Foaming Behavior Control and Cell Structure Modification of Microcellular Injection Molded Parts by High Pressure Packing and Mold Opening

doi:10.3901/JME.2020.18.035

Abstract

Abstract: In view of the existing process and product quality problems of microcellular foam injection technology, a high pressure packing and mold opening microcellular foam injection system is established in this paper. The melt foaming behavior of microcellular foam injection co-PP and the evolution of product cell structure under different process conditions were experimentally studied. The results show that the foaming behavior of microcellular foam injection melt can be well controlled by high pressure packing and mold opening, and the cell structure of the product can be improved. Under the action of high packing pressure and long packing time, the bubbles formed in the filling stage of microcellular foam injection molding further deform and re-dissolve into the melt. At the same time, the melt of "foam after filling" keeps non-foaming, which makes the whole melt in the cavity return to a relatively stable non-foaming state. When the mold is opened for foaming, the mold is opened for a certain distance to give the melt a sufficient foaming space, so that the pressure of the unfoamed melt in the mold cavity drops rapidly, and the foam cell grows stably. Finally, the microcellular foam injection product with high foaming ratio and good foam cell structure is obtained. The key to control and improve the foaming behavior of microcellular foam injection molding melt and the corresponding product cell structure lies in the control of foaming during the filling process and the promotion of foaming after the filling.

Key words: high pressure packing, mold opening, microcellular injection molding, foaming behavior, cell structure

CLC Number:

TQ328

DONG Guiwei, ZHAO Guoqun, WU Huan, WANG Guilong. Foaming Behavior Control and Cell Structure Modification of Microcellular Injection Molded Parts by High Pressure Packing and Mold Opening[J]. Journal of Mechanical Engineering, 2020, 56(18): 35-42.

References

[1] MARTINI J E,WALDMAN F A,SUH N P. The production and analysis of microcellular thermoplastic foam[J]. SPEANTEC Tech Papers,1982,28:674-676.
[2] WANG L,HIKIMA Y,OHSHIMA M,et al. Evolution of cellular morphologies and crystalline structures in high-expansion isotactic polypropylene/cellulose nanofiber nanocomposite foams[J]. RSC Advances,2018,8:15405-15416.
[3] KASEMPHAIBULSUK P,HOLZNER M,KUBOKI T,et al. Foam injection molding of glass fiber reinforced polypropylene composites with laminate skins[J]. Polymer Composites,2017,39:4322-4332.
[4] VOLPE V,LANZILLO S,AFFINITA G,et al. Lightweight high-performance polymer composite for automotive applications[J]. Polymers,2019,11:326-342.
[5] ZHOU Y,GONG W,HE L. Application of a novel organic nucleating agent:Cucurbit 6 uril to improve polypropylene injection foaming behavior and their physical properties[J]. Journal of Applied Polymer Science,2017,134:44538-44546.
[6] ZHANG L,ZHAO G,WANG G,et al. Investigation on bubble morphological evolution and plastic part surface quality of microcellular injection molding process based on a multiphase-solid coupled heat transfer model[J]. International Journal of Heat And Mass Transfer,2017,104:1246-1258.
[7] XIAO C,HUANG H,YANG X. Development and application of rapid thermal cycling molding with electric heating for improving surface quality of microcellular injection molded parts[J]. Applied Thermal Engineering,2016,100:478-489.
[8] SUN X,KHARBAS H,PENG J,et al. A novel method of producing lightweight microcellular injection molded parts with improved ductility and toughness[J]. Polymer,2014,56:102-110.
[9] YOO Y,WOO S,KIM S. Injection molding without prior drying process by the gas counter pressure[J]. Polymer Engineering and Science,2012,52:2417-2423.
[10] 李帅,赵国群,管延锦,等. 模具型腔气体压力对微发泡注塑件表面质量的影响[J]. 机械工程学报,2015,51(10):79-85. LI Shuai,ZHAO Guoqun,GUAN Yanjin,et al. Influence of mold cavity gas pressure on the surface quality of a microcellular injection molding part[J]. Journal of Mechanical Engineering,2015,51(10):79-85.
[11] CHEN H,CHIEN R,CHEN S. Using thermally insulated polymer film for mold temperature control to improve surface quality of microcellular injection molded parts[J]. International Communications in Heat and Mass Transfer. 2008,35(8):991-994.
[12] CHEN S,LIN W,CHIEN R,et al. Variable mold temperature to improve surface quality of microcellular injection molded parts using induction heating technology[J]. Advances in Polymer Technology,2008,27(4):224-232.
[13] HUANG H,TIAN J,GUAN W. Microcellular injection-compression molding (micm):A novel technology for effectively improving cellular structure of polystyrene foams[J]. Polymer Engineering and Science,2014,54:327-335.
[14] HOU J,ZHAO G,WANG G,et al. A novel gas-assisted microcellular injection molding method for preparing lightweight foams with superior surface appearance and enhanced mechanical performance[J]. Materials & Design,2018,127:115-125.
[15] BLEDZKI A,KUHN J,KIRSCHLING H,et al. Microcellular injection molding of PP and PC-ABS with precision mold opening and gas counterpressure[J]. Cellular Polymers,2008,27:91-100.
[16] DONG G,ZHAO G,GUAN Y,et al. Formation mechanism and structural characteristics of unfoamed skin layer in microcellular injection-molded parts[J]. Journal of Cellular Plastics,2016,52:419-439.
[17] 董桂伟,赵国群,管延锦,等. 超临界流体辅助微孔发泡注塑技术及其熔体发泡行为[J]. 机械工程学报,2018,54(18):42-48. DONG Guiwei,ZHAO Guoqun,GUAN Yanjin,et al. Supercritical fluid assisted microcellular injection molding and the melt foaming behaviors[J]. Journal of Mechanical Engineering,2018,54(18):42-48.
[18] HEIM H,TROMM M. General aspects of foam injection molding using local precision mold opening technology[J]. Polymer,2015,56:111-118.
[19] CHU R,MARK L,JAHANI D,et al. Estimation of the foaming temperature of mold-opening foam injection molding process[J]. Journal of Cellular Plastics,2016,52:619-641.
[20] WANG G,ZHAO G,DONG G,et al. Lightweight,super-elastic,and thermal-sound insulation bio-based PEBA foams fabricated by high-pressure foam injection molding with mold-opening[J]. European Polymer Journal,2018,103:68-79.
[21] WANG G,ZHAO G,DONG G,et al. Lightweight,thermally insulating,and low dielectric microcellular high-impact polystyrene (HIPS) foams fabricated by high-pressure foam injection molding with mold opening[J]. Journal of Materials Chemistry C,2018,6:12294-1230.
[22] ZHAO J,ZHAO Q,WANG L,et al. Development of high thermal insulation and compressive strength BPP foams using mold-opening foam injection molding with in-situ fibrillated PTFE fibers[J]. European Polymer Journal,2018,98:1-10.