Papers by Keyword: Spot Welding

Abstract: Alumina dispersion strengthened copper (ADSC) is nowadays well-researched material. Its properties make it an excellent candidate for use in electrical engineering applications such as material for welding electrodes. The subject of this study was a joint of ADSC and precipitation-strengthened Cu-Cr alloy. ADSC was prepared by powder metallurgy method using Spark Plasma Sintering (SPS). While SPS allows the preparation of low porosity compacts it's limited by the size and shape of compacts it can prepare. This work aimed to prepare different joints between ADSC and Cu-Cr alloy and examine their properties as well as chemical composition and microstructures. Three types of joints were tested. A joint made by pressing ADSC into Cu-Cr sleeve shows the forming of oxides in the joint as well as the hardening of Cu-Cr on the contact surface due to deformation strengthening. Joint made by SPS flash sintering showing the formation of relatively big cavities and the formation of oxides on the materials interface. The in-situ joint was produced using a method where a Cu-Cr sleeve replaced the bottom punch in SPS compaction. The In-situ interface shows very little change in chemical composition and seemingly made a diffusion connection. However, these samples show higher porosity of composite compared to regularly SPS prepared compacts.

Abstract: Welding technologies are constantly evolving, and their applicability is expanding, considering also the construction domain. Steel structures benefit from the advances in welding technologies due to the use of thin gauge steel sheets which can now be connected at high quality and automatically. The resistance of the connection between the thin steel sheets is crucial for the durability and safety of a structure made of built-up thin-walled cold-formed steel elements. Generally, self-drilling screws or bolts are used for the connection between thin-walled elements, but the quantity of time and manpower necessary for a large number of connections demands an improved solution. Conventional welding techniques are unsuitable for joining thin sheets, ranging from 0.4 to 1.0 mm to thicker ones measuring 1.0 to 3.5 mm. This article compares the results of an experimental investigation into lap joints connected by spot welding and MIG brazing with the design code provisions. The study examines single-lap joints in steel sheets of 0.8, 1.0, 1.2, 1.5, 2.0 and 2.5 mm thickness, connected using these welding technologies. The results obtained are then compared with analytical relations and processed according to EN 1990. Depending on the thickness of the connected sheets, spot welding can lead to two failure modes: button pull-out fracture and interfacial fracture. MIG brazing, a welding technology that deposits material below the melting point of the base material, is known for its advantages, such as low energy consumption, spatter-free operation, high welding speed, and compatibility with thin sheet metals. However, its application in the structural engineering of cold-formed elements lacks documentation. In the study, the MIG brazed specimens failed in the heat-affected zone of the connection. The results indicate the dependence of the spot weld lap joint resistance on the connected sheets' thickness, while the resistance of the MIG brazed lap joints is influenced by the minimum thickness of the connected steel sheet. The study aims to demonstrate the feasibility of the proposed solutions, evaluate their performance, and establish the limits of their applicability. A statistical interpretation of the results highlights the precision and reliability of joint resistance.

Abstract: Amorphous alloys exhibit exceptional characteristics not typically associated with other known classes of materials. These alloys are industrially manufactured in the form of ribbons with thicknesses below 50 μm, which presents challenges in their welding process. Resistance spot welding utilizing energy stored in capacitors is employed for thin sheets or foils due to it’s precise energy control during capacitor discharge. This paper presents the findings from experimental research conducted on spot welding metallic amorphous ribbons with a thickness of 30 μm using stored energy in capacitors, aiming to establish effective welding technologies. Several tests with varying parameters were conducted to optimize the welding process and determine the most effective technology for this foil.

Abstract: Extensive efforts have been undertaken worldwide to develop new high strength steels with substantial fractions of retained austenite, for lightweight automobile manufacturing and other applications requiring improved combinations of strength and formability. These “3rd Generation” Advanced High Strength Steels (AHSS) are being implemented, and spot-welding has been found to present new challenges for these steels when Zn-based corrosion resistant coatings are involved, wherein zinc liquid metal embrittlement (LME) can occur. Some recent work is highlighted here that was designed to examine the separate effects of prior microstructure and alloy composition on LME sensitivity. LME behavior was assessed by comparing hot-ductility of steels with and without a Zn coating tested under conditions simulating spot-weld thermal cycles. Effects of prior microstructure on LME susceptibility were assessed with a single AHSS alloy composition, using annealing modifications to produce martensitic, Q&P, TBF and dual-phase substrates. The dual-phase steel exhibited less sensitivity to LME, perhaps because the Zn penetration and cracking are unable to follow (prior) austenite boundaries in this microstructure. With respect to alloy composition, carbon and manganese variations did not lead to noticeable effects on LME sensitivity, while silicon clearly leads to increased LME sensitivity. Addition of 1.3 wt. pct. aluminum to a 0.5 wt. pct silicon-containing AHSS steel further increased LME sensitivity at some test temperatures. The effects of alloying are interpreted in terms of the propensity to form an intermetallic reaction layer that consumes liquid and physically separates the substrate and liquid zinc.

