Autoclave, RTM or Wet Laminate: Why Curing Determines Quality

How a carbon part cures largely determines its strength, weight and appearance. Many buyers focus on the visible weave and the polished surface – but the true quality is created out of sight, namely during curing. The autoclave is considered the most demanding, but also the most powerful method here. You can read on this page which other processes exist and how they differ in production.

Carbon: A Material Made of Two Partners

Carbon fiber reinforced plastic – or CFRP for short – is a classic composite material. It is created through the interaction of two completely different components which are of little use on their own, but together become one of the strongest and lightest materials of all.

The two components:- The fiber: Thousands of ultra-fine carbon fibers are twisted into strands and woven into mats. They carry the mechanical load and are extremely tensile – but only in the fiber direction.- The matrix: A thermosetting resin surrounds the fibers, fixes them in position and makes the three-dimensional shape possible in the first place. The component only becomes load-bearing once this resin cures.

A thermosetting matrix cannot be liquefied again after curing – the process is irreversible. That is exactly why curing must take place in a controlled manner and under optimal conditions. In carbon fiber processing, the rule of thumb is: as much resin as necessary, as little as possible. Too much resin increases the weight and takes away the stable fibers’ load-bearing role.

What curing methods are there?

For the resin to cross-link, it needs energy – usually in the form of heat. Pressure, temperature and effort vary greatly depending on the process. And so does the result.

Wet laminate: Curing at room temperature

With the wet laminate process, the processor impregnates the dry fabric by hand with resin and then places it into a mold. Curing takes place exothermically: the resin itself generates heat during cross-linking and cures at room temperature – without any additional oven.

Advantages:- Low investment costs, hardly any technical equipment required- Well suited for large components and small series- Simple processing that can be learned quickly

Disadvantages:- Resin content difficult to control, resulting in higher weight- Air inclusions and uneven material density possible- Lower strength than pressure-based processes

Typical application: Boat hull construction, decorative fairings and prototypes.

RTM: Resin injection in a closed mold

The RTM process (Resin Transfer Moulding) uses a two-part, closed mold. The dry fiber fabric is placed inside, the tool is closed, and liquid resin is then injected into the cavity under pressure.

Advantages:- Smooth surfaces on both sides directly from the mold- Good reproducibility in medium to large quantities- Lower emissions thanks to the closed process

Disadvantages:- High tooling costs due to two-part molds- Complex design of the resin flow paths- Less flexible for delicate geometries

Typical application: Automotive series parts and structural components in larger quantities.

Prepreg and autoclave: Pressure and heat in combination

In the prepreg process, the fibers are pre-impregnated by the manufacturer with a precisely dosed amount of resin. The material is laminated into a CNC-milled negative mold, packed into a vacuum bag and cured in the autoclave – a pressurized oven that applies heat and pressure at the same time.

The term prepreg stands for “pre-impregnated,” meaning pre-impregnated fiber fabric. This pre-dosing ensures that only the necessary amount of resin remains in the component. An absorbent fleece in the vacuum bag additionally absorbs excess resin during the process.

Advantages:- Optimal fiber-resin distribution and therefore maximum strength- Minimal weight due to pressed-out excess resin- Virtually no air inclusions thanks to vacuum and overpressure- Uniform, high-quality surface finish

Disadvantages:- High technical and financial effort in production- Prepreg must be stored and transported under refrigeration- Long process times and expensive equipment technology

Typical application: Formula 1, MotoGP, aerospace and high-quality motorcycle components.

Why does the autoclave prevail?

If the processes are compared side by side, a clear picture emerges. Wet laminate scores on price, RTM on suitability for series production – but as soon as maximum strength with minimum weight is required, there is no way around the autoclave.

The decisive factor is the combination of vacuum, overpressure and controlled temperature. The vacuum removes even the smallest air inclusions, the overpressure compresses the layers tightly together and presses out excess resin. What remains is a component with an almost perfect fiber-resin ratio – neither weakened by voids nor burdened by too much matrix.

That this effort is worthwhile is proven by its use in the most demanding disciplines. Wherever every gram counts and components must withstand the highest mechanical loads, autoclave-manufactured carbon is trusted. The same care goes into every component at Ilmberger – as described in the journey from prepreg blank to finished carbon part.

What does this mean for your carbon part?

For you as a customer, the curing process translates into tangible properties: lower weight, greater stability and a surface with the typical depth effect. Added to this is the value retention that characterizes high-quality CFRP over many years.

These features speak in favor of autoclave carbon from Ilmberger:- Exclusively prepreg material with controlled resin dosing- Curing in the autoclave under pressure and heat- TÜV-tested quality and parts with ABE (general operating permit – approval for road use without individual inspection)- Protection through the in-house plastic powder coating

Conclusion: Effort that pays off

Every curing process has its justification – from cost-effective wet laminate to series-capable RTM to the top class in the autoclave. Anyone looking for uncompromising quality, low weight and maximum strength makes the best choice with autoclave carbon. The higher production effort pays directly into the durability and performance of your component.