Conventional Welding Methods Research Articles

7075-T651 알루미늄 판재의 마찰교반용접과 피로균열전파 특성

Friction stir welding (FSW) method has extensively been used in manufacturing methods because of the several advantages over conventional welding methods, such as better mechanical properties, reduced occurrence of joining defects, high material saving, and low production time, etc. The aim of this paper is to review the optimal FSW conditions using the previous experimental results and is to investigate the fatigue crack growth rate in three different zones, WM, HAZ and BM for FSWed Al7075-T651 aluminum plates. As far as our experiments are concerned, the optimal conditions are obtained as rotation speed, 800rpm and travelling speed, 0.5mm/sec. The fatigue crack growth rate showed strong dependency on three different zones WM, HAZ and BM, and crack driving force.

Expulsion Reduction in Resistance Spot Welding by Controlling of welding Current Waveform

There is a welding problem such as expulsion in resistance spot welding of high strength steel. This is due to overheating induced by increase of total heat input. Recently, many studies are carried out to solve the problems using electrode force control and current control. In this study, we tried to achieve expulsion reduction through controlling welding current. Steel sheet coated by Al-Si that has strength of 1500MPa was selected as a base material. The control results were compared with conventional welding method. Also, it is characterized how the variation of the heating and cooling by pulse current waveform control have an effect on expulsion.

Liquid Phase Bonding of 316L Stainless Steel to AZ31 Magnesium Alloy

The excellent corrosion resistance, formability and strength make stainless steels versatile for diverse applications. However, its high specific strength and good crashworthiness make it suitable for transportation and aerospace industry. On the other hand, the need to reduce the weight of vehicle and aerospace components has created renewed interest in the use of magnesium alloys. Due to their differences in physical and metallurgical properties, bonding of the 316L steel and AZ31 magnesium alloy using conventional fusion welding methods encountered many limitations. Therefore, the use of liquid phase forming interlayers is required to overcome the differences in their properties, eliminates the need for a high bonding pressure to achieve intimate contact between the bonded surfaces. Both Cu and Ni interlayers successively formed a eutectic phase with magnesium. The formation of intermetallics and Mg diffusion caused the eutectic phase to isothermally solidify with increasing bonding time. The formation of ternary intermetallic phases (γ1 and B2) impaired the bond shear strength particularly at the end of the isothermal solidification stage where no eutectic phase was observed. However, the joints showed a higher shear strength value of 57 MPa when bonding with Cu interlayer at 530°C for 30 min compared to 32 MPa when Ni interlayer was used at 510°C for 20 min.

HIGH EFFICIENCY WELDING PROCESS FOR STAINLESS STEEL MATERIALS

The high efficiency tungsten inert gas (TIG) welding process has been developed, including active flux welding process, mixed shielded welding process and double shielded welding pro- cess, to increase the weld depth/width ratio (D/W ) of conventional TIG welding method. Compared to the active flux method, mixed shielding method can make penetration deeper and the industrializa- tion can be realized easily due to the simplification in operation. Double shielded method can avoid the oxidation of tungsten electrode. The results of experiment and simulation show that the change of the Marangoni convection direction which arises from the adjustment of the oxygen content in the weld pool is one of the main factors contributing to the increase in TIG weld penetration, and the large D/W ratio can be obtained by adjusting the active element content in the liquid pool. High efficiency TIG welding process is not sensitive to welding parameters (welding speed, welding current and electrode gap) and therefore is suitable to be applied in industry easily.