Abstract: This investigation is performed to compare the resistance spot welding (RSW) of aluminum alloy (2024-T3) with friction stir spot welding (FSSW) techniques. In this work, parameters of both resistance spot welding (RSW) and friction stir spot welding (FSSW) techniques were optimized and the optimum welding variables for both techniques were obtained. For FSSW, the tensile shear strength increased with increasing probe length, tool rotational speed and tool holding time. Tensile shear force value of RSW is about 66% of that of FSSW. This is explained by the coarse dendritic structure in resistance spot welding compared to the plastically deformed stir zone and heat affected zone in FSSW. The ratio of nugget shear strength of RSW and FSSW to base metal is about 71% and 149% respectively. The maximum hardness was obtained in stir zone at the surface of the tool. Very fine grain size of about 4 microns was obtained in stir zone followed by elongated and rotated grains in TMAZ where dynamic recrystallization did not occur.

Abstract: A series of experiments were conducted to optimize the welding of similar and dissimilar alloys i.e AISI-321 with AISI-321, Inconel-X750 with AISI-321 and Inconel-X750 with Inconel-X750. Single phase rectification type resistance spot welding machine was utilized for this purpose. Breaking load against different welding parameters was observed. Further, the defects of the welded zone were also studied by optical and stereo microscopes. It was noted that the welding current, welding time and the welding force play an effective role in the strength of the welding joint and the spot welding of Inconel-X750 with AISI-321 can be possible if the welding parameters are carefully selected.

Abstract: Within the WELLFORMED research project, ongoing at the CEMSIG Research Center of the Politehnica University of Timisoara, a new technological solution was proposed for built-up beams made of corrugated steel sheets for the web and thin-walled cold-formed steel profiles for the flanges, connected by spot welding. The research project integrates an extensive experimental program on such beams, using full scale specimens, to demonstrate the feasibility of the proposed solutions and to assess their performance, followed by numerical simulations to characterize and optimize the connecting details. The present paper presents the results of a large experimental program, on small specimens subjected to shear, consisting of two or three layers of steel sheet connected by spot welding.

Abstract: In this paper the authors present the methodology and results of computational studies of the stress state and the evaluation of the construction durability with multipoint welded joints in the event of random vibration. A special feature of the technique is a detailed simulation of the stress state in the most stressed connection junctions, taking into account the change in the properties of the base material during welding. The empirical equations between the microhardness and the material yield point in the local zone of the welded point are used for this. The developed technique for numerical simulation of the dynamic stressed state of a construction with a point-welded joints can be used to assess the vibration strength of such constructions under conditions of random loading.

Abstract: In 2012, a novel production line was developed to produce electric arc furnace steel sheet for automotive structure, as a national project in Japan. From the viewpoint of crashworthiness, the evaluation of joint strength under dynamic loading is essential. In this study, single-lap spot-welded joint specimens are prepared with the variation of welding current. The specimen sheet is 980-MPa grade electric arc furnace steel and 1.0 mm in thickness, which is supplied by Tokyo Steel Co., Ltd. Nugget diameter is recommended by a well-known empirical equation, , where is sheet thickness. The nugget diameter can be adjusted mainly by welding current. In order to find the optimum nugget diameter under dynamic tensile-shear, five values of welding current, 6.1, 6.4, 6.7, 7.0 and 7.3 kA are tried. The values are set for the recommended nugget diameter 5.00 mm, and ±5% and ±10% of the recommended diameter. Experimental results of quasi-static (loading velocity: 2.0 mm/min = 3.3×10^-5 m/s) and dynamic (initial loading velocity: 7 m/s) tensile-shear tests shows that, despite of loading velocity and welding current (equivalent to nugget diameter), tensile-shear strengths are almost constant. Absorbed energies up to the strength give complicated tendencies. At the recommended welding current (equivalent to mm), the most stable strengths and energies are obtained.

Abstract: This paper presents a method with whose help it is possible, to quickly and precisely predict the influence that thermal spot-shaped joining processes has on the dimensional stability of complex component structures even in early planning phase. The welding distortion is calculated in the context of reduced computing time, based upon an experimentally calibrated mechanical substitute model. This expands existing approaches of substitute models and defines both an experimental and numerical procedure for creating adequate calibration samples. In turn, this makes use of the potential obt ained for standardizing the experimental basis for calculating and modelling the distortion to automatically carry out painstaking calibration processes in simulations and experiments in future based upon mathematical model functions. Finally, the limits to applying the substitute spot welding model are verified with reference to its predictability using a complex joining situation of a car body construction.