LRTM (Light Resin Transfer Moulding)

LRTM differs from the RTM process in that LRTM uses a lighter top mould (male mould) compared to RTM. During the tool making stage, tool makers determine the thickness of the final part and calibrate it to the cavity (space) between the top and bottom mould.

In the first step of the LRTM process, gelcoat is applied on the bottom mould and then the layers of fiberglass reinforcement specially made for the LRTM process is laid out. The top mould is lowered using a chain block/hoist into the female bottom mould. Vacuum is applied to the mould to hold them together as well as pull out the vacuum inside the mould. RG Fibrotech uses a Busch Branded Vacuum System for this purpose.

https://www.buschvacuum.com/in/en/products/r5-ra-0165-0305-d.html?product_technical_data=ISO_50

Resin is injected into the mould using a RTM Injection Machine which feeds resin in small strokes so that it is evenly spread inside the mould. Once the part cures, it is demoulded.

Features of LRTM

  • Suited for high volume jobs.
  • Can be used for plain parts without any reverse flanges.
  • Smooth surface can be given to both sides of the part by applying gelcoat on the male
  • mould as well.

Vacuum bagging/Silicone Bagging (Vacuum Assisted Resin Transfer Moulding/VARTM)

The VARTM technique is a type of closed moulding process where there is a rigid lower mould (Female mould) and a flexible material (Male mould) which fits inside it. The flexible material may be a plastic film or a silicone bag.

Plastic films are used for VARTM when the volume of production is low. They’re not used otherwise since it’s got a high environmental impact as they can be used only for a single lamination. Silicone bags are the preferred female mould material for the VARTM process since they can be reused.

The VARTM process starts with the application of the gelcoat layer onto the bottom mould and once it’s tacky the fiberglass reinforcement layers numbering to the desired thickness is cut into shape and laid across the bottom mould. Then the upper film or bag mould is kept on top of the bottom mould. Vacuum is applied to lock the bag into position and to suck out air. When the size of the part is small resin is simply poured inside the mould cavity before lowering the upper mould. The vacuum automatically pulls the resin throughout the laid fiberglass reinforcements and impregnates them. If the size of the part is bigger, a Resin Injection material is used which uniformly injects resin into the mould cavity. RG Fibrotech is equipped with 2 MVP Patriot Systems https://www.mvpind.com/product/patriot-innovator-rtm-systems/ .

Features of VARTM

  • Lower investment on tooling as only the bottom mould needs to be rigid.
  • Higher turnout time compared to LRTM due to usage of different consumables.
  • Silicone bags can be used for moulding complex parts more effectively.
  • Large parts with less volume can be done with Plastic Film lamination.