Arc sensor is a conventional technique toward the compensation of aiming deviation which causes from the heat distortion or unevenness of work piece. But, at present, only less than 5% of arc welding robot has arc sensing function. It is hard to use in actual welding line because of occurring of miss sensing. Many studies have been performed about arc sensing, but most of them are about the performance of sensing. So, we began to reconsider over arc sensing in the meaning of reliability. We will apply theoretical equations so as to separate the signal and the noise toward unsettled arc phenomena. This report shows the research toward the behavior of arc itself at first. We developed an averaging method of arc voltage by using histogram so as to get accurate arc length. Next, we research the effect of molten pool toward the sensitivity of arc sensor. Wider weaving width leads better sensitivity. But even if the weaving width becomes small, we found the noise level does not increase.
Dissimilar materials joining of an A5052 plate and a carbon fiber reinforced thermoplastic (CFRTP), which consisted of polyamide 6 (PA6) with 20 wt% carbon fiber addition, was performed using friction lap joining (FLJ) with the Al alloy plate as a top and the CFRTP plate as a bottom. The joint characteristics were evaluated to investigate effects of the surface treatment by the silane coupling treatment for A5052 and the joining speed on the joining properties. The joint strength was increased by inducing the silane coupling treatment for the A5052 plate surface. The tensile shear fracture load of the silane coupling treated FLJ joint increased with increasing the joining speed up to 6.67mm/s, and then decreased. The maximum tensile shear fracture load of 5.0kN was obtained at the joining speed of 6.67mm/s, and the fracture occurred at the CFRTP base plate with the joint efficiency of 97%. The shear strength of the joint interface of the joint formed at the joining speed of 1.67mm/s, which fractured at the joining interface by the tensile shear test, was estimated about 19MPa. The covalent bondings between the A5052 plate and the silane coupling layer, and the silane coupling layer and the CFRTP plate were indicated by inducing the silane coupling treatment.
The present study investigates laser irradiating and hot-wire feeding methods, specifically vertical laser irradiation with double hot-wire feeding and oblique laser irradiation with single hot-wire feeding. The effect of the laser irradiating angle was obtained by making cross-sectional observations of a joint with a 10-mm gap. Oblique laser irradiation with single hot-wire feeding was then applied to a relatively small gap (5 mm) to investigate the gap tolerance of the method. A laser diode with a large rectangular beam spot and hot-wire system were employed in the proposed process. Results showed that while oblique laser irradiation at an angle of 15° achieved almost the same weld bead as vertical laser irradiation (0°), the larger laser irradiating angle of 30° resulted in extremely large imperfection and a small amount of base metal melting. Oblique laser irradiation and single hot-wire feeding could be used practically, and their combination with laser weaving could allow large gap tolerance.
In this study, the convective flow in a weld pool during a GMA welding process was clarified by a numerical simulation using an incompressible smoothed particle hydrodynamics method. The computational domain of this simulation was a two-dimensional vertical section of a base metal along the welding direction in a system whose consumable electrode moved. The simulation revealed that the molten metal droplet fell into the weld pool and generated a wave which travelled backward. When the wave hit the solid bead, it swelled up as it solidified generating a wavy surface, which is observed in actual GMA welding. The flow inside the weld pool was also simulated. Both the height of the formed reinforcement and the depth of the penetration agreed with experimental results, which presented the validity of this simulation.
The purpose of this study is to discuss the effect of high strength second phase in Ferrite-Martensite dual-phase steel on ductile fracture mechanism. Ferrite and Martensite single-phase steels with the same properties as Ferrite and Martensite phases in the dual-phase steel were made. The smooth and circumferentially notched round-bar tensile tests for the steels were conducted. The Martensite single-phase steel has low ductility and toughness. However, no cleavage surface was observed in the fracture surface of round-bar tensile specimen of the dual-phase steel. The micro-voids were nucleated mainly in the Ferrite phase near Ferrite/Martensite boundary. The strain of Martensite phase in dual-phase steel below fracture surface was greater than critical strain obtained by round-bar tensile test for Martensite single-phase steel. Elastic-plastic analysis using 3D micro-structural model was conducted to obtain localization of stress/strain due to micro-structural heterogeneity. The plastic strain and the stress triaxiality in the Ferrite phase near Ferrite/Martensite boundary where micro-voids were nucleated in the experiments were higher than those in the other region. The Martensite phase was compressed in the perpendicular direction to loading direction due to deformation of Ferrite phase. Therefore, stress triaxiality in the Martensite phase was lower than that in the Ferrite phase.
