RTM production method
RTM is an advanced technological process used to manufacture composite products using closed moulds. The method involves injecting resin into a prepared mould, which has been previously filled with reinforcement or sandwich material. The entire process is carried out under pressure or using vacuum, which guarantees thorough saturation of the fibres and elimination of voids. This makes the process fast, clean and ensures repeatable results.
In an industrial context, RTM production works well where optimising time and costs is crucial. The technology enables the creation of components with high-quality surfaces, eliminating the need for additional processing. Another significant advantage of this solution is the reduction of volatile substance emissions, which translates into improved workplace ergonomics and compliance with environmental regulations.
How does the RTM method work?
The Resin Transfer Moulding process begins with the precise preparation of a composite mould. A dry glass mat or carbon fibre is placed in it, as well as structural spacers, if necessary. The mould is then sealed tightly. At this stage, vacuum or pressure is applied to ensure even distribution of the resin inside the mould, resulting in a uniform laminate structure.
Once the resin has been formed and cured, the finished component can be removed from the mould – it is attractive, durable and resistant to deformation. What is important, the manufacturer using the RTM method can easily control each stage of the process, which guarantees repeatability and stability of technical parameters even with large production volumes.
What are the advantages of RTM production?
The implementation of RTM production offers a number of technological and economic benefits. One of the most important advantages of this technique is the possibility of mass production at relatively low unit costs. The moulding process is quick, which significantly reduces production time compared to traditional manual methods.
Another advantage is the high quality of the finished elements – the smooth surface on both sides reduces the need for further processing. It is also worth noting the low level of volatile organic compound emissions, which makes the method environmentally friendly. The use of RTM technology also minimises material losses, and the high proportion of reinforcements increases the durability and resistance of the finished products.
What products can be manufactured using the RTM method?
The RTM method can be used to manufacture a wide range of composite elements – from lightweight covers and technical shields, through architectural panels, to components for the automotive and transport sectors. This technology is excellent for the production of tanks, structural elements, infrastructure components and parts requiring high aesthetics.
It is worth noting that this solution is also used in the manufacture of components for the commercial vehicle industry. A great example of this is the construction of special vehicles, which require a combination of low weight, mechanical resistance and precision workmanship. These types of components can be moulded repeatedly and with high dimensional accuracy, which guarantees compliance with technical specifications.
Examples of applications for RTM production
Products manufactured using RTM technology are used in many industries. The most common ones include:
- automotive and transport industry,
- road and urban infrastructure,
- components for the railway industry,
- elements for construction and architecture,
- technical and industrial equipment.
In each of these cases, process reliability, quality control and the possibility of serial production are essential – and all this is offered by modern RTM production technology.
RTM technology tooling
The basis of every successful RTM production is precisely manufactured, two-part tooling, consisting of a mould (matrix) and a matching punch (patrix). Unlike open moulds, RTM tools must guarantee absolute tightness around the entire circumference in order to withstand the injection pressure and prevent resin leakage. Depending on the scale of production, we use composite moulds (for shorter series) or machined metal moulds (aluminium, steel – for large-scale production). We often integrate heating or cooling channels into them, which allows us to control the process temperature and reduce cycle times.
What is Light RTM (LRTM)?
Light RTM (often abbreviated as LRTM) is the most popular variant of RTM technology, which we use especially in the production of large-size components. This process combines low-pressure resin injection with the simultaneous application of vacuum pressure on the other side of the mould. The vacuum ‘sucks’ the resin, facilitating its flow through the reinforcement and ensuring perfect saturation even in complex geometries. The use of LRTM allows for a reduction in injection pressure, which in turn enables the use of lighter and cheaper composite tooling, making this technology more accessible even for medium-sized production runs.
The role of reinforcement preforms in RTM production
In order to ensure full repeatability and speed up the production cycle, dry reinforcement is most often prepared in the form of a so-called preform. It is a three-dimensional insert, tailored to the shape of the mould, made of cut and joined layers of fabric and mats. We use CNC plotters for precise cutting of materials and special powder adhesives which, when heated, bind the reinforcement layers into a stable shape that is easy to place in the mould. The use of preforms is crucial in serial RTM production, as it eliminates the risk of reinforcement displacement during mould closure and resin injection.
Key process parameters in RTM production
The quality of the final product depends on strict control of the injection moulding process parameters. An experienced RTM manufacturer manages the entire process in real time. The most important variable is the resin injection pressure, which must be high enough to overcome flow resistance, but not so high as to damage the mould or reinforcement. The temperature of the mould and resin is equally important, as it affects its viscosity and gelation time. By precisely controlling these parameters, we ensure that the mould is filled at the right time and that the entire laminate is evenly and fully saturated before the curing process begins.
RTM production compared to other technologies
The decision to choose RTM technology should be dictated by the specific nature of the project. Compared to manual laminating, RTM production offers significantly higher repeatability, two perfectly smooth surfaces, a better strength-to-weight ratio, and lower emissions of volatile compounds. However, it involves higher initial costs associated with the manufacture of sealed, two-piece tooling. With regard to thermoplastic injection moulding technology, RTM is much more cost-effective for the production of large components and in series of several hundred to several thousand pieces, where the cost of manufacturing an injection mould would be economically unjustified.
In-Mould Coating (IMC) – coating during the moulding process
In order to maximise process optimisation in RTM production, we also offer advanced In-Mould Coating (IMC) technology. It involves applying a specialised coating (primer or top coat) directly onto the surface of the hot mould just before the resin is injected. During the curing cycle, this coating cross-links and forms a chemical bond with the composite material. The result is a detail that comes out of the mould with a final, perfectly smooth and durable layer of coat. The use of IMC eliminates the need for a subsequent time-consuming coating process, significantly reducing total production time and lowering costs, which is a key benefit for our customers.