接合 高溶着溶接技術「ホットマグ溶接法」の開発とその適用

The thermal metallurgical modeling of liquid aluminum supersaturation was further developed through couple of heat transfer model, dendrite selection model, multicomponent dendrite growth model and nonequilibrium solidification model during three-dimensional nickel-based single-crystal superalloy weld pool solidification. The welding configuration plays more important role in supersaturation of liquid aluminum, morphology instability and nonequilibrium partition behavior. The bimodal distribution of liquid aluminum supersaturation along the solid/liquid interface is crystallographically symmetrical about the weld pool centerline in (001) and [100] welding configuration. The distribution of liquid aluminum supersaturation along the solid/liquid interface is crystallographically asymmetrical throughout the weld pool in (001) and [110] welding configuration. Optimum low heat input (low laser power and high welding speed) with (001) and [100] welding configuration is more favored to predominantly promote epitaxial [001] dendrite growth to reduce the metallurgical factors for solidification cracking than that of high heat input (high laser power and slow welding speed) with (001) and [110] welding configuration. The lower the heat input is used, the lower supersaturation of liquid aluminum is imposed, and the smaller size of vulnerable [100] dendrite growth region is incurred to ameliorate solidification cracking susceptibility and vice versa. The overall supersaturation of liquid aluminum in (001) and [100] welding configuration is beneficially smaller than that of (001) and [110] welding configuration regardless of heat input, and is not thermodynamically relieved by gamma prime γˊ phase. (001) and [110] welding configuration is detrimental to weldability and deteriorates the solidification cracking susceptibility because of unfavorable crystallographic orientations and alloying aluminum enrichment. The mechanism of asymmetrical solidification cracking because of crystallography-dependent supersaturation of liquid aluminum is proposed. The eligible solidification cracking location is particularly confined in [100] dendrite growth region. Moreover, the theoretical predictions agree well with the experiment results. The useful modeling is also applicable to other single-crystal superalloys with similar metallurgical properties for laser welding or laser cladding. The thorough numerical analyses facilitate the understanding of weld pool solidification behavior, microstructure development and solidification cracking phenomena in the primary γ phase, and thereby optimize the welding conditions (laser power, welding speed and welding configuration) for successful crack-free laser welding.

Manufacturing productivity can be improved by increasing the welding speed. However, humping bead will occur when welding speed is beyond a certain value. An experimental system of double-electrode gas metal arc welding (DE-GMAW) was developed to implement high speed welding and prevent from humping bead formation. The DE-GMAW appropriately partition the heat energy between the wire and the base metal so that higher deposition rate of filler wire and suitable shape and size of weld pool are ensured. The arc images captured during DE-GMAW process were used to optimize the geometric parameters between the gas tungsten arc welding and the gas metal arc welding (GMAW) torches. The main arc and bypass arc integrated well and satisfactory weld bead formation was obtained. Through observing the weld pool behaviors from side view during DE-GMAW process, it was found that the height of both solidified and molten region at the pool tail is almost flat so that no humping bead was formed during DE-GMAW with the welding speed up to 1.7 m/min. The side view images of weld pool in DE-GMAW were compared with those in conventional GMAW, and the reason why DE-GMAW can suppress humping bead is shortly discussed.

Summary A series of systematic studies was undertaken to clarify the effect of CO2 laser welding conditions on melting characteristics, porosity formation, cracking susceptibility, hardness profiles, macro- and micro-distribution of Mg, and tensile properties of aluminium alloys. Bead-on-plate welding was performed on different commercially available alloys such as A5052, 5083, 5182, 6061 and 7N01 with a CO2 laser under various conditions of laser power, welding speed and defocused distance. In this paper, the influence of various welding conditions on melting characteristics was investigated from a fundamental viewpoint. In particular, laser beam modes and pressure distribution under various gas flow rates were measured, and it was consequently demonstrated that melting behaviour was greatly affected by the laser mode in the welding direction and the gas flow rate or pressure. Also the effect of Ar/He gas ratio on melting was investigated, and it was revealed that the use of Ar was beneficial to weld more highly-conductive and reflective alloys at lower power and higher welding speed, while a higher content of He was good for higher power and lower welding speed. Furthermore, it was confirmed that a larger amount of Mg was evaporated even under conditions producing a shallow weld molten pool leading to more deeply penetrated welds.

Spatter formation is a major issue in deep penetration welding with solid state lasers at high welding speeds from 8 up to 20 m/min. One approach to describe spatter formation is based on the assumption of an unstable keyhole. This leads to a temporary constriction of the keyhole due to the melt pool whereby the keyhole pressure increases. Finally, the keyhole collapses and spattering occurs. Therefore, the stabilization of the capillary is a possible way to limit spatter formation. For this purpose, several potential solutions have been tested in the past. However, investigations regarding a precisely local adjustable shielding gas flow on the keyhole stability under the condition of high welding speeds (≥ 8 m/min) is not given in the state of the art yet. To investigate these interactions, a shielding gas supply was developed, which can be adjusted in four axes with a reproducibility of 0.02 mm. Furthermore, the assembly was provided with a coaxial alignment laser for determining the interaction region of the gas. Under the processing of stainless steel (1.4301), different flow rates of argon, helium and nitrogen were tested. Additionally, Schlieren videography was used to visualize the gas flow. The spatial orientation has been varied in angles from 20° up to 48°. The experiments were recorded by means of HV-camera and subsequently analyzed by image processing (number, velocity and trajectory of spatters). Thereby, it was possible to reduce spattering by up to 91 % at welding speeds of up to 16 m/min.

