Issue 53

Y. Lu et alii, Frattura ed Integrità Strutturale, 53 (2020) 325-336; DOI: 10.3221/IGF-ESIS.53.25 328 5) Do the selection crossover and mutation to produce the best fitness values; It went on the step 5's process of iterative evolution until getting the Near-Optimal fitness value or going to the default maximum generation of evolution. The output of this process was the individual with the best fitness, and the individual consists of the weights and threshold, which would be used as the final weights and thresholds of the BPNN. Fig. 1 illustrates the solution procedure of the GA optimized BPNN method for deformation forecasting of aluminum- steel CMT welding. Data input and normalization t i t r li ti Code BPNN training to obtain fitness value tr i i t t i fit ss l Selection l ti Crossover r ss r Mulation l ti Recalculate the individual fitness l l t t i i i l fit ss Termination conditionis satisfied? r i ti iti is s tisfi N Design the sturcture of the BP neural network si t st r t r f t r l t r Initial weight and threshold I iti l i t t r s l The best weights and thresholds st i ts t r s l s Simulation results i l ti r s lts Y Figure 1: The flow chart of GA Optimized BPNN method After the GA-BPNN model is established, it can be used to deal with complex nonlinear problems, which provides a reference for the subsequent prediction of aluminum steel welding deformation. The inverse deformation method The inverse deformation method [20] pre-estimates the direction and size of the structural deformation, and gives the sheet a deformation in the opposite direction during assembly, which is used to offset the deformation caused by the welding, so that the post-weld member maintains the design requirements. After extensive experimental observation, the aluminum-steel sheet CMT welding will undergo warping deformation. The warping deformation shape of the aluminum sheet side is low in the middle and high on both sides. Therefore, the same deformation in the opposite direction is applied to the sheet before welding, so that the sheet is restored to a flat shape after welding. In this paper, the estimated size of deformation is given by GA-BPNN. The anti-deformation treatment diagram is shown in Fig. 2.