Recently, the electron beam welders with high acceleration voltage (more than 100kV) and high electrical power (more than 15kW) has been reviewed the role of the high energy electron beam density again, due to space or aircraft development or automobile industry desired high productivity and high accurate welding for save energy. NEC group have supplied these electron beam welders. This time, the automatic alignment adjustment system of the electron beam orbit, and the automatic adjustment system of filament current, were developed and put to a practical use. As a result, the great effectiveness for stability of welding quality was apparent.
A shape of arc plasma in gas shielded arc welding is an important factor for the quality and efficiency of the welding. The arc plasma changes its shape by an external magnetic field because the arc is a flow of electricity and is subjected to the electro magnetic force. In this study, we examined the control of arc plasma by a cusp type magnetic field. The field produces a high and low magnetic area alternatively, and changes the cross section of the arc plasma from a circular to an elliptical shape. The Previous study using solenoid coils to produce a cusp type magnetic field reported that magnetized arc plasma provides deeper penetration. However, the solenoid device developed for the cusp magnetic field was too large in comparison with the size of the welding torch used for production welding. Therefore, this study investigated the magnetic control of arc plasma with permanent magnets that have recently become smaller in size and higher in intensity. Theoretical analysis model was constructed to determine the optimum arrangement of the magnets. This analysis requires a three-dimensional numerical model because the temperature-, velocity-, electromagnetic-fields of arc plasma change three-dimensionally by the additional magnetic field. It was analytically and experimentally shown in TIG arc welding that the arc shape could be elliptical cross section even using the permanent magnets. Furthermore our analysis showed that the effective magnetization direction of magnets was vertical, and this result was confirmed experimentally. As a result, we obtained the good bead appearance in the high speed welding with this magnetic control.
This study investigated influence of preheating temperature and welding speed on microstructure of dissimilar lap friction stir weld of ductile cast iron FCD450 and 304 stainless steel. The stainless steel was placed on FCD450, and then FSW was carried out at tool rotational speed of 200, 400 and 600rpm and welding speed between 1 and 10mm/s. Preheating was conducted at 573 and 773K. Martensitic structure was formed in HAZ of FCD450 without the preheating, while the preheating resulted in formation of a pearlite structure. Even when the preheating was employed, however, stir zone (SZ) of FCD450 had the chill structure at lower welding speed, because the SZ temperature exceeded the eutectic temperature. Formation of the chill structure in the SZ could be prevented at higher welding speed. This study showed that friction stir welding would be available as a dissimilar welding method between ductile cast iron and stainless steel.
A tightly-focused high power fiber laser beam can produce a narrower and deeper penetration weld than a conventional laser weld of wine-cup shape, which is expected to improve laser absorption. The objective of this research is to assess laser absorption in a wide range of conditions such as laser powers of 2 kW to 10 kW or welding speeds of 17 mm/s to 250 mm/s in bead-on-plate welding of Type 304 austenitic stainless steel with a laser beam of 200μm spot diameter by water-calorimetric method. Furthermore, the relationship between the laser absorption and the keyhole formation location to a focused laser beam was revealed by using X-ray transmission in-site observation system and high-speed video camera with diode-laser illumination. It was found that the absorption at 10 kW laser power and 17 mm/s welding speed was 89% high. Compared X-ray transmission observation images of the keyhole with the focusing feature of the fiber laser beam, the center part of the incident beam with a bell-shape profile were delivered directly to the tip of a keyhole. Moreover, the increase in the welding speed from 17 mm/s to 250 mm/s reduced the absorption from 89% to 65%. The high-speed observation pictures indicated that the incident fiber laser beam was partially exposed out of the keyhole inlet at higher welding speed, which led to the decrease in the laser absorption. Consequently, it was confirmed that the tightly-focused high-power fiber laser welding was high-efficiency process at the maximum of about 90% in laser absorption at low welding speeds, owing to the irradiation of almost all the incident laser beam into the keyhole inlet. It was also assessed that the energy loss due to evaporation was smaller than 1%.