In general, flange is fixedly connected with tubular parts or cylindrical parts through manual welding. For high labor intensity, low efficiency and poor welding quality of manual welding, a special automatic welding machine for adaptor flange of tubular parts or cylindrical parts is developed. It mainly consists of machine frame, rotary worktable, swing arm, sliding shelf, wire feeder, drive unit, control cabinet and welding torch. The welding machine has two rotary worktables controlled by PLC. With the advantages of simple structure, low production cost, high welding speed, good welding quality and low labor intensity, it is particularly suitable for small and medium sized enterprises

Spatter formation is a major issue in deep penetration welding with solid-state lasers at high welding speeds above 8 m/min. In order to limit spatter formation, the use of local gas flows represents a technically feasible solution. By using the gas flow, the pressure balance inside the keyhole, and therefore the keyhole stability, is affected. Existing investigations demonstrate a reduction in spatter and pore formation for partial penetration welding up to a welding speed of 5 m/min. However, the effect of the gas flow is not yet clarified for full penetration welding at welding speeds above 8 m/min. By using a precisely adjustable shielding gas supply, the effect of a local gas flow of argon was characterized by welding stainless steel AISI304 (1.4301/X5CrNi18-10). The influence of the gas flow on the melt pool dynamics and spatter formation was recorded by means of high-speed videography and subsequently analyzed by image processing. Schlieren videography was used to visualize the forming flow flied. By the use of the gas, a change in melt pool dynamics and gas flow conditions was observed, correlating to a reduction in loss of mass up to 70%. Based on the investigations, a model of the acting effect mechanism was given.

Tandem GMA welding technology has high deposition rates and good welding quality. But the electromagnetic interference (EMI) between the tandem GMA welding arcs is the most important factor which can influence the welding quality .Via Orthogonal Experiments and variance analysis, this paper did some basic theory research of the mutual arc interference mechanism in the GMA welding. The study was carried out from three mainly aspects ,the welding arc length control mode ,the parameters of the control pulse and the optimal range parameters in high-speed welding .The high-speed camera system was used to observe the metal transfer .In this paper the researchers realized the stability work of high-speed movement of tandem GMAW welding .

Low spatter CO2 arc welding is often used for ultra-thin steel sheets with a thickness of under 1.0-mm. In this paper, a high speed forward and reverse motion control algorithm for the motor in a welding torch and a dedicated controller for it are presented. The dedicated controller is designed with a motor driver IC (A3930) and a DSP (TMS320F-28069) coded with the proposed motion control algorithm. It is easy to optimize the operating parameters in the proposed algorithm according to various thin steel sheets. Since the torch motor must be able to feed or retract welding wire at a high speed while cooperating with the brushed DC motor in the wire feeder, the performance required in selecting the torch motor is examined and presented in this paper. With the proposed control algorithm, an optimal torch motor and the developed controller, the feeding and retracting motions of the welding wire at high speeds are possible. This results in low heat inputs to the base material and low spatter short-circuiting transfer. To verify the superiority of CO2 arc welding with the proposed torch motor control algorithm and the developed controller, an arc welding robot prototype system was fabricated and 100% purity CO2 gas arc welding with thin steel plates with a thickness of 0.8-mm was performed. This was accomplished with an interlocking a 50 W class brushless DC motor as the torch motor, the developed low spatter motion controller and an arc welding power supply.

We discuss the characteristic melt flows inside the melt pool that are observed when we vary the welding speed from very low welding speed (a few m/min) to very high one (30 m/min). At low welding speed, the keyhole is quite vertical embedded inside a large pool that fluctuates due to friction effects induced by the quite vertical ejected plume. At high welding speeds, laser interaction is only localized on the keyhole front whose inclination increases with the welding speed. Induced melt flow then dominates and can generate the humping regime, with severe undercuts. For intermediate welding speeds, it is the interaction of the vapor plume with the melt pool that controls its stability. It is concluded that the interaction of the vapor plume, which is emitted with a variable dynamic pressure and direction, perpendicularly from the inclined keyhole front, has an essential role for melt pool stability and its dynamics in laser welding.We discuss the characteristic melt flows inside the melt pool that are observed when we vary the welding speed from very low welding speed (a few m/min) to very high one (30 m/min). At low welding speed, the keyhole is quite vertical embedded inside a large pool that fluctuates due to friction effects induced by the quite vertical ejected plume. At high welding speeds, laser interaction is only localized on the keyhole front whose inclination increases with the welding speed. Induced melt flow then dominates and can generate the humping regime, with severe undercuts. For intermediate welding speeds, it is the interaction of the vapor plume with the melt pool that controls its stability. It is concluded that the interaction of the vapor plume, which is emitted with a variable dynamic pressure and direction, perpendicularly from the inclined keyhole front, has an essential role for melt pool stability and its dynamics in laser welding.

