Arc sensor is a conventional technique so as to compensate the aiming deviation which causes from the heat distortion or unevenness of work piece. But, at present, only less than 5% of arc welding robot equips arc sensing function. It is hard to use in actual welding line because of occurring of miss sensing. So we began to reconsider over arc sensing in the meaning of reliability. Our approach is separating arc welding process into several physical phenomena, and research how the unstable factors act to the sensing results. And we try to find the countermeasures toward miss sensing. Our final target is short arc welding. As the road to that target, this report shows the effect of unstable factors to the arc plasma phenomena. So the experiment is performed with TIG welding on copper plate so as to ignore the melting of electrode and workpiece. By analyzing the effect of unstable factor, we proposed the several countermeasures toward miss sensing.
Friction stir welding (FSW) is a solid phase process which can produce high quality dissimilar joints. However, due to the difference of material properties between A6N01 aluminum alloy and AZ31 magnesium alloy, optimization of process parameter is difficult for dissimilar FSW. In this study, the relationship between process factors (material arrangement, tool offset and probe diameter) and quality of the joint was investigated. After the optimization of these process factors, the AZ31 and A6N01 dissimilar joints with high joint efficiency could be obtained at circumferential velocity of the probe from 0.147 to 0.183m/s regardless of probe diameter. This result indicates that the circumferential velocity is one of the most important factors for AZ31 and A6N01 dissimilar FSW.
Bondability of thermosonic flip chip bonding using ramp bond force profile was investigated. Compared with a conventional method using constant bond force profile, ramp bond force profile achieved higher bond strengths with same amount of bump deformation. This was because that expansion amount of contact area between bump and electrode under applying ultrasonic vibration increased. Furthermore, we found out that pressure in bonding process at interface between bump and electrode of ramp bond force profile became lower than constant bond force profile. Bondability was considered to have been improved by incrementation of slip between bump and electrode cause by lower pressure.
In this study, the oxygen contamination and the heat input on the anode surface were investigated by experimental measurements in order to guarantee a high-quality welding in TIG welding with a constricted nozzle. As a result, it was clarified that the energy density which was one of the heat source characteristics became higher at the center of the anode surface by attaching the constricted nozzle. Moreover, the oxygen concentration on the anode surface during TIG welding with constricted nozzle was as low as that during a conventional TIG welding. In addition, the oxygen concentration on the center of anode surface was changed by operating conditions such as a welding current and a shielding gas flow rate. Finally, the suitable welding condition was proposed from the tendency of the oxygen concentration on the anode surface, in which the oxygen concentration on the anode surface kept low.
For the purpose of higher welding speed and lower force in friction-stir-welding (FSW), we investigated the feasibility of preheating using gas-tungsten- arc-welding (GTAW). It can be expected to assist heat input for the plastic flow by using GTAW with high energy density. Defect-free bonding by a GTAW-FSW hybrid process was successfully achieved at a welding speed less than 8.3mm/s, while normal FSW left a defect at welding speed of 5.0mm/s. The axial forces during friction stirring in the GTAW-FSW process were lower than 40% of that in the normal FSW. The joints of GTAW-FSW had stir zones with fine grains similar to the FSW joints. This process could obtain higher productivity, that is, higher welding speed and lower force than the conventional FSW. It is also possible to obtain a high strengthen and unique structure with fine grains of FSW.
Current work deals with investigation of the effect of the use of low transformation temperature welding wire (LTT welding wire) on distortion reduction of parts made by wire and arc additive manufacturing technique (WAAM). LTT welding wire and SUS308L wire, which was austenitic stainless steel wire, were used for making WAAM test pieces. Distortion of base plates of test pieces were evaluated by 3D non-contact coordinate measurement system. As a result, longitudinal bending distortion of the base plates of test pieces in which LTT welding wire was partially or fully used was smaller than those of the test piece which was made only by SUS308L wire. Especially, longitudinal bending distortion of the base plates of test pieces which was made only by LTT welding wire was reduced drastically from those of the test piece which was made only by SUS308L wire. However, angular distortion of the base plates were not reduced drastically even if the test piece was made only by LTT welding wire. The difference of the reduction effect of the use of LTT welding wire was discussed by considering the position of neutral plane of each distortion mode.
