高反射率材料大功率光纤激光/MIG电弧复合焊气/液界面热-力耦合行为及调控机理研究

Noting that laser welding of materials with high reflectivity has the problem of low heat transfer efficiency and that ejection, pores and poor bead appearance occur in laser deep penetration welding of these materials due to the significant inhomogeneity of absorbed laser energy on keyhole wall along the direction of keyhole depth, we take copper as test material and fiber laser/MIG arc hybrid heat source as welding heat source to study the thermo-mechanical coupling behavior on vapor/liquid interface in high power fiber laser/MIG hybrid welding of materials with high reflectivity and to discover the regulation mechanism through both experiment and simulation. After experimental study on the effects of welding parameters on the threshold from heat-conduction to deep-penetration welding and the stability of hybrid laser/arc welding process of materials with high reflectivity, an numerical model of hybrid laser/arc welding process, which takes into account the basic phenomena in the welding process and has the capability of describing the dynamic evolution of keyhole, will be established and verified, and then this model would be used to simulate the hybrid laser/arc welding process of materials with high reflectivity. Base on the computed results, the thermo-mechanical coupling behavior on vapor/liquid interface during keyhole formation, keyhole evolution and the quasi-stable welding process of materials with high reflectivity would be analyzed. Furthermore, effects of the thermo-mechanical coupling behavior on keyhole wall on the keyhole-pool interaction will be discussed. Then, taking laser power modulation as the main regulation method, we will discuss the main factors on which the optimum regulation parameters depend and the relationships between these factors and regulation parameters. Finally, the methodology and principle of optimizing regulation parameters would be concluded. The results of this work have both academic significance and application potential and would lead to high quality and high-efficiency welding of materials with high reflectivity.

针对高反射率材料激光焊存在能量耦合效率低和小孔内激光能量在孔深方向上分配严重不均衡，导致气孔、飞溅和焊缝成形差的问题。拟采用光纤激光/MIG电弧复合焊、选择紫铜为试验材料，通过试验测试和模拟相结合的方法研究高反射率材料复合焊过程气/液界面热-力耦合行为及调控机理。试验研究工艺参数影响热导焊向深熔焊转变临界功率的规律和影响焊接过程稳定性的规律。建立考虑激光/MIG复合焊主要物理现象、能够描述小孔形成和发展动态过程的复合焊数值模型，用试验结果对模型进行验证。模拟研究小孔在高反射率材料熔池表面形成和扩展时的热-力耦合过程；模拟研究高反射率材料深熔焊时小孔内表面热-力耦合行为特征及其对小孔-熔池相互作用的影响。以激光功率调制为主要调控措施，分析理想调控参数的主要决定因素及其影响规律，揭示制定优化调控参数的方法和原则。研究成果对于促进高反射率材料的优质、高效焊接生产具有重要理论意义和工程价值。

针对高反射率（HR）材料激光焊过程热效率低和稳定性差的问题，先采用光路追踪法比较铜和钢这两种对激光反射率有显著差异材料深熔焊时激光能量在孔深方向上的分布，指出HR材料激光焊小孔内能量在孔深方向上分配严重不均衡是导致气孔、飞溅和焊缝成形差的根本原因。进一步研究了：（1）激光功率波形正弦调制对HR材料激光焊热效率和稳定性的影响；（2）激光功率波形正弦调制影响HR材料激光焊热效率和稳定性的机理；（3）HR材料功率调制激光-MIG复合焊过程的热效率和稳定性。结果表明：（1）激光功率调制显著降低HR材料由热导焊向深熔焊转变的临界功率，可在较低平均功率下形成小孔，激光束在孔内多次反射使焊接过程热效率显著提高。焊速1m/min时，常功率焊接和功率调制焊接将1.5mm紫铜焊透的临界平均功率分别为约2.6kW和2.1kW。此外，功率正弦调制对抑制气孔、飞溅缺陷和改善焊缝成形质量有显著效果；（2）功率正弦调制激光焊中，当功率从瞬时最大值开始减小时，低反射率材料中熔深马上开始同步减小，HR材料中熔深开始减小的时刻则明显滞后(约滞后一个正弦周期的30%)。HR材料调制激光焊中在瞬时功率峰值下形成大深宽比小孔会使激光在小孔内反射次数增加、能量耦合效率陡增，在激光瞬时功率下降的过程中依然可以使大深宽比小孔继续维持大约三分之一个正弦周期，大深宽比小孔形成并在较长时间内维持存在是调制可以改善HR材料激光焊热效率的关键。调制焊中大深宽比小孔形成后激光瞬时功率是不断下降的，因此还可以有效抑制激光能量在孔底的集中、使小孔和熔池稳定性得到改善。（3）HR材料激光-MIG复合焊具有显著协同效应。功率调制对HR材料复合焊过程稳定性的改善与贯穿型小孔的形成几率密切相关，功率调制使中贯穿型小孔的出现几率显著增加，多余的激光能量从底部孔口逃逸，从而避免盲孔型深熔焊中存在的小孔底部能量过度集中现象。上述结果促进了对HR材料(铜及其合金、铝及其合金和镁合金等)激光深熔焊接机理的认识，对HR材料优质高效激光焊接方法的开发和推广具有理论意义和应用价值。