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A simplified sketch keyhole geometry of steel/copper welding for different laser power where f s and r s are the front and rear keyhole wall for steel, respectively, and f c and r c are the front and rear keyhole wall for copper, respectively.
The effect of the distance shift between the beam axis and the steel/copper interface line was investigated. The shift distance towards the copper was considered as a negative value and towards the steel as a positive. Zhou, J.; Tsai, H.L. Investigation of mixing and diffusion processes in hybrid spot laser-MIG keyhole welding. J. Phys. D Appl. Phys. 2009, 42, 095502. [ Google Scholar] [ CrossRef]It is evident from Figure 16 that as the travel speed increases, the recoil pressure on the copper front wall keyhole surface ( P r.c) becomes higher than the recoil pressure on the steel front wall surface ( P r.s). Because the interaction time between laser and front keyhole surface decreases with increasing laser travel speed, this, therefore, suggests that the recoil pressure has a dynamic magnitude depending on the rate of heat transfer of the metal. This is often expressed in terms of “thermal conductivity.” The thermal conductivity of copper (401 W/m °C) is very high compared with steel 316 L (16.3 W/m °C), and this may explain why the keyhole elongated more in the direction of the copper front wall. Continuous Yb:YAG laser keyhole welding of the pure copper plate to steel 316L sheet is performed for different laser parameters. The laser-generated welding keyhole and weld melted zone are observed by a high-speed camera. The image is treated by MATLAB and simple code is built to calculate the keyhole and melted zone area. This treatment is validated by the actual welding measurements, and the accuracy of the measurements is tested by the confidence interval law. The images obtained of keyhole and melt zone area in dissimilar laser welding are treated and analyzed to study the effect of changing the laser parameters. 1. Introduction
Real weld seam for copper/steel metals and the extracted keyhole and weld pool geometry for different shift distances from the initial joint plan. (a) −200 μm, (b) −100 μm, (c) 0 μm, (d) +100 μm, (e) +200 μm, (f) +300 μm, (g) +400 μm, and (h) +500 μm, where the negative shifts indicate a shift towards the copper side. 6. Conclusion For 2 m/min, 2.5 m/min (left), and 3 m/min (right), where f s and r s are the front and rear keyhole walls for steel, respectively. The copper front keyhole wall is f c and the copper rear keyhole wall is r c. 5.3. Effect of Laser Shift Esfahani, N.M.R.; Coupland, J.; Marimuthu, S. Numerical simulation of alloy composition in dissimilar laser welding. J. Mater. Process. Technol. 2015, 224, 135–142. [ Google Scholar] [ CrossRef][ Green Version]
Also, laser beam energy absorption and optimization of the laser welding method is the subject of many previous studies [ 6– 8], particularly in the case of dissimilar welding [ 9, 10]. Assuncao et al. studied the behavior of different metals under laser welding in the transition from conduction to keyhole modes [ 6]. Their experiments showed that the thermal properties (thermal conductivity, melting and vaporization temperatures, and specific heat) of the materials have the most important role in the transition between laser welding modes. Sibillano et al. developed a real-time monitoring technique based on the analysis of the plasma plume optical spectra generated during laser welding to determine the laser welding mode [ 11]. Figure 12 shows that the keyhole area, length, and width match parallel to each other and that all three increase from 1 to 4 kW within laser speed ( V = 2 m/min) which leads to increase of all keyhole dimensions, with increasing laser power to reach a saturated region at 5 kW. This may be because of the increases of keyhole opening (M.A) which leads to more laser radiation loss. High-quality dissimilar welding has many applications in power generation, and in the chemical, petrochemical, nuclear, and electronics industries for the purposes of tailoring component properties or weight reduction. More recently, laser-welding technologies have been successfully used to manufacture hybrid microsystems consisting of different materials. The welding of dissimilar metals is determined by their crystal structure and compositional solubility in their liquid and solid states. Diffusion in the weld pool often results in the formation of intermetallic phases. When no filler materials are used, the formation of intermetallic compounds is dependent on the interaction of the joining materials and the welding parameters [ 1– 3].
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