In recent years, long glass fiber reinforced plastic and carbon fiber reinforced plastic have begun to be used for structural components that require high strength. As a result, thick-walled injection molded products are being manufactured. However, defects, known as voids, are generated inside the molded product and decrease the strength of the molded product, posing a significant problem at molding production sites. The partial compression method, which is a type of injection compression molding, is effective in preventing voids in thick-walled injection molding. However, there have been limited studies that comprehensively investigated the effects of the compression conditions on void prevention in thick-walled injection molding products or the shape and dimension of the molded product, or the issues in the molded product produced by applying compression. The authors have previously proposed the in-mold pressing (IMP) method, which allows the application of partial compression without the use of an injection compression molding machine and verified its validity. In this study, we proposed a compression device in which a servomotor-driven hydraulic pump actuator is used to propel a movable rod to apply compression to the melt inside the mold cavity. The IMP method using this device was applied to mold thick-walled products with thicknesses of 10 mm and greater, and the effects of compression on the generation of voids inside the molded product and the shape and dimensions of the product were investigated. The results indicate that the generation of voids can be prevented by application of this method. In addition, it was found that marginal deformations, which can pose issues, occur in the molded product when compressive stresses generated inside the molded product by compression are released after demolding.

1. [1] Y. Suga, “Technology Trend on CFRP Development,” Preprints of Seikei-Kakou Autumnal Meeting 2011, pp. 167-168, 2011.
2. [2] Textile and Clothing Division Manufacturing Industries Bureau, “The State of National Projects Related to the Thermoplastics CFRP,” J. of the Japan Society of Polymer Processing, Vol.27, No.3, pp. 78-81, 2015.
3. [3] A. Hiroe and M. Motoyoshi, “Plastic Seikei-kakou Nyumon,” Nikkan Kogyo Shimbun, Ltd., pp. 243-244, 1995.
4. [4] Japan Society of Polymer Processing, “Text Series – Polymer Processing I –,” Sigma Publishing Co., Ltd., p. 148, 1996.
5. [5] H. Yokoi and A. Orino, “Experimental Analyses of the Melt Behavior and the Void Generation Process in a Thick Cavity,” Preprints of Seikei-Kakou Annual Meeting 1999, pp. 91-92, 1999.
6. [6] A. Orino and H. Yokoi, “Experimental Analyses of the Melt Behavior and Void Generation Process in a Thick Cavity II,” Preprints of Seikei-Kakou Annual Meeting 2000, pp. 93-94, 2000.
7. [7] Y. Murata, T. Inoue, and T. Fujibayashi, “Investigation of Flash Generation Process for Engineering Plastic by Flash Generation-Evaluating Mold,” Int. J. Automation Technol., Vol.11, No.1, pp. 90-96,2017.
8. [8] S. Izawa, N. Nakamura, H. Sumen, and K. Yakemoto, “Trend of Polymer Processing Machines (16),” J. of the Japan Society of Polymer Processing, Vol.10, No.4, pp. 263-278, 1998.
9. [9] S. Matsumaru and K. Warino, “Precise Injection Molding for High Quality,” J. of the Japan Society of Polymer Processing, Vol.6, No.1, pp. 33-40, 1994.
10. [10] “Molding Technique for Large Parts,” Modern Plastics, Vol.42, No.9, p. 165 and p. 184, 1965.
11. [11] M. Yoshii, H. Kuramoto, and A. Kaneda, “Residual Stress and Strains in Injection Molding Substrates for Optical Disc,” J. of the Japan Society of Polymer Processing, Vol.2, No.4, pp. 301-316, 1990.
12. [12] S. Masui, T. Hara, M. Matsumoto, and N. Usui, “Low-Pressure and Low-Strain Molding Process, SP-Mold,” J. of the Japan Society of Polymer Processing, Vol.3, No.6, pp. 402-408, 1991.
13. [13] H. Holt, “New Techniques in Shrinkage Control,” Proc. Society of Plastics Engineers Annual Technical Conf. 1964, pp. 519-521, 1964.
14. [14] Y. Imatomi, “Injection Molding of Optical Parts,” Japanese J. of Optics, Vol.25, No.2, pp. 82-87, 1996.
15. [15] H. Yokoi, Y. Shimatani, Y. Sato, H. Ohkawa, K. Hanamoto, and R. Fujiki, “Development of an Injection Molding Die with a Built-in Actuator and Effects of Its Applications,” Proc. of the Japan Society for Precision Engineering Autumn Conf. 1988, pp. 231-232, 1988.
16. [16] 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.
17. [17] T. Abe, T. Tanaka, Y. Saito, S. Matsumoto, and M. Ohkubo, “Development of Injection-Compression Molding Unit System,” J. of the Japan Society of Polymer Processing, Vol.7, No.7, pp. 411-416, 1995.
18. [18] A. Motegi and Y. Murata, “Improvement of Injection Molded Products Characteristic by In-Mold Pressing Method,” Preprints of Seikei-Kakou Autumnal Meeting 2010, pp. 121-122, 2010.
19. [19] A. Motegi and T. Yamada, “Injection Molding Apparatus,” Japanese Patent, No.4628476, 2011.
20. [20] Toray Plastics Precision Co., Ltd., http://www.toplaseiko.com/product/shape_02.html [Accessed October 23, 2017]