Weldlines are a type of defect in polymer injection molding and are known to impair the appearance and mechanical strength of the molded product. A previous study involved designing and fabricating an induction heating and cooling mold that incorporates an induction coil, allowing it to rapidly heat up. The study verified that the use of this mold prevents weldlines and improves the surface properties of the molded product. Although it is possible to prevent impairment of the external appearance caused by weldlines or the exposure of glass fibers on the surface when the mold is applied to glass fiber reinforced thermoplastic, the results of the previous study indicated that it did not significantly improve the mechanical strength. Hence, the present study involved designing and fabricating an injection mold capable of melt flow control in addition to induction heating and cooling by incorporating a melt flow control mechanism that employs a movable core pin to control the flow direction in the mold used in the previous study. The mold is used to form samples of short- and long-glass fiber reinforced polypropylene while simultaneously performing heating and cooling and melt flow control to obtain samples with smooth flat surfaces in which the exposure of glass fibers is prevented while exhibiting increased bending strength.

1. [1] E. M. Hagerman, “Weld-Line Fracture in Molded Parts,” Plast. Eng., Vol.29, No.10, pp. 67-69, 1973.
2. [2] B. Fisa, J. Dufour, and T. V-Khanh, “Weldline Integrity of Reinforced Plastics: Effect of Filler Shape,” Polym. Compos., Vol.8, No.6, pp. 408-418, 1987.
3. [3] K. Tomari, H. Hamada, and Z. Maekawa, “Study on the Weld Strength of Fiber Reinforced Polyamide Injection Moldings,” J. of the Japan Society of Polymer Processing, Vol.1, No.1, pp. 71-78, 1989.
4. [4] A. Ebisawa, “Heat and Cool System to Get the Excellent Surface Finishing,” J.of the Japan Society of Polymer Processing, Vol.11, No.5, pp. 397-400, 1999.
5. [5] ONO SANGYO Co.,Ltd., Rapid Heat Cycle Molding. http://www.onosg.co.jp/heatandcool/ [accessed May 20, 2017]
6. [6] NADA Innovation, E-Mold. http://www.witswell.co.jp/HTM/emold/emold.html [accessedMay 20, 2017]
7. [7] R. Yoshino, “Cavity Surface Quick High Temperaturize Technology with Slender Tube Heater,” J.of the Japan Society of Polymer Processing, Vol.20, No.3, p. 192, 2008.
8. [8] T. Iwasawa, Y. Fukushima, H. Kuroiwa et al., “A Basic Study on Spot Heating Weld-less Manufacturing System – Die Temperature Distribution by CAE Analysis for a Design –,” Preprints of Seikei-Kakou Annual Meeting 2011, pp. 91-92, 2011.
9. [9] A. Wada et al., U.K. Patent GB2 081 171A, 1982.
10. [10] R. Nicolas and F. Jose, “How Inductive Heating can Improve Plastic Injection,” J.of the Japan Society of Polymer Processing, Vol.23, No.12, pp. 705-710, 2011.
11. [11] Y. Murata, K. Kino, H. Hida et al., “Improvement on Injection Molded Products Appearance by Induction Heating Mold,” J.of the Japan Society for Precision Engineering, Vol.75, No.3, pp. 407-411, 2009.
12. [12] Y. Murata and M. Kuramochi, “Development of Heating and Cooling Injection Mold with Far-Infrared Radiation Heater,” Int. J. of Automation Technology, Vol.10, No.1, pp. 79-86, 2016.
13. [13] Y. Murata, M. Koike, and S. Pan, “Improvement on the Properties of Injection Molded Products with Induction Heating and Cooling Molds,” Int. J. of Automation Technology, Vol.9, No.1, pp. 3-9, 2015.
14. [14] M. Koike, Y. Hukuda, S. Kobayashi et al., “Investigation of Influence on Glass Fiber Rein forced Molded Product Characteristic by Induction Heating and Cooling Mold,” Preprints of Seikei-Kakou Autumnal Meeting 2010, pp. 113-114, 2010.
15. [15] H. Yokoi et al., “Injection Molding Encyclopedia,” Sangyo Chosakai, p. 554, 2002.
16. [16] H.-C. Ludwig and G. Fischer, “A Quantitative Comparison of Morphology and Fiber Orientation in Push-Pull Processed and Conventional Injection Moulded Parts,” Compos. Sci. Technology, Vol.53, No.2, pp. 235-239, 1995.
17. [17] K. Tomari, S. Sawada, R. Nakano et al., “Resin/Resin Bonding Strength and Control of Interface Geometry in Simultaneous Composite Injection Molding,” J. of the Japan Society of Polymer Processing, Vol.5, No.3, pp. 197-204, 1993.
18. [18] P. Allan and M. J. Bevis, “Development and Application of Multiple Live-Feed Molding for the Management of Fibers in Molded Parts,” Compos. Manufact., Vol.1, No.2, pp. 79-84, 1990.
19. [19] Y. Utaka, N. Ogura, and H. Yoshida, “Cavity Local-Pressurizing/ Vibrating System “Press α”,” J.of the Japan Society of Polymer Processing, Vol.5, No.11, pp. 712-718, 1993.
20. [20] N. Mori, K. Gondou, K. Shimada et al., “The Influence Capitalize of Properties Improvement for Reinforced Plastics by Resin Flow Control Molding Method,” Int. J. of Automation Technology, Vol.6, No.4, pp. 522-528, 2012.
21. [21] A. Motegi, Y. Fukushima, T. Hishida et al., “A Study on the Strengthening of Weld Part by Core Pin Drive Method,” J.of the Japan Society of Polymer Processing, Vol.27, No.12, pp. 540-545, 2015.
22. [22] Y. Kanetoh and H. Yokoi, “Visualization Analysis of Side-Edge Flow Phenomena in Different Thickness/Width Rectangular Cavities Using a Rotary Runner Exchanger System,” Polym. Eng. Sci., Vol.51, No.4, pp. 721-729, 2011.
23. [23] Fuji Seiko Co.Ltd. http://www.fuji-gr.co.jp/products1025.html [accessed May 20, 2017]