| Due to the advantages of high precision, low pollution and easy to control, laser transmission joining technology has more and more been applied to joining thermoplastics. However because of the compatibility and melting point difference, different kinds of polymers are not easy to be connected.In this thesis, the laser transmission joint strength of PC/GFR-PA66 and PVC/PA66 is enhanced through coating the Al film on the surface of GFR-PA66 and PA66 to improve the compatibility. Then the joining mechanism and process parameters are studied between PC/GFR-PA66 and PVC/PA66 and the thermal field distribution in PVC/PA66 is simulated by finite element analysis.First of all, the cold spraying and magnetron sputtering technology are respectively used to cover a Al coating on the surface of GFR-PA66 and PA66 to improve the compatibility between the upper and lower materials. Through VHX-1000 super depth of field three-dimensional microscope the microstructure, fiber distribution and aluminum atoms migration in PC/GFR-PA66 and PVC/PA66 joints are observed. The mechanical micro-joining effect between high pressure bubbles, glass fiber and melted polymers and aluminum atoms migration effect on the joining quality are analyzed. Using the surface contact angle measurement to study the effect of aluminum atoms on surface contact angle of PA66(the surface free energy change after coating), and the van der Waals interaction force change is calculated, then the joining mechanism is explained in the physical aspect. Through XPS the chemical information in welding region is observed and the new generated chemical bonds Al-O-C and Al-Cl are analyzed, then why the joining strength is improved is explained in the chemical reaction aspect.Secondly, the Response Surface Methodology(RSM) is used to do experimental designing, build the mathematical model between the process parameters(sputtering and welding parameters) and joint width, joining strength. Then the interactive effect of process parameters on joining quality is analyzed. Based on the principle of the largest joining strength and the minimum joining cost(the minimum weld width), the process parameters combination is optimized.Finally, the finite element model of laser transmission joint PVC/PA66 is built by the software ANSYS to obtain the thermal field changing rule of joining interface. The thermal field and joint width changing trend is simulated under different laser power and different scanning speed, it is proved that the simulated results are consistent with the experimental results and the thermal field simulation result is precise. So it provides a basis for optimizing process parameters by finite element simulation.This thesis establishes a theoretical foundation for the laser transmission joining different kinds of thermoplastics, and provides technical support for laser transmission joining PA66 with other polymers in actual industrial application. |
PDF Full Text Request