A feasibility of combined heat sources, which provide wide heat source distribution, was investigated to improve the weldability of a square butt-joint with a wide gap. Two welding methods were examined in this study : one was welding with twin YAG laser beams and a filler wire, and the other was welding with YAG laser -TIG arc hybrid welding and a filler wire. In twin beam welding of 5 mm thick Type 304 stainless steel, two 2 kW Nd : YAG lasers were used and arranged in tandem or parallel to the weld line. Without a filler wire, the gap tolerance to obtain a sound weld bead was approximately 0.7 mm and 1.6 mm with tandem and parallel arrangement, respectively. With Type 308 filler wire, the gap width of 2.2 mm was successfully welded with tandem arrangement, but lack of fusion occurred at the bottom part of the weld bead at the gap width of 1.9 mm. In the parallel arrangement welding with filler wire, however, good welding was achieved up to 2.2 mm by optimizing the distance of two spots. As for porosity, it was found that the number of porosity detected by the X-ray inspection test was different according to the beams arrangements. More porosity was generated near the fusion boundary in welding with the parallel arrangement. However, there was little porosity in the weld bead produced with the tandem arrangement. Welding with a 4 kW YAG laser combined with TIG arc with a filler wire was successfully performed in 8 mm thick stainless steel with the gap of up to 3.7 mm. Such YAG laser-TIG arc hybrid welding was found to be extremely effective to the improvement of gap tolerance. In this method, the number of porosity in the weld beads was much smaller than that in the welding with a single laser beam.
As a welding method in space, the authors have proposed the GHTA (Gas Hollow Tungsten Arc) welding method in the previous papers, where some GHTA welding experiments have been conducted under the condition of low pressure (10-2 Pa) and/or the micro-gravity. In the present paper, a feasibility study has been conducted whether the method can be used under such a high vacuum condition (10-5 Pa) as on the space station orbit. As a result, it is made clear that the GHTA method is quite feasible under the high vacuum condition and its melting process strongly depends on the operating gas species such as Ne, Ar and Kr. Increasing the flow rate of operating gas decreases the mass of metal vapor from molten pool and the use of a heavy operating gas such as Kr also decreases the mass of metal vapor.
In the Japan railway company group, rails are welded at over 50,000 points every year, of which those welded by the gas pressure welding (GPW) method account for approximately 30 %. Because gas pressure welds have as good performance as flash welds, and the GPW equipment is highly mobile due to its compactness when compared with that of flash welding. However, GPW requires special skill for grinding end surfaces and controlling oxyacetylene flame and pressure. In the future, a number of skilled operators to perform GPW will decrease, and the improvement of the operational efficiency will be strongly demanded. Therefore, investigations have been performed to simplify end surface grinding. Consequently, new gas burners and the new applied pressure method used for GPW were developed in order to improve its reliability.
The characteristics of welded joint like as tensile strength or fracture toughness depend on welding conditions and multiple welding heat cycles particularly affect the joint performance. The effects of heat input and interpass temperature at multi-pass welded joint of beam-to-column connections on the strength and fracture are investigated in this paper. Tensile test, Charpy impact test, and three-point bending CTOD test are performed by using welded joint specimen fabricated with various welding conditions. The results of experiments actually show that there exists a welding condition which decreases joint performance. Three-dimensional thermal elastic-plastic finite-element analysis is also performed by using the moving heat source and with phase transformation effect. The parameters of heat input, interpass temperature, and welding direction are changed in the analyses, and the results are used for the consideration of the effect of multiple heat cycles on joint performance. The analytical and the experimental results are shown that controlling heat input and interpass temperature is much important to assure the quality of welded joints in beam-to-column connections of steel framed structures.
Numerical simulation of temperature, mictostructure, and hardness is performed in multi-pass welded joints of beam-to-column connections of steel framed structure. The effects of temperature history on microstructure and hardness are investigated in this paper. Three-dimensional thermal elastic-plastic finite element analysis is performed by using the moving heat source and considering phase transformation effect. The relation between cooling rate and Vickers hardness in the weld metal is pigeonholed from the result of the simulation. Elapsed cooling time t8/5 is effective to evaluate the hardness in the weld metal. Vickers hardness in heat-affected zone is also computed and well explained from heat cycles. It is found that tensile strength of the weld metal and the heat-affected zone might be predicted by numerical simulation.
In order to improve the fatigue strength of welded structure, compressive residual stress is induced by means of marten site expansion of weld metal using developed low transformation temperature welding wire. Fatigue limit could be improved on repaired box welded joints.