Recently, many studies have reported the distribution of temperature and metal vapor concentration in MIG arc plasma by the optical emission spectroscopy. However, these studies required the assumption of axial symmetry of the plasma. Most of MIG welding phenomena are not axially symmetric, therefore, a tomographic approach is required. In this study, we constructed the simultaneous and multidirectional measurement system by 12 detectors to measure 3D distribution of temperature and iron vapor concentration. The detectors consisted of the CCD cameras equipped with the interference filters, which acquired the spectral line intensities for one Ar I line and two Fe I lines. Each spectral line intensity was laterally integrated with 4 directions and converted into 3D distribution by image reconstruction method. In metal plasma region, we used the relative intensity method for temperature and Saha equation for iron vapor concentration. In Ar plasma region, temperature were calculated by using absolute intensity calibration. We measured MIG arc plasma in globular, globular to spray, and spray transfer mode. As a result, increasing welding current caused the enlargement of high iron vapor concentration region and the expansion of high temperature region of the outer arc plasma. It was found that there was large deviation of Ar plasma region although Fe plasma still exits near the center of arc axis and symmetrical arc plasma were captured by one-side measurement. In addition, this state has a possibility to be measured as a symmetrical-like state by one-side measurement.
In order to guarantee the weld quality, the ultrasonic inspection is widely used as a method of checking the presence of weld defects. Conventionally, the defects are detected by a contact type ultrasonic inspection after the welding process because this method cannot be used under a high temperature/noise environment such as during welding. Therefore, we aim at the development of contactless and in-situ measurement system during welding by using laser ultrasonic technique. This system enables to conduct the welding and inspection simultaneously with monitoring. In this study, we first measured the test piece shape of half rounded groove on the top surface to investigate the performance of our system. As a result, we could measure echoes from the bottom of the groove and visualize the test piece shape. Then, we measured the molten pool shape by hammering method and laser ultrasonic technique during the bead on plate welding by TIG arc. In addition, we calculated the 3D heat conduction model to apply the temperature distribution to the results of the measurement because the velocity of laser ultrasonic depends on the temperature. As a result, the measured distance from the bottom of work to the molten pool interface reasonably corresponded to the actual position obtained by the hammering method.
Submerged arc welding (SAW) is widely used in heavy industry fields, such as ship buildings or steel pipe mills. Some papers pointed out that recycle use SAW slag to SAW flux is effective to conserve natural resources and also to save flux cost. In this paper, we have compared chemical compositions, crystal structure, and melting behavior between flux and slag in SAW process. Most of chemical compositions of slag were the same as those of flux except Fe and P. Fine metallic steel particles were recognized in slag and the size of them were very similar to welding fume. Major differences were not detected in crystal structure and melting behavior in comparison between flux and slag.
Submerged arc welding (SAW) is widely used in heavy industry fields, such as ship buildings or steel pipe mills. Some papers pointed out that recycle use SAW slag to SAW flux is effective to conserve natural resources and also to save flux cost. In this paper, we have investigated reasons why M. Fe content of slag changed when different chemical composition flux was conducted in SAW. We have also investigated which one either welding wires or base metal plates are main source of M. steel particles in SAW slag. We have concluded that change of M. Fe content in slag resulted from difference of arc temperature in SAW, and welding wires were main source of fine M. steel particles in SAW slag.
Reducing auto body weight by use of high strength steel is an important issue. Although it is necessary to increase the strength of steel sheets for underbody parts, use of high strength steel sheets has not progressed sufficiently due to the problems of fatigue and corrosion. Corrosion of underbody parts mainly occurs in arc welded joints, but the detailed corrosion mechanism had not yet been clarified. The author investigated the corrosion behavior in arc weld by laboratory corrosion tests using Ar-20%CO2 gas shielded arc weld, and clarified the corrosion mechanism. Based on that work, Ar-5%CO2 gas shielded arc weld was applied as an approach to improve corrosion resistance. The corrosion behavior of arc welded joints was classified into three phases. In the 1st phase, rust occurred at the slag portion as a paint defect on the weld bead and toe. In the 2nd phase, under-film corrosion occurred from the weld toe. In the 3rd phase, perforation corrosion progressed at the film peeling portion near the weld toe. When Ar-5%CO2 gas shielded arc weld was applied as an improvement technique, slag generation was suppressed and as a result, corrosion resistance was improved.
Cold cracking is a serious concern in the welding of large-scale steel structures. And, diffusible hydrogen is a major factor affecting to it. Several general techniques are known for preventing cold cracking, however there are no examples of approach in the past from welding apparatus side. The new welding process was developed to reduce diffusible hydrogen content in the weld metal with special welding torch in GMAW and FCAW. Furthermore, the factors were researched that affecting the effectiveness of the new welding process. The special welding torch was designed by calculation results of wire temperature distribution and analysis results of hydrogen source behavior during welding. It slightly sucks the gas around the wire through the suction nozzle. The effectiveness of developed process was showed by comparative experiment with conventional process, namely confirmed the correctness of the structural design. Meanwhile, it was revealed that wire structure (i.e. seamed or seamless) affects strongly the effectiveness of the process. This process was very effective with seamed flux cored wire.
