Abstract Scanning electron beam welding (SEBW) is a very important process for welding of thick plates in aerospace, aeronautical and power industries. However, since the invention of this process, the scanning parameters are typically selected through time consuming and costly trial and error. No existing mathematical criterion can be used to select the optimal parameters due to lack of physical understanding of the welding process. In this study, we developed a three-dimensional mathematical model of SEBW capable of modeling the coupled keyhole and weld pool dynamics for the first time, and used it to understand the underlying physics of the welding process and explore the process optimization criterion of circular mode beam scanning by combining welding experiments and modeling. We showed that beam scanning may not always stabilize the keyhole and weld pool, and may not improve the final weld quality of electron beam welding. However, beam scanning can modulate the movement of high temperature positions on keyhole wall, and contribute to a better uniformity of weld pool dynamics behind the keyhole. For circular beam scanning, we proved that low frequency scanning may lead to more welding defects such as porosity, spiking, and spatters because it increases the tendency of keyhole oscillations as compared to the no scanning case. High frequency scanning could stabilize the keyhole to a certain degree and modulate the fluid flow of the weld pool to make it more regular. Additionally, the scanning radius should be neither too small nor too large. Too small radius may lead to more defects, and too large radius can decrease the penetration depth significantly. A dual direction energy uniformity (DDEU) criterion was proposed to select the scanning parameters by considering the energy uniformity degree in the welding direction and the transverse direction. It was demonstrated that process parameters including beam scanning frequency and radius can be successfully optimized using the proposed criterion.

中文翻译：

---

电子束焊接的束扫描优化可能性：物理理解和参数选择标准

摘要 扫描电子束焊接（SEBW）是航天、航空、电力等行业中厚板焊接的重要工艺。然而，由于该过程的发明，扫描参数通常是通过耗时且昂贵的试错法来选择的。由于缺乏对焊接过程的物理理解，没有现有的数学标准可用于选择最佳参数。在这项研究中，我们首次开发了能够对耦合小孔和熔池动力学进行建模的 SEBW 三维数学模型，并用它来了解焊接过程的基本物理原理并探索圆形模式的过程优化准则结合焊接实验和建模进行光束扫描。我们表明束扫描可能并不总是稳定锁孔和熔池，并且可能不会提高电子束焊接的最终焊接质量。然而，光束扫描可以调节小孔壁上高温位置的运动，并有助于提高小孔后面焊池动力学的均匀性。对于圆形光束扫描，我们证明低频扫描可能会导致更多的焊接缺陷，如气孔、尖峰和飞溅，因为与无扫描情况相比，它增加了小孔振荡的趋势。高频扫描可以在一定程度上稳定小孔，调节熔池的流体流动，使其更规则。此外，扫描半径不应太小或太大。半径太小可能会导致更多的缺陷，过大的半径会显着降低穿透深度。提出了一种双向能量均匀性（DDEU）准则，通过考虑焊接方向和横向能量均匀度来选择扫描参数。结果表明，使用所提出的准则可以成功地优化包括光束扫描频率和半径在内的工艺参数。