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.
Grinding ofweld toesis generally used toimprovethe fatigue strength of fillet weld joints. In this study,a technique employingadditional weldswas applied toout-of-plane gusset welded jointsand the ...relationship between the shape of the additional weld and fatigue strength was investigated. The shape of the additional weld was controlled by changing the aiming position. When there was more distance between the first weld toe and the aiming position of the additional weld, the flank angle and toe radius tended to be smaller and larger, respectively. In the nominal stress range of 150 MPa, fatigue life was extended to 2.7 times that of weld jointswithout additional welds. Although the toe radius of the additional weld was smaller than that created bygrinding, the resultant fatigue strength of the additional weld joint was almost equivalent to that of the grinding case. This can beexplained in terms of stress concentration, since the flank angle and toe radius in the additional weld toe canbe improved without reducing the throat thickness.
It has been well known that, in GMA welding, various welding phenomena are largely affected by the type of shielding gas used. However, up to the present time, almost no attempt has been made to ...utilize 'gas composition' for controlling welding phenomena. This study focused on this point and, thus, an investigation was made to understand how dynamic gas compositional modification affected various welding phenomena. In this study, pulsed Ar gas was injected periodically into CO2 shielding gas so that the gas composition of arc atmosphere largely modified in a very short period of time. It was found that this quick gas compositional change from CO2 to Ar led to a large decrease in arc voltage and an arc shape change from a constricted shape to a flare shape and that a molten droplet formed at the electrode tip during the CO2 period was released due to a sudden change in force balance between the molten droplet and the arc. The increase in current stimulated by the voltage drop may have assisted the metal drop detachment due to an increase in electromagnetic pinch force. If the cycle of this periodical Ar gas injection was selected to be shorter than that of repelled metal transfer in CO2 atmosphere, the repelled transfer was avoided and stable drop transfer occurred instead with far less spatter. Appropriate selections of the duration time of pulsed Ar gas injections avoided spray transfer which might cause undesirable finger-like penetration profiles. This new conceptual welding method, namely 'Pulsed Gas MAG Welding', required only a small amount of Ar gas to obtain the effects mentioned above.
This study investigated the applicability of low transformation temperature (LTT) arc welding consumables to improve fatigue strength against weld root failure. Transverse attachment joints formed by ...single-sided welding, similar to rib-to-deck connections in orthotropic steel bridge decks, were fabricated using an LTT welding consumable and conventional welding consumable. Fatigue tests were performed with out-of-plane bending loads using a vibration-type fatigue testing machine. The test results indicated that higher fatigue strength can be achieved in the joint with an LTT consumable compared with a conventional one. In addition, residual stresses around the weld bead were clarified by X-ray diffraction measurements and finite element analyses. The results revealed that the LTT consumable weld metal can reduce residual stress around the weld and also introduce compressive residual stress to the weld root, which can contribute to improved fatigue strength.
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.
CO2 gas shielded arc welding, which is widely used in the industrial world, has been recognized as an efficient and economical GMA welding process. However, it’s characteristic repelled transfer ...produces a large amount of spatter which results in costly cleanup and, thus, practical methods to overcome this weakness have been highly demanded. In this study, ‘Pulsed Gas MAG’ welding was proposed as a new approach to reducing spatter. The amount of spatter was reduced to the levels as low as that of the conventional MAG welding with 80%Ar + 20%CO2 shielding gas mix and penetration profiles were round shape like those obtained in CO2 arc welding.
CO
2
gas-shielded arc welding, which is widely used in the industrial world, has been recognized as an efficient and economical GMA welding process. However, its characteristic repelled transfer ...produces a large amount of spatter which results in costly cleanup and, thus, practical methods to overcome this weakness have been highly demanded. In the series of this study, 'Pulsed Gas MAG' welding was proposed as a new approach to reducing spatter, in which Ar gas pulses were periodically injected into CO
2
shielding gas so that gas composition of arc atmosphere was largely modified in a very short period of time and a metal droplet formed at the electrode tip during CO
2
atmosphere was released before repelled transfer had occurred. In this report, the influence of parameters of Ar gas injections, such as frequencies, average gas flow rates and gas injection periods, on the metal transfer was investigated. It was found that synchronous metal transfer stimulated by pulsed Ar gas injections was achieved at any frequencies from 35 to 65 Hz under the conditions of gas injection periods longer than 4 ms and of Ar gas volumes larger than approximately 1mL/pulse. This is because Ar gas injections below these critical levels resulted in lack of time for arc shape changes and metal drop detachment. From these experimental results, a model to explain the metal transfer phenomena was developed. The amount of spatter was reduced to the levels as low as that of the conventional MAG welding with 80 %Ar +20 %CO
2
shielding gas mix and penetration profiles were round shape like those obtained in CO
2
arc welding.
Fatigue crack is often initiated around weld toe, mainly caused by high stress concentration. Various techniques for improving the fatigue strength of joints have been proposed up to the present. ...Additional welding is known to be one of the effective techniques to improve the fatigue life of welded components. Recently, the authors have conducted fatigue tests on joints with additional weld. The tested welded joints were fabricated with different additional welding conditions. The tests revealed that smaller flank angles and bigger weld toe radii were obtained under certain additional weld conditions and the fatigue tests indicated that fatigue strength of out-of-plane gusset was remarkably improved by additional welding. In this study, 3D finite element (FE) analyses were conducted based on the in-house experimental campaign carried out to characterize the effect of additional welding on fatigue life. The crack initiation and crack propagation simulations were conducted using elastoplastic and linear fracture mechanics analyses, respectively. The results show that an additional weld treatment reduced remarkably the stress concentration at weld toe, leading to longer fatigue life.
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