The gas metal arc (GMA) welding process involves metal transfer, in which molten droplets detach from the tip of the electrode wire and move to the base metal. Such metal transfer influences the arc plasma behavior, and affects the performance and productivity of the entire welding process. Therefore, controlling metal transfer is important for improving the welding process. However, metal transfer is not understood sufficiently because of its complexity. The objective of the present study was to obtain a deeper understanding of the metal transfer process, and we performed a numerical investigation to visualize 3D metal transfer. We focused on the free-flight transfer that is observed under relatively high-voltage conditions and the influence of the current path on the transfer mode was investigated. In order to simplify the calculation model, we did not take into account the arc plasma. We assumed a conical current path from the wire electrode to the cathode plate in order to include the electromagnetic force. The model could numerically describe the straight mode with a fixed hypothetical arc. On the other hand, when the arc moved temporally, the tip of the liquid swung and generated small droplets similar to spatter, likely as a result of rotating transfer. The current path was found to play a very important role in determining the metal transfer mode.
The research and development of nuclear fusion reactors are going on to acquire a next-generation energy source. The reduced activation ferritic/martensitic steel F82H is adopted as a structural material of the blanket module, which is the device set on the inner wall of fusion reactors. As welding for each thickness of F82H, the most suitable welding method will be selected. Laser beam welding is examined to adopt in thin part. However, by laser beam welding in the actual weld joints, weld defects should be considered. And performing post weld heat treatment (PWHT) is necessary because F82H is based on 9Cr-1Mo steel. Therefore, the objectives in this research are to clarify of laser beam welding condition for performing no defect weld joints and to be adequate PWHT condition. Appropriate laser beam welding condition of F82H is evaluated by cross-section observation in welds. As PWHT condition, heating time and heating temperature is selected by Vickers hardness and ductile brittle transition temperature (DBTT) from Charpy impact test. From cross-section observation in welds of F82H, some no defect weld joints are identified. 710°C∼730°C×1h was adequate in PWHT condition to reduce welds hardness to base metal hardness and to shift DBTT to sufficiently low level. Therefore, in this study, it is found that sound weld joints can be realized by selected the appropriate welding condition.
High power laser welding has an advantage of remarkable improvement of productivity. However, now the application of laser welding to large structures is limited due to severe control of joint gap, lack of available in-process control and small spot size as compared with arc welding. In the present paper, the fundamental performance of seam tracking system has been investigated in order to apply laser welding to large welded structures using 6kW fiber laser and a 6-axis robot. Seam tracking is a method of mainly detecting a weld line by a light cutting method. In other words, the weld line is irradiated with light for weld line detection from the outside. The reflection form of the light and the intensity distribution of the reflected light are acquired by the camera. A unique algorithm or image processing is executed for detection of the weld line. It is one of methods to perform seam tracking6)7)8). If there are a lot of tack welds in the weld line, laser welding must be performed while seam tracking system detects the tack welds in real time during welding. In order to recognize the outline of a tack weld, data of four monitoring parameters were extracted in image processing so that it was possible to judge accurately whether a weld line or tack welds. As a result, the average tracking accuracy of the seam tracking system for linear laser welding using a 6-axis articulated robot was plus 0.072mm. The precision of laser positioning for sound welding was able to be kept within the tolerance range of ±0.15mm.
Underwater laser welding for single pass full penetration without backing was achieved under a water pressure equivalent to that at a depth of 100m under the sea level. For the welding, a 304-type material with a thickness of 4.5 to 6mm and a disk laser with a maximum power of 3kW were used. Nitrogen gas was used to shield the surface of laser irradiation, thereby providing a locally dried environment. We confirmed that the weld penetration became shallower with an increase in the surrounding pressure in both water and air. By appropriately adjusting the gap distance, the molten metal flowed into the back bead, and the full penetration bead was formed without underfill or humping bead under a water pressure. Under high-pressure conditions, an increase in the austenite content in the nitrogen-based weld metal was observed, but no crack was detected. In addition, it was shown that the amount of diffusible hydrogen in melt metals can be reduced by nitrogen gas shielding on the back side. The mechanical properties of the final material, such as tensile strength, bend strength, and hardness, were comparable to those of the base metal.