In the shipbuilding and bridge construction industries, shop primer paint is coated to the surface of steel plates in order to protect them from rusting during a long fabrication period. However, when arc welding is applied to the primer-coated plates, the arc heat make decompose and vaporize the coating. Then, the generating gas will be enclosed in the weld metal during the solidification process, causing the porosity defect like the blowholes and the pits. In this study, the effects of penetration depth and non-penetrated joint root length on the blowholes generation were clarified with varied welding parameter, and a new horizontal fillet welding process called "Hybrid tandem MAG(HTM)" was developed by reflecting this knowledge, which uses combination with a solid wire for the leading electrode and a flux-cored wire for the trailing electrode featured deep penetration and excellent porosity resistance. In order to reduce porosity in the fillet welding of primer-coated steel plate, it was found that the following measures are effective: (a) increasing the penetration depth, (b) decreasing the non-penetrated joint root length. The reduction of porosity by increasing the penetration depth is achieved by the formation of consistent ejection passage for vaporized gas. Estimated phenomenon mentioned above was be verified by observing directly the interior of the weld pool by using an X-ray video camera. It is effective to reduce the leading electrode torch angle and to use combination with the high-current and low-voltage welding condition to create the buried arc to realize above measures. In regards to improvement of blowhole resistance, blowholes by HTM process are reduced to approx. 1/10 against the conventional process, even at high welding speed of 1600mm/min.
The effect of additional cooling by splaying liquid CO2 during friction stir welding (FSW) on the microstructure change in the stir zone of Fe - 24 wt.%Ni - 0.1 %C alloy steel was investigated. When the cooling rate after the stirring increased by the adoption of a faster welding speed and the use of CO2 cooling, a larger amount of retained austenite with lath martensite was present in the stir zone. The room temperature tensile test clarified that the retained austenite contributes to the high strength without loss of elongation due to the transformation induced plasticity (TRIP) effect.
This study clarifies the collective growth processes and size distributions of fume primary particles generated around an arc plasma in welding by numerical analysis using a model which can treat growth through homogeneous nucleation, heterogeneous condensation and coagulation among particles with any size distribution ranging from sub-nanometers to a few hundreds nanometers. In a representative case, almost all iron vapor is converted into iron particles in a very short time of 218 μs after nucleation starts. The particles grow mainly by nucleation and condensation in an early period, whereas coagulation becomes dominant after vapor consumption. The vapor consumption rate of condensation exhibits approximately 400 times as high as that of nucleation at their maxima. Homogeneous nucleation rate is high when both the temperature and the cooling rate are also high. In a region closer to the base metal, a fewer particles are generated because the cooling rate is lower and the vapor concentration is higher, which cause a lower homogeneous nucleation rate. As a result, heterogeneous condensation becomes more effective. Furthermore, the particles take longer time to reach their melting points. In consequence, the particles generated in the vicinity of the base metal have larger sizes.
Prevention of cleavage fracture is one of the most significant problems in securing the structural integrity of welded structures. Although embedded flaws from cold cracking are realistic flaws that should be considered for the structural integrity assessment of a welded structure, experimental fracture evaluations through wide-plate tensile tests using a welded joint with an embedded flaw from cold cracking have never been conducted. In this study, therefore, a manufacturing method of welded joints with intentionally introduced embedded flaws from cold cracking is first developed based on the y-groove weld cracking test. A series of weld cracking tests is next performed by the above method. It is determined that a more deeply embedded flaw is more stably cracked as higher heat-input and more diffusible hydrogen is applied. Subsequently, a wide-plate tensile test for the welded joint with the embedded flaw using the established technique is performed to evaluate the fracture load and fracture behavior. It is determined that the introduced embedded flaw is nearly rectangular and positioned near the fusion line in the heat-affected zone. A fracture-origin survey of the wide-plate tensile specimen reveals that the cleavage fracture occurred from a local brittle zone at the tip of the introduced embedded flaw. Consequently, it is confirmed that this test meets the requirements for application to an evaluation on the significance of defects. Finally, fracture evaluation is performed by comparing the fracture stress with allowable stress to verify the applicability of the evaluation method using a failure assessment diagram (FAD) of the cold-cracking embedded flaw. It is determined that the fracture load is sufficiently higher than the allowable stress; therefore, fracture will not occur even if similar embedded flaws exist in the welded structures. Furthermore, it is confirmed that a BS7910-based FAD evaluation can be applied to cold-cracking embedded flaws with a specific degree of safety margin.