| Water-assisted injection molding(WAIM)of short glass fiber reinforced polypropylene is an innovative injection molding technology,which uses short glass fiber reinforced polypropylene as raw materials to form hollow or partially hollow polymer-based composite products.Due to the promising application prospect of WAIM,its development mainly focuses on the quality indexes of WAIM,such as the residual wall thickness,water penetration length,and crystal configuration,while there are few kinds of research on the factors affecting the quality indexes of similar fiberreinforced polymer composites.Therefore,in this paper,short glass fiber reinforced polypropylene(SGFRPP)was used as the research object,and the water-assisted injection molding device made by the research group was used to prepare SGFRPP water-assisted injection products.The influence mechanism of injection molding method,molding process parameters,mold structure parameters,and physical properties parameters on the residual wall thickness,water penetration length,and the distribution of short glass fiber along the melt flow direction were studied systematically through conventional testing methods and SEM characterization methods.The main research contents and results are listed as follows:1)Numerical simulation and experimental research were carried out for waterassisted injection molding,and the influence of parameters such as melt injection volume,melt temperature,water injection pressure,water injection delay time and short glass fiber mass content on water penetration behavior was explored.The research results show that:(1)With the decrease of melt injection volume,the increase of melt temperature,the increase of water injection pressure,the shortening of water injection delay time and the reduction of short glass fiber mass content,the residual wall thickness of the products becomes thinner,but the water penetration length becomes shorter in short-shot water-assisted injection molding;because of the molding method is completed in a certain volume of the main cavity,the melt injection volume has the greatest influence on the water penetration behavior.(2)In the overflow water-assisted injection molding,these parameters have similar effects on the residual wall thickness of the products as in the short-shot water-assisted injection molding,however,for the degree of influence on the residual wall thickness of the products,the water injection delay time is the largest,followed by melt temperature and water injection pressure,and finally the short glass fiber mass content;for the degree of influence on the uniformity of the residual wall thickness of the product along the melt flow direction is that the melt temperature is the largest,followed by the water injection delay time and water injection pressure,and finally the short glass fiber mass content.2)SEM characterization and numerical simulation analysis of the short glass fiber distribution of the product at the beginning,middle,and end of the main cavity runner were carried out.The influence of parameters such as melt injection volume,water injection pressure,water injection delay time,melt temperature and short glass fiber mass content on the orientation degree of short glass fibers along the melt flow direction were studied.The research results show that with the decrease of melt injection volume,the increase of melt temperature,the increase of water injection pressure,the shortening of water injection delay time,and the reduction of short glass fiber mass content,as a result,the residual wall thickness of the products was reduced,the shear rate and the gradient difference of the shear rate along the thickness direction of the melt were increased near water channel layer,and finally,the orientation degree of the short glass fiber along the melt flow direction was improved.3)Based on the short-shot and the overflow water-assisted injection molding,the high-pressure water penetrating the melt section in the main cavity for numerical simulation analysis and the measurement of residual wall thickness and short glass fiber distribution.The residual wall thickness of the products and the orientation degree of the short glass fiber along the melt flow direction under the same process parameters were studied by two molding methods.The research results show that:(1)With the increase of melt temperature,the thinning degree of the residual wall thickness of the short-shot water-assisted products was greater than that of the overflow water-assisted products,but the uniformity of the residual wall thickness along the melt flow direction was opposite;when the temperature of melt was 210??215?,the orientation degree of the short glass fiber of the short-shot water-assisted products along the melt flow direction was greater than that of the overflow water-assisted products,while the other temperature ranges were opposite.(2)With the increase of water injection pressure,the thinning degree of the residual wall thickness of the short-shot water-assisted products was greater than that of the overflow water-assisted products,but the uniformity of the residual wall thickness along the melt flow direction was opposite;when the water injection pressure was 4MPa?6MPa,the orientation degree of the short glass fiber of the short-shot water-assisted products along the melt flow direction at the beginning of the main cavity was approximately equal to that of the overflow water-assisted,even at4MPa?5MPa,the orientation degree of the short glass fiber of the short-shot waterassisted products along the melt flow direction at the middle of the main cavity was greater than that of the overflow water-assisted,while the other pressure ranges were opposite.(3)With the extension of the water injection delay time,the residual wall thickness of the products of the two molding methods increased.When the water injection delay time was 0s?3s,the residual wall thickness of the overflow waterassisted products had better uniformity along the melt flow direction,but as the water injection delay time continued to extend to 5s,the residual wall thickness of the shortshot water-assisted products along the melt flow direction was more uniform;during the entire water injection delay time,the orientation degree of the short glass fiber of the overflow water-assisted products along the melt flow direction was greater than that of the short-shot water-assisted products.(4)With the increase of the mass content of short glass fiber,the thickening degree of the residual wall thickness of the short-shot water-assisted products was greater than that of the overflow water-assisted products,but the uniformity of the residual wall thickness along the melt flow direction was opposite;throughout the process of the increasing the mass content of short glass fibers,the orientation degree of the short glass fiber of the overflow water-assisted products along the melt flow direction was greater than that of the short-shot water-assisted products.Although the residual wall thickness of the short-shot water-assisted products was thinner than that of the overflow water-assisted products under the abovementioned process parameter changed,the orientation degree of short glass fiber along the melt flow direction was smaller than that of the overflow water-assisted products.4)The water penetration behavior of three different flow channel cross-section cavities and the orientation distribution of short glass fibers at the middle of the flow channel was studied.The research results show that:(1)With the decrease of melt injection volume,melt temperature increase,water injection pressure increase,water injection delay time shortened and short glass fiber mass content reduction,the water penetration length shorter and residual wall thickness thinning of the short-shot waterassisted products with three different flow channel cross-section cavities,and the overflow water-assisted products also similar changed.(2)In the case of the same process parameters changed,the water penetration length shortest and residual wall thickness thinnest of the circular channel cross-section product,followed by the upper circle and lower square channel cross-section,and finally the square channel crosssection and the overflow water-assisted products also similar changed.(3)In the case of the same process parameters changed,the short glass fiber of the circular channel cross-section product had the highest orientation degree along the melt flow direction,followed by the upper circle and lower square channel cross-section,and finally the square channel cross-section. |
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