The method to automatically remove the spatters which stick to the torch nozzle during GMA welding using magnetic electrode wire without touching them has been developed. By selecting the suction method with magnetic force which does not require the maintenance work of both torch and removal equipment from various nontouching method, the countermea-sures for decreasing the sticking force by spatters, removal mechanism and suitable removing force for them have been examined. In case of a carbon nozzle, the sticking force to it by spatters is less and stable for a long time. In case of a silicon nitride nozzle, the sticking force by spatters is unstable even at the initial stage and there are some cases where it increases to about 10 times of the carbon nozzle. In case of a copper nozzle, the sticking force by spatters is less at the initial stage but after its use for a long time, it becomes impossible to remove them due to the strong sticking force by their fusion. The impulse and peak value of the suction force which are necessary for success in removing the spatters in case of using the carbon nozzle become higher according as lowering the increasing speed of current. Both condenser power source and air-core coil are used for the equipment to provide the suction force and the dependability on their actual application has been confirmed.

View full abstract

We made time resolved measurements of laser-plasma interaction to study the effects of laser-induced plasma on laser processing during laser irradiation. A probe laser of 40 microns diameter was used for the measurements. The reduction of the probe laser intensity by laser-induced plasma was observed in the latter part of a laser pulse. The radial distributions of plasma absorption coefficients and removal depth were measured at various diameters of uniform intensity beams. A plasma absorption model where plasma expands vertically was developed and, using the model, the effect of laser-induced plasma on drilling speed was estimated.

View full abstract

A freely falling experiment, in which a molten metal droplet fell freely and impinged on a flat substrate, was conducted as a simulation of the thermal spray process. The relating factors to the flattening and solidification behavior of the droplet were explored and their effects were clarified.
A flattening ratio ; D/d has been introduced into consideration and used as an estimation factor of the flattening degree of the splat. It was found in our experiments that the larger Re and We numbers of the splat were, the higher the flattening ratio was. Comparing with the flattening ratio of the conventional Madejski's equation, that obtained in the experiment was fairly small. This suggests that some other factors relating to the actual flattening, for example surface tension, solidification and wetting at splat/substrate interface, have to be taken into account to the analyses. Further investigation results showed that both interface wetting and thermal conductivity of the substrate affected the flattening ratio of the splat. The observation results of the bottom surface of the splat indicated that the solidification affected the flattening behavior of the splat, especially in the central region.

View full abstract

A YAG laser processing system in which the beams of three YAG lasers (two 2.0 kW continuous wave oscillators and one 1.5 kW pulsed oscillator) were combined on the input end of single optical fiber and transmitted through the optical fiber was developed. It was confirmed that the energy density distribution and the complex pulse shape control of the laser power were similar to those of one oscillator. The effect of three types of oscillation waveforms (continuous wave, rectangular modulated wave, rectangular modulated wave superimposed pulse wave) on penetration depth was examined by using this system. As a result, it was confirmed that the penetration depth with the rectangular modulated laser beam superimposed the pulse laser beam was deeper than that with the rectangular modulated laser beam and the continuous laser beam, though the average output powers of the three type laser beams were equal each other. The effective delay time of the pulse laser beam after rising of the rectangular modulated laser beam was two or three millisecond to obtain the deepest penetration. Moreover, the penetration depth increased with an increase in the pulse laser beam power to the total one. The deepest penetration depth with a rectangular modulated laser beam superimposed pulse laser beam became 1.7 times deeper than that with a continuous laser beam.

View full abstract

In order to make factors of generation of pit and blowhole in arc fillet welding of lap joint of zinc-coated steel sheets clear, the relationship between the properties of zinc layers and the generation of pit and blowhole was investigated by carrying out CO₂ arc fillet welding of lap joint of zinc coated steel sheets and Zn-Fe coated steel sheets made with base metal with different surface roughness. As the result, it was obvious that decreasing Fe content in zinc layer and decreasing surface roughness of base metal remarkably restrained generation of pit and blowhole. Decreasing Fe content of zinc layer decreased the melting point of zinc layer, so zinc layer became easy to melt fast, then liquid zinc could escape from molten pool faster. Decreasing surface roughness of base metal increased the mobility of liquid zinc on its surface near molten pool, so liquid zinc became easy to move quickly. When zinc coated steel sheets (Zn : 40 g/m²) made with smooth surface base metal (Ra : 0.1 μm) were welded at welding speed 1.0 m/min, pit and blowhole were remarkably suppressed to the same level as welding cold rolled steel sheets.

