Custom Fiberglass Fabrication & Laminate

Open Molding Process

Open molding fiberglass fabrication is the most extensively used process for manufacturing fiberglass reinforced plastic (FRP) products.  Open molding at Structural Composites of Indiana is done in controlled shop conditions.  The mold is one-sided and generally fabricated from fiberglass-reinforced plastic (FRP).  The mold can be either male (the fiberglass part is molded onto) or female (the fiberglass part is molded into).  The cosmetic surface of the custom fiberglass part is fabricated next to the fiberglass mold.  The backside of the mold remains open.

Unlike other fabrication processes where the exterior coating is applied after the main structure of the part has been built, open mold fiberglass parts are built from the exterior (outside) to the interior (inside).  The first step in the open molding process is to apply the gel coat (the exterior coating of the part) to the fiberglass mold. The remaining layers of the laminate design listed below back the gel coat:

  • Bulk Laminate
  • Reinforcing/Coring Materials
  • Skin Laminate

Glass fiber reinforcement used in bulk and skin fiberglass laminates can be applied by hand lay-up or spray-up.  Hand lay-up is used when applying materials such as chopped strand mats, and textile products that are woven or stitched.  Rollers, brushes, or wet-out guns can be used to apply the resin.  When the fiberglass laminate reinforcement is chopped roving, spray-up is used.  Catalyzed resin and chopped roving are sprayed onto the lamination surface with a chopper gun.  The glass is wet out and compacted with lamination rollers.  Spray-up and hand lay-up can be combined within the same part or laminate.  Typical process tolerances for hand lay-up are plus or minus 0.032” and spray-up are plus or minus 0.064”.

Closed Molding Process

Another fiberglass molding fabrication process utilized at Structural Composites of Indiana is closed molding.  The closed molding process involves a composite part produced in a cavity formed by the joining of two or more molds.  Examples of fiberglass composite closed molding processes include: SMC, BMC, RTM, VARTM, and Vacuum Infusion. These processes yield different results compared to open molding.  Some characteristics of closed molding are: higher tooling costs, higher production rates, reduced labor, two-sided finish, greater design latitude, and reduced emissions of Hazardous Air Pollutants (HAP).

In Resin Transfer Molding (RTM), the liquid resin is transferred into a closed cavity mold. The reinforcing fibers, embedded cores, and inserts are placed into the cavity before the resin is introduced.  Over time, a number of RTM variations have been developed.  Two of the RTM variations are RTML and Vacuum Infusion. In these two methods, a vacuum is used to draw resin into the mold cavity as opposed to the use of resin injection equipment which would be found in conventional RTM.  RTML uses one rigid and one semi-rigid mold half, whereas vacuum infusion uses one rigid cavity and a flexible membrane as a counter-mold (either disposable bags or silicone bags).

Contact Structural Composites of Indiana today for all of your custom fiberglass fabrication and fiberglass composite needs!