Compression resin transfer molding (CRTM), combining resin transfer molding (RTM) and compression molding, have been developed to fabricate fiber reinforced plastic (FRP) components with large dimensions or high fiber volume content. Although a lot of literature on CRTM is available, relatively little useful technical information is present regarding the proper choice of molding conditions for component optimization. The objective of this research is to investigate the effects of process variables, including injection pressure, mold opening distance, resin temperature, compression pressure, pre-heated mold temperature, and cure temperature, on the quality of CRTM products. The influence of these process variables on the part quality are investigated by applying Taguchi’s method. The ultimate stress measured by tensile test serves as an indicator of the part quality. Experimental result show that the compression pressure and the resin temperature are significant variables for improvements in the mechanical properties of the part, while the effect of pre-heated mold temperature on the mechanical properties appears to be trivial.

In the present article, an open gap is present between the fibrous reinforcements and the upper mold during the filling stage of resin injection/compression molding (I/CM). Thus resin can quickly fill up the gap. After that, the mold platens are brought together and drive the resin through the preform. The resin motion in the gap is simplified using the Hele-Shaw flow model, while Darcy’s law is used to calculate the flow fields in the fiber mats. The numerical simulation is based on the body-fitted finite element method (FEM). Results show that the resin injection time is short and most filling time is elevated to the closing of the cavity in the simultaneous I/CM filling process. Small gap size and high compression speed can be used to achieve the minimum mold filling time. However, the improper process parameters can cause the incomplete filling or reversed flow at the gate. In order to avoid the above conditions, the restrictive conditions of simultaneous I/CM are also discussed. The simultaneous I/CM can reduce either the mold filling time or injection pressure significantly compared to resin transfer molding (RTM).

A non-isothermal filling process of vacuum assisted compression resin transfer moulding (VACRTM) has been developed to reduce cyclic period in this study. In VACRTM, the state of the fabric stack is controllable by stretchable film. During infusion, the resin is isothermally infused into the loose fabrics. After that, a hot fluid with high pressure is applied on the film to heat the resin and compact the preform. A one-dimensional flow and two-dimensional heat transfer model coupled with preform deformation is numerically analysed to investigate the influences of various scenarios on the non-isothermal filling process. Results show that the effects of pressure and temperature distributions at the onset of compression stage are transitional. The main mode of heat transfer is conduction in the thickness direction. Through evaluation of various scenarios, a preferable method is proposed by integrating the concept of fully wetted preform, less excess resin, hot compression and two-sided drainage.

Thin-wall gas assisted injection molding of thermoplastics has become an important process in industry because of its light weight, relatively lower resin cost per part, and faster cycle time. This report is devoted to investigate the effects of different processing parameters on the length of gas penetration in thinwall gas assisted injection molded parts. The first part of this report is to find ways to optimize the gas penetration of molded parts. An L'18 experimental matrix design based on the Taguchi method was conducted to investigate the processing parameters that affect the length of gas penetration in thin-wall gas assisted injection molded parts. The second part of this report is to identify the relative significance of each processing parameter on the gas penetration of molded products. Two materials were used in the study: an amorphous acrylonitrile-butadiene-styrene (ABS), and a semi-crystalline polypropylene (PP). Experiments were carried out on an 80-ton reciprocating injection molding machine equipped with a high pressure gas injection unit. A plate cavity of various thicknesses (0.6, 1.2 and 2.0 mm) with a gas channel across the center was used for the experiments. After molding, the length of gas penetration in the molded parts was determined. For ABS materials, melt temperature and gas pressure were found to be the principal parameters affecting the thin-wall gas assisted injection molded parts, while for PP materials, the gas pressure and gas injection delay time were found to be the key processing parameters. In addition, warpage of molded parts was found to decrease with the length of gas penetration.

Vacuum-assisted compression resin transfer molding, a flexible resin transfer molding process, has been developed to reduce a cycling period in the present study. The vacuum-assisted compression resin transfer molding utilizes an extra elastic film placed between the upper mold and the mold cavity compared with resin transfer molding. Through the stretchable film, the state of the fabric stack is under control. During resin injection, a loose fiber stack is present and then resin is easily introduced into the cavity. Once enough amount of resin is injected, a compression pressure is applied on the film that compacts the preform and drives the resin through the preform. Prior to vacuum-assisted compression resin transfer molding experiment, a compression test is performed to understand the variation of the preform thickness at various loads. Through observing vacuum-assisted compression resin transfer molding experiments, some experimental shortcomings are inevitable including the edge effect and excess of injected resin. More resin leads to a longer injection and compression phase and more wastes. At all events, vacuum-assisted compression resin transfer molding is a feasible process and can be expected to fabricate a better part quality. It also reduces the mold filling time/injection pressure and cleaning mold time compared with resin transfer molding.