powerful tools of the digital age can accelerate the pace of solution and help in producing reliable and betterengineered welds. Sulfur Strikes Back When each half of the joint contains steels with significantly different concentrations of sulfur, a totally unexpected result is observed. Since the arc is positioned just above the original joint of the two plates, it is expected that both plates melt equally. Instead, melting occurs mainly in the low-sulfur plate (Ref. 14) — Fig. 11. The point of maximum penetration, B, is laterally shifted from the location of the original joint, A. The figure shows the weld bead has clearly shifted toward the plate with lower sulfur content. The extent of shift depended on the difference between the sulfur concentrations of the two plates and the heat input per unit length (Refs. 14, 15). Furthermore, the arc was asymmetric with a flare toward the low sulfur side (Ref. 15). To examine the role of arc flaring and the Marangoni convection, experiments were also done with a laser beam to avoid the effect of arc flaring (Ref. 16). Pronounced centerline shift and selective melting of the low-sulfur steel were still observed when a laser beam was placed directly above the original joint interface. Numerical modeling established that Marangoni convection was an important factor in transporting metal from high- to low-sulfur steel, which caused selective melting of the low-sulfur plate (Ref. 14). A pronounced rotational asymmetry (Ref. 16) of the weld bead during laser welding of steels with dissimilar sulfur concentrations was also observed. A mechanistic understanding of the rotational asymmetry still remains to be developed (Ref. 17). So, the enduring mystery of the surface-active elements still persists in a different form. Welding Engineering as a Career The welding mystery described here shows the diversity of scientific subfields within welding engineering. Many of today’s welding engineers have academic degrees in metallurgy and materials, mechanical, electrical, and several other branches of engineering. But a degree is just the beginning. From heat transfer to robotics, computers, control theory, corrosion, materials performance, and properties, there are many technical areas of opportunity for lifelong on-the-job learning. Highly sought after in the automotive, aerospace, construction, energy, shipbuilding, electronics, and appliance industries, welding engineers perform many important tasks. Welding process selection, quality control, code compliance, and design of hardware and software are just a few examples of the crucial tasks for welding engineers in diverse activities ranging from underwater construction to numerous manufacturing processes to building a spaceship. Some welding engineers work in research and development in universities, national labs, and industrial labs to solve problems and advance the knowledge base that supports the practice of welding. After four years of engineering college, you will be among a highly select group of people, much smaller than 1% of the population, with technical skills that are essential in today’s world. If you select the fascinating field of welding engineering as a career, you will have an awesome opportunity to assimilate new contemporary technologies into welding and improve our world in numerous ways. Better welding can build more reliable machinery for better agriculture, housing, energy, clean water, transportation, health care, and practically all equipment that support our standard of living. I hope you will consider the exciting field of welding engineering as a career. Epilogue and Lessons Synthesis of the knowledge base of a mature and important field such as welding with the emerging awesome digital data processing capabilities has helped in the production of better welds and made the world a better place. Apart from more rigorous analysis and solution of complex problems, the synthesis of welding and computational capabilities has also incubated a transformative new technology. Additive manufacturing, which has been hailed as the future of manufacturing, evolved from this merger. It starts with a digital picture of a part in a computer and builds it by adding liquid metal, layer by layer. Machines that use an electron beam welding gun and deposit 7 to 20 lb of metal per hour to make large parts are already available (Ref. 18). This disruptive additive manufacturing process is an example of welding’s evolution in the digital age and proof that better welding can build a better world for all. References 1. Welding the world’s highest walkway. 2006. Welding Journal 85(10): 40, 41. 2. DebRoy, T., and David, S. A. 1992. Physical processes in fusion welding. Science 257: 497–502. 3. http://video.mit.edu/watch/themarangoni effect-how-to-make-a-soap-propelled boat-13540/ Snapshots from a video downloaded on 30 June 2014. 4. DebRoy, T. 1995. Role of interfacial phenomena in numerical analysis of weldability. Mathematical Modelling of Weld Phenomena II. London, UK: The Institute of Materials, pp. 3–21. 5. Kou, S., and Sun, D. K. 1985. Fluid flow and weld penetration in stationary arc welds. Metallurgical Transactions A – Physical Metallurgy and Materials Science 16(2): 203–213. 6. Linnert, G. E. 1967. Weldability of austenitic stainless steel as affected by residual elements. Effects of Residual Elements on Properties of Austenitic Stainless APRIL 2015 / WELDING JOURNAL 63 Fig. 11 — Weld geometry when welding two stainless steel plates with different sulfur contents. The white vertical line passing through point “A” indicates the original interface of the two plates. The location of maximum weld penetration is indicated by point C, and AB indicates the shift of the maximum penetration from the original joint of the two plates (Ref. 14). WJ
Welding Journal | April 2015
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