Laser Welding Method Research Articles

Robotic Nd:YAG Fiber Laser Welding of Ti-6Al-4V Alloy

In the present study, Ti6Al4V titanium alloy plates were joined using a robotic fiber laser welding method. The laser welding process was carried out at two different welding speeds. Effects of different heat input conditions on the microstructure and mechanical properties of robotic fiber laser welded joints were investigated. Some grain coarsening was observed in the microstructure of weld metal in samples joined using high heat input, compared to those using low heat input, and volume rates of primary α structures increased in the weld metal. The microstructure of weld metal in samples joined using low heat input was made of basket-weave or acicular α' grains and primary β grains in grain boundaries. Tensile and yield strength of samples joined using low heat input were higher than for those joined using high heat input, but their ductility was lower.

Microstructure and Plastic Deformation of the As-Welded Invar Fusion Zones

The as-welded Invar fusion zones were fabricated between cemented carbides and carbon steel using a Fe-Ni Invar interlayer and laser welding method. Three regions in the as-welded Invar fusion zones were defined to compare microstructures, and these were characterized and confirmed by scanning electron microscopy and X-ray diffractometry. The structure and plastic deformation mechanism for initial Invar Fe-Ni alloys and the as-welded Invar fusion zones are discussed. (1) After undergoing high-temperature thermal cycles, the microstructure of the as-welded Invar fusion zones contains γ-(Fe, Ni) solid solution (nickel dissolving in γ-Fe) with a face-centered cubic (fcc) crystal structure and mixed carbides (eutectic colonies, mixed carbides between two adjacent grains). The mixed carbides exhibited larger, coarser eutectic microstructures with a decrease in welding speed and an increase in heat input. (2) The structure of the initial Invar and the as-welded Invar is face-centered cubic γ-(Fe, Ni). (3) The as-welded Invar has a larger plastic deformation than initial Invar with an increase in local strain field and dislocation density. Slip deformation is propagated along the (111) plane. This finding helps us to understand microstructure and the formation of dislocation and plastic deformation when the Invar Fe-Ni alloy undergoes a high-temperature process.

Effects of active flux on plasma behavior and weld shape in laser welding of X5CrNi189 stainless steel

In this paper, stainless steel was welded by active flux-aided laser welding method. The effects of single active flux (Cr2O3, SiO2 and TiO2) and composite active flux on laser welding were studied. In the welding process, laser plasma behavior was recorded by a high-speed imaging system. The results show that, with the addition of active flux, the absorption of laser energy and melting efficiency increase. In the laser power of 750 W, effects of active flux on weld depth to width ratio are given by the order: composite active flux [Formula: see text] SiO[Formula: see text] Cr2O[Formula: see text] TiO2. The effect of composite active flux is the most significant and it can increase the weld depth to width ratio to 85%. Active flux can restrict the laser plasma. With the addition of composite active flux, the projected area of laser plasma obtained obviously reduced, and it can be reduced by 41.39%. Active flux cannot obviously change the main components in weld zone, but can change the grains of austenite and ferrite.

Weldability of 5754 aluminum alloy using a pulsed Nd:YAG micro scale laser

Abstract Use of laser welding is constantly increasing as it allows attainment of a high welding efficiency and weld quality. In this study, 5754 grade aluminum plates were joined on both sides by means of pulsed Nd:YAG power intensified micro scale laser welding method at three different laser powers in flat position by using supplemental welding wire. Mechanical properties of joints were examined by means of tensile and bending tests and by micro hardness measurements, and their structural changes were examined by means of optical microscope, SEM and EDS. As a result, it was determined that the welded joints could display an adequate tensile strength when exposed to tensile strain under action of static loads, but their bending strength remained relatively weaker. Mechanical properties of welded samples were observed to improve with increasing penetration depending on the increase in the laser power. It is believed that use of siliceous supplemental welding wire was also effective in strength improvement.