In non-pulsed gas metal arc welding (GMAW), spatter can be reduced by lowering the short-circuit current to a low level just before the re-arcing. The reduction of spatter requires an improvement in the accuracy of predicting the re-arcing by stabilizing the metal transfer and improving the robustness of the accuracy against disturbances. The controlled bridge transfer (CBT) process optimizes the accuracy of predicting the re-arcing in real time in response to the metal transfer, realizes spatter reduction and stable arc in non-pulsed GMAW. Traditionally, GMAW is carried out using electrode positive polarity. However, this polarity is not sufficient for welding extra-thin steel sheets, specifically those thinner than 1.0 mm. With electrode negative (EN) CBT process, although slight arc voltage fluctuation occurs caused by behavior of cathode spots on the tip of the wire during EN polarity GMAW, instantaneous voltage is used command computation to improve the transient response against the disturbance. Consequently, a stable arc can be obtained without increasing the number of short circuits in a unit time to obtain spatter-free welds.
In non-pulsed gas metal arc welding (GMAW), spatter can be reduced by lowering the short-circuit current to a low level just before the re-arcing. The controlled bridge transfer (CBT) process, which optimizes accuracy of predicting the re-arcing in real time in response to the molten metal transfer, realizes stable, low spatter level. In this research, the methods for controlling short-circuit transfers to minimize spatter and realize stable arcs in GMAW of stainless sheet using argon-rich shielded gases are investigated. The new CBT process has been developed by applying the specific arc length control that is not affected by abnormal rise in arc voltage in argon-rich shielded gas welding. This process can suppress the spatter generation caused by fluctuation in the vibratory motion of the weld pool or inaccurate prediction of the re-arcing in the succeeding short-circuit/re-arcing cycle, and thereby spatter-free GMAW in the short-circuit transfer mode can be carried out even on stainless steels.
Authors tried to weld a steel plate to Mg alloy plate using a resistance spot welding method. In welding of the dissimilar materials, the authors employed SUS304 insert metal and investigated the effect of the insert metal and the electrode tip geometry on the strength of the welds. The following results were obtained. When the steel plate was directly welded to Mg alloy plate without the insert metal, the temperature around the welded area and the strength of the weld increased with increasing welding current. The reason seems to be that the bonded area increases due to the increase in nugget diameter of Mg alloy and that the oxide film on the faying surface of the steel is easily reduced by the molten magnesium. The insert metal of SUS304 with optimal thickness significantly improved the strength of the weld, however, the excessively thick insert metal increased the amount of magnesium expulsion and resulted in decreasing the weld strength. The electrode tip with flat geometry attached a steel washer improved the strength of welds because the plunging depth of the electrode tip into the Mg alloy plate was decreased, resulting in the decrease of the molten magnesium expulsion.
It hasn't been well known which heat of joule and arc discharge is dominant factor in flash welding process. The objective of this study is to clarify heating mechanism of flashing. The flashing is a cycle consisting of local contact, joule heating, melting, spattering and arc discharge. Numerical model of flashing cycles was developed by assuming initial contact conditions. It has been evaluated heat input and welding parameters of DC flash welding. As the results, arc discharge heat is higher than joule heat for a wide range of flash current. Optimum flashing of DC is large contact and low frequency compared with general continuous flashing of AC. Heat input and platen velocities are 50% higher than those of AC at the same conditions and welding quality. The calculated velocities and crater depth of DC flashing are in good agreement with hot-billets welding data. It was found that DC flash welding compares very favorably with AC for short-time welding.
In cold spray, feedstock powders are accelerated by supersonic jet with solid phase and deposited onto substrate. Compare with the conventional thermal spray, the coatings have low porosity without oxidation and decomposition. This study examines the effect of the powder compressive strength of each particle on coating deposition characteristics using two types of Ni powders, manufactured in a different process, in cold spray. The result indicated that heat treatment reduced the powder compressive strength, and the decrease of the powder compressive strength was related to the increase of bond strength of particles and deposition efficiency. In addition, it was shown that the powder compressive strength has an influence of deposition mechanism.
