Finite Element Analysis Of Temperature Fields In Keyhole Plasma Arc Welding

As one of the high energy density welding processes, keyhole plasma arc welding(K-PAW) has great application potential in industry. But its applicable range of process parameters is narrow and the adjustability is lower, which result in the poor stability of the keyhole and limit the wide application of K-PAW. Conducting numerical simulation of temperature fields in K-PAW will be helpful and useful to deeply understand the process mechanisms and optimize the process parameters, and promote its industrial applications. During K-PAW process, a keyhole forms to fully penetrate the workpiece. Corresponding to this characteristic, the K-PAW weld is like a "reversed bugle" in geometry. The available welding heat source modes, such as the Gaussian plane source, double-elliptic plane source, double-ellipsoidal body source, conic body source, Gaussian rotary body source, and so on, can not be used to describe the characteristics of K-PAW weld with high depth-to-width ratio. Further study must be carried out to propose adaptive volumetric heat source mode which fully takes account of the features of the process and the weld geometry.From the point of view in macroscopic phenomena of heat transfer, the keyhole effect is indirectly described through considering the heat flux distribution along the workpiece thickness. Suitable and adaptive volumetric heat source mode is developed to completely reflect the geometric characteristic of high depth-to-width ratio of K-PAW weld. A combined volumetric heat source model is proposed, i.e. a double-ellipsoidal body mode is used at the upper part of the workpiece while a linearly-increased peak value of heat flux in Gaussian cylinder mode is employed at the lower part of the workpiece along its thickness direction based on the "reversed-bugle" configuration of K-PAW weld. The temperature fields on the workpieces of thickness 6mm and 8mm are numerically simulated using the combined heat source "double-ellipsoid + linearly-increased peak value of heat flux in Gaussian cylinder". The calculated and measured weld dimension and geometry match well to demonstrate the reasonableness and suitability of the combined volumetric heat source mode.From the point of view in physical mechanism of keyhole establishing, on the basis of determining keyhole geometry by developing a mathematical mode for keyhole dynamics, the volumetric heat source mode is proposed. This is another way of dealing with the thermal phenomena in K-PAW. Initial study is conducted in this aspect. An axisymmetric keyhole mode in K-PAW process is developed by considering energy balance and momentum conservation inside the keyhole and surface tension equation on keyhole surface. After correlating the dimensions of keyhole geometry to the distribution domain of the volumetric heat source in the K-PAW process, an adaptive volumetric heat source model based on the geometry of keyhole is put forward. To apply this heat source mode to the numerical simulation of temperature field and weld formation in K-PAW, some progress is made.K-PAW experiments on stainless steel workpiece are carried out, and weld geometry and dimension are measured. The experimental results and the predicted ones are compared together, and the results show that they are in good agreement.