Study on deformation and residual stress of laser welding 316L T-joint using 3D/shell finite element analysis and experiment verification

In this paper, T-joint of 316L steel is obtained by subsection laser welding method without jig, while a thermal elastic-plastic finite element model considering multi-linear yield stress curves and multi-point constraint equations is developed to estimate welding deformation and residual stress. A simplified heat source model with the actual bead geometry is proposed to reduce the number of finite element meshes. Prediction errors between the simulation and experimental measurement results of angular distortions of three reference lines are −11.0, 0.9, and 7.9 % respectively, and the maximum residual stress is 396 MPa. Meanwhile by microstructure analysis, austenite and ferrite are consisted in weld, segregation and dendritic structures are also observed, while the heat-affected zone is very narrow. In a word, weld line with large travel can be welded by subsection laser welding method without jig, while the finite element method proposed in this paper is effective to predict welding deformation and residual stress.

The influence of cryogenic and heat treatment on the mechanical properties of laser-welded AZ91D

The crack that mostly occurs at the heat-affected zone is a major challenge for welded magnesium alloys including AZ91D. This study proposed a new method of laser welding of this alloy assisted with a combination of cryogenic and heat treatment to remedy this problem. It was found that when the new process is used, the crack transformed from heat-affected zone to fusion zone and the tensile strength of the sample were 32.57 % higher than that welded by traditional laser welding. Through studying the changes of hardness, precipitates, and micro-structure in welded joint, it was found that the conversation of Mg17Al12 from dendritic state into short rod state as well as the appearance of dispersed Al8Mn5 particles played a major role in improving the mechanical properties of the welded magnesium alloy.

ホットワイヤ・レーザ溶接法を用いた厚鋼板立向き溶接技術の開発

ホットワイヤ・レーザ溶接法を用いた厚鋼板立向き溶接技術の開発

Comparison of microstructure and mechanical properties of TIG and laser welding joints of a new Al–Zn–Mg–Cu alloy

Sheets of a new Al–Zn–Mg–Cu alloy with T6 temper were welded using TIG and laser welding method. Microstructure characteristics and mechanical properties of joints were contrastively analyzed. Results show that the width of the fusion zone (FZ) and heat affected zone (HAZ) in laser joint is obviously smaller. The FZs in TIG and laser joints are both made up of dendritic equiaxed grains and lots of coarse particles, the mean grain size is 33.9μm and 6.1μm respectively, and the coarse particles are identified as the T (AlZnMgCu) phase. The two factors of grain size and alloying elements distribution are combined to result in almost the same microhardness of the two FZs. Moreover, the grain morphology, grain size and degree of recrystallization of the two HAZs are almost the same with base metal (BM). Due to the higher heating and cooling rate of welding thermal cycles in HAZ of laser joint, the microhardness is obviously higher. The minimum microhardness of the two joints is obtained in FZ where the fractures always occur in the tensile tests, the ultimate tensile strength of TIG and laser joints is 436.2MPa and 471.1MPa, the elongation of them is about 7.5% and 5.1% respectively.

Retention of bonded titanium copings fixed to implant abutments

Statement of problemConical abutments can be laser welded to the abutment base to compensate for differing implant axes. As laser welding requires expensive equipment, alternative methods for bonding the conical abutment part with the abutment base should be considered. PurposeThe purpose of this in vitro study was to evaluate the retention of Ti-6Al-7Nb copings bonded adhesively to Ti-6Al-7Nb abutments and to compare it with the stability achieved by laser welding. Material and methodsA total of 104 two-part Ti-6Al-7Nb specimens were prepared and divided into 13 groups with 8 specimens each. In this 2-part study, 3 luting resins (Panavia F 2.0 [PF]; Multilink Automix [MA]; Superbond C&B [SB]) were used with or without metal priming (PR). The laser welding group (LW) served as the control. After storage for 1 or 150 days (150 days with thermal cycling [TC]), push-out retention and welded joint stability were tested. The data were analyzed with ANOVA and the Tukey HSD multiple comparison tests. ResultsThe choice of resin, thermal cycling, and metal priming had a significant effect on resin push-out retention. LW provided the strongest retention, followed by PF, MA, and SB. For PF and SB, TC decreased retention. PR did not lead to higher retention but provided better bonding stability when TC was applied. ConclusionsThe retention values suggest that considering the maximum mastication forces, resin bonding is an appropriate substitute for the laser welding method.

