Experimental Study And Numerical Simulation On Laser Transmission Welding Of PMMA And PBT With Intermediate Material

With the advantages of high welding efficiency,good welding quality,small residual stress and easy control,laser transmission welding(LTW)is widely used in medical equipment,auto parts,electronic device products,packaging industry and so on.However,the weld strength of dissimilar materials is not high because of the poor compatibility between the dissimilar materials.So the further research is required.In this dissertation,poly(methyl methacrylate)(PMMA)and poly(butylene terephthalate)(PBT)were used as upper and lower materials in LTW;however,poor compatibility between two materials lead to poor weld strength.Polycarbonate(PC)has good compatibility with PMMA and PBT.Therefore,the welding method was that PC film as intermediate material was used to enhance weld strength in LTW of PMMA and PBT.The welding mechanism and process parameters were studied in this dissertation and the thermal field distribution was simulated by finite element analysis.Firstly,according to the laser absorption surface selection and the film thickness selection experiment to selected the laser absorption surface and the thickness of the PC film.Through the LTW experiment,the weld strength was tested by mechanical testing and it was found that the best weld strength was improved more than four times than the weld strength without intermediate material.Then,by observing the micro morphology of the weld zone,bubbles of LTW PMMA and PBT with intermediate material in weld zone are more than bubbles of LTW PMMA and PBT without intermediate material in weld zone,and one reason was founded that the bubbles can be used to form micro-mechanical riveting to enhance the weld strength.According to the results of rheological experiments and the reptation model to calculate the reptation time of PMMA,PC and PBT,it was founded that three reptation time were in the level of milliseconds;the reptation time of PMMA was largest and the reptation time of PBT was smallest.If the reptation time is much shorter than the processtime,the higher weld strength is feasible.It can be concluded that the weld strength of PC and PBT is stronger than the weld strength of PMMA and PC.The equilibrium interfacial width and welding ability were calculated through Helfand's theory to analyze the compatibility of dissimilar materials.It can be concluded that the welding ability of PMMA and PBT was poor and the welding ability of PMMA and PC,PC and PBT were relatively high.That is the reason for weld strength enhancement.Subsequently,the central composite rotatable design(CCRD)was used to design and plan the experiment;the response surface methodology(RSM)was used to build the mathematical model of LTW PMMA and PBT with intermediate material between weld strength and process parameters(laser power,moving speed,clamping pressure).The influence of process parameters on the weld strength was analyzed and the process parameters were optimized according to the target optimization criteria.At last,the finite element model of LTW PMMA and PBT with intermediate material was built by the software ANSYS to obtain the thermal field changing rule of welding surface.It was found that the trends of simulated weld width at the two interfaces with the change of the process parameters were consistent.The reliability of the model was verified by comparing experimental and simulated values.This dissertation provides a theoretical basis for the study of LTW of dissimilar materials with poor compatibility and provides practical technical reference for LTW PMMA and PBT with film.