GMAW焊接熔敷成形中质量与热的过渡机理及其控制研究

GMAW welding deposition-based forming technology has wide perspective on the metal part direct manufacturing and worn part remanufacturing. But its application is affected by its low dimensional accuracy and incline surface forming ability, serious heat accumulation. The dimensional accuracy, incline surface forming ability and heat accumulation are decided by heat and mass transfer process induced by the process of metal droplet impinging on the substrate. A mathematical simulating model for the heat and mass transfer process would be built based on the fluid dynamics theory, which is used to analysis the mechanism of heat and mass transfer process and make out the influences of forming parameters on the forming quality, such as droplet transfer character, welding arc force and heat, substrate temperature etc. Based on the simulating analysis results, the forming parameters are optimized, and then are used to control heat and mass transfer during the forming process. As the results, the problems and limits now existing in GMAW welding deposition-based forming technology would be solved in some extent, and promote the application of this technology in remanufacturing engineering. The research method and some results of this project are also useful to other droplet deposition-based forming methods.

GMAW焊接熔敷成形技术具有较高的成形效率，在金属零件的直接成形制造与缺损零件的再制造中有广阔的应用前景,但其目前存在成形精度差、倾斜面成形能力不足及热累积问题严重等缺点，限制了其应用发展。熔敷成形时熔滴过渡产生的传热、传质过程最终决定了成形精度、倾斜面成形能力及热累积问题等。根据流体动力学理论建立熔滴过渡数值分析模型，研究熔敷成形过程中的传热、传质机理，弄清熔滴过渡特征、电弧力与电弧热、基体温度等各成形参数对熔敷成形质量的影响规律。在此基础上优化各成形参数，依此控制成形过程中的传热、传质过程，显著改善GMAW焊接熔敷成形技术目前存在的缺点与问题，推动其在再制造工程中的应用发展。本项目的研究方法与部分研究成果也适用于其它基于熔滴过渡的成形工艺。

熔滴过渡引起的传热、传质过程直接决定了电弧焊熔敷成形技术的成形质量。研究其机理及实现对其精确控制，对电弧焊熔敷成形技术有重要意义。采用VOF法及焓-多孔介质法等流体动力学理论，建立了熔滴在基板上铺展及凝固过程的三维数值分析模型。通过对计算精度影响的研究，确定出了合适的网格尺寸、临界固相分数等模型参数及基体处理状态。利用所建立的熔滴沉积数值分析模型，模拟分析了熔滴沉积速度及基体温度等对成形形貌的影响规律，分析了熔滴在倾斜面上的沉积成形规律。利用多物理场耦合分析技术建立了焊接电弧的三维数值分析模型，计算分析了熔滴过渡过程对熔池表面处热流密度与电弧力的影响情况，并计算了电弧热与电弧力作用下的熔滴沉积成形情况。采用高速摄像技术研究了电弧电流波形参数对熔滴过渡特征的影响，并研究了熔滴过渡特性对成形精度及成形层组织的影响。高速摄像研究结果表明：相比较于多脉一滴和一脉多滴的熔滴过渡方式，一脉一滴熔滴过渡方式同时兼顾了成形层平整度与热输入量，成形层平整度与热输入量均较为适中；熔滴过渡方式对成形层组织的影响并不明显，只是一脉一滴方式下成形层组织表现的更为均匀些。建立了随焊热源作用下电弧熔敷成形过程的温度场与应力场数值分析模型，计算了成形温度场和应力应变场，证实了随焊热源可降低成形过程的应力应变。研究了激光与电弧之间的相互作用对熔滴过渡特性及熔敷成形层组织形貌的影响规律，结果表明激光作用可提高高速熔敷成形时熔滴过渡的稳定性。