View full abstract

The high power CO₂ laser utilizes widely for practical applications such as cutting and welding of metals because of its large scale of output power. However laser welding of superalloys which required a high quality and a high efficient welding, is rarely applied in practical use in the field of heavy industry. An ordinary laser welding of metals with filler wire produces the columnar structure which meets at the center of weld bead, so this leads to decrease of creep properties. At this point of view, we have developed to improve creep rupture behavior of joints by laser melting the surface of weld bead again. In this experiment, Co-base superalloy of less than 3 mm thickness was used as a base metal. The spot size of laser beam to irradiate on the first laser weld bead surface was approximately 3 mm. The depth of this surface melting layer was changed by traveling speed within this experiment. As a result, it was found that both its elongation and creep rupture life time after laser melted were improved to twice compared with as welded. The laser surface melting on laser welds of Co-base superalloy shows that the creep properties can be greatly improved by re-distribution of the boundary of the columnar structure.

View full abstract

This work is intended to develop a three-dimensional numerical model for circumferential GTA (Gas Tungsten Arc) welding of pipes. A model for circumferential welding of pipes with single-Vee groove is developed in the last report. In the present paper, the calculated result by using the model has been compared with the experimental results in GTA welding. And the influence of surface tension or arc pressure on GTA weldine process has been discussed experimentally and theoretically.
As a result, it is concluded that the model, developed in the present work, is a useful guide for circumferential welding of pipes.

View full abstract

Heat-transfer surfaces for cooling system of high power semiconductor such as G.T.O (Gate Turn Off Thyrister) is developed. The surface which has high efficient heat-transfer rate is consisted with porous structures formed by brazing.
Ball like particles in diameter of about 0.4 mm with Ni-P prepared by plating on the surfaces are accum ulated on substrates with a few layers. Then the substrates with porous structure are obtained by heating under the brazing conditions of at 1223 K for 600 s in the 10^-1 Pa atmosphere.
Efficiency of heat transfer rate of the brazed porous structure is about twice as high as the one of coarse surfaces by conventional shot-blast process.

View full abstract

It is often difficult to grasp clearly an entire view from partial images of welds (circumferential joint) of inside of small caliber (about 50-300 mm) pipe or tube by industrial endoscopes because of their narrow sight.
In this study, an effective system which helps inspect welds of inside of pipes or tubes accurately and immediately by composing panoramic views from their partial images is proposed. The partial images of inside of pipes or tubes were taken with the instrument with built-in CCD camera which was developed in this study. The partial images were composed using the overlapping image data. If geometric distortions exist on images, it is impossible to compose those by reason of the disagreement of overlapping areas, so geometric distortions were corrected as preprocessing. As a result, it is possible to get complete panoramic views of welds of inside of small caliber pipes or tubes automatically. Quality of pictures and operating time reaches a practical level.

View full abstract

The mechanism of embrittlement at Ta/Zr diffusion bonded interface was clarified by employing Zr-Ta binary alloys which were synthesized the bonding interface region between Ta and Zr. Zr-3 mass%Ta, Zr-10 mass%Ta and Zr-20 mass% Ta binary alloys were used for the hardness test and microstructural analyses after solution and/or annealing treatments. The hardness of Zr-Ta alloys increased quickly with increasing the annealing time at the early stage of aging and fell down after long term aging. TEM observation revealed that α'-(Zr, Ta) supersaturation solid solution (martensite) was formed in as solution treated specimens, and that Ta and ω-Zr were precipitated in the aged specimens. The hardening of Zr-Ta alloys at the early stage of aging was due to the precipitation of Ta and ω-Zr from the ω' martensite, and the overaging was subsequently occurred with coarsening the Ta precipitates. It was deduced that the precipitation of Ta which was attributable to the spinodal decomposition of supersaturation solid solution of Zr, and that Ta was the main cause of embrittlement at Ta-Zr diffusion bonded interface.

View full abstract

The behavior of helium bubble in helium-doped austenitic stainless steel weldment was investigated using scanning electron microscopy, transmission electron microscopy and numerical calculation technique. The stainless steel was helium ion-implanted and welded by YAG laser apparatus. Helium ion implanting to the sample was carried out using 8 MeV implantation apparatus. The sample was doped 1.0×10¹⁹ atoms/m² at 5 MeV and then doped 2.45×10¹⁹ atoms/m² at 6 MeV.
The region where helium bubbles formed in the heat-affected zone increased with increasing laser power. For low laser power, the helium concentration was above 10 appm in the weld metal and many large helium bubbles larger than 3μm in diameter were observed at the bond region. The volume of weld metal increased and the size of helium bubble decreased with increasing laser power respectively. Number of fine helium bubbles below 0.2μm in diameter were observed along the dendrite cell boundary in the weld metal.
The increases of laser power and travel speed led to the initiation of cracking at the dendrite cell boundary in the weld metal, even at 2.9 appmHe.

