Current Status of RTM Process Development

Introduction to RTM Process

RTM (Resin Transfer Molding) process is to pre-lay the designed reinforcement material preform in the mold cavity, inject low-viscosity resin into the mold cavity under the action of pressure or vacuum or both, and complete the infiltration of the reinforcement material preform in the process of flow filling, and solidify and shape to obtain composite material components. It is an advanced composite material low-cost preparation technology and has attracted widespread attention.

RTM Process Evolution

In the process of RTM process development, various types of RTM processes have been evolved on the basis of traditional RTM, such as lightweight RTM (L-RTM), silicone mold RTM, cold pressing, multi-embedded surface mold RTM, and vacuum introduction process. When choosing which process to use for product production, we can choose the appropriate process according to actual needs.

For example, when manufacturing large products, such as yachts, large blades, nacelle covers, high-speed rail fronts and large parts on airplanes, the vacuum induction process can be used, because the resin content of this process is low, higher mechanical properties can be obtained, half of the operation time can be saved, core materials can be added to the fibers, and thicker products can be produced in one step; small products are more suitable for traditional RTM processes and other RTM derivative processes, because when making small products, the cost of consumables will increase the manufacturing cost of the product; medium-sized products are suitable for lightweight RTM or silicone mold processes. Under vacuum adsorption, the mold does not need to bear a lot of pressure, and the upper mold can be made light; and products that do not require high surface quality and large batches are more suitable for cold pressing processes; the multi-embedded surface mold RTM process puts the most time-consuming mating process and gel coat spraying process in the process on the embedded surface mold of the main mold, and the main mold only undertakes the infusion and heating and curing parts, so it can greatly improve the production efficiency, and is also suitable for large-scale product production.

Resin Transfer Molding, referred to as RTM, started in the 1950s and 1960s. It is a closed mold molding technology that improves the hand lay-up molding process. It can produce products with two-sided gloss, high molding efficiency, and no styrene volatilization.

The preform of the reinforcement material designed according to the performance and structural requirements is laid out in the mold cavity, and the resin system is injected into the closed mold cavity by injection equipment. The mold is surrounded by a sealing, fastening and exhaust system to ensure smooth resin flow, exhaust all the gas in the mold cavity and thoroughly infiltrate the fiber. The gas in the fiber reinforcement is removed under a vacuum state, and the fiber and fabric are impregnated by the flow and penetration of the resin, and it is cured at room temperature to form a process method with a certain resin and fiber ratio.

It can produce products with two-sided finish and complex shapes and structures
The molding efficiency is average, suitable for medium-scale FRP product production
The soft film has a long service life and can be used repeatedly, with relatively low consumable costs

The main mold is only responsible for the injection and heating and curing parts, which can greatly improve the production efficiency and is also suitable for mass production.

Advantages of RTM Process

The product has two smooth molding surfaces

It can produce complex components with high dimensional accuracy and good surface quality

High molding efficiency, suitable for medium-scale FRP product production

The product has a constant shape and weight, stable quality, and the product quality is less affected by the operator. Whether it is the same component or between components, there is a high degree of consistency, uniform thickness, and low void ratio (less than 0.5%).

The mold manufacturing and material selection are highly maneuverable, and complex large components can be manufactured without large and complex molding equipment. The investment in equipment and molds is small, the investment in plant construction is small, and the start-up is fast

The fiber is pre-laid, which can be enhanced in any direction, and the product strength is good (fiber content 25~35%, L-RTM, vacuum induction molding fiber content can reach 65~70%)

Environmentally friendly. The RTM process is a closed mold process, which reduces styrene emissions, greatly improves the working environment of operators, stabilizes the workforce, and expands the range of available materials

The product design has a large degree of freedom. RTM process is not only better than autoclave molding process, but also better than filament winding molding process and pultrusion molding process.

Application Fields of RTM Technology

1) Boat industry – hull, deck, rudder, radar shield…

2) Wind power energy – blades, engine cover…

3) Sports and leisure – helmets, windsurfing…

4) Automobile industry – various roofs, windshields, carriages…

5) Construction field – building top parts, building formwork…

6) Agriculture and horticulture – granary dome, agricultural machinery protection cover..