Jeong Han Kim

Total and Soluble Metal Contents in Flux-Cored Arc Welding Fumes

The chemical composition and solubility of metals in welding fumes is thought to be related to the welder health but is not well characterized. We quantified and compared the total (insoluble + soluble) and soluble metal contents in fumes from flux-cored arc welding using non-stainless steel (FCAW/NSS) and stainless steel (FCAW/SS) wire. Welding was performed in an American Welding Society standard fume collection chamber. The total content of 13 analyzed metals was significantly higher in FCAW/NSS fumes than in FCAW/SS fumes (51.6 ± 5.7 vs. 40.2 ± 5.2%, p < 0.001). Soluble metal content was significantly higher in FCAW/SS fumes than in FCAW/NSS fumes (15.5 ± 5.8 vs. 6.49 ± 2.4%, p < 0.001) due to the presence of potassium and sodium. Different proportions of each element were observed between welding types. Iron, magnesium, and aluminum were significantly higher in FCAW/NSS fumes, whereas chromium, nickel, and potassium were more common in FCAW/SS fumes. The metal composition of FCAW fumes was more similar to that of shielded metal arc welding fumes than that of gas metal arc welding fumes. It seems unnecessary to measure soluble iron, nickel, aluminum, and barium to compare with their soluble ACGIH-TLVs at the FCAW welding process. But chromium should be specified in terms of its valance and solubility.

Welding Phenomena in Hybrid Laser-Rotating Arc Welding Process

Hybrid laser-rotating arc welding (HLRAW) process was designed by combining the laser beam welding (LBW) process with the rotating gas metal arc welding (RGMAW) process. In this study, comparing with conventional HLAW, weld bead characteristics as a function of the various process parameters were evaluated for HLRAW. Moreover, welding phenomena were analyzed by high speed monitoring with laser illumination. The arc rotation enhances the weld pool motion, therefore it reduces the undercut formation which is one of most critical weld defects in the conventional laser-arc hybrid welding.

Optimization of Laser-Arc Interspacing Distance during CO2 Laser-GMA Hybrid Welding by Using High-Speed Imaging

Laser welding has not easily been adopted in shipbuilding industry because of its poor gap bridging ability. Recently, laser-GMA hybrid welding process showed possibility to overcome the tight gap tolerance with improved productivity. The laser-arc hybrid welding process is inherently complex because it has three kinds of process parameters: arc welding, laser welding and hybrid welding parameters. In this study, welding phenomena were investigated to optimize the hybrid process parameter; interspacing distance between laser and arc. The bead surface and cross-sectional shapes were evaluated, and weld pool shape and droplet transfer were monitored by high speed camera to clarify welding phenomena.

Modeling of Weld Beads for Laser-GMA Hybrid Welding

For laser-GMA hybrid welds, the relationship between the process parameters and bead shapes was investigated by using the experimental design and the non-linear regression. The weld beads were fitted by two quadratic functions. By the statistical analysis, the primary bead was mainly affected by GMA welding parameters and the root bead was mainly by laser welding parameters. The root bead shaped deeper penetration and shallower width, as the laser power increased for the constant arc power. High laser power resulted in the martensite phase, therefore exhibiting the sudden increase of hardness as approached to the fusion line of the root bead.

Precise Quantitative Evaluation of Nano-Ordered Intermetallic Compounds in Sn-3.0Ag-0.5Cu Lead-Free Solder Bump by Using TEM

The growth behaviour of the intermetallic compounds (IMCs) in Pb-free solder bump is investigated. The Pb-free micro-bump, Sn-50%Bi, was fabricated by binary electroplating for flip-chip bond. The diameter of the bump is about 506m and the height is about 60 6m. In order to increase the reliability of the bonding, it is necessary to protect the growth of the IMCs in interface between Cu pad and the solder bump. For control of IMCs growth, SiC particles were distributed in the micro-solder bump during electroplating. The thickness of the IMCs in the interface was estimated by FE-SEM, EDS, XRF and TEM. From the results, The IMCs were found as Cu6Sn5 and Cu3Sn. The thickness of the IMCs decreases with increase the amount of SiC particles until 4 g/cm2. The one candidate of the reasons is that the SiC particles could decrease the area which be reacted between the solder and Cu layer. And another candidate is that the particle can make to difficult inter-diffusion within the interface.