Experimental Research,Process Optimization And Numerical Simulation Of Laser Transmission Welding Between Polyethylene And Polyoxymethylene

Laser transmission welding has become one of the most potential connection methods among thermoplastics,and been widely used in the automotive,electronic packaging,and medical equipment industries because of its high efficiency,reliability,speed and aesthetics.Polyethylene(PE)and polyoxymethylene(POM)are widely used in industrial field,which their polarity and compatibility are different,and they cannot be welded together by laser transmission welding.This dissertation use two different modified methods to realize the laser transmission welding of PE and POM,and the strengthening mechanism is analyzed.And the process parameters optimization and welding temperature field simulation of laser transmission welding between plasma-treated PE and POM are studied.The main work and results of this dissertation are as follows:First,the PE was grafted with maleic anhydride,and the laser transmission welding of PE and POM was successfully realized.The effects of graft modification on optical properties and thermodynamic properties of materials were studied.It was found that modification had little effect on the properties of polyethylene.Meanwhile,the enhancement mechanism of their welding strength was also revealed.The study found that: The compatibility between graft modified PE and POM is improved.The high-pressure uniform bubbles can force upper fused PE material to the pits and cracks on the surface of lower POM material,and the micro anchor effect can be achieved.The grafting modification increases the polarity and the surface free energy of the polyethylene,which reduces the polarity difference between PE and POM and makes the intermolecular diffusion and entanglement easier,and the laser transmission welding performance becomes better.Secondly,another method of plasma treatment is used to achieve the laser transmission welding of PE and POM.Plasma treatment can significantly improve the laser transmission welding properties between PE and POM.Compared with graft modification,plasma treatment has advantages such as short treatment time,obvious effect,environmental protection and no pollution.The effect of plasma treatment on the properties of polymers was explored.It was found that plasma treatment can improve the transmittance of PE,but it has little effect on the optical properties of POM.The mechanism underlying the welding strength enhancement between PE and POM after plasma surface treatment was revealed from the aspects of surface free energy,surface morphology and surface chemical composition.The study found that: The surface free energy of the polymers is improved after plasma treatment,significantly improving the wettability;The increase in polymer surface roughness and the generation of homogeneous bubbles allowed the easy formation of mechanical micro-interlocking in the laser welding process;The oxygen-containing groups such as O-C=O and C-O improved the compatibility between PE and POM.These three aspects effectively enhance their performance of laser transmission welding.Then,the process and optimization of laser transmission welding between PE and POM were studied.Experimental scheme for laser transmission welding of plasma-treated PE and POM was designed by the central composite rotatable design(CCRD).A model between welding strength and processing parameters was established by response surface method(RSM).Through the analysis of the model,the interactive influence of the process parameters on the welding strength is obtained,and the optimal process parameters combination is obtained through the optimization of process parameters.Finally,ANSYS is used to simulate the temperature field of laser transmission welding between plasma-treated PE and POM.The temperature field finite element analysis model of laser transmission welding between PE and POM is established,and the change rule of temperature field under different treated time,different welding power and different scanning speed is analyzed.Meanwhile,the reliability and accuracy of the finite element analysis model of the temperature field are verified by comparing the simulated value and the experimental value of the weld width.This dissertation provides a solution and technical support for the realization of laser transmission welding of PE and POM.Meanwhile,it also provides a new method and new idea for laser transmission welding between dissimilar polymers with poor compatibility,and lays a theoretical foundation for the mechanism research of laser transmission welding of dissimilar polymers.