In this paper, analytical relations of energy and exergy efficiency are written for GMA welding. Then the effects of parallel heating on these two efficiencies are checked. The difference between these two efficiencies is due to welding processes irreversibility. Residual stresses are type of irreversibility. So, the effect of parallel heating on welding residual stresses are checked by difference between these two efficiencies (dimensionless entropy).Flame heating are assumed as point and spot heat sources. Also, it is shown that the temperature distribution is quasi-steady. What’s more, a parameter is introduced as a ratio of exergy efficiency to energy efficiency that it can help to investigate the amount of cost saving for parallel heating process. The results are adopted with data sources. The results show that by increasing flame power, energy and exergy efficiency will decrease, while; the slope of these efficiencies decreases gradually. In addition, increasing the speed of welding is caused to rise up both efficiencies. Dimensionless entropy decreases because of increasing the internal flames heat. It demonstrates that decreasing the residual stresses are due to welding. This reduction is greater at higher speeds. So, parallel heat at higher speed is more effective to increase the welding quality. As well as, the ratio of two efficiency shows that the heating about 1800 j/s would be economically optimal amount. Finally, considering the results with previous data, use of dimensionless entropy generation for checking the residual stresses of welding has recommended.

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