Materials Science Forum Vols. 580-582

Abstract: All of the experiments performed on friction welding combinations of 304SS and mild steel are modeled using the ABAQUS code and the Johnson-cook equation is used to define coupled thermo-mechanical properties of materials. The variations of temperature, von-Mises stress, plastic strain, and strain rate during continuous welding are systematically investigated and analyzed. The calculated results of temperature distribution are in good agreement with the infrared detected ones. The numerically calculated results for the shape of the welded joint also show an excellent fit with experimental observations. The von-Misses stress and equivalent strain distributions are more influenced by the initial pressure than the final pressure. The metallographical examinations, hardness and tensile tests of the samples are carried out. In all the tension tests carried out the samples were broken from their base metals and not the welds.

Abstract: The formation of stable back beads in the first layer weld during one side multilayer welding is important to achieve high quality welded metal joints. The authors thus employed the switch back welding method for the welding of V groove joints without backing plates. In this method, the personal computers control a welding robot, a digital welding power source and a wire feeder, simultaneously. Each unit is connected together with Ethernet and UDP (User Datagram Protocol). The personal computer for controlling the welding robot is synchronized with other computers. The suitability of the welding conditions for each root gap was verified by observation of the arc, molten pool and external appearance of back beads.

Abstract: The HAZ softening of the ultra fine grained steel weldment occurs when welding heat input is higher than the critical value. The critical welding heat input was found to be about 10kJ/cm for the steel studied. The lowest hardness value and the width of the softened HAZ are dependant on the applied welding heat input. For obtaining high productivity with the low heat input, less than 10kJ/cm, a high speed FCA welding process with 2 electrodes was developed and verified to be an efficient method for the ultra fine grained steel. The weldment made by this process did not have the softened HAZ; and thus, satisfied the tensile strength required.

Abstract: In order to achieve single pass welds without edge preparation, instead of multipass procedures, one of the most notable techniques is to use activating flux with GTA welding (GTAWflux) process. In autogenous GTA welding mixed fluxes (oxide SiO2 and Cr2O3), were applied on the weld area of type 310 stainless steel through a layer of the flux to produce a bead-on-plate weld. Many parameters affect the GTAW-flux process quality. The Taguchi method can improve on the disadvantages of full factorial design. However, in practice, it has certain limitations. In this work, a Taguchi-Neural approach (Combine Taguchi method and a neural network) was used to select the GTAW-flux process parameters. The experimental procedure of GTAW-flux process, via the proposed approach produced full penetration of the weld root in 8 mm thick type 310 stainless steel with single pass welds.

Abstract: Lap joint of AZ31 Mg alloy extruded sheet can be successfully made by friction spot joining (FSJ) process. Joint strength was strongly affected by the probe thread, which increased the plastically deformed zone around a rotating probe and increased the tensile shear strength of the joint in comparison with the joint made by a thread-less probe.

Abstract: Galvanized steel sheets with a lap joint were welded by a laser-arc hybrid process. The hybrid system consisted of 2kW LD or YAG laser oscillator and frequency-modulated DC pulsed MAG welding machine. In this experiment, the arc traveled on the specimens, following the laser beam with the interval of 2 mm. The results showed that the hybrid process had some advantages, such as deep penetration depth, high welding speed and high gap-tolerance, in comparison with the conventional MAG welding. Observations from a high-speed digital video-camera suggested that the zinc and iron vapors induced by laser beam irradiation stabilized the arc plasma. Effects of the incidence angle between a welding head and a specimen on the weld bead formations were also discussed. As a result, the welding speed of 2.0 m/min was achieved at 1.0 mm of gap length condition when the incidence angle was 50 degree.

Abstract: A numerical model of time-dependent gas shielded metal arc is described, which was developed in order to make clear the kinetics of arc plasma together with metal transfer. It is possible to calculate and visualize time-dependent temperature and fluid flow field of argon shielded metal arc plasma with the grow-up and the subsequent detachment of the liquid metal drop at the wire tip. Numerical calculation shows that the arc shape in globular transfer abruptly changes at the moment of metal drop detachment. Whereas, the spray transfer arc seems to be stable and almost does not fluctuate with metal transfer.

Abstract: The optimization of electric resistance welding conditions has been investigated in order to improve the resistance to hydrogen induced cracking at bondline in API 5L X60 line pipes from center-slit coils. It was found that the elongated (Si, Mn, Al) rich oxide inclusions at bondline provided a preferential site for HIC, but no evidence on the center segregation effects was found. Design of experimental (DOE) method was used to find out the optimum ERW condition in the viewpoint of the minimization of defects ratio at bondline. The optimum ERW condition suggested by DOE successfully led to an excellent HIC resistance at bondline. Furthermore, it was observed that there was no relation between segregation and HIC resistance at bondline.

Abstract: While resistance spot welding (RSW) has been the most successful sheet metal joining process in automotive industry, there are still certain quality and reliability issues due to the control system and its application process. Some weld spots have hard-to-reach areas and new materials make the process more complicated resulting in new challenges for quality welds. Recently, a new welding machine called one-sided RSW was introduced to make a weld of hard-to-reach areas in automotive application. Intelligent current regulation algorithm of welding machine timer helps to control welding current and time with more stablility than conventional constant current regulation. Newly developed RSW simulation tool is another advanced technology to improve weld quality and production stability. In this research, advanced RSW technologies, including one-sided RSW, intelligent adaptive control, and simulation of RSW process, are discussed with various automotive applications.

Abstract: AC4C cast aluminum alloy and zinc-coated steel were friction stir lap welded, and the microstructures and mechanical properties of the joints were examined and analyzed. Experimental results show that the welding speeds have a significant effect on the tensile properties and fracture locations of the joints at a rotational speed of 1500 rpm. When the welding speed is higher than 60 mm/min, the joints fracture in the zinc-coated steel base material and the tensile strength is equal to that of the zinc-coated steel; when the welding speed is lower than 60 mm/min, the joints fracture in the interface and the shear strength is about 50 MPa. The change of the fracture locations is attributed to the presence of large quantity intermetallic compounds adjacent to the interface of the joints. The composition and formation mechanism of the intermetallic compounds and its effect on the mechanical properties of the joints were discussed.