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Optimal welding condition in resistance spot welding of 7075-T6 aluminum alloy sheets with the thickness of 0.4mm was investigated by the tensile-shear strength tests and Taguchi method in experimental design with changing various welding conditions respectively. The tensile-shear tests were carried out at cross-head speeds of 0.1mm/min in accordance with the KS B0851. Design methods were systematically performed using an L₂₇(39) orthogonal array table. In the experimental design, three control factors of resistance spot welding conditions were electrode force, welding current and welding time. Electrode force conditions were 882N, 1323N and 1764N, and welding current were 13.5kA, 14kA and 14.5kA, and welding time were 3cycle, 4cycle and 5cycle.

Resistance spot welding is a major metal connecting method in vehicle and other domestic electronic domains. Among all the welding techniques, the spot welding inverter is an important direction at the present time. The high nonlinearity and strongly coupled multiple parameters in the resistance spot welding process challenge the classical control theory based on some specific conditions and ideal assumptions, which in real practice obstacle the high-quality welding. This paper put the fuzzy neural network into a constant-current-controlled spot welding inverter, where the welding current peak and its variation are adopted as the input parameters and the duty ratio of the switches is regarded as the output. Eventually a five-layer feed-forward network was constructed, back propagation (BP) algorithm was applied to revise the adjustable parameters in the network, and a mathematical model was established to obtain the training samples serving for the network. The ultimate precision could reach 1.75%, the relative control error is 2.28% with strong external disturbances, the overmodulation is 3.35%, and the total modulating period is seven switching period, which indicated that the proposed algorithm has good performance.

17-4PH steel, also known as UNS 17400 steel or called SAE type 630 stainless steel, is a very important category of steel which has tremendous and extraordinary properties. The superior properties include high corrosion resistance, high hardness and high strength due to the conversion or phase change of the austenite to martensite by cooling the material to room temperature after heating to a temperature around 1030$–1060^{\circ }$C. Normally, this procedure is called as precipitation hardening and hence the name. Due to its extensive properties, the 17-4PH steel finds its applications in a variety of industries including pump shafts, oil path, mechanical seals, and within the aerospace industry, parts of the aircrafts, chemical industries and petroleum industries. When a material is used in any kind of applications, fastening is the major process involved. Hence, there should be a standard welding procedure involved in generating a permanent fastening. In this work, resistant spot welding is considered as the welding process and the major parameters are considered which have a crucial effect on the whole process. The responses are considered to be the nugget diameter and tensile strength which denote the weld quality majorly. The process parameters with the help of literature are considered and they are electrode force, voltage and weld current. Taguchi method is used to design the experiments along with the NN tool to generate and predict the new response values. The results show that the major affecting factor is electrode force followed by current and then the voltage. Comparison is done to choose a better model for predicting the optimum responses with the given values of the input parameters. The results are pretty much accurate for both but still the regression model yields better results and almost similar values to the experimental values. Therefore, better results can also be obtained by ANN model by continuous training of the model.

In this paper, a series of impact tests to advanced high strength steel (AHSS) were carried out through the special equipment. Base on test results, the effects of some key factors such as welding parameters, loading conditions, material properties and specimen structure, etc to the dynamic mechanics property of spot welds were discussed which may be helpful to the actual automobile design and manufacture areas.

In this paper, the spot welding technology of 22MnMoB hot stamping quenched steel was systematically studied. Through a series of experiments, the optimal spot welding technological parameter has been obtained. The interfacial fracture tendency of spot welds of hot stamping quenched steel behavior was more obvious than that of mild steel. The test results showed that the traditional prediction equation of critical nugget diameter for the changing of fracture mode was not in accordance with test results. A new kind of sphere model which considering the structural complexity of spot weld of hot stamping quenched steel was created to obtain the critical fracture diameter value. The fracture test results of five kinds of hot stamping quenched steel showed that the model has a perfect accuracy which is more accurate and helpful to actual engineering.

To validate the manufacturing feasibility of a novel Press Hardening Steel (PHS 1800), the B pillar reinforced panel was trail-produced by hot forming at temperature of 875 °C and 900°C. Besides, resistance spot welding was also carried out at welding current of 6-10 kA. Microstructure and mechanical properties of the B-pillar were examined using tensile test and scanning electron microscope (SEM). The results showed that the sample after hot formed at 900 °C exhibited the better mechanical properties, the tensile strength exceeded 1800 MPa; meanwhile, the elongation reached up to 8.6% which is comparative to conventional 1500 MPa counterparts. Under the fixed electron pressure and duration, the optimal welding current was determined to be 8.0-9.0 kA.