Search

Reliability and cost-effectiveness are very important factors in welding processes used in a wide range of manufacturing industries. Selection of welding processes varies widely from application to application and from industry to industry. Generally, it is difficult to obtain quality weldments with desired mechanical properties economically while maintaining high reliability. Furthermore, it is desirable to perform welding operations that can satisfy individual applications and requirements specifically, and produce tailor-made weldments to suit specific requirements. This paper presents the ability of process optimization in customizing required quality weldments with respect to desired mechanical properties. Gas Metal Arc Welding (GMAW) for samples of mild steel was performed in optimizing input weld-parameters. Welded samples, produced with different combinations of welding parameters, were investigated for their mechanical properties and metallographically characterized to explain the observed property variation. In addition to finding optimum parameters for a quality weld, a critical welding current (CWC) at which a brittle weldment is formed could also be discovered during this work. It is expected that process optimization for the customization precisely conceivable for tailor-made applications through modeling and simulation with software developed based on further research to improve welding quality in the global manufacturing industry.

Measurements of CO2, CO, N2O and CH4 mole fractions, O2/N2 ratios and the stable isotopes 13C and 18O in CO2 and CO have been performed in air samples from the highway tunnel Islisberg (Switzerland). The CO:CO2 ratios, with an average of (4.15±0.34) 5 ppb : ppm, are lower than reported by previous studies, pointing to a reduction in CO emissions from traffic. The 13C in CO2 reflects the isotopic composition of the fuel. 18O in CO2 is slightly depleted compared to the 18O in atmospheric O2, and shows significant variability. In contrast, the 13C values of CO show that significant fractionation takes place during CO destruction in the catalytic converter. 13C in CO is 10 enriched by 3% compared to the 13C in the fuel burnt, while the 18O content is similar to that of atmospheric O2. We compute a fractionation constant of (−2.7±0.7)% for 13C during CO destruction. The N2O:CO2 average ratio (1.8±0.2)×10−2 ppb : ppm is significantly lower than in past studies, showing a reduction in N2O emissions likely related to improvements in the catalytic technology. We also observed small CH4 emissions, with an average CH4 :CO2 ratio of (4.6±0.2)×10−2 ppb : ppm. The O2 :CO2 ratios of (−1.47±0.01) ppm : ppm are very close to the expected, theoretically calculated values.