In manufacturing of the steel bridge, fillet welded T-joint is widely used and angular distortion is often generated. So, reduction or control of angular distortion without additional processes to welding is strongly demanded because it takes great time and effort to correct the angular distortion. In this study, the effectiveness of welding with trailing reverse-side flame line heating for preventing angular distortion was investigated through the welding experiment and numerical simulation in submerged arc welding of fillet T-joint with three different thick flange plate. First, the heat source models for numerical analysis of both submerged arc welding and flame line heating were constructed based on the comparison with the measured temperature histories and angular distortion. And then, these heat source models were used in combination with various kinds of distance between two heat sources to make clear the appropriate distance condition for smallest angular distortion was 150 mm, and it doesn't depend on thickness of flange plate. It was also confirmed that the experimental angular distortions were in good agreement with those calculated. With a focus on the influence of thickness of flange plate, the reduction of angular distortion by welding with trailing reverse-side flame line heating becomes smaller with increasing thickness of flange plate. However, angular distortion could be adequately prevented under the appropriate flame line heating condition in either thickness of flange plate because the welding-induced angular distortion also becomes smaller with increasing thickness of flange plate. Thus, it was concluded that welding with trailing reverse-side flame line heating could be useful for preventing angular distortion of fillet T-joint, which is a component of steel bridge, enough not to correct it after welding.

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Lap joints of an upper Al alloy (1.0-mm-thick A5052) and lower Zn-coated steel (1.2-mm-thick GA steel) were welded by a novel spot welding process for dissimilar metal lap joints using a new tool with the tip made of spherical ceramics, i.e., "Friction Anchor Welding." As a result, the Al atoms in the Al alloy diffused into the Zn-Fe layer on the GA steel, and the layer transformed into an altered layer which was mainly composed of Al-Fe intermetallic compounds. Because of this altered layer, a steel projection could not extend straight when the rotating tool was plunged through the Al alloy into the GA steel. Consequently, the height of the steel projection was small and exhibited a rugged shape while the steel projection was formed in the Al alloy. Furthermore, large amounts of Al-Fe intermetallic compounds existed near the steel projection. Additionally, Zn atoms in the Zn-Fe layer on the GA steel penetrated into the Al alloy and cracks occurred due to the Al-Zn eutectic melt. Thus, the tensile shear strength reached only about 2.7 kN/point, compared to that of the weld between A5052 and SPCC, which reached about 3.6 kN/point.

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Laser peening can introduce compressive residual stress to the surface and, therefore, is effective in enhancing the fatigue strength. This study targets 780 MPa grade high-strength steel (HT780) in order to clarify whether laser peening generates compressive residual stress on the surface of HT780, and whether such stress would account for prolonged fatigue life in the welded zones of HT780. As a result, large and deep compressive residual stress was generated on the base metal surface and at the boxing toe of HT780 under the peening conditions employed for 490 MPa grade steel. The smaller the applied stress range, the greater was the improvement of the fatigue life of the high-strength steel boxing toe by laser peening.

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In this study, the effect of welding conditions on the opening and closing behavior of root gap during butt-welding was systematically investigated through the use of thermal elastic-plastic finite element analysis. The foci of welding conditions were weld heat input per unit weld length and plate thickness, welding speed, plate width and thickness ratio of weld metal to base metal. And then, parameters of dimensionless transverse temperature distribution to width and mechanical melting length behind weld heat source were derived respectively from weld thermal conduction theory for evaluating the root gap behavior during butt-welding. As the results, it has been clarified that the root gap behavior during butt-welding is dependent on the proposed two parameters in both single layer butt-welding and first layer butt-welding of thick plates. Also, the closing behavior of root gap is conceivable in the abstract when both of parameters becomes sufficiently-small, but in reality difficult to occur in single layer butt-welding because elements of weld metal remains unmelted. Meanwhile, the closing behavior of root gap becomes that much easier to occur in first layer butt-welding of thick plates because both parameters are possible to be sufficiently-small. Thus, more detailed understanding of opening and closing behavior during butt-welding, which can explain the cause of the differences in root gap behavior in previous studies, has been obtained.

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Gas metal arc welding (GMAW) is an indispensable technology in various industrial fields as a highly productive process. It uses consumable wire electrodes, and involves metal transfer phenomena. In the metal transfer phenomena, a molten metal detaches from a wire tip to the base metal. Properties of the metal transfer such as droplet size and frequency of transfer is closely related to the stability and quality of overall process. Therefore, appropriate control of the metal transfer is highly desirable. However, there are many transfer modes, and the process is not yet fully understood due to its complexity, so it is difficult to control the metal transfer completely. In this study, in order to make clear about the phenomena of MIG welding process, a unified numerical model is constructed. This model contains both of the arc plasma, metal transfer and weld pool phenomena. In case of arc current is under 230 A, globular transfer is appeared. In case of using higher current, the transfer mode becomes spray transfer. The average temperature of the droplets are depends on the transfer mode. When the transfer mode is globular transfer, the droplet temperature is about 2700 K, and in case of spray transfer, the droplet temperature is about 2900 K.

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Recently, weight reduction and improvement of crashworthiness of auto bodies have been important issues. At the same time, stiffness of auto bodies is also needed to ensure a smooth ride. Using hollow parts, such as bended pipes and hydroformed parts, is one of the solutions to the demand for both rigidity and light weight.
To weld hollow parts and sheet panels together, welding methods which allow us to access from one side are required. Single side resistance spot welding (single side RSW) process is one of those, and has recently been attracting attention.
However, because of the long current path and small electrode force, it is difficult to concentrate the electric current in the welding spot compared with conventional direct resistance spot welding (direct RSW). Furthermore, in multipoint welding, shunt current will occur easily, and the nugget formation will be inhibited.
To obtain a guideline for making sound nuggets, influencing factors for shunt current were investigated. And a numerical study was carried out to discuss the difference between direct RSW and single side RSW.
According to the CAE analysis, the shunt current of single-side RSW will be higher rate than direct RSW. The rate of shunt current was influenced by the electrical resistance of its current path. For this reason, with shorter distance between welding points, or with lower electrical resistance of material, it is difficult to get large nuggets. By enhancing the electrical resistance of shunt current path, shunt current could be reduced and a larger nugget would be obtained.

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In order to realize both of low spattering and low heat input, controlled GMA short-circuiting transfer processes have been developed and practically used in various fabricating sites: Controlled Bridge Transfer (CBT) method by current waveform control, Cold Metal Transfer (CMT) method by wire feeding control, etc. Actually higher performance of GMA welding processes have been provided by deeply understanding mechanism of short-circuiting transfer process. So, we developed three-dimensional numerical model of GMA short-circuiting transfer process including control of welding current and wire feeding speed.
It is shown that welding current control method can effectively adjust electromagnetic force for breakup time of liquid bridge in increasing deposition rate and wire feeding control method can effectively improve regularity of short-circuiting transfer process. Both advantages of increase in deposition rate and improvement in regularity of short-circuiting transfer process are provided by hybrid control method combining two control methods.

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