It is a key issue to establish an appropriate model of the heat source in the simulation of the keyhole plasma arc welding (PAW). It requires that the model account for the keyhole effect and have the characteristic of volumetric distribution along the direction of the plate thickness. For available heat source models, neither Gaussian nor double ellipsoidal modes of heat source is applicable to keyhole PAW process. With considering the force of the high speed plasma jet and the associated strong momentum, a modified three-dimensional conical heat source model is proposed as the basis for the numerical analysis of temperature fields in keyhole PAW process. Further, a new heat source model for quasi-steady state temperature field in keyhole PAW is developed to consider the “bugle-like” configuration of keyhole and the decay of heat intensity distribution of the plasma arc along the direction of the workpiece thickness. Based on this heat source model, finite-element analysis of temperature profile in keyhole PAW is conducted and the weld geometry is determined. The results show that the predicted location and locus of the melt-line in the PAW weld cross section are in good agreement with experimental measurements.

The gas tungsten arc welding process is an uncertain nonlinear multivariable system. In order to control the welding process, the nonlinear dynamic relationship between the weld pool geometry reflecting the weld quality and the welding parameters must be developed. A three-dimensional numerical model is developed to investigate the dynamic characteristics of the weld pool geometry when the welding current and welding speed undergo a step-change. Under the welding conditions employed in this research, the transformation periods are about 4s for a 20A down step-change of welding current, and about 2s for a 20mmmin−1 up step-change of welding speed, respectively. At the initial stage during the step-change of welding current and welding speed, the responses of weld pool geometry are quicker, but they slow down subsequently until the weld pool reaches a newquasi-steady state. Welding experiments were conducted to verify the simulation results. It was found that the predicted weld pool geometries agree with the measured ones.

在分析TIG焊接弧光谱的基础上，设计出复合滤光镜头，与普通CCD摄像机组成视觉传感器，从试件正面观测熔池图像。焊接过程中根据电流大小通过软件调整采集图像亮度，得到了比较清晰的TIG焊接熔池图像。利用自行开发的图像处理算法。检测出了熔池正面的形状参数。该算法处理一幅图像像用时不超过70ms，满足实时检测的需要。

It is of great significance to determine the sheath potential of gas tungsten arcs because it has a marked e ect on the heat flux at the anode. In this paper one of the parameters a, i.e., the percentage of the electrons entering the lattice of anode, is introduced for determining the sheath potential. The results indicate that the sheath potential is strongly dependent on the parameter a which is used to make a di erence between an anode conducting electricity and a cool wall isolated. For determining the sheath potential, a formula is established, which takes account of the electron temperature, the electron flux and the ion flux at the free-fall edge as well as the parameter α.

根据当前制造业对高效、优质、低耗焊接技术的迫切要求，研发出低成本的高速电弧焊接新工艺DE-GMAW。该工艺在常规GMAW焊接设备的基础上，通过附加GTAW焊枪构成旁路电弧，分流了一部分通过焊丝的焊接电流，在施加于焊丝的电流较大的情况下（保证了熔敷率），减小了作用于母材的热输入，解决了高速焊接面临的矛盾，实现了高速电弧焊接。建立了适用于DE-GMAW焊接工艺的有限元模型，并对该工艺条件下的温度场和应力变形进行了数值模拟。结果表明：计算出的DE-GMAW焊缝横断面形状尺寸与实验结果吻合良好；在通过焊丝的总电流相同时，DE-GMAW焊接时焊缝尺寸、热影响区宽度、应力、应变及变形均小于常规GMAW焊时的结果。这为DE-GMAW焊接工艺参数优化提供了基础数据。