Lightweight construction with lasers and robots

Lightweight construction with carbon fiber reinforced polymers (CFRP) offers climate protection for air and road travel. In order to bring CFRP components up to the cost and quality standards of mass production, laser-based automated manufacturing processes are required.

By combining textile and plastic technology, air travel and automobile businesses can create featherweight components that are as strong and stiff as most metals. To do this, they use the procedures of textile technology to process extremely fine carbon filaments into preforms, which are then embedded into thermosets or thermoplastics. While this part of the process chain is increasingly automated, there is potential to make the further processing of CFRP components more efficient. This still involves time and cost-intensive operation which leads to high tool and labor costs.

In a project funded by the EU and the state government of North Rhine-Westphalia, the Fraunhofer Institute for Laser Technology ILT Aachen, Trumpf subsidiary AMPHOS and other partners have optimized one of these processes. To connect CFRP components to other parts, manufacturers previously drilled holes into which they pasted metallic connecting elements. This takes time and comes with a lot of tool wear due to the carbon fibers. As an alternative, the researchers use ultrashort pulse (USP) lasers to drill holes matched to the exact shape and size of the connecting elements; the holes are drilled in the textile preforms, which are then embedded in the plastic matrix together with the connecting elements. The whole process is fully automated in a robot cell.

Using lasers to create cost-effective, material-saving CFRP components

In order for the ultrashort laser pulses to remove material in exactly the right place, precise to the micrometer during the dynamic robot process, the beams are not guided by mirrors. Instead, the specialists at Fraunhofer ILT and AMPHOS have developed a new approach to coupling and uncoupling the laser pulses: using a hollow-core fiber to connect the source of the USP laser beam with the robot’s scanner. The precise, form-fitting connections between the non-crimp fabrics, plastic matrix and connectors reduce time and costs in CFRP production while resisting tensile forces up to 50% higher than pasted-in connectors. This opens up new possibilities for reducing weight and saving material in component design. The new laser process is also highly flexible. Robots and scanners can switch between meters and micrometers upon the instructions of the project partners far more freely than was possible in previous mechanical processing.

Fast, precise, contactless and flexible

The Laser Zentrum Hannover (LZH) has also recently concluded a publicly funded research project with TRUMPF and other partners, resulting in efficient laser processing for CFRP components. The focus was on CFRP struts which aircraft manufacturers use to stabilize the floors of cargo holds. Previously, these “cargo struts” were drilled in due to time constraints. Saving time this way typically involves high level of wear for tools used for CFRPs: in this case, high-value diamond drills. If these are not changed quickly enough, it can cause damage to the plastic matrix. In order to solve this problem, the researchers developed a laser process that is managed by software and monitored by thermography, and that creates drill and rivet holes at the same speed as a mechanical drill. To optimize the quality and precision of the holes, the software continuously adjusts the parameters and drilling strategy in the process. This way, aircraft manufacturers gain access to a fully-automated yet flexible laser process which not only drills all common types of CFRP at high speeds and top quality, but also glass fiber reinforced materials and special composite materials such as copper mesh. The flexible project management also makes it easy to drill laser holes in various laminates placed on top of each other to the specifications of the project partners.

In both projects, laser technology is the key to increasing flexibility and optimizing time and cost efficiency in lightweight CFRP construction. Bit by bit, this technology is approaching use in mass production, where every gram saved has huge leverage—for a wide range of electric vehicles and aircraft, as well as for reducing energy demand in climate friendly mobility.

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