View full abstract

Precipitation behaviors in W alloyed 9Cr weld metal during PWHT (Post Weld Heat Treatment) and creep rupture test have been studied by analyzing extracted residues from the weld metals after PWHT and creep rupture test. The results of analysis were compared with the prediction by THERMO-CALC.
M₂₃C₆ and MX type carbo-nitrides were predicted to precipitate at PWHT temperatures in equilibrium states by THERMO-CALC. In addition to M₂₃C₆ and MX type carbo-nitrides, Laves phase was predicted to precipitate at creep rupture test temperatures in equilibrium states by THERMO-CALC. X-ray diffraction analysis showed that M₂₃C₆ and MX type carbo-nitrides precipitates in the weld metal during PWHT in accordance with the results from THERMO-CALC. Less than 100 hours in creep rupture test at 873 K, M₂₃C₆ and MX type carbo-nitrides were detected in weld metals by X-Ray diffraction analysis. Laves phase precipitates more than 100-1000 hours during creep rupture test at 873 K. Presence of Laves phase in the weld metal after creep rupture test at 873 K/1126.7 hours was revealed by X-ray diffraction analysis. Content of W in extracted residues from weld metals after creep rupture test at 873 K increased substantially with time more than 100-1000 hours. This increase in W content in extracted residue is probably due to the precipitation of Laves phase. Contents of W and Mo in extracted residues from weld metals after creep rupture test at 873 K reach constant values at roughly more than 10000 hours, and these values are in good agreement with those predicted by THERMO-CALC. Time dependence of W content in extracted residue from weld metals of creep rupture test at 873K and 923K are in good agreement with the calculated results based on Jhonson-Mehel-Avrami type equation.

View full abstract

The effect of nitrogen addition into the laser treated region on sensitization behavior was investigated in this study. The laser surface melting treatment was performed by a CO₂ laser by using nitrogen and argon for the shielding gas. Specimens for the laser treatment were heat-treated at 773K for 30ks to imitate the condition to cause low temperature sensitization in weld metals of austenitic stainless steels. The EPR method was adopted for evaluation of sensitization in the melted region. EPR test results indicated that in the case where δ-ferrite was contained in the laser-treated region, improvement of sensitization was insufficient at lower laser traveling velocity. By contrast, striking improvement was obtained even at the lower laser traveling velocity when nitrogen was used for the shielding gas. This is because that re-sensitization in the melted region heat-treated after laser treatment with nitrogen gas shielding was suppressed. Micro-structural analysis revealed that the primary phase at solidification in the melted region by the laser treatment changed from δ to γ, resulting in the decrease in the amount of δ-ferrite at the lower laser traveling velocity by using nitrogen for the shielding gas. Such microstructural change seemed to be responsible for the fact that sufficient improvement was obtained even at the lower laser traveling velocity, because theoretical analysis revealed that sensitization at γ/γ boundary occurred much longer time than that at δ/γ boundary. Thus, re-sensitization in the laser-treated region was prevented by using nitrogen shielding gas in the laser remelting treatment.

View full abstract

Crystallographic orientation analysis over the bonded region in TLP-bonded joints of Ni-base single crystal superalloy, CMSX-2 was investigated three-dimensionally using the electron back scattering pattern (EBSP) method. The (200)-pole figure and the stereographic triangles for three directions indicated that each analyzed point was projected at the almost same location in the stereographic triangles for any directions. EBSP analyses for the specimen bonded at 1523 K for 1.8 ks when the isothermal solidification was complete, and for the specimen post-bond heat-treated were also conducted. All analyzed points possessed the almost same orientation across the joint interface and misorientation OB was negligibly small in as-bonded and post-bond heat-treated situations. HRTEM observation revealed that the atoms were arranged continuously across the bonded interface and were quite coherent at the bonded interface. It was confirmed that single-crystallization could be readily achieved during TLP-bonding. It followed that epitaxial growth of the solid phase occurred from the base metal substrates during isothermal solidification.

View full abstract

Wire bonding technology is being applied to narrower pad piches and longer spans in LSI packages with the increase in number of input-output pins and shrinkage in chip size. This makes adjoining wires liable to touch during the molding process. To solve fundamentally this problem, the authors have been developing bonding technologies, using coated gold wires which do not suffer from short circuit failures even if the wire touch occurs.
In this study, various coated wires were evaluated to select the optimum coating film with improved resistance to the wire touch at high tempratures and improved bonding continuity. Packages were then assembled with the selected wires, and various reliability tests were conducted.
The best properties were obtained with the coating film of 0.4 μm thick heat-resistant formal, which showed high insulation reliability in a high temperature wire-crossing test and enabled continual bonding for more than one hundred thousand wire connections. It was confirmed that the assembled packages have sufficient insulation reliability between touching wires and that no failures occurred in various reliability tests including temperature cycling and high temperature high humidity bias tests.

View full abstract