脉冲旁路耦合电弧MIG焊三维焊接快速成形工艺及多物理场耦合机理研究

Aiming at the existing problems in 3D welding rapid prototyping technology, a new process, named pulse by-pass coupled arc MIG welding rapid prototyping process, is put forward initiatively. Under the condition of accurately controlling heat process, basic science problems of coupling mechanism of multi physics field in forming process, such as heat, flow, stress and strain etc, will be studied. By combining use of experimental measurements, theoretical research and numerical simulation analysis, the following researches are going to be carried out: 1) three dimensional welding rapid prototyping test of pulse by-pass coupled arc MIG welding in order to gain the best welding parameters and develop research of heat input and form accuracy closed loop control during forming process, 2) droplet transfer, molten pool behavior and their interaction mechanism during stacking forming process, 3) the stacking structure and grain growth under repeated heat action, and the relationship between the mechanical properties of the forming work piece and wire composition and stacking process, 4) accuracy control of work piece forming size considering heat, flow field, stress and strain coupled interaction during three dimensional welding rapid forming process. Based on the above, numerical model of multi physics field is set up under the condition of all coupled interaction and numerical analyses are carried out to research accuracy control of work piece forming size by three dimensional welding rapid prototyping technology. The theoretical foundation for pulse by-pass coupled arc MIG welding rapid prototyping technology and technical support for efficient and high quality 3D welding rapid prototyping will be offered through the project implementation.

针对三维焊接快速成形技术存在的问题，本项目提出脉冲旁路耦合电弧MIG焊快速成形方法，在热过程精确控制条件下，对热、流、应力应变等多物理场相互耦合作用的基础科学问题进行研究。采用试验测试、理论研究及数值分析相结合的方法，主要开展以下研究：1）脉冲旁路耦合电弧MIG焊三维焊接快速成形试验研究，获得最佳工艺参数，并进行成形过程中的热及成形尺寸精度闭环控制研究；2）堆垛成形过程中熔滴过渡、熔池行为及其相互作用机理；3）反复热作用下堆垛组织及晶粒生长，研究成形零件的力学性能及其与丝材成分、堆垛工艺的相关性；4）三维焊接快速成形过程中热、流场、应力应变耦合作用的工件成形尺寸控制的理论研究。在此基础上，建立全耦合作用条件下多物理场数值模型，研究三维焊接快速成形工件尺寸精度控制策略。通过本项目的实施，为脉冲旁路耦合电弧MIG三维焊接快速成形技术提供理论基础，为实现高效、优质三维焊接快速成形提供技术支撑。

项目围绕旁路耦合电弧焊三维焊接快速成形，以电弧增材制造的过程稳定性与成形精度为目标，以旁路耦合电弧焊多物理场耦合为切入点，主要开展了旁路耦合电弧焊增材制造的方法及工艺、过程控制、多物理场的相互耦合机理三方面的研究，获得了过程稳定性与成形精度的关键性因素，并进行了闭环控制研究，阐述了热过程、变形规律、熔池内部流动及组织生长规律。主要研究结果如下：旁路电流对基板和堆垛层具有分流控热作用，可以改善电弧增材制造过程中的热积累；在沿着堆垛高度方向，堆垛件组织经历了由胞状晶、胞状枝晶再到树枝晶的转变，枝晶间距在逐渐增大，且往复堆垛的相邻层间枝晶组织生长方向发生了改变，而单向堆垛的枝晶生长方向相同。通过X-Ray技术对旁路耦合电弧增材制造过程中的熔滴过渡及熔池流动行为进行了观察分析，发现熔滴在初入熔池时仍然保持为一熔滴的整体，之后通过熔池内部流动才逐步分散到熔池中，同时也发现熔池内部流动具有典型的流动涡流。旁路耦合电弧焊增材制造的熔滴过渡模式有自由滴状过渡、接触过渡、以及自由+接触的混合过渡模式，且自由过渡时的熔滴对熔池的流动行为的冲击远大于接触过渡时的情况，与熔滴的自由过渡模式相比接触过渡模式的焊缝更均匀、更美观；利用实时控制实现了薄壁墙体较高精度的堆垛成形，各层之间无缺陷，边缘较整齐，并优化了堆垛成形过程，解决了堆垛层重熔塌陷等问题；并通过电弧增材制造曲面零件成形系统，实现了曲面零件从三维建模、成形路径规划和仿真到堆垛成形的一体化和自动化，且结合铣削加工技术完成零件的加工制造，这为本技术的推广与应用奠定了基础。