Study On Effect Of Ultrasonic Field On Qualigy Of Precision Injection-molded Parts

Injection molding parts have been used widely in the industrial, because of their light quality、 high specific strengths high corrosion resistance n low cost and easy mass production. But compared with metal parts, the low dimensional accuracy、the difficulty of molding shrinkage controlling and the relatively weak mechanical property are the main obstacle which affect the wide use of injection molding parts in high technology fields.Based on the multianalysis of precision injection molding theory and the current state of molding technology research in this paper, the ultrasonic field energy is used in the process of the precision injection to affect the rheological behavior of melt in process of filling flow and the condensed structure of polymer molecule and to realize the effective control of dimensional accuracy and molding quality of precision injection products.Based on the elaborate analysis of ultrasonic vibration theory and characteristic of precision injection, the plate-type plastic parts with two slot was chosen as the object of study. A ultrasonic precision injection mold with ultrasonic vibration is designed and manufactured to study the filling rate of polymer melt HDPE^PP^POM^PS and the shrinkage of parts under the different injection technological conditions and ultrasonic fields by the non-complete filling and single-factor experiments. Results of non-complete filling experiments show that the filling rate of the4kinds of polymer materials with ultrasonic vibration increase by2.75%、4.27%、0.48%、2.49%respectively. It was indicated that ultrasonic field can decrease the resistance of melt filling, and help melt filling of mould cavity. The results of single-factor experiments show that the lengthwise minimum shrinkage rate of HDPE、PP、POM、PS products with ultrasonic vibration are2.34%n1.67%、1.91%、0.11%respectively, and these data are33.69%n25.24%、27.68%、61.54%lower respectively than the shrinkage of products without ultrasonic vibration. So the ultrasonic field can reduce the shrinkage of plastic parts effectively. The data of x-ray testing and infrared spectroscopic analysis show that ultrasonic vibration can reduce the shrinkage of products by changing plastic products internal molecular crystalline and orientation.The mechanical property of4kinds of plastic products made by single-factor experiments is tested by the material testing machine, and the results show that the lengthwise tensile strength of POML PS increase by5.32%、14.50%than plastic products without ultrasonic vibration respectively, but there is almost no change for the lengthwise tensile strength of HDPE、PP. The widthwise tensile strength increase by41.55%、0.02%、18.30%.38.34%respectively. The lengthwise and widthwise flexural strength of PS parts with ultrasonic vibration increase by18.45%and19.44%. The analyses suggest the changing of mechanical property relates to the effect of ultrasonic vibration on plastic parts internal crystal morphology, grain size and molecular orientation.