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Arc sensors have been used in seam tracking and widely studied since the 80s and commercial arc sensing products for T and V shaped grooves have been developed. However, it is difficult to use these arc sensors in narrow gap welding because the arc stability and sensing accuracy are not satisfactory. Pulse gas melting arc welding (P-GMAW) has been successfully applied in narrow gap welding and all position welding processes, so it is worthwhile to research P-GMAW arc sensing technology. In this paper, we derived a linear mathematical P-GMAW model for arc sensing, and the assumptions for the model are verified through experiments and finite element methods. Finally, the linear characteristics of the mathematical model were investigated. In torch height changing experiments, uphill experiments, and groove angle changing experiments the P-GMAW arc signals all satisfied the linear rules. In addition, the faster the welding speed, the higher the arc signal sensitivities; the smaller the groove angle, the greater the arc sensitivities. The arc signal variation rate needs to be modified according to the welding power, groove angles, and weaving or rotate speed.

Nonlinear partial differential equation of temperature distribution with material properties varying was linearized by choosing appropriate linearization coefficient and solved through Green's function and Fourier transform methods. According to these results deduced, analytical model of arc welding temperature distribution under material properties varying condition was obtained. To verify precision of the analytical model obtained, temperature distribution of semi-infinite body under moving spot heat source was calculated through three different methods, including analytical model with and without considering material characters varying and finite element model. By comparing weld pool size calculated through the three methods, results got from analytical model of this paper were found more close to which got from finite element method. Conclusion was that, by taking material properties varying into account, analytical model deduced in this paper had higher precision, especially near the area of weld pool where temperature gradient was very great in welding process.