Research On Process And Numerical Simulation Of Laser Transmission Welding PC Based On Lap Surface Contact State

Laser transmission welding is a kind of new and advanced welding method with high welding precision,small heat affected zone,high bonding strength,it has become one of the most promising method among thermoplastic welding.Temperature field in the process of welding is unstable and uneven,the study which based on ideal surface contact can not satisfy the requirement of practical production,so the changeable lap surface contact state during welding needs to be considered.It is of great theoretical and practical significance to study the mechanism of heat generation and energy transfer and the mechanism of energy transfer and conversion,and benefit the further study of the formation,flow,expand the behavior of weld.On the basis of laser transmission welding of polycarbonate,mathematical model between welding parameters and welding quality is expored to optimize the welding parameters.Heat transfer modal between laser absorbent and laser transmission part is established to analyze the effect of lap surface contact state on heat transfer.Then the extrusion and melting model with gaps is built to explore the influence of bridging gaps on welding quality.The finite element analysis model based on contact state of the lap surface the bridging gap is established to analyze the the influence of welding parameters on temperature field and welding quality.The contents of study are as follows:Firstly,the interaction mechanism of laser and polymer,and heat transfer in the polymer is analyzed and it helps to understand the connection mechanism of laser transmission welding effectively.Then polycarbonate plates of laser transmission welding are obtained according to the preparation process of experimental materials.Subsequently,the transmissivity,reflectivity,the temperature dependence of density,and specific heat of polycarbonate with the are studied.Secondly,the experimental research on laser transmission of polycarbonate is conducted.Taking lap surface contact state into consideration,the influence of the laser power,welding speed and bridging gaps on welding quality is studied.Through response surface method,the mathematical models of the laser transmission maximum break load and welding width are established on the basis of lap surface contact state.The interactive effects of the welding process parameters on the welding quality is explored.Then,the models are verified and then used to optimize the welding process.At last,the optimal process parameters are obtained.Thirdly,lap surface contact state between laser absorbent and laser transmission part is analyzed during the laser transmission welding.The contact state of the lap surface gradually transforms from solid to solid contact to solid liquid contact,and gap bridge is finally filled with molten polymer.Then,the influence of lap surface contact state on heat transfer is conducted.The heat conduction equation of the lap surface is established,which is more in line with the actual welding.The temperature distribution on the basis of changeable lap surface contact state is obtained by the finite element model established in COMSOL software.The relationship between welding temperature field,laser power and welding speed is obtained,and the temperature distribution difference between contact state and without contact state is compared.The simulation result is basically consistent with the actual welding,which verifies the reliability of the heat transfer model of lap joint contact state.Finally,based on the heat conduction model of lap contact state,the thermal deformation of absorbing layer material and the heat transfer process from absorbing layer to the transmission layer under gap condition are analyzed.Then the extrusion and melting model with gaps is established.On the basis of simplified extrusion and melting model,the maximum welding gap and maximum temperature during welding are obtained,and the range of welding parameters is further determined.With the help of the established extrusion melting model,the finite element analysis model under the bridging gap is established in the COMSOL software,and the distribution of temperature field under the gap condition is obtained.The welding temperature,weld width and welding quality are analyzed,then the welding parameters are optimized.Thus the number of welding tests is reduced,and the quality of welding plated is improved.The heat transfer model of lap surface contact state and extrusion melting model of thermoplastic polymer for laser transmission welding established in this paper can provide important theoretical support for experimental research and numerical simulation,and it also provides important support for wide application of laser transmission welding.