Tetsuo Suga

Laser brazing of a dissimilar joint of austenitic stainless steel and pure copper

In many industries, there are applications that require the joining of stainless steel and copper components; therefore, the welding of dissimilar stainless steel/copper joints is a common process. For this investigation, the optimal brazing conditions and suitable filler metals for laser brazing of stainless steel/copper lap joints were studied. Tensile shear force increases with increases in the laser spot diameter or in the laser irradiation angle, which is associated with increased bonding width; however, as bonding width approaches 2 mm, tensile shear force reaches a saturated value due to fracturing at the HAZ of the Cu base plate. In order to obtain joints with high tensile shear strength, laser brazing was optimized by using Cu–Si-based filler metal under the following conditions: laser power, 4 kW; spot diameter, 3 mm; laser irradiation angle, 80°; irradiation position shift, 0.6 mm; brazing speed, 0.30 m/min; and filler metal feed speed, 0.30 min. Concerning filler metals, it was found that the Ni–Cu type showed relatively large tensile shear force even at high welding speeds in comparison with those of the Cu–Si, Cu, Cu–Ni, Ni–Cu and Ni types, respectively.

A Semi-Analytical Nonlinear Regression Approach for Weld Profile Prediction: A Case of Alternating Current Square Waveform Submerged Arc Welding of Heat Resistant Steel

The complexity in weld profile caused by abrupt change in polarity in square waveform welding is investigated through the development of a model capable to accurately predict weld profile. A semi-analytical model is conceived wherein characteristic attributes of a composite parabolic-elliptic function, which represent the weld profile, are obtained through nonlinear regression (NLR). The proposed model is demonstrated for its efficacy in the prediction of weld profile over a wide range of welding parameters, vis-a-vis, welding current, frequency, electrode negative (EN) ratio, and welding velocity. The investigation suggests that the center and outer cores of welding arc remains more active during positive and negative polarity, respectively, that leads to distinct macroscopic zones in weld cross section and thus, necessitates a composite profile for representation of weld profile. The intersection of the zones forms a metallurgical notch which the investigation offers a method to estimate and thus control. Unlike the convention continuous arc welding, the waveform arc welding caters welding at higher velocity without compromising the weld penetration and almost abolishing the metallurgical notch as well.

Effects of oxide layer on adhesion and durability of titanium and transparent polyamide joint by laser joining

A joint of titanium and transparent polyamide with desirable strength was achieved by laser joining. A maximum load capacity of 3400 N was obtained from a lap joining area of 25 × 25 mm2 at a laser power of 350 W and a travel speed of 4 mm/s. The effects of surface oxide layers with different thicknesses and stability were investigated. A joint with a thick oxide layer exhibited lower load capacity due to excessive thermal degradation of polyamide caused by heat buildup inside the thick thermal insulating oxide layer. With UV exposure, more pronounced reduction in joint strength was observed in the joint with the thick oxide layer. Cracking of the oxide layers was responsible for lower strength and expected to be a result of stress from polyamide contraction combining with internal stress of the oxide layer.A joint of titanium and transparent polyamide with desirable strength was achieved by laser joining. A maximum load capacity of 3400 N was obtained from a lap joining area of 25 × 25 mm2 at a laser power of 350 W and a travel speed of 4 mm/s. The effects of surface oxide layers with different thicknesses and stability were investigated. A joint with a thick oxide layer exhibited lower load capacity due to excessive thermal degradation of polyamide caused by heat buildup inside the thick thermal insulating oxide layer. With UV exposure, more pronounced reduction in joint strength was observed in the joint with the thick oxide layer. Cracking of the oxide layers was responsible for lower strength and expected to be a result of stress from polyamide contraction combining with internal stress of the oxide layer.

An estimation of factors influencing residual stress characteristics of fillet welded lap joints

Abstract The residual stress behaviours in fillet welded lap joints of sheet metal have been researched in a systematic testing procedure with varied steel types, steel thicknesses and welding wires having different transformation points. Consequently, under the simulated fabrication welding conditions (with a constant amount of deposited metal), the transverse residual stress at the weld toe, which is deemed critical in fatigue strength, has been found almost invariable to a change in steel type and thickness, but it has been clarified to become compressive to a greater extent as the wire’s transformation point is lower. Moreover, as for the residual stress inside the weld metal, the compressive residual stress area has been found to expand as the welding wire’s transformation point reduces, from the results of the thermo-elastic-plastic analysis.

Qualitative and quantitative analyses of arc characteristics in SMAW

This study was conducted to develop a quantitative evaluation system for arc characteristics such as arc stability and welding spatter generation related to shielded metal arc welding (SMAW) without human sensory evaluation. Factors that correspond to sensory evaluations by welders were investigated based on image processing. For the quantitative evaluation of arc stability, results show that the root mean square and the standard deviation of the arc center fluctuation, respectively, correspond to welders’ sensory evaluation at AC and DC discharges. For welding spatter generation, a method of counting white pixels in a binarized image evaluates the number and size of welding spatters which closely coincide with welders’ sensory evaluations.

Improvement of the deformation capacity of the column-to-beam joint by the reinforce welding method around the scallop bottom

Abstract Improvement of deformation capacity for a column-to-beam joint is an important theme for improving the earthquake-resistance performance of building structures. One of the causes of decreasing deformation capacity is the existence of stress concentration against the beam flange by the scallop (access hole). The non-scallop method is generally recommended to improve this problem, but it has a large disadvantage in that it is not able to apply to the on-site joint process. The reinforce welding method around the scallop bottom has been developed to be able to apply to an on-site joint and obtain better performance than the non-scallop method. The improved mechanism is a combination of: (1) decreasing the stress concentration; (2) increasing effective thickness; and (3) increasing total length of the breaking line. The deformation capacity by the reinforce welding method around the scallop bottom is a maximum 3.2 times that for the conventional scallop method in the reverse repeating bend test using an actual structure with a beam flange of 19 mm thickness and 490 N mm−2 class steel. This improving effect is better than the non-scallop method.