AbstrAct Purpose: A statistical model that explains the interaction between cross-section dimensions of a GTA remelted spot area and remelting parameters is presented. It will be utilized in the repair of an investment casting made of nickel-based superalloys. Design/methodology/approach: An experimental design of response surface was used to elaborate the model of GTA remelting. Results of experiments were verified experimentally. Findings: The dimensions and volume of a remelted area are a linear function of the GTA welding process parameters. It is possible to remelt small surface defects and keep a smooth surface. Research limitations/implications: Research results are limited to the tested range of parameters and base material properties. Changes in thermal conductivity can strongly influence the presented results. Crack sensitivity of material can restrict the range of parameters. Practical implications: Results of the research will help in the repair of surface spot defects of nickel-based superalloys. The proposed method of repair can help to minimize the number of rejected parts.
Abstract The results of investigations on autogenous laser welding of 5.0-mm-thick high-strength steel Domex 960 are presented in this article. The experimental plates delivered directly from the steel manufacturer were used for butt joint welding. The disk laser with maximum output power (maximum capacity of the laser generator) of 3.3 kW, emitting at 1.03 μm, and with the beam spot diameter of 200 μm was used for the trails of welding. Initially, the bead-on-plate welding tests were carried out, and then the test butt joints were laser welded. The influences of basic technological welding parameters, especially the energy input of laser welding on the shape of the fusion zone, the microstructure of weld metal and heat affected zone, and the impact toughness were analyzed. Laser welding trials were conducted in a wide range of energy input from 100 to 400 J/mm. Despite the low energy input of the laser welding process and also the short cooling times t8/5, tendency to cold crack was found neither in the weld metal nor in the heat affected zone. The carbon equivalent (CET), determined by the chemical analysis of the experimental melt, was just 0.341, indicating moderate tendency to increase hardness after welding because of martensitic transformation. It was found that the energy input has a clear influence on the microstructure and the impact toughness of the weld metal. The weld metal of the test butt joint welded at the energy input of 198 J/mm showed the average impact toughness at approximately 80 % of the base metal, whereas the weld metal of the test butt joint welded at a lower energy input of 132 J/mm showed the average impact toughness at the level of just 60 % of the base metal of Domex 960 steel.
Autogenous laser welding of 0.8 mm thick butt joints of car body electro-galvanized steel sheet DC04 was investigated. The Yb:YAG disk laser TruDisk 3302 with the beam spot diameter of 200 μm was used. The effect of laser welding parameters and technological conditions on weld shape, penetration depth, process stability, microstructure and mechanical performance was determined. It was found that the laser beam spot focused on the top surface of a butt joint tends to pass through the gap, especially in the low range of heat input and high welding speed. All test welds were welded at a keyhole mode, and the weld metal was free of porosity. Thus, the keyhole laser welding of zinc coated steel sheets in butt configuration provides excellent conditions to escape for zinc vapours, with no risk of porosity. Microstructure, microhardness and mechanical performance of the butt joints depend on laser welding conditions thus cooling rate and cooling times. The shortest cooling time t8/5 was calculated for 0.29 s.
