Technologies

VARTM

Proccess : A variant of LRTM, vacuum-assisted resin transfer molding is used to produce large, non-cosmetic parts – often with encapsulated cores. This closed molding process utilizes a rigid, flanged mold (core or cavity) and a lightly-reinforced counter mold or even a disposable bag. Typically, cored parts are not gel-coat finished; cores bundled in dry reinforcement are loaded into the mold; a bag or light shell is placed over the reinforcement. The space between the mold/counter mold is evacuated, and catalyzed resin is drawn into the cavity, saturating the reinforcement. Typically, there is a shorter cure cycle, and a higher glass-to-resin ratio compared to hand-laid parts. VARTM mold construction and its atmospheric mold clamping pressures limit overall in-mold pressures to less than 0.5 bar (8 psi), thus limiting the resin flow rates into the mold to lower than those typical of full RTM. The main advantages over open molding are: rapid lamination of very large parts, better thickness control, geometry on the “B” side can differ from that of the “A” surface, mechanical properties are superior to hand laid parts, and CLTE is considerably less.

Mold : VARTM tooling can range from classic gel-coat finished, glass reinforced polyester or epoxy, to simple fabricated and welded metal forms, depending on the complexity of the geometry, and desired finish. Production through-put can vary substantially, depending on what is loaded into the mold; however, it is not impossible to achieve a rate of 5 parts per day per mold. Prototyping is relatively easy and inexpensive. The process is a less tooling intensive, less volume sensitive means of producing closed molded, structural FRP parts. Typical life span: 400 – 1000 parts before the mold is scrapped.

LRTM

Proccess : A closed molding process utilizing a rigid, flanged mold (core or cavity) and a flexible or lightly-reinforced counter mold. After gel-coating, dry reinforcement is loaded into the mold; it is closed, the space between the mold/counter mold is evacuated, and catalyzed resin is drawn into the cavity, saturating the reinforcement. Typically, there is a shorter cure cycle, and a higher glass-to-resin ratio compared to hand-laid parts. LRTM mold construction and its atmospheric mold clamping pressures limit overall in-mold pressures to less than 0.5 bar (8 psi), thus limiting the resin flow rates into the mold to lower than those typical of full RTM. The main advantages over open molding are: better thickness control, smoother quality of the “B” side surface, geometry on the “B” side can differ from that of the “A” surface, mechanical properties are superior to hand laid parts, and CLTE is considerably less. RTML is not recommended for parts requiring a cosmetic gel-coat finish and is primarily specified for parts with a paint finish.

Mold : LRTM tooling costs are basically half the price of equivalent RTM molds because the counter mold can range from a simple, disposable bag to a glass-reinforced polyester shell. Production through-put is half the rate of RTM, in the range of 2 – 4 parts per mold per shift, depending on complexity. The process is a less tooling intensive, less volume sensitive means of producing closed molded FRP parts. Typical life span: 800 – 1500 parts before the mold is scrapped.