The task of 1.2GPa ultra-high strength steel sheet in short time's high current spot welding has been clarified. High current and short time spot welding system and high frequency power supply has been developed. In order to prevent spatter, new double pulse welding method in which primary energization, cooling and secondary energization has been proposed. By using this novel welding method, nugget diameter and tensile shear strength satisfied the target and spatter did not occur. New method of 1.2GPa ultra-high strength steel sheet in short time and high current spot welding has been established.

抄録全体を表示

A6063S-T5 is a material that is frequently used in construction materials, and in many cases, the surface of the material is coated with a composite coated films for durability and design purposes．However, if the composite coated films is interfered with as a foreign substance in the joint while the material is still coated, it may easily have an adverse effect on the joint strength． Therefore, it is usually necessary to remove the coated films before joining or to coat the part after joining．In this paper, the effect of composite coated films on the joining process of friction stir spot welding is clarified, and an efficient joining method for materials with composite coated films is proposed．It was shown that the effect of the composite coated films could be removed by using a triangular prism-shaped tool, and that the bonding area and strength could be controlled．

抄録全体を表示

The self fusion solidification bonding process occurs the isothermal fusion and the isothermal solidification by the reaction diffusion between the base metal and the dissimilar insert metal. The bonding process is carried out below the melting points of the base metal. 60/40 brass was used as the insert metal for the self fusion solidification bonding of aluminum in this study. The periodic motion under the load control was applied to the bonding interface at the bonding temperature. The joint by 60/40 brass insert metal was obtained at the bonding temperature of 893 K. The phases by the isothermal fusion and solidification in the bond were evaluated by the chemical composition of the phase and the ternary phase equilibrium diagram.

抄録全体を表示

Laser cutting provides more precise and higher quality cuts than other thermal cutting processes, and is adaptable to automation requirements. On the other hand, laser cutting with oxygen assist gas of thick steel plates is a complex process in which various factors affect laser cutting quality compared to the thin plates. When laser cutting of the plate with mill scale is performed, the mill scale on the surface of plate generally plays a role in supporting stable laser cutting, although self-burning may also occur due to peeling of the mill scale. Therefore, this paper focuses on the mill scale and investigates the effects of the adhesion, thickness, and surface roughness of the mill scale on the laser cutting quality. As a result, it was found that the laser cutting quality is higher when the adhesion of the mill scale is high, the thickness of the mill scale is between 20 μm and 40 μm, and the surface roughness is small.

抄録全体を表示

High-spatial resolution synchrotron X-ray imaging was combined with X-ray diffraction for a detailed investigation of FA mode solidification in Fe-Mn-Si (FMS) alloys during tungsten inert gas (TIG) spot welding. The solidification sequence of X-ray radiographs and X-ray diffraction patterns clearly revealed that the formation of equiaxed γ-Fe dendrite occurred in front of the growing columnar δ-Fe dendrites without any observable phases in the interdendritic regions. The solidification behavior of the FMS alloy was different from the conventional FA mode for the type 304 stainless steel, in which the cellular γ-Fe was independently formed in the interdendritic regions of the primary δ-Fe. During the columnar dendrite growth of δ-Fe for the FMS alloy, the ratio of the temperature gradient to the growth velocity was remarkably decreased and solute enrichment in the remaining liquid occurred, which likely led to the formation of equiaxed γ-Fe dendrite.

抄録全体を表示

Carbon dioxide gas-shielded arc welding, which is widely used in industry, generates a large amount of spatter in the medium and high current range. To solve this problem, we developed a new welding process with low spatter and low gas cost that we call “Pulsed Gas MAG” (PGMAG) welding. In PGMAG welding, the metal transfer is controlled by the suitable addition of Ar gas, but the effect of the welding current has not been clarified. Therefore, we investigated metal transfer in the 235- to 325-A range and found that the pulse frequency of Ar gas must be adjusted between 35 and 65 Hz to match the welding current (i.e., wire feed rate) to control metal transfer. A wide area where metal transfer is controllable is obtained by adjusting the Ar addition frequency for a current of 235-325 A. It was considered that there is a suitable volume for the droplet to be released and that the growth speed depends on the wire feed rate.

