Fuzzy Orthogonal Optimization for Determining the Optimal Resistance Spot Welding Parameters

Friction welding is a solid-state joining process where heat is produced by scouring of two faying surfaces of materials. The dissimilar joints of Monel and ETP copper are used in boiler industry for the production of stop valves, pipe couplings, and heat exchangers. Monel is a nickel alloy having greater strength and hardness. Normally, it is difficult to weld by fusion methods due to its associated properties of heating under controlled. So that micro-microscopic particles Ni3 (Al, Ti) are precipitated throughout matrix. Such problem can be alleviated by friction joining process. Friction welding process parameters play an important role in making quality weld joints. In this research work, friction welding of ETP copper and Monel is analyzed using design of experiments. The process parameters such as friction pressure, upset pressure, and friction time are designed by Taguchi’s L16 orthogonal array. The significance of quality of welding process was found by analysis of variance (ANOVA). The empirical relationship is established to predict the higher ultimate tensile strength of welded joints of dissimilar materials.

Numerical simulation of tensile strength of upset welded joints with experimental verification

Resistance spot welding has been widely used for joining sheet metals, especially in automotive and aerospace industries. However, since the formation of weld nugget is invisible in resistance spot welding, traditionally off-line destructive test is applied for inspection of the weld quality, which is costly and inefficient. Therefore, in recent years, a lot of efforts have been made in estimating or detecting the weld quality nondestructively by on-line welding parameter monitoring. This paper presents a review on techniques of monitoring resistance spot welding process or weld quality, and the advantages as well as limitations of these techniques are discussed.

Resistance spot welding is used in the assembly of automobile bodies. The use of high tensile strength steel plates in automobile bodies is expanding, and there is a need to develop a welding process that improves the joint strength per resistance spot weld point. To improve the joint strength per resistance spot weld, resistance spot welding can be combined with other joining methods, such as the WeldBond method. As an additional joining method around the nugget, other than using adhesives as in the WeldBond method, brazing can be used to obtain a strong joint without melting the base metal. In this paper, it was proposed that the joint strength can be enhanced by using resistance spot welding and brazing or soldering based on the rule of mixture. And, based on this concept, effect of additional joint around a nugget, such as brazing or soldering, on rotational deformation of joint part and tensile shear strength of resistance spot welded lap joint was examined.

Microstructure evolution and tensile strength of Al/Cu inertia friction welded joint

Effect of governing metal thickness and stack orientation on weld quality and mechanical behaviour of resistance spot welding of AA5754 aluminium

The most widely used welding joining method in the automotive industry is resistance spot welding. Resistance spot welding (RSW) is the welding area where heat is produced by the effect of resistance against the flow as a result of exposing the welded parts to a local electric current. It has become an important issue to apply an effective approach method to guarantee weld quality and optimize welding parameters. This is of high value in theory and practice. In the literature, the effects of spot welding process parameters on the weld core diameter and electrode penetration depth are mostly investigated. Weld strength in RSW is affected by many process parameters such as applied electric current, compression force, welding time. Due to the contact resistance and joule heating, a molten weld nugget zone is formed on the work pieces. It is desirable to have the maximum temperature at the interface of the parts to be joined. In practice, the production of welds of acceptable quality depends on the definition of optimum weld parameters and the application of appropriate controls to ensure constant weld quality over a long production period. In the experimental studies, the optimization of the welding parameters was studied in order to obtain the maximum tensile-shear strength. The most prominent process parameters in experimental studies are electrode force, welding currents and welding times. Different algorithms have been developed for the optimization of welding parameters. The verification tests clearly show that it is possible to increase the tensile-shear strength of the connection with the combination of appropriate welding parameters. As a result, the experimental results confirm the validity of the algorithms used to improve welding performance and optimize welding parameters in resistance spot welding processes.

