Resin Transfer Molding (RTM) is a closed-mold composite manufacturing process in which resin is injected into a mold containing dry fiber reinforcement. This method enables the production of high-strength, lightweight composite parts with precise dimensions and high surface quality.
Resin Transfer Molding (RTM)
When Should You Use Resin Transfer Molding (RTM)?
Resin Transfer Molding (RTM) should be used when high dimensional accuracy, repeatability and surface quality are required. It is particularly suitable for medium to high production volumes and applications where both mechanical performance and aesthetic finish are important.
In this method, composite products are manufactured using closed moulds. The first step is the application of gelcoat (although production without gelcoat is also possible). The next stage involves placing structural layers such as glass mats, synthetic mats, sandwich mats, coremat and roving in the mould, together with additional reinforcements and inserts.ould.
RTM vs Hand Lay-Up – Key Differences
Resin Transfer Molding (RTM) differs from hand lay-up primarily in process control, repeatability and surface quality. RTM is a closed-mold process that ensures consistent production and high-quality finishes, while hand lay-up is more flexible and cost-effective for low-volume or large composite structures.
| Property | RTM | Hand Lay-Up |
|---|---|---|
| Production Volume | Medium to high | Low to medium |
| Surface Quality | High | Moderate |
| Repeatability | Excellent | Limited |
| Tooling Cost | Higher | Lower |
| Design Flexibility | Moderate | High |
Compressed Air and Special Clamping Systems
Compressed air together with special clamps, actuators or presses is used to apply the appropriate pressure to the mould. Because the moulds are subjected to significant closing forces and pressure during resin injection, they must have high durability and structural strength. For this purpose, we use special pastes, composite materials, metal frames and additional reinforcements. Once the mould is closed, the resin is injected through dedicated injection openings.
Advantages of the RTM Method
- Cost-effectiveness for large-volume production series
- Low emissions of volatile substances into the environment
- Excellent product quality and uniform laminate structure
- Reduced wall thickness thanks to appropriate mechanical properties
- High glass content and exceptional product durability
- Smooth and aesthetic surface finish on both sides (even without gelcoat)
- High process efficiency
- Greater thickness accuracy compared to hand lay-up lamination and LRTM
- Possibility of producing parts with variable wall thickness
- Low waste and reduced material consumption
- Very low unit production cost, although tooling costs are higher compared to other technologies mentioned above
- High Quality
If you are considering Resin Transfer Molding (RTM) for your project, Astromal offers full support from design and tooling to serial production. We help select the optimal composite manufacturing process based on your technical and production requirements.
Contact Astromal to discuss your RTM composite project.mponents, unless additional tooling and machinery are used.