Productions+Processes: Solutions in Composite Materials

PulPress technology with ROHACELL® brings short-cycle times to large-volume parts production.

By Evonik Industries AG and Lightweighting World Staff

Large volumes at reasonable prices—often that goal is a contradiction in terms when it comes to producing fiber-reinforced composite materials. PulPress technology developed by Evonik Industries AG, in cooperation with Secar Technologie, demonstrates how it can be achieved by using a novel continuous process to make sandwich-profile components from composites.

A number of technologies are available for manufacturing complex molded parts from fiber-reinforced composites, but they all have one thing in common: cost-effectiveness does not necessarily go hand in hand with the desired level of component complexity. The best example of this is lamination by hand—the oldest method for making composite components. While this method can be used for producing complex geometries, by definition, it cannot be automated, which eliminates it as an economical option for mass production.

A greater degree of automation can be achieved with what is known as resin-transfer molding, a process that has attracted some attention lately, not least as a result of the bodies of BMW’s i3 and i8 electric cars, which were made from carbon-fiber-reinforced plastic. Current cycle times are still relatively long, however, much longer than typical times for a BIW (Body-in-White) cell in large-scale automobile production. One alternative is to make elements such as fiber-reinforced plastic profiles via the pultrusion method, even though for a long time, manufacturers could only use this process to produce straight profiles.

It was against this backdrop that Evonik developed a new, highly automated, continuous process for manufacturing components with complex geometries from fiber-reinforced composite materials. The development partner for the project was Secar Technologie GmbH, a company located near Vienna, Austria, specializing in the production of components from a variety of fiber-reinforced composites.

Pultrusion + Molding Processes = PulPress

Known as PulPress, the new method represents a novel combination of pultrusion and molding processes. In terms of the materials used, development began with Evonik’s ROHACELL®, a closed-cell, high-performance structural foam that serves as a core material in sandwich components. For more than 40 years, this polymethacrylimide (PMI) foam has proven to be a lightweight, yet strong material in composites such as those used in auto racing, aviation and athletic equipment (hockey sticks, skis, etc.).

In addition to its low specific weight, ROHACELL® is also thermoformable and highly pressure resistant, with a glass-transition temperature of 180°C. These properties make the material perfect for the PulPress method. In PulPress, the rigid structural foam serves as the core through which reinforcing fibers are woven. Afterward, resin is introduced for fiber impregnation. Once prepared in this way, the material is fed into a press system that processes the continuous material at elevated pressure and temperature to create a 3-D profile with defined dimensions. Today, the production plant produces sandwich-profile components for customers, especially in the automotive industry.

Basic principle of the new PulPress process—Fibers are woven through the sandwich core, which is first impregnated with resin and then pressed into the desired shape at elevated temperatures. Thirty sandwich profile components an hour can currently be produced in this fully automated process.

In these components, ROHACELL® serves as shaping core material. Additional metal or polymer inserts can be added during processing, as well. Evonik and Secar worked together to build the plant, which is capable of a fully automated throughput of 30 components an hour, or one component every two minutes. That rate could be further increased by using additional movable press systems or a resin system that cures faster.

The structural foam core of fiber-reinforced plastic parts ensures that the resulting component will withstand the desired application of energy and force. To illustrate the performance of PulPress parts, a car-bumper demonstrator was produced and tested to the RCAR vehicle crash standard used in setting German insurance ratings. In comparison to an aluminum bumper, the type commonly found in today’s automobiles, the PulPress bumper showed a reduction of intrusion depth at nearly one-third of the part weight.

Huge Cost Reductions

Unlike today’s processes, in which a structural foam core with fibers is processed into a composite material, PulPress involves almost no waste—of either the foam core or the fiber. The simplicity of the technology eliminates several intermediate processing steps, such as pre-shaping, draping, binder activation and form lay-up, used in standard methods today. These advantages, combined with excellent cycle times, produce tremendous cost savings of up to 60 percent for producing complex composite parts. Benefits of PulPress technology has already won a number of customers for Evonik, especially in the automotive industry. This process will also benefit customers in the aviation industry, as well as the athletic-equipment sector and other industrial markets.

Using the new PulPress method to produce complex molded profiles from composite materials cuts costs up to 60 percent per component over other production methods. The resulting components weigh 75 percent less than their steel counterparts.

PulPress is an ideal solution combining part complexity with economic feasibility.

 

The compact production line supplies currently complex sandwich-profile components for customers.

 

 

Top left: Crash scenario of a reference part made in aluminum; top right: crash scenario of a PulPress part made in FRP sandwich construction;Bottom: Bumper demonstrator

 

For more information, please contact: Dr. Sivakumara Krishnamoorthy

Evonik Resource Efficiency GmbH

High Performance Polymers

Phone +49 6151 18-4836

sivakumara.kri

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