Research On Polymer Melting Mechanism And Micro- Structures Molding Characteristics By Laser Irradiation

Polymer micro structure has important applications in MEMS and micro-analysis system, and the molding process technology is a hot research of scholars. Based on the analysis of existing polymer microstructure molding processing methods, the polymer microstructure melt molding method of laser irradiation was proposed. The polymer laser irradiation transient temperature field and microstructure features melt molding were investigated by combining theoretical analysis, numerical simulation and experimental methods, the main tasks are as follows:(1) The theoretical model of polymer melting by laser irradiation was investigated. Based on the analysis of photo-thermal effect model between laser power and polymer melting, the macroscopic morphologies and microscopic motion mechanism of polymer were studied. The physical model of plasticized polymer by absorbing laser energy was assumed. The relationship between the polymer temperature and laser parameters were derived theoretically by establishing an energy balance equation of the polymer melting process. Typical analytical calculation of laser threshold parameter on melting polymer was performed, and thus to analyze the process characteristics and controlling method of surface and overall melting of the polymer, which provides a theoretical basis for further analysis of mechanism in laser irradiating melting.(2) The morphologies and microstructures of melted polymer by laser irradiation were examined. The CO2 laser irradiation experiments were performed on polyamide PA 12, TPU polyurethane and poly (methyl methacrylate) PMMA by locating irradiation and scanning irradiation respectively. The macroscopic and microscopic surface morphologies of melted samples after laser irradiation were analyzed by using optical microscopy and scanning electron microscopy (SEM). The microstructure evolution of melted sample after laser irradiation was observed by using X-ray diffraction (XRD). The effect of laser irradiation melting on the microstructures of laser irradiation was investigated, which provides a reference on the selection of parameter in laser-melt molding.(3) The numerical simulation of polymer transient temperature field during laser irradiation was analyzed. Comsol finite element software was selected to simulate the temperature distribution of melting samples under various of irradiation methods including linear scanning, rectangular scanning, circle scanning and locating irradiation. The influence of the scanning path, scanning speed, laser power, laser spot diameter and sample thickness on sample temperature was investigated. The effects of laser power, spot diameter and irradiation time on temperature distribution were discussed in laser locating irradiation. The maximum and minimum temperature as well as two-dimensional and three-dimensional transient temperature distribution of samples were studied. A relational model between laser parameters and sample melting temperature distribution was established, providing a basis for the selection of parameters in laser-melt molding.(4) The experiments of melt molding of polymer microstructure by laser irradiation were carried out. A laser-melt molding method of polymer microstructure was proposed, and elaborated basic working principle of polymer micro molding and process characteristics was determined. The laser-melt molding experimental device was designed and developed. The experiments of laser-melt molding of PMMA micro-structures were conducted. The digital microscope system (VHX-1000) was utilized to test the surface morphologies and dimension of molded parts, and thus to validate the feasibility and effectiveness of laser-melt molding process.(5) The quality evaluation and controlling on polymer microstructure melt molding by laser irradiation was studied. Based on the molded specimens with PMMA microstructure, firstly test the size-deviation and surface roughness of the molded specimens, and then analyzed the effects of laser power, laser irradiation time, laser scanning speed, mold temperature, template surface roughness, molding pressure and dwell time etc. on the molding quality. The MINITAB software was used to conduct an orthogonal experiment. The effects of process parameters on the molding quality were investigated by variance analysis. The process principle of laser-melt molding was established lastly to provide a guidance for the molding quality controlling.