Residual stress in a bonded dissimilar material induced by the mismatch of material properties significantly reduces its bonding strength. For the purpose of the reduction of bonding residual stress, low yield strength materials have been widely used as an insert layer. However, introducing such a low yield strength material layer usually increases the mismatch of thermal expansion. There are two ways to reduce the bonding residual stress ; one is the decrease in the mismatch, which reduces the residual stress induced during the bonding process, and the other is the relaxation of bonding residual stress after bonding process. The later method seems to be more effective and economic. This paper proposed a simple method to relax the bonding residual stress by employing the properties of cyclic plastic deformation. Both the effects of cyclic pre-loading on the static and the fatigue strengths of the bonded dissimilar material were investigated experimentally by using bonded W/Cu joints. It is found that only the first few cycles of the pre-loading corresponds to the relaxation of the residual stress, and the relaxation effect depends on the amplitude of the cyclic pre-loading. Numerical analysis by finite element method was also carried out to explain the relaxation mechanism of the residual stress. It is also found that it is possible to raise the static and fatigue strength of the bonded material up to the level of monotonic Cu strength, if proper pre-loading condition is selected.
In this study, we have developed new shot materials of tungsten carbide (150 and 100 μm in average diameter) with high hardness and large specific gravity, which is about 1.7 times (HV1400) in hardness and about 1.9 times in specific gravity (specific gravity 14) compared with the conventional one. And we have examined the improvement in the fatigue strength of SM490A welded joint, the outbreak of noise and the use of projection air when this shot material is used. The following experimental results were obtained : 1) The fatigue strength of welded joint was improved very well even in low projection air pressure 0.2 MPa when the peening was performed with the tungsten carbide shot materials of 150 μm in diameter, which has higher hardness and larger specific gravity than the conventional steel ball shot materials. 2) When the tungsten carbide with 100 μm in diameter or the conventional steel ball with 177 μm in diameter was used as the shot material, the higher projection air pressure above 0.4 MPa was needed in order to obtain the same fatigue strength improvement when the tungsten carbide with 150 μm in diameter was applied. 3) This improvement of the fatigue strength was mainly an effect of hardness increase by peening, but there was an additional effect of the compressive residual stress, too. 4) It was possible to reduce the noise value by approximately 10 dB and also the amount of projection air by more than 50 %, when the shot material with the high hardness and large specific gravity in particle diameter 150 μm was used in order to obtain the similar peening effect of the conventional steel ball shot materials.
This paper deals with experimental data and a predictive method of longitudinal shrinkage and bending distortion which are important in the development of the high accuracy production system of the large welding structures. The longitudinal shrinkage and bending distortion can be calculated from the inherent force, namely Tendon Force, which is related to the total of the inherent strain. First the experimental values of the longitudinal shrinkage, longitudinal bending distortion and the inherent strain were obtained under various welding conditions. Next, the theoretical equation was proposed to calculate the longitudinal shrinkage and bending distortion from the inherent strain. As the results, the validity of the theoretical equation on the longitudinal shrinkage and bending distortion is shown by the comparison between values predicted from inherent force and experimental values.
Thermite welding is widely used in the world. In the Japan railway company group, the application ratio of this method is approximately 40 % every year. The reasons why the thermite welding method is widely used are that the equipment has good mobility and the total working time of that is shorter than that of the enclosed arc welding method on site. Moreover, the operating skill, which is required for thermite welding, is less than that for enclosed arc welding. This welding method used now was introduced into Japan from Germany in 1979. After that, the thermite welding technique has been improved and developed. A wide gap method is one of newly proposed thermite welding in Japan. The root gap of this method is three times for that of conventional method. Therefore, it is feared that welds produced by wide gap method have less fatigue strength than those by conventional method. Because a welding heat input of wide gap method is much larger than that of conventional method. In this investigation, a new process with rail head air cooling for wide gap thermite welding is proposed in order to improve fatigue strength of thermite welded joint on rails.
In the civil engineering and architecture, welding for large sectional steel members, such as I section and H section, are usually required. A flash welding system, by which large I section or H section can be welded for a short time, was newly developed. A series of experiments was carried out in order to know the characteristics of the flash welded joints. The joint efficiency of welded joints by flash welding was 100 % for the specimens with reinforcements and 93 % for without reinforcements. The fatigue strength of welded joints with reinforcement was about 50 % of that of the base metal. The fatigue strength of welded joints without reinforcement was 75 % of that of the base metal. After a couple of fatigue cracks had propagated, in case of welded joints with reinforcement, ductile fracture of occurred at the toe. On the other hand, in welded joints without reinforcement, fracture occurred at the bond or at HAZ (the heat affected zone). In case of fracture at the bond, fracture was brittle, and in case fracture at HAZ, fracture was ductile. Flash welded joints with reinforcement had the same grade of fatigue strength as arc welded butt joints with reinforcement and the non-load-carrying fillet joints by arc welding. The flash welded joints without reinforcement had the same grade of fatigue strength as the arc welded butt joints without reinforcements.