In this work, resistance spot welding of AISI 201 stainless steel is investigated experimentally and numerically. In the experimental work, based on design of experiments with Box–Behnken design and response surface methodology, effects of process parameters such as welding current, welding time, electrode force and cooling time on tensile-shear strength and failure mode of resistance spot welds are investigated. The results show that tensile-shear strength of spot welds is increased with increasing the welding current and welding time due to increase in the generated heat and consequently plastic deformation area. Also, it is concluded from results that tensile-shear strength is increased with increasing the electrode force. However, with increasing the electrode force, electrode indentation in the sheets is increased, and when the electrode force is excessively raised, the cross section of weld metal and consequently the strength of welded joints are decreased. It is obtained from results that tensile-shear strength of spot welded joints is increased with increasing the cooling time. However, when the cooling time is increased excessively, the welded joints strength is decreased. During tensile-shear test, two failure modes were observed, namely pullout and pullout with tearing of the sheet modes. In the numerical simulations, using an electro-thermo-mechanical analysis, the effect of welding current on fusion zone size is investigated and compared with experimental measurements. The results show that numerical simulations are in good agreement with experimental works. Also, it is concluded that the nugget diameter is increased with increasing the welding current.

On-line quality assessment becomes one of the most critical requirements for improving the efficiency of automatic resistance spot welding (RSW) processes. Accurate and efficient model to perform non-destructive quality estimation is an essential part of the assessment. Besides the usual welding parameters, various measured variables have been considered for quality estimation in RSW. Among these variables, dynamic resistance (DR) gives a relative clear picture of the welding nugget formation and presents a significant correlation with the RSW quality indicators (QI). This paper presents a structured approach developed to design an effective DR-based model for on-line quality assessment in RSW. The proposed approach examines welding parameters and conditions known to have an influence on weld quality, and builds a quality assessment model step by step. The modeling procedure begins by examining, through a structured experimental design, the relationships between welding parameters, typical characteristics of the RD curves and multiple welding QI. Using these results and various statistical tools, different integrated quality assessment models combining an assortment of DR attributes are developed and evaluated. The results demonstrate that the proposed approach can lead to a general model able to accurately and reliably provide an appropriate assessment of the weld quality under variable welding conditions.

Resistance spot welding (RSW) involves joining of contacting surfaces by heat generated by resistance to electric current . The process is swift and finds demand in automobile industries for mass production. In spite of all the assets of the process, it yields a poor quality welds and inferior weld strength at the inner region of the joint interface. This may be improved by accurate setting of control parameters. The objective of this study is to determine the effect of various control parameters like electrode tip diameter, welding current, and heating cycle on the nugget size and tensile shear strength of dissimilar metal spot welding of 2-mm-thick AISI 316L austenitic stainless steel and 2205 Duplex Stainless Steel sheets. The Taguchi’s L27 orthogonal array (OA) design is selected to conduct the experimental spot welding trials on the dissimilar materials. Subsequently, the specimens are examined usinganalysis of variance (ANOVA) technique to customize optimal parameter setting to obtain high tensile strength and favorable weld quality characteristics. The results reveal that welding current is the most dictating factor to achieve highest tensile strength with superior weld quality. Also, weld samples are prepared for metallographic examination from cross section areas of resistance spot welds to examine microstructure changes and ferrite content measurement in different regions of weld nugget. The microstructure examination shows that the weld nugget consists of ferrite and austenite and ferrite and there is no precipitate of detrimental phases in the weldment.

Resistance spot welding (RSW) quality substantially influences the autobody’s mechanical properties and safety performance. Nondestructive testing (NDT) method is widely used to evaluate the quality of RSW, but the traditional ultrasonic testing method has high requirements for coupling conditions and flat surface of the weld part. The electromagnetic acoustic transducer (EMAT) is a novel NDT technology, which has advantages of noncontact, no coupling media, and low requirements for surface flatness of the workpiece. Therefore, the electromagnetic ultrasonic transverse wave (EUTW) is developed to realize the evaluation of RSW quality in this paper. Under the COMSOL platform, the finite element method (FEM) modeling is proposed by multiphysics simulation. The multiphysical fields include electromagnetic field, acoustic field, and solid mechanics. The generation mechanism and propagation rules of EUTW in various spot welds are studied by simulation analysis. The correctness of FEM modeling is validated by EUTW experiments; results show that the experimental waveforms of EUTW are consistent with the simulation waveforms. Finally, an evaluation method of the nugget size of RSW is proposed based on the simulation and experiments analysis of EUTW detection of RSW with different nugget diameter and indentation depth. The approach presented in this paper can provide the theoretical foundation and new method for the noncontact, high efficient, and low-cost detection of RSW quality of the autobody.

