Bending for fiber-reinforced plastics

At Fraunhofer IGCV, we are researching bending processes for the controlled, thermally assisted deformation of fiber-reinforced composites.

Bending is one of the forming manufacturing processes in which materials are permanently shaped into new, usually complex geometries by applying targeted forces – without machining or loss of shape. In the field of fiber-reinforced composites, the material properties are particularly important. In contrast to metal forming, where plastic deformation is possible, fiber-reinforced composites (FRCs) must be shaped in a targeted manner with the application of heat to ensure their formability.

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Forming technologies such as bending and thermoforming enable the precise shaping of fiber-reinforced plastic components under controlled conditions. It is crucial to protect the fibers from damage or breakage and to keep the matrix intact in order to maintain the mechanical properties and prevent delamination or cracks. Unlike metallic materials, the deformation behavior of these materials depends on the fiber architecture, the matrix properties, and the laminate structure. These processes are either applied in a formable state, such as with prepreg or B-stage materials, or they require special heating techniques, especially for thermoplastic materials.

Applications of bending technology

Bending offers a wide range of industrial applications — especially where lightweight construction, high rigidity, and design flexibility are required. Through the targeted shaping of thermoplastic semi-finished products, components can be designed to suit the load path and mechanically optimized without adding additional material or weight.

A key area of application is in injection-molded structures (DRIFT technology), in which bent inserts or skeleton structures act as load-bearing reinforcement elements. This integration results in components with high functional density, improved rigidity, and reduced weight.

In addition, bending can be used in the manufacture of thermoplastic piping systems to achieve complex geometries with high dimensional accuracy and dimensional stability. Another area of application is the replacement of metallic and thermoset reinforcement elements with formable fiber-reinforced thermoplastic structures. This significantly reduces weight, susceptibility to corrosion, and maintenance costs.

Bending technology is therefore used in numerous industries – from the automotive and aviation industries to construction and plastics technology.

An innovative version of this technology is based on the principle of rotational bending, originally used in metalworking, and was adapted for the processing of thermoplastic, continuous fiber-reinforced profiles as part of the BMBF-funded project »DRIFT«. Developed in collaboration with the machine manufacturer WAFIOS, Fraunhofer IGCV plays a central role in the material-specific further development and implementation.

By integrating a heating unit, currently in the form of contact heating, the thermoplastic matrix is brought to the required forming temperature in a targeted manner. Heating the profile in the bending area softens the thermoplastic matrix, enabling bending with variable radii and bending lengths. This enables the local and precise forming of continuous fiber-reinforced composite profiles with high dimensional accuracy and minimal damage to the fiber structure.

This bending technology allows the forming of continuously fiber-reinforced thermoplastic profiles with different geometries, such as rods, tubes, and flat profiles. Various bending geometries can be realized through variable programming.

At the start of the bending process, the profile is inserted into the machine's collet chuck. With the help of a robot, the profile is guided into the heating unit and heated there for a specified time so that the thermoplastic matrix softens. After heating, the heater opens and the profile is guided to the bending tool. The robot ensures that the softened composite part retains its shape and does not sag.

In the bending tool, the profile is fixed between the tool and the clamping jaw. The rotational movement of the bending head bends the profile to the desired angle. Different tools enable variable bending radii and angles to be achieved. The component then cools down in the tool, either passively through ambient air or actively through compressed air cooling.

The process is repeated for each additional bending point, allowing complex three-dimensional geometries to be produced within the machine's capacities. To shorten process times, the next bending point can be heated up while the current bend is cooling down.

General:

• Bending of pipes up to a diameter of 35 mm
• Temperatures: up to 350 °C with contact heating (heating of the thermoplastic by contact heating, expandable to other heating types such as hot air, infrared, induction, etc.)
• Robot support: Improved component stability during bending

Suitable for all types of technical fibers

Customized features:

• Bending process can be adapted to specific profiles/bending geometries
• Bending of 2- or 3-dimensional parts

Flexible setup:

• 8 CNC axes enable complex bending geometries
• Custom-designed bending tools for various shapes (round, oval, flat, etc.)
• Capable of bending in two directions (left/right)

Areas of application:

• Bending complex geometries
• Load path-oriented reinforcement
• Reduced complexity when assembling multiple straight profiles: bending eliminates connection points
• Infrastructure, sports and leisure, aviation, automotive

Research focus

• Bending of continuously fiber-reinforced rods
• Bending of hollow profiles, e.g., pipes, square pipes
• Influence of fiber orientation and additive materials on bending behavior and process speed
• Investigation of different heating approaches
• Reduction of cycle times by increasing the bending speed and optimizing the heating and cooling times
• Investigation/improvement of the bending range

Research projects