Diffusion Bonding of Austenitic Stainless Steel 316L to a Magnesium Alloy

Dissimilar metal combinations are often necessary when manufacturing a component in order to meet particular functional and engineering requirements or protect against environmental degradation. Stainless steels are used in a diverse range of applications due to their excellent corrosion resistance, formability and strength. The 316L stainless steel also shows good crashworthiness due to its high strain rate sensitivity which makes it suitable for the transportation industry. The joining together of the 316L steel and AZ31 magnesium alloy cannot be achieved using conventional fusion welding methods and therefore, diffusion bonding using interlayers was used to overcome the differences in their physical properties. The results show that Cu and Ni interlayers form a eutectic with the magnesium which enhances wettability and bond formation through isothermal solidification. The effect of hold time on the microstructural developments across the joint region was studied at a bonding temperature of 530oC and 510oC for the Cu and Ni interlayers respectively using a bonding pressure of 0.2 MPa. This preliminary investigation shows that by increasing the bonding time from 5 to 60 minutes results in a Cu-Mg and Ni-Mg eutectic phase structure forming along the bond interface. By holding the joint at the bonding temperature for 15 minutes initiates isothermal solidification of the joint and this was confirmed by DSC analysis. However, the movement of the solid/liquid interface on solidification pushes intermetallic phases into the center of the bond during the solidification stage. The intermetallics increase the hardness value of the bond interface and lower final bond strengths.

Numerical Simulation Research on a New Spinning Process: Double-Roller Clamping Spinning Process

Thin-wall rotary parts with complex flange geometry have been widely used in many equipments, especially industrial fans and blowers. Conventional stamping and welding methods for those parts have some limitations such as low manufacturability, poor quality and low utilization ratio of material. Thus in this paper, a new spinning process, double-roller clamping spinning process (DCSP), is introduced to form the complex flange shape. During the process, the cylindrical workpiece made from sheet metal is held by the internal expanding clamp device and rotates together with the device, while two spinning rollers deforms and shapes the material of flange region according to the rollers moving paths. In order to deeply investigate deformation mechanisms of DCSP, both 2D and 3D FE simulation models are built and the spinning process for rectangular cross-section shape of flange is simulated by using explicit FE code ABAQUS/explicit. Simulation results show large flange length can induce wrinkles on the inner region of flange. After spinning process simulation, the springback of workpiece is calculated by implicit FE code ABAQUS/standard. The effect of flange length on the thickness reduction of workpiece is obtained by theoretical analysis.

Novel Approaches to Friction Spot Welding Thin Aluminium Automotive Sheet

Conventional welding methods, like resistance spot welding, are inefficient and difficult to apply to light alloys. Two alternative new solid state friction joining techniques, which have not yet been fully optimized, are high power Ultrasonic Spot and Friction Stir Spot Welding (USW & FSSW). Here we have compared the performance for these two processes for producing ‘keyhole-less’ welds in thin aluminium automotive closure panels. For friction stir spot welding this was achieved through using a novel ‘pinless’ tool to create a joint without a retained keyhole and reduce the weld cycle time. The properties of the welds that can be produced by each technique are compared, together with the stages of weld formation, and the relationship between welding conditions and joint performance.

Spot welding between aluminium alloy and low-carbon steel by friction stirring

The application of aluminium alloy, which is a typical lightweight material, has been expected in the construction of transportation vehicles to achieve energy saving by reduction of weight. However, structures made of whole aluminium alloy have problems with low strength and high cost. Thus, hybrid structures made of Al alloy and steel are useful because of light weight and higher strength. To construct the hybrid structure, it is necessary to weld aluminium alloy and steel. However, conventional welding methods, like brazing and mechanical fastening, have problems such as low mechanical strength and low productivity. Also, it is difficult to weld Al alloy and steel by conventional fusion welding. In this study, spot welding between aluminium alloy and low carbon steel by friction stirring was carried out. Especially, optimization in welding conditions was carried out. Moreover, the effect of welding conditions on the joint strength and weld interface was studied. As a result, relatively higher tensile shear strength of the weld, which was achieved at optimum welding conditions, was obtained. Temperature near weld interface measured by K-type thermocouple during welding was found to be lower than the melting point of A5052. From the observation results on microstructure of the weld interface, it was found that a Fe/Al intermetallic compound layer was formed.