抄録全体を表示

The thermal shrinkage technique with previously proposed input parameter values for single-pass welding was applied to a multi-layer butt-welded joint with four layers and six welding passes to validate whether these input parameters are applicable to multi-layer welded joints. The out-of-plate displacement distributions of the multi-layer welded joint obtained using the thermal shrinkage technique were in good agreement with those obtained in a thermal elastic-plastic analysis and an experiment. The angular distortion and transverse shrinkage at the center of the welding line obtained using the thermal shrinkage technique well agreed with the experimental and thermal elastic-plastic analysis results for each welding pass. Furthermore, the calculation time for the thermal shrinkage technique was 1/6 of that for the thermal elastic-plastic analysis. Our results demonstrate that the thermal shrinkage technique with the previously proposed input parameter values could be applicable to multi-layer welded joints.

抄録全体を表示

Thermal elastic plastic (TEP) finite element analysis (FEA) is widely used to analyze welding mechanical phenomena such as welding deformation and residual stress. One of the problems of welding mechanical analysis using finite element method (FEM) is that it requires a lot of time for preprocessing such as modeling and meshing. In this study, the explicit master-slave elimination with multipoint constraints (MPCs) was introduced to the Idealized explicit FEM (IEFEM) for efficient FE modeling and welding mechanical analysis of large-scale complex structures. The proposed method was applied to T-joint welds to verify its accuracy when using the explicit master-slave elimination, and the effects of the ratio of master and slave element sizes on results of the heat conduction (HC) analysis and TEP analysis were investigated. As a result, it was confirmed that the welding mechanical analysis using the proposed method is in good agreement with the analysis results using the ordinary node-shared model. It was also confirmed that the analysis results did not agree when the element size of the slave was large compared to the element size of the master. Finally, the proposed method was also applied to the analysis of a welded structure including multi-layer welds and fillet welds for steel column-beam connections. It was confirmed that the proposed method was useful in performing fast calculations with highly efficient FE modeling for large-scale steel column-beam joint welds.

抄録全体を表示

Trans-Varestraint test is basically used for hot cracking susceptibility of materials. In the Trans-Varestrain test, bending deformation is applied to the specimen during welding to produce cracking. From the shape and size of cracks, the hot cracking susceptibility indices such as Brittle temperature range (BTR) and critical strain are obtained. The nominal strain generated by the bending can be calculated from the specimen thickness and the radius of the bending block. However, it has been reported that in this test, the estimated nominal strain and the actual strain acting on the weld metal differ significantly due to localized heat. In this study, hot cracking analysis using Idealized explicit FEM, which can compute large-scale thermal elastic-plastic analysis with smaller computing time and memory, is applied to the Trans-Varestraint test. The effects of heat input and test conditions on the mechanical behavior of the welded part during the Trans-Varestraint test are investigated. The results indicate that the strain acting on the welded part during the Trans-Varestraint test is larger than the nominal strain. In addition, it is found that the welding speed has a significant effect on the amount of strain acting on the molten part. It is suggested that these were caused by local melting of the specimens, resulting in a decrease in strength. In addition, bending speeds and welding speeds affect the amount of strain produced by bending and the size of the area in which the strain occurs. In other words, they affect the size of the region and the amount of strain generated in the BTR and have a significant effect on the maximum crack length obtained in the Trans-Varestraint test.

抄録全体を表示

To have a better understanding of the wetting behavior of Sn-based solders on the aluminum substrate, s series of comparative experiments with Sn, Sn-3.5Ag (SA), and Sn-3.0Ag-0.5Cu (SAC305) were performed by direct heating on the hot plate with normal flux in the air. The wetting morphology was measured by the cross-section images using a scanning electron microscope (SEM), and the intermetallic compounds, at the interface after heating, were identified by the phase diagram calculated by the FactSage, and confirmed by the energy dispersive X-ray spectroscopy (EDS) equipped with the SEM. The results showed that the SA soldered aluminum samples had better wetting behavior after considering the non-reactive wetting stage and the interfacial reactions during the reactive wetting stage.

抄録全体を表示

Complex thin-plate structures such as ships and bridges are welded together with numerous thin plates and stiffeners. Thermal elastic-plastic analysis based on the finite element method is a fundamental tool for predicting welding deformations and residual stresses in large steel structures. The shell-solid coupling method can improve the analysis scale and efficiency compared to the solid element method. This study aims to introduce the shell-solid coupling analysis method into welding mechanical analyses to improve the efficiency of computation and modeling. The guideline for the use of the proposed method was also investigated. The proposed shell-solid coupled analysis was constructed based on a multipoint constraint technique which erases the degrees of freedom at the shell-solid interface. It was applied to the analysis of welding mechanics of the fundamental T-joint model to validate the accuracy of the proposed shell-solid coupling analysis. The proposed method was also applied to the welding deformation analysis of a panel structure model for a car-carrier ship. The results revealed that computing time of the proposed method was less than 30 percent of that of the conventional FEM and the proposed method has almost the same analysis accuracy as conventional techniques. The proposed method could achieve a more efficient analysis than the conventional method.

