Numerical Simulation Of Welding Deformation Behavior Of Excavator Lower Frame And Optimization Of Process Parameters

As the core component of the excavator,the lower frame of the excavator not only controls the walking of the excavator,but also has a certain supporting effect on the upper frame and assists the implementation of the working device.Therefore,strict tolerances on the shape and position are required.The manufacturing process of the lower frame is to process the left and right longitudinal beams,and then assemble the points to weld them together finally,so the dimension guarantee capability is low.Therefore,it is necessary to optimize welding process parameters to suppress or reduce welding deformation behavior,thereby improving welding production accuracy.In order to improve the welding quality,the factors that affect the welding quality are classified and optimized,which are mainly divided into:(1)Welding heat source is very important for the numerical simulation efficiency of welding,especially for large-sized and complex structured welding members.Welding heat source has a significant impact on the accuracy of simulation results.Therefore,a segmented mobile temperature-controlled heat source model is proposed,which will enter the temperature field.The temperature steady state value is used as the calculation step,which will greatly reduce the amount of calculation,In addition,by increasing the calculation step in time,the calculation time will be greatly shortened and the work efficiency will be improved.The I-beam was used as the heat source verification model,and compared with the double ellipsoid heat source model,the welding sequence and direction were optimized.The results show that the segmented moving temperature-controlled heat source and the double ellipsoid heat source model have similar simulation results,but the calculation speed is more efficient.At the same time,the optimization of the welding sequence of the I-beam is as follows: lower left ? upper right ? lower right ? upper left;the welding scheme with the same direction is the best.The proposed model of segmented moving temperature-controlled heat source is of great significance for the numerical simulation of large and complex structural parts.(2)When formulating the welding sequence plan for large and complex structural parts,it is important to control their influence on the deformation and residual stress of the welded components.According to this welding principle,the structure of the lower frame of the excavator is layered and optimized item by item,and finally the optimal welding sequence plan is found.At the same time,the segmented mobile temperature control heat source is applied to the numerical simulation of the lower frame of the excavator In the analysis of the temperature field,the size distribution of the molten pool is more in line with the size after welding in the model,and the accuracy and feasibility of the temperature control heat source for segmented movement are verified again;according to the analysis results of the stress field,Choose a reasonable welding sequence can reduce the amount of deformation and residual stress of the welded structural parts,the deformation and residual stress of scheme three is the smallest of the four welding sequence schemes,the deformation of the top ring of the main part after welding is 0.46 mm,not Exceeding the relevant provisions of flatness,the maximum value of residual stress is located on the compression side of the gear ring.(3)Aiming at the problem of randomly generated initial population distribution of multi-objective particle swarms,the Henon chaotic map is introduced,and an improved multi-objective algorithm based on the Henon chaotic map is proposed.This algorithm(H-CMOPSO)can not only make the objective function Fast global optimization can also reduce the optimal solution set of most particles into local optimal solutions.In addition,external storage performance has been greatly improved,and the solution set can occupy a larger space.Through three typical multi-objective test functions,the performance of the algorithm is compared with NSGA? and MOPSO.The results prove that the improved algorithm has better performance.(4)Optimize the three key parameters of welding process parameters: welding voltage,welding current,and welding speed.Welding deformation,residual stress,and welding man-hours are the optimization goals.The finite element analysis results are embedded in the improved multi-objective particle swarm optimization algorithm.(HCMOPSO)algorithm optimization.Through the secondary development of MSC.Marc,the optimization process is programmed to greatly improve the simulation efficiency.The I-beam is used as the research model.The research results have shown that the welding residual stress is reduced by 10% and the amplitude of welding deformation is reduced by 24.24%,The welding man-hour has been reduced by 17.78%,and the time after programming the simulation process is about 1/3 of the traditional simulation.The optimized welding quality has been significantly improved.