A 3-D string heat source model was developed to simulate the thermal process for gas metal arc welding (GMAW) with a new transient solution of heat transfer. Reflection heat sources, the imaginary heat source and the imaginary heat sink were introduced to make the solution more reliable. The moving welding heat input during GMAW welding process was presented with a moving 3-D string heat source model made up of a group of elementary point heat sources along the moving coordinate axes. Using established models, the whole process from arc starting, quasi-steady state (QSS), to arc extinguishing during welding Q195 steel has been simulated. Meanwhile, some calculations and experiments for JG590 steel have also been made. The predicted weld cross-sections and welding thermal cycles show a good agreement with experimental measurements.

The injection-rolling nozzle is one of the most important components in polymer's continuous injection direct rolling process. The basic theory for molten polymer mould channel design and the advantage of extrusion channels lead us to design a new channel for the injection-rolling nozzle. Simulation results show whether the channel structure design is feasible, and will allow the molten polymer flow to be even, yet also optimized for uniform velocity. The finite element method is used to optimize several key structural parameters for nozzle, which are then used as optimization object parameters. Compared with the previous results, molten flow velocity is more uniform after optimization. The velocity difference of 0·3 mm s −1 is slower at the outlet compared with 60 mm s −1 , and the total length of the nozzle has decreased. Finally, experiments results show that the channel with optimization has better flow speed uniformity.