input，the probabilities of producing highly textured microstructures and anisotropic mechanical properties were significantly increased. So，the microstructure and mechanical properties of WAAMed titanium parts were discussed. A brief review on the control methods of microstructure and mechanical properties was given. In order to regulate the forming process，it was essential to understand the defects formation mechanisms. The main defects of WAAMed titanium components included poor surface quality，low dimensional accuracy and severe residual stress and deformation. Besides，oxidation，porosity，delamination and crack were also commonly observed in WAAMed titanium components. Based on the formation mechanism of the defects，the future development of WAAM equipment was discussed. WAAM forming process was sensitive to process parameters. The defects were susceptible to be formed due to the turbulence during the deposition. Although nondestructive testing methods could detect the defects of the finished WAAMed components，these methods were usually time-consuming and expensive. Online monitoring and feedback control of the forming process was an effective method to realize the predictable and repeatable quality of the built components. The use of monitoring and control method was an important way to promote the industrial application of WAAMed titanium components. At present，there were three main types of research on WAAM online monitoring and control，including monitoring and control of the morphology of the molten pool and the weld beam，monitoring and control of the arc length，identification and classification of the defects of the built components and the abnormal behavior in forming process. The formation of defects in WAAMed components was often accompanied with the changes of the thermal，acoustic，optical and electrical signals. The signal changes could reflect the variation of the processing status and the shape and location of the defects. Hence，the signal changes could be used as the basis of the online monitoring. The monitoring methods based on visual signal，voltage signal，sound signal and multi signal fusion were summarized and discussed. After realizing the online monitoring and the accurate extraction of the relevant features，the reliable controller design became the key for the process control. Thus，the development of the control system in the forming process was summarized. The performance of the controller had a decisive impact on the quality of the process control. Nevertheless，WAAM was a nonlinear and complex process with multivariable and strong coupling characteristics. Adaptive control method and fuzzy control became the choices to improve the stability of the process. The closed-loop feedback quality control based on multi-sensor data fusion could effectively improve the forming quality and efficiency. Besides，developing corresponding graphical user interface or human-computer interaction module for specific controllers could effectively improve the efficiency of the control algorithms and the level of the automation of WAAM. Finally，the future research directions of WAAMed titanium alloys were prospected. In order to promote the application of WAAMed titanium components，profound study on the establishment of the processing-microstructure-property relationships were critical. Based on the understanding of the relationships，continuous optimization and improvement were necessary for the development of WAAM equipment and technology. With the development of machine learning，the intelligent online monitoring methods and integrated control systems could be achieved. The monitoring and control of the whole production process of WAAMed titanium components could be further promoted.