Resin Transfer Molding


A material made from two or more constituent materials with significantly different physical or chemical properties is known as composite material. When the constituent materials are combined it produces a material which has different characteristic from the individual components. There are three types of composite manufacturing processes namely open molding, closed molding and cast polymer molding.

Resin Transfer Molding (RTM)

RTM is an intermediate process in closed molding where resin is injected under pressure into a mold cavity. RTM is primarily used to mold components with large surface areas, complex shapes and smooth finishes. To remain undamaged from hydraulic pressure RTM uses heavy structured tooling like low-cost composite molds to temperature controlled tooling. The outputs of RTM is light in weight and high in strength.

RTM process

The process of RTM starts with gel coating of the mold to provide a high-quality and durable finished product. Then the reinforcement and required material is placed in the mold and the mold is closed and clamped. Using mix or metre injection, the resin is injected under pressure and the rigid part is preserved in the mold by heating. Tooling used in this process can be hard or soft depending on the duration of heating time. Soft tooling would be of polyester or epoxy molds whereas hard tooling consist of cast machined aluminium/ steel or electroformed nickel shell.


Some of the major application areas of RTM are truck panels, boat hulls, wind turbine blades, aerospace and automobile parts, medical composites, bathroom fixtures, car body, helmet, etc.


Good surface quality

Wide range of reinforcements

Large and complex shapes

Dimensional tolerances

Low capital investment

Less material wastage

Tooling flexibility

Low environmental impact

Labour savings

Ability to add inserts and reinforcements at a point of infusion for greater strength

Zero air entrapment within the product.


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