Kinematics analysis and optimization of the fast shearing-extrusion joining mechanism for solid-state metal

Dynamical Joining of the solid-state metal is the key technology to realize endless hot rolling. The heating and laser welding method both require long joining time. Based on super deformation method, a 7-bar and 2-slider mechanism was developed in Japan, and the joining time is less than 0.5 s, however the length of each bar are not reported and this mechanism is complex. A relatively simple 6-bar and 1-slider mechanism is put forward, which can realize the shearing and extrusion motion of the top and bottom blades with a speed approximately equal to the speed of the metal plates. In order to study the kinematics property of the double blades, based on complex vector method, the multi-rigid-body model is built, and the displacement and speed functions of the double blades, the joining time and joining thickness are deduced, the kinematics analysis shows that the initial parameters can’t satisfy the joining process. Hence, optimization of this mechanism is employed using genetic algorithm(GA) and the optimization parameters of this mechanism are obtained, the kinematics analysis show that the joining time is less than 0.1 s, the joining thickness is more than 80% of the thickness of the solid-state metal, and the horizontal speeds of the blades are improved. A new mechanism is provided for the joining of the solid-state metal and a foundation is laid for the design of the device.

Development of remote pipe welding tool for divertor cassettes in JT-60SA

Remote pipe welding tool accessing from inside of the pipe has been newly developed for JT-60SA. Remote handling (RH) system is necessary for the maintenance and repair of the divertor cassette in JT-60SA. Because the space around the cooling pipe connected with the divertor cassette is very limited, the cooling pipe is to be remotely cut and welded from inside for the maintenance. A laser welding method was employed to perform circumferential welding by rotating the focusing mirror inside the pipe. However, the grooves of connection pipes are not precisely aligned for welding. The most critical issue is therefore to develop a reliable welding tool for pipe connection without a defect such as undercut weld due to a gap caused by angular and axial misalignments of grooves. In addition, an angular misalignment between two pipes due to inclination of pipe has to be taken into account for the positioning of the laser beam during welding. In this paper, the followings are proposed to solve the above issues: (1) Cooling pipe connected with the divertor is machined to have a jut on the edge so as to expand the acceptable welding gap up to 0.5mm by filling the gap with welded jut. (2) Positioning accuracy of the laser beam for reliable welding is realized to be less than ±0.1mm along the circumferential target for welding by a position control mechanism provided in the tool even in the case of up to angular misalignment of 0.5° between connection pipes. Based on the above proposals, we have achieved robust welding for a large gap up to 0.5mm as well as the maximum angular misalignment of 0.5° between connection pipes by using this newly developed tool.

Effects of Focusing Condition on Micro-Welding Characteristics of Borosilicate Glass by Picosecond Pulsed Laser

Glass materials are widely used in products such as optical components and semiconductor devices. In these products, precision welding techniques of glass are required to manufacture small and complicated shape. The laser welding method can perform the joining without an intermediate layer and an adhesive agent. In addition, an ultra-short pulse laser can reduce the heat affected zone with the high space accuracy. However, heating and cooling cycles are repeated even in the case of ultra-short pulsed laser. The temperature distribution and change of molten area are influenced not only by laser energy condition but also focusing condition. Therefore in this study, effects of focusing condition of laser beam on micro-welding characteristics of glass were experimentally investigated by using a picosecond pulsed laser. A usage of object lens with the spherical aberration correction led to a large molten area even at the same pulse energy, which related to the efficient welding of glass materials. An optical system with the spherical aberration correction led to stabilizing the shape of molten area, which resulted in the reliable weld joint.

The Evaluation of Different Types of Welding in the Orthodontic Expanders

The purpose of our paper was to evaluate the effect of different methods of welding in the laboratory procedures of orthodontic expanders. The results of flame, ultrasound, resistance and laser welding methods were evaluated by means of mechanical testing. Metallographic investigations were also used in order to compare the results of different welding testing. A combination of techniques which offer optimum mechanical, biological, physical and chemical properties must be selected. New results are presented in comparison to previous research with published results.