Determination of Optimum LASER Welding Parameters and the Development of a LASER Welding Technique to Enhance the Lateral Impact Strength of a Spacer Grid Assembly for a PWR Fuel Assembly

A spacer grid assembly, which is an interconnected array of slotted grid straps welded at the intersections to form an egg crate structure, is one of the core structural components of the nuclear fuel assemblies of a Pressurized light Water Reactor (PWR). The spacer grid assembly is structurally required to have enough buckling strength under lateral loads so that the nuclear fuel rods are maintained in a coolable geometry, and that control rods are able to be inserted. The ability of a spacer grid assembly to resist lateral loads is usually characterized in terms of its dynamic and static crush strengths. Since the crush strengths of a spacer grid assembly are known to depend on the weld qualities at the intersections of the slotted grid straps, high-tech welding methods, such as a TIG welding, LASER beam welding or Electron beam welding method, have been used recently in the nuclear fuel manufacturing fields. In this study, to meet the above requirements, two kinds of researches were carried out. First, by adjusting the LASER beam welding parameters, an optimum welding combination of the LASER beam welding parameters was obtained for welding a spacer grid assembly. Second, a new LASER beam welding technique was proposed to obtain a longer weld line and a smaller weld bead size by tilting the LASER beam. The buckling strength of the spacer grid welded by the new LASER beam welding technique was enhanced by up to 30 % when compared to that by the conventional LASER beam welding method.

摩擦攪拌作用を用いたAl合金/低炭素鋼板の重ね点接合

The application of aluminum alloy, which is a typical lightweight material, has been expected to the construction of the transportation vehicle to achieve energy saving by reduction of its weight. However, the structure made of whole aluminum alloy had problems with low strength and high cost. Thus, hybrid structure made of Al alloy and steel is useful because of lightweight and higher strength. To construct the hybrid structure, it is necessary to weld between aluminum alloy and steel. However, the conventional welding methods, like brazing and mechanical fastening, have some problems such as low mechanical strength and low productivity. Also, it is difficult to weld Al alloy and steel by conventional fusion welding. In this study, spot welding between aluminum alloy and low carbon steel by friction stirring was carried out. Especially, optimization in welding conditions was carried out. Moreover, the effect of welding conditions on the joint strength and weld interface was studied. As a result, relatively higher tensile shear strength of the weld which was achieved at an optimum welding conditions was obtained. Temperature near weld interface measured by K type thermocouple during welding was found to be the value lower than the melting point of A5052. From the observation results on microstructure of weld interface, it was found that Fe/Al intermetallic compound layer was formed.

Effect of process parameter on mechanical properties of friction stir welded tailored blanks from aluminium alloy 6181-T4

Tailor welded blanks (TWBs) are produced by joining at least two sheets of dissimilar gauge and/or properties to achieve a lighter blank of desired stiffness and strength. In this way, the properties of the blank may be tailored to meet the design requirements of a panel. As in steel structures, cost and weight can be saved when using the TWB concept for aluminium. However, use of aluminium is a concern in the automotive industry because of well documented weldability and reproducibility problems, since relatively minor changes in welding parameters may affect the quality of the weld. Friction stir welding offers an attractive alternative to conventional fusion welding methods because of the excellent properties (particularly ductility), reproducibility, robustness and surface finish obtained. However, the working envelope for friction stir welded tailored blanks has yet to be fully explored. In the present study TWBs of the alloy 6181-T4 in a thickness combination 1 to 2 mm have been produced. The influence of welding parameters and welding tools on the weld quality and mechanical properties has been determined. Satisfactory surface finish with no detrimental effects to the mechanical properties has been observed. Weld efficiencies >90% have been consistently achieved.

Experimental study on improving welding efficiency of twin electrode TIG welding method

Twin electrode TIG (T-TIG) welding is a new method, which woks with two electrodes insulated from each other in a welding torch. In the present study, the T-TIG welding system was established. Then the force and heat effects of T-TIG coupling arc were analysed by measuring arc pressure and arc static voltage–ampere characteristic respectively. After that, high speed thin plate and high deposition grooved thick plate welding experiments were carried out with both T-TIG and conventional TIG welding methods. The results show that with similar arc heat input, the T-TIG coupling arc has much lower arc pressure than TIG single arc. The characteristic makes T-TIG welding suitable for high efficiency welding on the basis of maintaining the original advantages of TIG welding.

