made at 21 V (120 J/mm), the bead was continuous but with large spatter. With GMAW-CSC, on the other hand, a smooth single bead with slight spatter could be made over the much wider range of 56.3 to 120 J/mm as shown in Fig. 5. Examples of the transverse crosssections of single-bead cladding made by conventional GMAW are shown in Fig. 6. Similar results are shown in Fig. 7 for cladding made by GMAW-CSC. In either case, the cladding is not very densely packed with large tungsten carbide particles. To increase the fraction of large tungsten carbide particles in the cladding, a tubular welding wire with a thin sheath and small crimp overlap can be used as pointed out by Mendez et al. (Ref. 1). The PolyTung NiBWC flux-cored wire of 1.6-mm outer diameter, which has a relatively thick sheath and large crimp overlap as can be seen in Fig. 2A, was selected for the present study mainly because of the intended comparison with the study of Vespa et al. (Ref. 3), in which the same wire was used. From the transverse cross section of the cladding, the extent it is diluted by the melted base metal can be determined. Table 4 summarizes the dilutions in the single-bead cladding. As shown in Fig. 6, with conventional GMAW, the dilution varies from 2.6% at 107 J/mm to 12% at 120 J/mm. With GMAW-CSC, as shown in Fig. 7, the dilution varies from 0.6% at 75 J/mm to 5.4% at 107 J/mm and 5.7% at 120 J/mm. Thus, the dilution varies less in GMAW-CSC than conventional GMAW. The dissolution of WC particles appears to increase with increasing heat input as can be seen by comparing, for instance, Fig. 6A with 6B. Square Cladding Made with 3D Printer Since the dilution increases less with increasing heat input in GMAWCSC than conventional GMAW, the former was used to deposit cladding over a square area (about 27 ¥ 27 mm). Three single-layer square claddings, made at the travel speed of 15 mm/s, are discussed below. The pattern of the welding gun/ steel relative motion was found to affect the thickness uniformity and overall dilution of the resultant cladding. Figure 8 shows a single-layer square cladding (No. 13) made with a square spiral pattern. The cladding becomes thinner and thinner as its center is approached. Based on the enlarged transverse cross section of the cladding (not shown), the overall dilution is 2.28%. The micrographs taken at three different locations in the transverse cross section show WC particles are fewer and smaller near the center of the cladding. Figure 9 shows a single-layer square cladding (No. 14) made with a short serpentine motion pattern that covers the left one-third of the square cladding, reverses its direction to cover the middle one-third, and then reverses its direction again to cover the right one-third. As compared to cladding No. 13 in Fig. 8, its thickness is more uniform but the dilution was higher at 6.01%. Figure 10 shows a single-layer square cladding (No. 11) made with a longer serpentine motion pattern that covers the entire square cladding without reversing its direction like in cladding No. 14 — Fig. 9. The overall dilution is at 4.6%. As compared to cladding No. 13, No. 11 appears to be more uniform in thickness and have a more uniform distribution of tungsten carbide particles. It is likely that, with a closed-loop control strategy, the pool size can be better controlled to reduce variations in the uniformity and thickness of the cladding and its dilution by the substrate. However, the same pool size on the surface may not necessarily mean the same pool depth, which affects the level of dilution. By the way, some soot is visible in the middle of the top surface of cladding No. 11 — Fig. 10B. The soot WELDING RESEARCH 456-s WELDING JOURNAL / DECEMBER 2016, VOL. 95 Fig. 7 — Transverse cross sections of singlebead cladding deposited by GMAWCSC. A — Sample No. 47; B — sample No. 50; C — sample No. 51. The average of three dilutions at three different locations along each sample is shown. Fig. 6 — Transverse cross sections of singlebead cladding deposited by conventional GMAW. A — Sample No. 53; B — sample No. 55. The average of three dilutions at three different locations along each sample is shown. A B A B C
Welding Journal | December 2016
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