Addressing key obstacles holding back opportunities for high-volume production with HP-RTM

HP-RTM is evolving. Learn how Active RTM combines high-pressure injection with active mold-pressure control to reduce voids, improve consolidation, and boost process stability for complex component designs.

July 27, 2026

In-mold pressure control unlocks new applications while improving quality, consistency, and production efficiency

High-Pressure Resin Transfer Molding (HP-RTM) has become one of the most important manufacturing technologies for creating lightweight composite components at industrial production rates. By combining dry fiber reinforcements with high-pressure resin injection, manufacturers can produce parts in minutes rather than hours, making it an attractive process for high-volume applications.

Composite materials will continue to replace metals in aerospace, hydrogen storage, energy, transportation and other sectors, but new opportunities often present new challenges. While conventional HP-RTM offers exceptional productivity (at the cost of in-mold pressure control), increasingly complex applications demand a higher level of process control to repeatedly achieve the exacting mechanical properties and surface quality required in the abovementioned industries.

Understanding the HP-RTM process

High-Pressure Resin Transfer Molding is a closed-mold composite manufacturing process in which a dry fiber preform is positioned inside a heated mold before a low-viscosity thermoset resin is injected under high pressure using an impingement mixing head.

The HP-RTM process typically has six stages:

The dry fiber preform is prepped and placed in the mold cavity
The mold is closed under high clamping force
Resin is mixed and injected at high pressure
Resin flows through the reinforcement, impregnating the fibers
Inside the mold, polymerization and curing take place
The component is demolded, trimmed and inspected

Compared with traditional RTM or manual pre-preg processing, HP-RTM offers shorter cycle times, high levels of automation, excellent dimensional repeatability and lower manufacturing costs for medium- and high-volume production — making it a preferred technology for creating composite components.

Why conventional HP-RTM can be challenging

Although resin injection only takes a few seconds, controlling the process inside the mold is more complex. During filling, resin pressure increases as the material flows through the fiber reinforcement. Conventional HP-RTM systems can accurately control injection pressure, but they have limited ability to actively manage pressure inside the mold cavity during filling and cure time. This lack of direct in-mold pressure control can contribute to several well-known manufacturing challenges.

1. Void formation & FVF

Microscopic air pockets remain one of the primary quality concerns in composite manufacturing. Excessive void content can reduce fatigue resistance, compressive strength and long-term durability while also affecting cosmetic appearance. Typical issues in adopting HP-RTM, compared to pre-prepregs, are due to having a lower fiber volume fraction.

2. Inconsistent fiber impregnation

Resin, as a liquid, naturally follows the path of least resistance. In complex fiber layouts, this can result in uneven wet-out, dry spots or incomplete impregnation, particularly in thicker laminates or in parts with intricate geometries or inserts.

3. Fiber wash

High velocity resin injection may disturb fiber orientation during mold filling. Even small changes in fiber alignment can influence structural performance and dimensional accuracy, especially in aerospace applications.

4. Processing delicate inserts

Many composite components incorporate lightweight foam cores, honeycomb structures or embedded functional elements. High injection pressures can make these inserts difficult to process without collapse or movement.

5. Narrow process windows

Small variations in resin viscosity, chemical shrinkage, mold temperature or injection conditions can significantly influence final part quality, making repeatability increasingly challenging as production volumes grow.

Cannon's patented Dynamic Overpacking System

Moving beyond the standard HP-RTM process

Rather than outright replacing HP-RTM, the next generation of composite manufacturing focuses on improving how the process is controlled.

One example is what we are calling Active RTM, which combines conventional high-pressure resin transfer molding with the patented Dynamic Overpacking System (DOS). Instead of controlling only the resin injection, our technology actively manages pressure inside the mold during the molding cycle.

By maintaining controlled cavity pressure during and after filling, Active RTM allows manufacturers to obtain more uniform fiber impregnation, reduce void formation, improve laminate consolidation and process increasingly complex component designs. In this way, all of the advantages of HP-RTM are retained, but with a higher level of process stability and quality control.

Next steps in composite manufacturing

As composite structures become larger, lighter and more technically demanding, manufacturing success will increasingly depend on more than cycle time alone. The future of HP-RTM will be in technologies that provide greater control over resin flow, pressure distribution and laminate consolidation during the process.

By addressing the longstanding challenges of conventional HP-RTM, advanced process control technologies like Active RTM help manufacturers adapt composites into newer applications and open a world of possibilities.

Are you looking for a tailored solution?

Contact us today to discuss your specific needs and find out how our custom solutions can enhance your production process. Don’t wait — let’s create excellence together!

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