In this paper, the plasma arc welding (PAW) is studied and stainless steel temperature field is gained in this process. The thermal effect of plasma arc that specially depends on the plasma and shielding gases type and temperature field of it in work piece, which is the main key of analysis and optimization. Simulation of this process begins precisely and the separated fields for work piece, plasma arc, shielding gas and field for environment as well considered. These field equations are derived and process optimization is done by SIMPELC method and by ANSYS software coding. This simulation for gaining the temperature field of stainless steel, the effect of parameter variation on temperature field and process optimization for different cases of plasma and shielding gases (Argon, Helium and mixture of them), are done. Finally, the results of experimental tests are used to compare. The results that are derived from thermal fields show the affected process parameters which can be used for PAW process optimization. The numerical results show the timedependant distributions of arc pressure and current density, and heat transfer at the work piece surface are different from presumed Gaussian distributions in previous models.

A high speed video survey of melt flow within fiber laser welding keyholes has revealed a number of interesting observations about the mechanics of weld formation. Using Streak Images and FFT (Fast Fourier Transform) techniques to interpret the video results, quantitative values of fluid flow velocities down the keyhole front have been established. The results have lead to a phenomenological understanding of some of the quality problems which arise at high welding speeds - such as undercut and humping.A high speed video survey of melt flow within fiber laser welding keyholes has revealed a number of interesting observations about the mechanics of weld formation. Using Streak Images and FFT (Fast Fourier Transform) techniques to interpret the video results, quantitative values of fluid flow velocities down the keyhole front have been established. The results have lead to a phenomenological understanding of some of the quality problems which arise at high welding speeds - such as undercut and humping.

As sulfur content increases in weld metals, hot cracking is likely to occur. Therefore, to prevent hot cracking, the sulfur content of the welding consumables is controlled to be as low as possible in general. On the other hand, sulfur can considerably reduce the surface tension of the molten iron. Utilizing the latter characteristics of sulfur, the authors have succeeded in the development of an innovative gas metal arc (GMA) welding wire that contains a higher amount of sulfur as compared with conventional wires and possesses the flowing characteristics of the molten pool more suitable for thin steel plate welding. It has also been found through this research that the hot crack resistance of the weld metal degraded by increasing sulfur can be canceled by decreasing the carbon content of the wire to a substantially low level. The newly developed wire offers the following advantages over conventional solid wires: (1) wider and more consistent bead shape, (2) less undercut at higher welding speeds, (3) easier setting of the welding conditions due to wider tolerability to voltage fluctuations, and (4) excellent paint adhesiveness due to less slag generation.

Recently, the production of products using pure titanium has increased in Japan, and the welding for the pure titanium has attracted the attention. Concerning the welding of titanium, there are many research reports on the oxidation of weld zone in the welding process. However, the research report on practical welding procedure is scarce. In this study, weld property, which arose when the pure titanium was welded by TIG, was examined. As a result, the following was clarified: (1) The melting of the surface is easy to advance further than the penetration to the depth direction. And the weld zone of the shallow penetration is productive. (2) The undercut is hard to generate in the high-speed welding in comparison with a stainless steel 304. But, if there is an undercut, the crack is productive even in the shallow undercut. Therefore, it is proposed that the following countermeasures will be effective for the welding procedure: (1) The plate thickness of the root part should be made at about 1 mm because of the sufficient penetration. (2) Helium-argon mixed gas, in which argon is included at about 20%, should be used as a shielding gas. (3) The joint should have the root gap and be welded using the filler rod. And the knife-edge electrode should be used too.

Today, copper is one of the most important materials and will become even more important in the future. It is used in a wide range of products, industry sectors, and plate thicknesses. The beam welding technologies laser beam welding and electron beam welding achieve high intensities and are thereby suitable to overcome the difficulties in the welding of copper, which are caused by properties such as high thermal conductivity. There is a high demand for the application of the laser beam in the welding of copper, but in industrial applications, a sufficient process capability is currently only achieved with a high welding speed and a high laser power level. At low welding speeds, process instabilities such as weld metal ejections occur. These ejections can cause critical welding defects which have to be prevented. At high welding speeds, the penetration depth decreases dramatically even if a high laser power is applied. In addition, the process control is hampered and the investment costs increase. By laser beam welding in vacuum, the process capability can be increased significantly. Weld metal ejections at low welding speeds are prevented. This increase in process stability can be transferred in a high penetration depth at a comparatively low laser power level. Sound welding of copper at a power level between 4 and 8 kW (intensity level 50–80 kW/mm2) of a multimode solid state laser becomes possible without weld metal ejections. A penetration depth of 3–8 mm is achieved.

Study on microstructure and mechanical properties of 304 stainless steel joints by TIG, laser and laser -TIG hybrid welding