| Long Glass Fiber Reinforced Polypropylene(LGFRPP)is one of the most popular highperformance composites in recent years.Fluid-assisted injection molding is a new technology for hollow parts forming.In this paper,based on the existing experimental platform,the influence of different forming process methods on the residual wall thickness and apparent mass of LGFRPP pipe fittings was studied by combining experiment with theory,and the suitable forming process for LGFRPP pipe fittings was selected.Then,according to the selected process method,the influence of glass fiber length and content on the residual wall thickness and pressure resistance of pipe fittings was investigated.The relationship between technology,glass fiber content,microscopic morphology and compressive performance was investigated by microscopic observation.Finally,based on the orthogonal experiment,the influence of the process parameters on the residual wall thickness and uniformity of pipe fittings was explored.Optimizing the process parameters to improve the quality of injection molding has important theoretical guiding significance for practical application,and promotes the application and development of LGFRPP in fluid-assisted injection molding process.The main work of this paper is as follows:(1)The research content of this paper was determined through the investigation and analysis of the fluid-assisted injection molding process(FAIM)and fluid projectile-assisted injection molding process(F-PAIM)and the application of long glass fiber reinforced composite in injection molding process.(2)According to the process characteristics and quality requirements,the experimental equipment,materials and analysis methods were determined.The rheological properties of LGFRPP and SGFRPP composites with 10%,20%,30% and 40% glass fiber content were tested.(3)The effects of water-assisted injection molding process(WAIM),gas-assisted injection molding process(GAIM),water projectile-assisted injection molding process(WPAIM)and gas projectile-assisted injection molding process(G-PAIM)on wall thickness mass(apparent mass,residual wall thickness and its standard deviation)and microstructure(glass fiber retention length and glass fiber orientation)of fluid assisted-injection molded pipe fittings of LGFRPP material were investigated.The results show that the inner wall quality and penetration of W-PAIM pipe fittings are better and the residual wall thickness is uniform.The glass fiber retention length of W-PAIM pipe fitting is shorter but the glass fiber orientation along the flow direction is the highest.W-PAIM process is more suitable for injection molding of LGFRPP materials.(4)The effect of glass fiber content on the quality and microstructure of long glass fiber reinforced polypropylene W-PAIM pipe fitting and short glass fiber reinforced polypropylene W-PAIM pipe fitting were studied by single factor experiment.Then,the samples of W-PAIM pipe fittings with different contents of long glass fiber were used to test the pressure resistance,and the influence of glass fiber content on the pressure resistance of W-PAIM pipe fittings of long glass fiber reinforced polypropylene composite was explored.The influence mechanism was obtained by combining the forming quality of pipe fittings and the microscopic observation results of glass fiber morphology.It is found that the residual wall thickness of LGFRPP WPAIM pipe fittings increases first,then decreases and then increases with the increase of glass fiber content.The glass fiber retention length and its distribution in the longer length range decrease gradually with the increase of glass fiber content.In the whole wall thickness,the orientation of the glass fiber with different content along the flow direction is the best in the channel layer.When the glass fiber content is 20%,its orientation is the worst in the middle layer along the flow direction.With the increase of glass fiber content,the pressure resistance of LGFRPP pipe fittings increases first,then decreases and then increases.The pressure resistance of pipe fittings is the best when the glass fiber content is 20%.(5)The influence of process parameters on the residual wall thickness of long glass fiber reinforced polypropylene composite W-PAIM pipe fitting was analyzed by orthogonal experiment.It was found that melt temperature had a significant effect on the residual wall thickness of pipe fitting,and the residual wall thickness increased with the increase of melt temperature.The influence factors on the uniformity of residual wall thickness are melt temperature,water injection pressure and water injection delay time.Finally,the process was optimized to improve the residual wall thickness and uniformity of pipe fitting,and the optimal process parameter combination was obtained. |