Gas pressure welding method does not need heavy equipments, and produces highly reliable joints. Therefore, it is often used for rails and reinforcing steel bars. However, if bonding work is poor, a large quantity of oxide inclusions remain at the weld interface, and those inclusions will cause the weld defect. So, in this study, oxide inclusions on weld interface were observed for clarifying existence state of oxide inclusions on each welding step by means of Scanning Electron Microscope and X-ray micro analyzer. As a result, it was clarified that Fe-O type oxide inclusions were formed on weld interface at early step, and then these oxide inclusions gradually changed to Si-Mn-O type oxide inclusions as welding process advanced. The transition behavior model of oxide inclusions on gas pressure weld interface was proposed. This result will contribute establishment of reduction of oxide inclusions.
This study investigated the electrode life and the electrode degradation characteristics during resistance spot welding of zinc-coated galvannealed steel sheets. As a result, it was found that the electrode life in alternate resistance spot welding of galvannealed steel sheets and bare steel sheets was extremely short in comparison with welding of only galvannealed steel sheets. During alternate resistance spot welding, the ring-shape nuggets were formed easily. The reasons for this is explained by the sticking of the alloy layers formed on the electrode top during previous welding of the galvannealed steel, to the bare steel sheet surface at the following welding of bare steel, so that notable wear took place and the surface profile of electrode tip became flat. Additionally an accumulation of highly resistant carbonaceous substance layer at the center of the electrode top caused an annular flow of the welding current to hinder the nugget formation.
This paper deals with the improvement in the weld metal toughness by the formation of the fully acicular ferrite microstructure in the high heat input electroslag welding. Applying the high Ti bearing welding wire and the low basicity flux provided a large number of Ti containing oxide inclusions in the weld metal, which were effective for the acicular ferrite formation. B addition to the weld metal suppressed the formation of the coarse grain boundary ferrite and the proper B/N ratio of the weld metal ranged from 0.5 to 0.8. In the B/N ratio exceeding 0.8, the weld metal toughness was reduced because of the increase in the M-A constituent. The weld metal with the fully acicular ferrite and the proper B/N ratio exhibited the excellent toughness (vE0>100J) even at the high heat input as high as 100kJ/mm.
The influence of Nb content on the SCC (Stress Corrosion Cracking) susceptibility of Inconel alloy 600 weld metals with C contents of 0.03—0.07mass% has been investigated, since in the recent nuclear power plant there is a tendency to increase the Nb addition to the weld metal to avoid the occurrence of SCC caused by the grain boundary depletion of Cr due to the preferential precipitation of Cr carbides. The SCC susceptibility of the weld metal was evaluated from the maximum depth and number of cracks occurring during the CBB (Creviced Bent Beam) test in high temperature pressurized water using plate specimens cut from shielded metal arc weld metals. For the weld metal specimens in the as-welded state, the Nb and C contents had only slight influences on the SCC susceptibility. When the specimen received a heat treatment consisting of stress relief annealing (SR) for 72 ks at 893 K and subsequent ageing (LTA) for 720 ks at 673 K, however, the significant influences of the increases in C and Nb contents on the SCC susceptibility were observed; the susceptibility of weld metals with higher C contents (∼0.07mass%) decreased with increasing the Nb content up to ∼2.6mass%, but a further increase in the Nb content enhanced the SCC susceptibility remarkably. The decreased SCC susceptibility with an increase in Nb content (less than 2.6mass%) observed in the weld metal of the higher C content can be explained as resulting from the suppression of Cr depletion layer at the grain boundary due to the formation of stable Nb carbides, since TEM-EDS analyses revealed that no Cr depletion at the grain boundary occurred at Nb contents of 2.6mass% or more. When the weld metal of the higher C content was subjected to the SR+LTA treatment, the hardness increased remarkably with the Nb content, suggesting that the higher stress was applied to the specimen during the CBB test, as the Nb content was increased. This increase in the applied stress is a possible factor that contributes to the increase in the SCC susceptibility with the Nb content in the weld metal free from the grain boundary depletion of Cr. For the weld metals with lower C contents (∼0.03mass%), the SCC susceptibility decreased with the Nb content after the SR+LTA treatment, probably owing to the suppression of the Cr carbide precipitation at the grain boundary and resulting Cr depletion.