WELDING RESEARCH Fig. 8 — Singlelayer square cladding No. 13 made by GMAWCSC. A — Pattern of motion of workpiece relative to welding gun; B — top view; C — transverse crosssection; D, E, F — optical micrographs. Dilution = 2.28%. was likely caused by surface oxidation after welding as the current and voltage waveforms indicated the welding process was stable. The results of the single-layer square cladding indicate that, out of the three motion patterns investigated, the long serpentine pattern shown in Fig. 10A seems to yield the best results, that is, uniform cladding thickness and moderate dilution of 4.6%. Thus, a four-layer cladding was made with the serpentine pattern, that is, cladding No. 9. As shown in Fig. 11, the cladding is essentially uniform in thickness and in the distribution of WC particles. To help reduce overheating, the travel speed was gradually increased from 16.7 mm/s at the beginning of the first layer to 26.7 mm/s at the end of the first layer. It was further increased gradually to 33.3 mm/s before the end of the second layer. To help distribute heat more uniformly, the pattern was rotated 90 deg after each layer. It was noticed that the tip of the Ni sheath was deformed into a bell shape, as shown in Fig. 12. The foam-like material visible outside the bell is likely to be a flux or binder added during the fabrication of the welding wire. As compared to GMAW-CSC with a solid wire (Refs. 8, 9), the level of spatter shown in Figs. 5 and 12 is much higher even though GMAW-CSC is known to be very effective in eliminating spatter. When the tip of a solid wire forms a liquid bridge with the weld pool, the controller can clearly sense a voltage of nearly zero — Fig. 3C. However, with the tip of a tubular wire like that shown in Fig. 12, the liquid bridge may not be as easy to form and control. Consequently, more spatter can be expected with a tubular wire. Some DECEMBER 2016 / WELDING JOURNAL 457-s A C B D E F Fig. 9 — Singlelayer square cladding No. 14 made by GMAWCSC. A — Pattern of motion of workpiece relative to welding gun; B — top view; C— transverse cross section; D, E, F — optical micrographs. Dilution = 6.01%. A C B D E F
Welding Journal | December 2016
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