Vacuum-assisted resin injection molding

Liquid Composite Molding (LCM) is the common name for several similar processes for the manufacturing of polymeric fiber reinforced composites. Widely used processes that belong to this class are Resin Transfer Molding (RTM), Vacuum-Assisted Resin Injection (VARI), and Structural-Reaction Injection Molding (S-RIM). 

Occasionally, fibers or tows are inserted or laid into a shape as a preform, and the whole preform is subjected to the injection of the resin system under pressure, such as resin transfer molding (RTM) vacuum-assisted resin transfer molding (VaRTM) or even partial injection of the resin or part of the resin system, with the same qualified resin transfer molding (SqRTM) process. In every case, there is the real possibility of fibers moving under the influence of the injected resin, producing considerable doubt as to the final formal structure, position, or integrity of the fibers after molding. 

Setup of the injection and double vacuum-assisted resin transfer Molding (IDVARTM) process proposed by Fan ef a/.The IDVARTM setup controls the preform porosity, compaction and the pressure inside the preform during the resin infusion process by changing the chamber vacuum pressure.The capillary flow effect and the Darcy s flow effect are both utilized in the IDVARTM process to infuse the MWCNTs enhanced epoxy into the glass fiber preform. (This original schematic Is created based on the work reported in reference 38.)... 

The textile preform is placed in a tool to shape the part. LCM processes can be structured according to the tool used. Infusion processes like Resin Transfer Molding (RTM), Compression Resin Transfer Molding (CRTM), and Structural Reaction Injection Molding (SHIM) utilize a double sided mold. In contrast, Vacuum Assisted Resin Transfer Molding (VARTM), Rotational Molding (RM), and the Cured-In-Place Pipe process (CIPP) need only one rigid tool wall,... 

Nalla A R, Fuqua M, Glancey J, Lelievre B (2007) A multi-segment injection line and real-time adaptive, model-based controller for vacuum assisted resin transfer molding. Composites Part A 38 1058-1069. 

In the vacuum injection process (Vacuum Assisted Resin Injection [VARlj), which is the most simple resin injection process, molds with a fixed and a flexible mold half and molds with two fixed mold halves are used (Figure 1.227). The textile semifinished part is inserted into the cavity, the mold is closed, and a vacuum is applied. The vacuum ensures that the mold stays closed and the reinforced structure is compacted. After opening the inlet, the structure is impregnated by infusing the matrix into the fiber material. After curing, the finished component can be removed from the mold. 

Vacuum assisted resin injection additional vacuum can be used in mold cavity to assist resin filling of fiber preforms. 

Resin transfer molding With vacuum assisted RTM, this process can be called infusion molding. RTM usually uses liquid TS plastics that is transferred or injected into an enclosed mold usually at low pressures of about 60 psi (410 kPa) in which reinforcement... 

Resin Transfer Molding (RTM) is accomplished with the use of a reinforcement system that has been preshaped to fit the mold cavity and a low-pressure resin in liquid form that is injected into a closed mold. The injection process can be assisted with the use of a vacuum system to provide for evacuation of any volatiles and to gain molded density. 

It is also useful for making fabric-reinforced laminates. The multiple layers of fabric are hand-laid into the mold in a predetermined pattern to optimize strength properties. Then the mold is closed, and the liquid mixture is injected to impregnate the fabric, often using vacuum assist to replace air tiioroughly by resin. The assembly is held in the press and heated until cured. The products are similar to those made by perform press molding. The process is called resin transfer molding. 

This technology is characterized by prc lacement of dry reinforcement in the mold bef(ne the mold is closed and resin is injected (Fig. 17). Normally a low viscosity resin is used and either low pressure or low vacuum employed to assist resin flow and w ut of reintocement. Complex preform sluqies are generated by shying of mats... 

If a resin injection process (which is exclusively working with the assistance of vacuum) is chosen for the manufacture of FRPC components, the two following concepts can be used for the construction of injection mold. 

The venting of the mold can also be important for the process control. In vacuum-assisted processes, the vacuum pump stays active during the entire injection process and is protected from penetrating matrix material by a resin trap. If a plastic tube is used for this venting line, the moment the resin flows out of the mold can be easily recognized. If more lockable exits of a cavity are used, an online flow path control can also be realized in ciosed mold concepts. The construction of a closed injection mold with two fixed moid haives is dependent on which effort for the actual application is justified or necessary for the process-related implementation. 

---