The Feasibility of an Internal Gas-Assisted Heating Method for Improving the Melt Filling Ability of Polyamide 6 Thermoplastic Composites in a Thin Wall Injection Molding Process

Abstract

In thin wall injection molding, the filling of plastic material into the cavity will be restricted by the frozen layer due to the quick cooling of the hot melt when it contacts with the lower temperature surface of the cavity. This problem is heightened in composite material, which has a higher viscosity than pure plastic. In this paper, to reduce the frozen layer as well as improve the filling ability of polyamide 6 reinforced with 30 wt.% glass fiber (PA6/GF30%) in the thin wall injection molding process, a preheating step with the internal gas heating method was applied to heat the cavity surface to a high temperature, and then, the filling step was commenced. In this study, the filling ability of PA6/GF30% was studied with a melt flow thickness varying from 0.1 to 0.5 mm. To improve the filling ability, the mold temperature control technique was applied. In this study, an internal gas-assisted mold temperature control (In-GMTC) using different levels of mold insert thickness and gas temperatures to achieve rapid mold surface temperature control was established. The heating process was observed using an infrared camera and estimated by the temperature distribution and the heating rate. Then, the In-GMTC was employed to produce a thin product by an injection molding process with the In-GMTC system. The simulation results show that with agas temperature of 300 °C, the cavity surface could be heated under a heating rate that varied from 23.5 to 24.5 °C/s in the first 2 s. Then, the heating rate decreased. After the heating process was completed, the cavity temperature was varied from 83.8 to about 164.5 °C. In-GMTC was also used for the injection molding process with a part thickness that varied from 0.1 to 0.5 mm. The results show that with In-GMTC, the filling ability of composite material clearly increased from 2.8 to 18.6 mm with a flow thickness of 0.1 mm.

Metal Additive Manufacturing of Plastic Injection Molds with Conformal Cooling Channels

“…However, in the case of complex constraints that can also cause dynamic lower and upper bounds during the transient process, the multiobjective optimization procedure can be a complicated step. For example, some plastic injection molding processes have additional and non-continuous heating steps [ 35 ], or some injection molding processes are aimed for thin walls [ 36 ]. These applications are not parts of traditional plastic injection molding processes and they bring additional constraints that can affect determining the lower and upper bounds.…”

Prediction of Morphology Distribution within Injection Molded Parts Obtained with Fast Cavity Heating Cycles: Effect of Packing Pressure

“…The modulation of cavity temperature can be conducted in several ways; for instance, gas‐assisted heating and conformational cooling channel were proposed for heating cavity surfaces also with complex shapes. [ 7,8 ] However, most of the proposed methods show slow heating and cooling rates (10 °C s −1 ), cause excessively long processing time. Induction heating, infrared heating, and high proximity heating [ 2,9,10 ] can realize cavity heating with a rate of 50 °C s −1 .…”

Improving the Melt Flow Length of Acrylonitrile Butadiene Styrene in Thin-Wall Injection Molding by External Induction Heating with the Assistance of a Rotation Device

“…Therefore, to address this issue, instead of heating the entire volume of the mold plate, recent research has suggested new heating methods in which only the cavity surface is heated. To achieve this, many methods for mold heating have been suggested, such as hot gas heating [ 30 , 31 , 32 , 33 ], induction heating [ 34 , 35 ], and infrared heating [ 36 , 37 , 38 ]. These methods could support high mold temperatures for improving the melt flow length by reducing the amount of frozen layer formed during melt flow.…”

“…However, despite achieving the target of reducing both the heating time and thermal energy wastage, the heating time was not adequately minimized. In general, when raising the cavity surface temperature to that of the glass temperature of the plastic material, the required heating time is around 10 s or longer [ 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 ]. This means that the molding cycle time is longer than the traditional cycle of around 10 s, i.e., it significantly exceeds 10 s.…”