Study of Underwater Laser Welding Repair Technology

IHI developed underwater welding process by using YAG laser and qualified the process to repair a thin wall stainless steel tank in a power plant in Japan. Important features of YAG laser welding are less welding distortion, and a small heat-affected zone (HAZ) due to the smaller heat input and higher cooling rate than with other conventional welding methods. In this study, we have conducted underwater laser welding of Ni-base alloy and stainless clad materials, such as Alloy 600 and E-309L / E-308L clad materials. Alloy 690 was selected as weld filler metal for a corrosion resistant overlay to prevent corrosion attack by the service environment. Welding trials were conducted on the surface of flat plates with simulated surface cracks, and the trial welds were assessed for soundness of welding. The preliminary results of the trial welds by using high power laser diode, and comparison between YAG laser and high power LD are reported.

Evaluation of welded titanium joints used with cantilevered implant-supported prostheses

Early failure of laser-welded titanium implant frameworks in clinical practice has prompted an investigation of the strength and durability of welded cantilevered titanium sections. The purpose of this study was to determine the effect that the use of filler wire in laser welding of titanium cantilever frameworks had on the flexural strength and fatigue resistance of the welded joints. Sixty titanium implant-supported frameworks with 12-mm cantilevers were fabricated in 4 groups (n=15), using 3 different laser welding protocols with 0, 1, and 2 weld passes with filler wire, and 1 conventional tungsten inert gas welding method. The volume of filler wire used (mean volumes 0, 1.7, 3.4, and 8.3 mm(3)) was determined by measurement of the length of wire before and after welding each joint. Ten frameworks from each group were tested for ultimate flexural strength by loading the cantilevers 10 mm from the abutment. The remaining 5 frameworks from each group were similarly tested under a simulated masticatory load of 200 N until failure, or to 1 million cycles. A 2-way analysis of variance was used to examine the flexural strengths, and log-rank statistics were applied to cyclic test data (alpha=.05). There were significant differences between the 4 groups for ultimate flexural strength (P<.001) and resistance to cyclic loading (P=.002). The volume of filler wire added was a significant predictor of ultimate flexural strength (P=.03), and was a borderline determinant of the number of cycles to failure at 200 N (P=.05). Each laser weld pass with filler wire roughly doubled the ultimate flexural strength and fatigue resistance of the joint relative to the previous weld. Tungsten inert gas welding with efficient argon shielding deposited the most filler wire and produced the strongest and most fatigue-resistant joints. The ultimate flexural strength and fatigue resistance of cantilevered joints in laser-welded titanium prostheses are improved by the use of filler wire. Tungsten inert gas welding with efficient argon shielding can be used in situations when a high-strength joint is required.

ONLINE CONTROL SENSORS FOR WELDING PROCESSES BASED ON OPTICAL RECOGNITION

In the automotive industry, laser welding processes increasingly replace conventional welding methods. The remaining flaw rate of the final product has to be below 5 parts per million (ppm). Therefore, the demands on quality control systems are correspondingly high. Only a combination of sophisticated plasma monitoring, power measurement, and image processing techniques can reliably maintain such low residual flaw rates in production. Plasmo™ is a modular system for automated online quality control of continuous wave laser welding and brazing processes widely used in the automotive industry. An overview of the features and physical background of the plasmo™ system is presented, and its capabilities are demonstrated in a representative example. The standard algorithms and signals in the time domain for online detection of failures and flaws are outlined, as well as new algorithms for special laser welding processes, like e.g. pulsed Nd:YAG laser welding, laser brazing. The potential and capabilities of time series analyses of the process signals are discussed.

