Welding current prediction in GMAW and UGMAW processes using response surface methodology

Abstract

Among all process variables in gas metal arc welding (GMAW) process, welding current is the most influential variable affecting heat input and weld quality. Its dependence on other process variables in GMAW and universal gas metal arc welding (UGMAW) processes (which makes use of a specially designed torch to preheat the filler wire independently, before its emergence from the torch) has been investigated using four factor five level central composite rotatable design to develop relationship for predicting welding current, which enables to quantify the direct and interactive effects of four numeric factors, namely wire feedrate, open circuit voltage, welding speed and electrode stickout and one categorical factor preheat current. Mathematical models developed show that welding current increased linearly with increaseing wire feedrate and open circuit voltage, whereas it decreased with increasing electrode stickout and preheat current. Numerical optimisation was carried out, and the optimal solutions generated indicate that under the same input conditions higher deposition rates are achievable in UGMAW process.     

High-Temperature Oxidation of a Sn-Zn-Al Solder

The oxidation of 91Sn-9(95Zn-5Al) solder in theliquid state, 250°C, was studied by thermalgravimetric analysis (TGA). The oxidation behavior of63Sn-37Pb, 91Sn-9Zn, 99.4Sn-0.6Al, and Sn was alsoinvestigated for comparison. The weight gains per unitsurface area descend in the order: 63Sn-37Pb > Sn> 91Sn-9Zn > 91Sn-9(95Zn-5Al) > 99.4Sn-0.6Al.The initial weight gains of the materials investigated increase linearly with reaction time, whileparabolic behavior exists after the linear stage. Therate constants of the oxidation reaction for the tworeaction stages were determined. Activation energies for oxidation of the five materials weredetermined in the range of 250 to 400°C. Theactivation energies, derived from the linear rateconstants for the early stages of oxidation, are 27.7kJ/mole for 99.4Sn-0.6Al, 23.3 kJ/mole for 91Sn-9Zn, 21.4kJ/mole for 91Sn-9(95Zn-5Al), 20.5 kJ/mole for63Sn-37Pb, and 19.8 kJ/mole for Sn. Thesurface-oxidation behavior was investigated further withelectron spectroscopy for chemical analysis (ESCA) and Auger electronspectroscopy (AES). AES profiles showed that oxides ofZn and Al formed on 91Sn-9Zn and 91Sn-9(95Zn-5Al)solders, while tin oxide is formed on 63Sn-37Pbsolder.     

棒形合成绝缘子的雷电冲击放电特性

在实验室中进行了 110、2 2 0kV不同伞盘结构的棒形合成绝缘子的雷电冲击放电特性试验 ,还与瓷绝缘子的特性进行了比较 ,用计算机处理分析试验数据得出了 5 0 %雷电放电电压与绝缘子结构长度的关系曲线。试验结果表明 ,伞盘结构影响因素较大 ,一大一小伞型结构最佳