| Summary: | 碩士 === 中原大學 === 機械工程研究所 === 86 === The main objective of present research is to characterize the process of coinjection molding and its product properties of plastic foam. In addition, thecomparison of the characteristics regarding three foaming methods─coinjectionmolding, traditional injection molding, and traditional forming are also pursued.In this thesis, traditional foaming and coinjection foaming techniques areutilized to study the thin-walled and thick-walled products for both PP and ABSmaterials. The effects of four parameters ─ filling time (injection rate ), moldingcompound temperature, mold temperature, back pressure, and two foaming agents onthe weights of products and their mechanical properties regarding PP and ABS areinvestigated. Tensile stress, bending strength and stiffness are the three mainproperties tested. Besides, for the aspects of coinjection molding, the bonding of thetwo materials is also discussed.Based on the experimental result，it is clearly reveals that the order of thesignificance of four parameters concerning the weight and bending strength of PP isas follows: Back Pressure > Injection Rate > Mold Temperature > Molding Compound Temperature. For the aspects of weight reduction, a total about 4% ~ 9%of weight is reduced for the thin-walled PP, and a large amount of weight reduction of 43% ~ 50.5% for the thick-walled PP is reached. For the case of ABS plastics, themost significant parameter is mold temperature both for the weight reduction andmechanical properties. A decrease of 4% ~ 6.5% and 30% ~35% for the thin-walledand thick-walled ABS is confirmed, respectively.Experimental data shows the foaming ratio of PP is better than ABS, and thefoaming agent of brand B is superior to brand A. It is observed that due to the outerskin formed by the coinjection foaming process, the remained flow pattern offoaming agent is alleviated, an quality improvement is accomplished and its tensile strength is also better than traditional foaming process. In addition, no indication ofslippery between the bonding of interface is identified. It appears that coinjectinfoaming process is quite promising, if it can be adapted by the industrial, thus notonly the product quality can be enhanced but also the cost may be reduced.
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