Roll bonding of low carbon steel and pure aluminium sheets is already an established process in industry. In this study, alloying additions were made to aluminium for understanding their effect on the joint strength and bonding mechanism. Heavy mechanical working leads to work hardening, which necessitates post heat treatment. However, such treatment causes formation of brittle intermetallic compounds (IMC) at the interface and considerably reduces the bond strength. Therefore, the effect of alloying elements on growth of IMC layer and on bond strength of the joints after post heat treatment was studied. Effect of carbon content in steel on the growth of IMC layer was also investigated. It was found that except for the SPCC/Al-1.5 % Si joint, the peel strength values of the joints made with different aluminium alloys were lower than that of SPCC/A1050 joint. The bond strength depends on area of aluminium remained on the steel surface after peeling. The joints with Al-5 % Mg showed very low peel strength indicating poor adherence due to hardening. However, on its post heat treatment at 623 K there was increase in its peel strength. As holding temperature increased, there was considerable growth in the IMC layer thickness which reduced the peel strength. On the other hand, joints with Al-Si alloys suppressed the IMC layer growth and therefore failed in aluminium base metal during peel test. Depending on the alloying elements in aluminium alloy, there is large difference in the growth of IMC at the interface. In case of Mg and Cu addition, the growth was fast whereas in case of Si addition it was slow. Variation in carbon content in steel did not affect the growth of IMC layer, but change in % reduction in steel had some effect on the IMC growth rate.
Cr3C2-25 %NiCr cermet coatings were deposited by HVOF spray process. The carbon content, carbide grain size and carbide content were estimated quantitatively. The mechanism of carbon loss in spraying and the effect of carbide grain size on the properties of sprayed coating were examined. The main conclusions obtained are as follows. (1) Carbon content of Cr3C2-25 %NiCr cermet coating deposited by HVOF spraying was lower than that of the powder. It was found that the carbon loss during particle in-flight is much limited. It can be suggested that the main mechanism of carbon loss is due to the rebound-off of large carbide particles. (2) It was recognized that the grain size and content of carbide in sprayed coating were lower than those in starting powder. (3) With the increase in carbide grain size and decrease in carbide content, the abrasive wear loss of HVOF sprayed coating was increased. Moreover, it was recognized that the erosion rate of HVOF sprayed coating was proportional to the ratio of carbide grain size to carbide content.
The joint strength and the joint interfaces between electroless Ni-P plating and Sn-Ag solders ,as replacement solders for the eutectic Sn-37 Pb, were investigated. The joint strength between Cu plated by electroless Ni-P and Sn-3.5 Ag and Sn-3.5 Ag-(8, 9, 10) In decreased after annealing at 373 K, 398 K and 423 K. The effect of Zn addition to Sn-3.5 Ag and Sn-3.5 Ag-8 In on the joint strength and thickness of reaction layers was investigated. The joint strength of as-joined interfaces between Sn-3.5 Ag and Sn-3.5 Ag-8 In and electroless Ni-P plating increased by 1 % Zn addition and decrease of the joint strength was inhibited by 1 % Zn addition after annealing. The joint interface between Sn-Ag solders and electroless Ni-P plating consists of Nix-Sny and P-rich reaction layers. It was found that the decrease of the joint strength relates to the growth of these reaction layers. The growth of these reaction layers is inhibited by 1 % Zn addition.
It is difficult to match joint phases at the particular position of a rotation side a fixed side using a conventional friction welding machine, because the rotating spindle does not control the exact stop position. A development of positioning controlled friction welding meets to be solved such difficulties as stop at the specified position during duration of braking. This positioning control friction welding was achieved by installing servo motor positioning system. A phenomenon of positioning control was examined by the friction welding of carbon steel. The positioning control was satisfactory performed with sufficient accuracy. The undershoot and the overshoot behaviors were observed to the specified position during operation. Heavy metal flow was observed in the vicinity of weld interface in case of positioning control. Characteristic flash was formed by the heavy metal flow during positioning control. The metal flow became heavy with the stopping period increase. The direction of metal flow was circumferential, when positioning control friction welding. The rotative direction of metal flow was changed due to the overshoot or the undershoot behavior. When stopping period was optimized, metal flow became minimized. In this examination, 0.3 s was optimum stopping period. The fracture of tensile test specimens occurred at the base metal, when the position was controlled. However, tensile strength of positioning controlled joints was equal to the strength of base metal. The positioning control did not affect on the tensile strength of welded joints.