自動車用高強度鋼板の溶接継手の疲労特性におよぼす溶接法の影響

In high strength steel sheets, it seems to be possible to improve the fatigue strength of joints welded by using laser welding due to the lower heat input of welding and the flatter weld beads compared with conventional welding methods such as arc welding or resistance spot welding. Therefore, in this paper, fatigue tests were conducted for the specimens with the butt joints of 780 MPa grade steel sheets welded by using laser welding, plasma welding and MAG welding and for the specimens flattened the weld beads to investigate the effect of welding methods on the fatigue properties of welded joints of high strength steel sheets for automobiles. And the macrostructure, the microstructure and the hardness distribution around the weld metal were observed to study the mechanism for the difference of the fatigue strength by the welding methods. It was found that the fatigue strength in arc-welded joints and plasma-welded joints is lower than that in laser-welded joints mainly due to the occurrence of softening in the heat affected zone. On the other hand, it was found that the stress concentration at the toe of the weld bead significantly deteriorates the fatigue strength even in the laser-welded joints.

Intergranular corrosion on Nd:YAG laser‐welded A653 steel for automotive application

AbstractLaser welding techniques produce a narrower heat‐affected zone than other conventional welding methods. However, laser welding is not exempt from high heat input during the welding process. This high heat input results in changes of the material properties including its corrosion behaviour; the formation of the heat affected zone increases the susceptibility of the material to intergranular attack. The residue of zinc at the weld due to condensation and splashing during the welding process may also influence adversely the corrosion behaviour of the material. The degree of susceptibility to corrosion strongly depends on the welding parameters. Electrochemical and microstructure characterisation were employed to study the influence of Nd:YAG (neodymium yttrium aluminium garnet) laser‐welding on an A653 galvanized steel at different welding parameters.

Observation of Joining Phenomena in Friction Stage and Improving Friction Welding Method

This report describes the observation result of joining phenomena in the friction stage, and an improvement of the conventional friction welding method with similar materials. The materials used were carbon steels and a brake type (direct drive) friction welding machine was used for joining. As the improving friction welding method, relative speed was instantaneously rendered to zero at the end of each friction time. The wear of both surfaces started at periphery portion (outer surface) of the joint and moved to center portion (center axis). Seizure and joining began at center portion and then extended toward periphery portion. The friction torque reached to initial peak torque when the welded interface was joined completely and upsetting of both base metals started. It was determined that friction welded joints with 100% joint efficiency and good bend ductility could be obtained by using only the friction stage up to initial peak torque and without the need for the forging (upsetting) stage. As a conclusion, friction welded joints made without using the forging stage has the same mechanical properties as those welded by the conventional friction welding process including that stage. The friction welding method without forging stage has the advantages of less burn-off (axial shortening) and less burr.

Plasma arc brazing in sheet metal construction

Because of the high heat input required, conventional welding methods may not always be ideal for mild and high strength steel sheets. A possible alternative in some applications is plasma brazing, which can also serve as a supplement to other joining techniques. A characteristic feature of the process is the separation between the energy input and filler material. Compared with high heat processes, plasma brazing causes considerably less distortion of joints or panels. Almost no spatter results from the process. The brazed seams exhibit sound mechanical properties as well as good appearance. However, there are difficulties associated with brazing some high strength steels using the filler wires commercially available at present.

ＹＡＧレーザによるガラス基板のマイクロ接合 第１報 レーザ透過性を利用したガラス界面の接合法の提案とその可能性検証

This paper deals with the micro-welding of the glass substrates by YAG laser beam. The micro-welding technology is required for the precision assembly of the micro components in the optical transmission devices, LCD plate and so on. In the conventional welding method of the glass materials, glass components were bonded to glass substrates by bond material which was melted by heat energy. In our proposed method, a pair of glass plates was overlapped, in which the absorbent was painted on the welding area of glass surface, and the YAG laser beam was absorbed in only the painted area. Therefore only the interface between two plates will be welded and glass surface will be clear. In this study a feasibility study of a newly developed welding method was carried out. In the experiments, slide glasses were welded by YAG laser beam, the welding point was observed and welding strength was measured.