Fundamental research of laser micro welding for practical use of titanium eyeglass frames

Micro welding of titanium eyeglass frames requires sound strength, good exterior appearance and stable production, which suit micro laser welding. The objective of this work is to fundamentally investigate butt welding conditions with a pulsed yttrium aluminium garnet laser beam for exterior appearance and joint strength. Eleven factors of welding conditions which influence joint strength were evaluated from the viewpoint of quality engineering. It was found that two factors of defocused distance and processing of welding surface of the welding parts led to fluctuation of the joint strength. Therefore, sub-millimetre scale control of the laser irradiated point along the optical axis and the removal of impurities lead to brittle metallic compounds on the surface and produce sound strength of the joints. Furthermore, the optimized laser condition is applied to fabrication of components with the shape of titanium eyeglass frames. The qualities of the obtained joints were confirmed by a stripping test, cyclic bending test, metallographic observation and hardness determination. It was revealed that the laser welding method is more reasonable than conventional resistance brazing methods.

Joining characteristics of titanium-based orthodontic wires connected by laser and electrical welding methods.

This study investigated the possibility of electrical and laser welding to connect titanium-based alloy (beta-titanium and nickel-titanium) wires and stainless-steel or cobalt-chromium alloy wires for fabrication of combination arch-wires. Four kinds of straight orthodontic rectangular wires (0.017 × 0.025 inch) were used: stainless-steel (S-S), cobalt-chromium (Co-Cr), beta-titanium alloy (β-Ti), and nickel-titanium (Ni-Ti). Homogeneous and heterogeneous end-to-end joints (15 mm long each) were made by electrical welding and laser welding. Non-welded wires (30 mm long) were also used as a control. Maximum loads at fracture (N) and elongation (%) were measured by conducting tensile test. The data (n = 10) were statistically analyzed using analysis of variance/Tukey test (P < 0.05).The S-S/S-S and Co-Cr/Co-Cr specimens showed significantly higher values of the maximum load (ML) at fracture and elongation (EL) than those of the Ni-Ti/Ni-Ti and β-Ti/β-Ti specimens for electrical welding and those of the S-S/S-S and Co-Cr/Co-Cr specimens welded by laser. On the other hand, the laser-welded Ni-Ti/Ni-Ti and β-Ti/β-Ti specimens exhibited higher values of the ML and EL compared to those of the corresponding specimens welded by electrical method. In the heterogeneously welded combinations, the electrically welded Ni-Ti/S-S, β-Ti/S-S and β-Ti/Co-Cr specimens showed significantly (P < 0.05) higher ML and EL than those of the corresponding specimens welded by laser. Electrical welding exhibited the higher values of maximum load at fracture and elongation for heterogeneously welded combinations than laser-welding.

Hot-wire Laser Welding Process Using Laser Diode for Large-Diameter Pipe with Narrow Gap Joint

We investigated a hot-wire laser welding method using a laser diode with a rectangular laser beam to weld a large-diameter pipe with a narrow gap. First, welding trials using plate specimens were performed to obtain the optimum welding conditions using a defocused beam. We achieved stable feeding of wire, a stable molten pool, and a well-formed weld bead, with few defects. Second, we welded a large-diameter pipe using optimum welding conditions discovered from the trials. Although some small lack of fusion occurrences were observed in the side bending test, we achieved a narrow gap, low dilution, narrow heat-affected zone weld without solidification cracks.

Welding Phenomena during Vertical Welding on Thick Steel Plate using Hot-wire Laser Welding Method

The objective of this research was to develop a single-pass vertical welding process for thick steel plates using hot-wire laser welding to reduce the heat input. A laser diode with a large rectangular beam spot and twin hot-wire feeding system were used. Welding phenomena were investigated using stationary and weaving laser irradiation with small and large groove widths. Single-pass vertical welding for thick steel plates with a low heat input and low dilution could be achieved. A critical energy density existed for each welding speed at which fusion of the groove surface could commence. The energy density affected fusion of the groove surface compared with welding speed. Weaving laser irradiation made it possible to maintain a high energy density and accommodate the large gap variation.

