New hydraulic press for automated processing of thermoplastic CFRP

The Center for Lightweight Production Technology (ZLP) in the German Aerospace Center (DLR, Augsburg) is tasked with developing lightweight carbon fiber reinforced plastic (CFRP) structures and economic production methods tailored to industries including aerospace, wind energy and automotive. Researchers there seek automated processes utilizing robotics and other technologies for cost-effective and robust manufacturing with high quality.

To help address this goal, Wickert Presstech (Landau in der Pfalz, Germany) has produced a multifunctional composite press for the DLR featuring high-temperature heating and cooling platens, an infrared heating system and a transfer system which transports components from the infrared oven into the press and the plant's loading and unloading points. The press also uses a parallel platen control for maximum accuracy, achieving a tolerance of 0.025 mm during the pressing process. Integration of additional path measurement with a resolution of 1 µm on the tool itself will facilitate high-precision production, and controls offer a choice between 'press path measurement' and 'tool path measurement'.

Suitable for processing all composite materials
The ZLP is developing a new production cell for processing complex thermoplastic fiber composites to aid research into automated production technologies for CFRP components. Wickert has designed its new press to enable maximum flexibility for researching a wide variety of processes and parts. It reports that the ZLP is aiming to consolidate and reform thermoplastic matrix CFRP materials, including high-performance thermoplastics such as polyetheretherketone (PEEK). "The plant's great flexibility is definitely a major advantage in the processing of all materials used in today's composites applications,” says Stefan Hertel, WICKERT design manager. “Also, studies, simulations and experiments have significantly improved the flow geometry and flow design of the heating and cooling platens. And because we have a highly efficient and economical solution for water cooling, we have achieved extremely high cooling gradients and cooling tolerances when compared with our previous systems. . . . the DLR's standards for the variotherm process required us to take new, different approaches and to continue pushing developments forward in this field."

WICKERT proposed an upper ram press, type WKP 4400 S Composite. A wide variety of optional packages integrated into the press enables processing different kinds of materials, such as PEEK or PPS. The press features a 1,800 x 1,200 mm heating platen, a pressing force of 4,400 kN and a minimum pressing force of only 25 kN. Heating platen temperatures can be controlled precisely between 40°C and 450°C. Maximum tool weight can be as much as 12,000 kg, and the maximum transfer time from initial movement to complete press closure/maximum pressing force is five seconds.

Its experience in the construction of presses for pharmaceutical applications enables WICKERT to comply with clean room specifications, including hydraulics that are 100% free of oil mist and reliably prevent contamination of CFRP parts.

Composite press adapted to individual requirements
For this installation in the Technology Hall of the ZLP, an existing infrared oven has to be integrated into the press plant. As part of the adapting process, WICKERT is converting the existing ZLP infrared system and extending it to meet the requirements of future production tasks. The infrared oven will be integrated into the production control system via a PROFIBUS interface and visualized via WIN CC-Flex. Both programming and visualization are customized for the DLR so that process images and sequences can be defined in close consultation with the responsible managers.

In addition, the system will feature a signal exchange with a linear axis robot already present in the ZLP to enable fully automated process implementation. WICKERT is developing an interface for the signal exchange between its press and the robot, resulting in a control system with programmable functions for maximum flexibility in process sequences. A selector switch allows manual and automatic operation or set up, and the press is equipped with a photoelectric barrier as a precautionary measure for when the robot operates in the security zone. Software to adapt the robot operation for component transfer from the infrared oven to the press is also part of the WICKERT service package. In general, the unit is designed to be fail-safe to EN 289, including the infrared oven. The DLR research mandate also requires measurement of energy consumption for evaluation of the economic efficiency of various process sequences. Thus, power consumption per cycle or total power consumption can be measured and logged.

Training and service included
To ensure that the press is commissioned smoothly and quickly, ZLP staff will be trained during WICKERT’s commissioning process in production-equivalent conditions. WICKERT will also conduct follow-up training after commissioning is complete.

At the DLR site in Augsburg, WICKERT will provide a telephone service — including remote diagnosis with designated contact persons — to enable rapid implementation of processes and machine settings for complex tasks. This facilitates immediate corrections, quite common when starting up this kind of system. The 'tool' for this service, which covers help with operator guidance, process optimization and fault detection, is the remote servicing function via a high-performance network link between the WKP.

WICKERT views itself as a press technology pioneer in the field of composite processing and believes the WKP 4 400 S Composite will stake new ground in composite production. "We are proud that we can develop and construct this press for the ZLP of the DLR," says managing director Stefan Herzinger. "The success of our presses in aircraft and automotive construction shows that we can meet the most stringent requirements and can create the basic conditions for the future production of quite new composite components. The need for lightweight structures will continue to grow and WICKERT is already providing innovative and yet proven production solutions for this."