Study On Properties Of Ultrasonic-assisted Injection Molding Of Glass Fiber Reinforced Polypropylene

As a new type of composite material,Glass Fiber Reinforced Polypropylene(GFPP)has the characteristics of high strength,low density and good impact resistance.It has been widely used in many industrial fields such as machinery and automobiles.However,the process conditions during injection molding of GFPP parts have a greater impact on its performance.How to control the mold filling flow behavior of the GFPP material,the condensed structure and the distribution of the glass fiber when the part is cooled,and then obtain a part with higher mechanical properties,is still an important issue that needs to be studied at present.In order to explore the influence of the molding process and the ultrasonic field on the micro structure and macro mechanical properties of GFPP parts,this paper has done the following work:Firstly,the benchmark process parameters of GFPP material molding were determined by MOLDFLOW simulation,and injection molding experiments were carried out on this basis.The results showed that the tensile strength of the part is the highest under the melt temperature of 250℃,the mold temperature of 55℃,the holding pressure of 8MPa,and the holding time of 9s.The mechanical properties of the molded part are mainly determined by the orientation and retention length of the internal glass fiber.;The increase in crystallinity promotes the mechanical properties of the parts.Subsequently,under the benchmark process parameters,the injection molding experiment was performed on the filling stage,the pressure holding and cooling stage,and the entire molding process with different power ultrasonic vibrations,and the micro structure and macro mechanical properties of the parts were observed and tested.The results show that applying the appropriate power of ultrasonic vibration during the whole process(30s)can maximize the crystallinity of the part and improve the orientation of the glass fiber in the part along the direction of the melt flow.Finally,the ultrasonic vibration of different powers was applied to the whole injection molding process under different process parameters to conduct a coupling test of ultrasonic power and process parameters,and a comparative analysis of the parts under each parameter.The results found that: the melt temperature will affect the promotion effect of the ultrasonic field on the crystallinity of the parts.When the melt temperature is high,only low-power ultrasonic vibration can promote the crystallinity of the parts;the continuous increase of the melt temperature will cause the parts The orientation state of the internal glass fiber keeps getting worse as the ultrasonic power increases.The application of an ultrasonic external field at a specific mold temperature can increase the crystallinity of the part;as the mold temperature continues to rise,increasing the ultrasonic power will make the adhesion of the glass fiber and the polypropylene matrix inside the part worse.When the holding pressure changes,the ultrasonic field has no effect on the crystallinity of the part;the proper extension of the holding time can strengthen the effect of ultrasonic vibration on the crystallinity of the part;whether it is changing the holding pressure or the holding time,the ultrasonic vibration It has little effect on the internal glass fiber state of the part.