抄録全体を表示

To investigate the effect of load changing on creep fatigue life of pipe joints, a creep fatigue analysis was conducted by introducing evaluation method of the creep fatigue life developed by Arai et al. to Idealized Explicit FEM which can perform large scale nonlinear structural analysis with realistic computing resources. First, an analysis for simulating experimental phenomena was performed and the predicted creep fatigue life was compared with the measured one to verify the analysis accuracy. As a result, it was confirmed that the predicted creep fatigue life by the constructed method was in good agreement with the actual creep fatigue life. In addition, the predicted fracture locations by the analysis and the actual damage locations agreed each other. To confirm the effects of the bending and torsional moments, 203 different bending torsional conditions were assumed and their analyses were performed. It is found that the creep fatigue life can be shorter with the larger bending moment ratio.

抄録全体を表示

In pulse GMA(Gas Metal Arc) welding, it is important that welding conditions are changed due to root gap of the groove during welding to ensure quality. The visual sensor and deep learning are useful to estimate the gap. In this study, fundamental experiments were carried out and images of the molten pool are taken under various root gaps. The gap identification is carried out using Resnet50. The gap was identified under the groove welding with 8mm gap. The accuracy of the identification was 100%. Moreover, the gap identification was carried out under the groove welding with the variation gap from 4mm to 8mm. The good performance of the gap identification can be obtained. The validity of the deep learning in GMA welding was verified.

抄録全体を表示

Electron density distribution during an alternative current gas tungsten arc generated under Mars-like atmosphere in a vacuum chamber was measured to clarify arc characteristics in Mars-like atmosphere. The electron density distribution was measured by Abel inversion processing and infrared method for plasma diagnostic, in which electron density was obtained by the spectral radiance of the arc. Measured results showed that the electron density distribution during electrode negative period in Mars-like atmosphere was spreader than that on Earth. Moreover, its peak value was about 2.5×10²² m^－3, which was almost one order lower than the result on Earth.

抄録全体を表示

As one of techniques to improve a penetration depth in a gas tungsten arc welding, it has been proposed that carbon dioxide gas is applied as a shielding gas using a double shielding torch. Two types of gases can flow independently in the double shielding torch: inner gas and outer gas. The purpose of this study was clarification of the carbon dioxide behavior to establish a guideline for controlling oxygen contamination which affects the toughness of welded part formed by this welding process. As a result, it was revealed that carbon dioxide in the outer gas was transported to the vicinity of central axis of a tungsten electrode by the vortex generated near the electrode. Then, oxygen was produced by dissociation of carbon dioxide. It was suggested that the dissociated oxygen increased the oxygen concentration in the gas flowing on a base metal surface.

抄録全体を表示

Electroslag welding is a high heat input, high deposition rate and highly efficient welding process that has been applied to large structures. However, the principle of electroslag welding makes direct observation of molten area difficult because the welding region is surrounded by base metal or water-cooled copper devices, and the phenomenon is not completely understood at present. Although the temperature of the molten area after current interruption has been measured, the temperature distribution during welding has not been measured. In this study, in order to better understand the phenomenon of ESW by clarifying the temperature distribution of the molten area during welding, the molten area was directly observed and the temperature distribution was measured by two-color pyrometry. As a result, it has been revealed that the maximum temperature is about 2200 K in the vicinity of the wire tip. The high-temperature and low-temperature areas measured in this study roughly represent at the molten slag and molten metal areas, respectively.

抄録全体を表示

A creep analysis method was developed to evaluate the creep damage of hot reheat pipes in thermal power plants. In this method, a large-scale thermo-elastic-plastic creep analysis was achieved by introducing Norton's law into the Idealized Explicit FEM(IEFEM). In order to achieve an efficiently analysis of a large-scale structure, a multigrid method was also introduced to the IEFEM. The developed method was applied to the prediction of creep strain in a hot reheat pipes of thermal power plant for over a 10 year period. The effect of structural inhomogeneity on creep strain distribution was analyzed. Finally, the computational results of whole model were compared with those of the zooming model. As a result, it was confirmed that the creep strain obtained by the zooming analysis and the whole analysis have a difference in the creep strain up to 15%. This indicated that analysis of the whole piping system may lead to more accurate evaluation on creep strain.

抄録全体を表示