There is a strong interest in the use of aluminum alloy sheet for vehicle applications, particularly the body, where resistance spot welding is the principle joining method. The resistance spot welding (R.S.W) quality has a great effected by the process variable such as, welding current, welding time, and electrode pressure beside other variable such as material thickness and type and electrode diameter.
 In this work the effect of process variable on welding quality was investigated. Trials were conducted on 1.2 mm thick 2014 – O aluminum alloy sheet. The tensile shear strength was used as primary index of welds quality. Experimental investigation show that the best current is 45 KA, best time is 10 cycle, and electrode pressure of 3 KN .

In this paper, an integrated artificial neural network (ANN) and multi-objective genetic algorithm (GA) are developed to optimize the resistance spot welding (RSW) of AZ61 magnesium alloy. Since the stability and strength of a welded joint are strongly dependent on the size of the nugget and the residual stresses created during the welding process, the main purpose of the optimization is to achieve the maximum size of the nugget and minimum tensile residual stress in the weld zone. It is identified that the electrical current, welding time, and electrode force are the main welding parameters affecting the weld quality. The experiments are carried out based on the full factorial design of experiments (DOE). In order to measure the residual stresses, an X-ray diffraction technique is used. Moreover, two separate ANNs are developed to predict the nugget size and the maximum tensile residual stress based on the welding parameters. The ANN is integrated with a multi-objective GA to find the optimum welding parameters. The findings show that the integrated optimization method presented in this study is effective and feasible for optimizing the RSW joints and process.

During resistance spot welding, the welding current is the most important process parameter, which determines the welding heat input and then has a great influence on the welding quality. In present study, the CR590T/340YDP galvanized dual phase steel widely used as automobile material was carried out using resistance spot welding. The effect of welding current on the weld formation, microstructure, and mechanical properties was studied in detail. It was found that the quality of weld appearance decreased with the increase of welding current, and there was a Zn island on the weld surface. The microstructure of the whole resistance spot welded joint was inhomogeneity. The nugget zone consisted of coarse lath martensite and a little of ferrite with the columnar crystal morphology, and the microstructure of weld nugget became coarser when the welding current was higher. There was an optimum welding current value and the tensile strength reached the maximum. This investigation will provide the process guidance for automobile body production.

The surface film of weld parts is a very important factor affecting the weld characteristics of diffusion welds. It is desirable to clarify the behavior of the surface film on the diffusion welded interface. In this study, the surfaces before and after diffusion welding were observed with Auger electron spectroscopy. Composition and thickness of the welding surface, and the relation between change of surface composition by diffusion welding and tensile strength of welded joints are investigated. The following results were obtained.1) The films of the welding surface of aluminum, copper, iron and SUS 304 stainless steel are composed of oxygen, carbon and base metal.2) Composition and thickness of the surface films of various materials do not so much depend on the surface treatment such as the degreasing with acetone and the annealing in a vacuum.3) The surface film along the welded interface of aluminum does not change during diffusion welding, but those of copper, iron and SUS 304 stainless steel disappear.4) When the surface film disappears during diffusion welding, metallic bonding is formed at intimate contact area along the welded interface. The stability of the surface film has an influence on tensile strength of welded joints.5) The segregation of sulfur is observed on no-contact surface along the welded interfaces of copper, iron and SUS 304 stainless steel, but it does not have much effect on tensile strength of welded joints.