LRTM (Light Resin Transfer Molding) & RTM (Resin Transfer Molding)
"Light Resin Transfer Molding (LRTM)" is similar to RTM but uses vacuum to hold the male & female tool together. This process will give you two finished sides and pretty high tolerance for part thickness & dimensions. Because it is held together by vacuum and not hydraulic pressure, heavy metal tooling is not required, making tooling less expensive.
Process - Fiberglass mat patterns are loaded into the female tool. The male tool is set into the female tool, then vacuum is applied to pull each other together. All of the air is vacuumed out of the part and then the resin is hooked up and pulled through the part. The tool stays under vacuum till resin is cured and then the part is pulled.
"Resin Transfer Molding (RTM)" is used when higher volumes are needed, finished inside and/or part thickness is critical. A benefit of this process is both surfaces have a "Class A" finish. Tooling cost is more for this process because of the heavy structured tooling needed to withstand the hydraulic pressure when the male & female tools are closed. But, the part piece price goes down because its less labor intensive and automated.
Process - Fiberglass mat pre-cut patterns are placed in the female tool. The male tool is hydraulically lowered into the female tool. With hydraulic pressure, the resin flows through the part. When the resin cures the male tool is removed and the part is taken out. The part can have a gel coat finish or top coat paint.