Construction Of Volumetric Heat Source Considering Light Scattering?Numerical Simulation And Welding Process Optimization During Laser Transmission Welding

Laser transmission welding(LTW),as a new kind of polymer bonding technology,is being used more and more in various industries and fields.With the development of LTW technology,numerical simulation plays a more and more important role in the process of LTW.In the process of LTW,the light scattering of the upper transparent material makes the change of the laser heat source energy distribution at the welding interface.Furthermore,the laser heat source is the decisive factor of the numerical simulation results in the numerical simulation of LTW.Therefore,it has important research value and significance for the investigation of the effect of light scattering on laser heat source during the process of LTW,which lays the foundation for improving the accuracy of numerical simulation and guiding the LTW process.In this dissertation,the polyoxymethylene(POM),widely used in the automotive field,is chosen as the research object.And during the process of LTW POM,the light scattering characteristics is investigated.The laser heat source model considering light scattering is constructed,and the LTW POM experiment is driven by this laser heat source.Then,based on the response surface methodology-genetic algorithm(RSM-GA),the LTW experimental design and optimization of multi-objective process parameters are carried out.The main research work and achievements are as follows:Firstly,the beam characteristics of semiconductor continuous laser are analyzed by means of the knife-edge experiment,and the laser beam normalized power flux distribution(NPFD)along y-direction is described.In addition,the light scattering characteristics of the upper transparent POM are studied by combining the non-contact line scanning experiment with the mathematical model of the laser beam power flux.Then the parameters of POM light scattering are determined,and the one-dimensional line energy density distribution along y-direction is obtained at the weld interface when the laser beam transmission through the upper transparent POM.Secondly,a mathematical model of energy transformation algorithm is proposed and constructed,which can transform the one-dimensional line energy density distribution into the point energy density distribution.And using the obtained point energy density distribution,the function of laser energy density distribution considering light scattering at the weld interface is described.Based on the described laser energy density distribution and Lambert-Bill law,the volumetric heat source model considering light scattering is constructed.Thirdly,the temperature field numerical simulation of LTW POM is carried out by using the constructed volumetric heat source as the loaded heat flux for numerical simulation of LTW.Under different laser power(P=10W,11 W,12W),the simulated and experimental molten pool morphology and size(molten pool width,upper depth of molten pool and lower depth of molten pool)are compared.The results show that the simulated results are in good agreement with the experimental results,which approves the accuracy of the numerical simulation model.And the reliability and accuracy of the volumetric heat source model considering light scattering are verified.Finally,based on the temperature field results of numerical simulation,the LTW POM experimental design and the optimization of multi-objective process parameters are carried out by RSM-GA method.The design and planning of the LTW experiment are performed by means of the central composite rotate design(CCRD).A mathematical model was established by using RSM to connect the response(width,upper depth,lower depth,tensile strength)and process parameters(laser power,welding speed,defocus).Then the ANOVA analysis was performed to evaluate the suitability of the mathematical model,and the interactive effects of the process parameters on the response were discussed.Using the desirability function as the fitness function of GA,the GA toolbox is used to optimize the multi-objective process parameters in MATLAB,and the optimized result is verified.The investigated results in this dissertation show that the volumetric heat source considering light scattering at the weld interface,constructed by the non-contact line scanning experiment and the energy transformation algorithm,has high accuracy of numerical simulation.Meanwhile,it is an effective method to adopt the numerical simulation-driven RSM-GA designing LTW experiment,modeling welding process parameters model and optimizing multi-objective.It provides a new way to guide the LTW experiment and improve the welding quality.