Analysis and characterization of microstructural evolutions, mechanical response and fracture mechanism of laser welded Fe–Co–V ultra-thin foils

Abstract The welding behavior of the Fe–Co–7 wt% V ultra-thin foils was examined using the Nd:YAG laser welding method. Scanning electron microscopy and electron backscattered diffraction were used to investigate microstructural changes and fracture mechanism of the weld joints. Tensile test and microhardness measurement were employed in order to study the mechanical behaviors of the welds. Microstructural observations indicated that a bimodal grain size distribution is seen in the fusion zone. It was found that the fracture surfaces of the welds consist of both cleavage sites and dimples. It was also revealed that the cleavage sites are mainly located in the coarse grain zone while numerous dimples are located in the fine grain zone. Considering the phase transformations which occur in the base metal, variation of the microhardness in different regions of the welds was discussed. The results demonstrated that the fusion zone and heat affected zone of welded samples experience a significant decrease in their hardness.

Effect of hot-wire on microstructure and mechanical property in weld metal formed with CO2 gas shielded arc welding method

The new welding method known as F-MAG, which has been developed based on the CO2 gas-shielded arc welding method (MAG), increases deposition rate of weld metal. The F-MAG welding method is combined with hot-wire, as has been used in TIG arc- and laser-welding methods. F-MAG is performed using hot-wire which is inserted into the rear part of the weld pool made with the leading electrode. Hot-wire melts by both electrical heating of itself and heat of the weld pool. Multi-layered weld metals were prepared using F-MAG and MAG. Microstructures and mechanical properties of both as-weld and reheated zones in the uppermost layer of the multi-layered weld metals formed with F-MAG and MAG were examined and the effects of hot-wire on microstructures and mechanical properties were analysed. Both the as-weld and reheated zones of the weld metal formed with F-MAG consisted of acicular ferrite (AF), equiaxed ferrite and so on. Both strength and elongation in as-weld and reheated zones formed with F-MAG were superior compared with those formed with MAG. It could be suggested that strength increased by refinement of AF due to increase in the concentration of alloying elements being contained in the hot-wire. Larger elongation of the weld metal in F-MAG compared with that in MAG could be analysed in terms of the Aggregate of AF Laths with nearly Parallel Slip systems between neighboring AF laths (ALPS). The number of AFs contained in an ALPS formed with FMAG is larger than that with MAG, in spite of the sizes of ALPSs formed with MAG and F-MAG being almost same. Deformation occurs over a lot of AFs in the case of finer AF formed with F-MAG through the rotation of the tensile test piece during deformation, resulting in the larger elongation.

Solidification cracking susceptibility of modified 9Cr1Mo steel weld metal during hot-wire laser welding with a narrow gap groove

Hot-wire laser welding with a narrow gap groove was applied to ASTM A213 grade T91 steel in the application of ultra super critical boilers. A filler wire according to AWS A 5.28: ER90S-G was used. The effect of the depth-to-width ratio (D/W) of a weld shape on the susceptibility to solidification cracking was investigated. With a groove width of 3 mm, solidification cracking did not occur with a D/W ratio of less than 0.6 and more than 1.2. The hot-wire laser welding method with a narrow gap groove seemed to be efficient for practical use, when the higher D/W condition was used without solidification cracking. The high temperature strain, which occurred during solidification, was computationally calculated in order to make clear the effect of D/W ratios on the susceptibility of solidification cracking in theory. From in situ observation using a high-speed camera of the hot-wire laser welding phenomena, a three-dimensional Finite Element Method (FEM) was simulated to estimate an equivalent plastic strain in the weld metal during welding. An approach to the moving heat source consistent with such phenomenon was proposed and validated based on experimental measurements. The simulation results presented that a moving heat source by hot-wire laser welding was able to produce a particular weld shape at a higher D/W ratio with a lower strain rate, which corresponded with the relationship between D/W ratios and solidification cracking in experiments. Therefore, such a hybrid process is a very interesting alternative process to reduce the solidification cracking in narrow gap welding, especially in modified 9Cr1Mo steel.