Numerical Simulation Of The 3-D Transient Temperature Fields In Keyhole Plasma Arc Welding

It is a key issue to establish an appropriate model of the heat source in the simulation of the Keyhole Plasma Arc Welding (K-PAW). It requires that the model embody the Keyhole Effect and have the characteristic of volumetric distribution along the direction of the plate thickness. Numerical simulation of 3-D temperature fields in PAW process is carried out based on the software SYSWELD and its 2nd development. The three-dimensional conical mode of heat source is modified through analyzing the heat source modes attached to the software SYSWELD, and the modes of heat sources for the quasi-steady state PAW and the transient PAW are put forward, which consider the "digging-action" of the arc plasma. These models of volumetric heat sources are the basis for the numerical analysis of temperature fields in K-PAW process.The numerical simulation results of quasi-steady state temperature fields in K-PAW process indicate that neither the general double ellipsoidal mode of heat source nor the three-dimensional conical mode of heat source can be appropriate for the finite element analysis of the K-PAW process. With considering the heat flux distribution along the direction of the work piece thickness, a modified model of 3-D conical heat source mode is put forward. Though it can be used to calculate the weld width on both the top and the bottom surfaces of the work piece exactly, but for the location and locus of the melt line in the weld cross section, the calculating precision is lower.The model of the heat source for the quasi-steady state K-PAW, i.e. QPAW, can depict the character of the K-PAW process quite well, because it considers the "bugle-like" configuration of the Keyhole, and the "attenuation-feature" of heat flux distribution of the plasma arc along the direction of the work piece thickness. The QPAW heat source mode is applied in the software SYSWELD by modifying its corresponding aspects. The quasi-steady state temperature fields in K-PAW process is analyzed with the finite-element method. The result shows that the calculated weld geometry at the cross section is in good agreement with the experimental one.For simulating the K-PAW process, the model of the heat source for transient K-PAW process i.e. TPAW is developed. It combines the modified 3-D conical modefor the upper of part of the weld pool with the 3-D conical mode for the lower part of the weld pool, so that the mode TPAW is a hybrid mode. It demonstrates that the predicted weld geometry of the cross-section at the different moments matches basically with the measured one, and the time reaching the quasi-steady state agree with the experiment results. It can be concluded that the QPAW and TPAW mode of heat source can be used for the FEM analysis of thermal processes in K-PAW.