Experiment Study Of The Effect Of Ultrasonic Field On The GF/PP Composite Materials’ Injection Molding Characteristics

With the development of high-tech, fiber-reinforced polymer matrix composites is playing an increasingly important role in the fields of automobile, aerospace, bio-medical, etc. by its advantages of lightweight, high strength and high modulus. But the fiber-reinforced polymer products formed by conventional injection molding are often cannot meet the requirements in some special areas. Seeking the new forming method with high accuracy and efficiency is important.Based on the understanding of fiber-reinforced composites processing technology at home and abroad, an innovative method which combines the ultrasonic vibration and visualization technology to process the fiber-reinforced composites in the injection molding was proposed in this paper. The mold cavity insert vibrates with ultrasonic vibrator which can ensure the ultrasonic energy evenly acting on the composites melts. The flow behavior of the composite melts was recorded by high-speed camera with visual technology, which can provide a reliable basis to investigate the effect of ultrasonic field on the molding characteristics of composite materials.First, a rectangular plate,42mm long×14mm wide×3.5mm(lmm) thick, was chosen as the research object in this paper and a series of visualization experiments were conducted to record the filling process of short glass fiber reinforced polypropylene (GF/PP) composites under different ultrasonic power, injection rate and glass fiber content. The results showed that the improve effect of ultrasonic field was more obvious under the high injection speed conditions. The optimal ultrasonic power grew big as the glass fiber contents increased. Due to the heat exchange effect, the shear flow behavior and the injection process parameters etc elements relatively obvious during the injecting experiment in the thin cavity, the effect of ultrasonic power on the flow behavior of composite materials in3.5mm cavity was more prominent than in1mm cavity.The injection sample was made into a metallographic specimen and observed by metallographic microscope. Besides, the metallographic photograph can be analyzed by professional image analysis software Image-Pro Plus, and the glass fiber orientation tensor on the melt flow direction can be calculated. The results show that the glass fiber orientation state changed more obviously in the thick wall cavity than in the thin wall cavity when imposed the same ultrasonic power; don’t consider the thickness of cavity, the effect of ultrasonic vibration on glass fiber orientation was more prominent under the high injection speed condition than under the low injection speed condition.Temperature test experiment results indicates that the temperature rise in the thick-wall cavity grew big as the ultrasonic power increased; the temperature rise under the high injection speed condition is greater compared with it under the low injection speed condition; the influence of ultrasonic power is relatively weaker and even reduced the temperature rise in the thin wall cavity.