By Mike Davey
Oak Ridge, Tennessee — May 30, 2016 — Carbon fibre composites are incredibly strong and very lightweight. The material would therefore be almost perfect for both body panel and structural components, but high production costs have helped to limit its use. Carbon fibre also requires a lot of surface preparation prior to bonding at the factory.
The cost is almost certain to come down as more and more industries see its advantages and pour in research funds. A news release from the US-based Oak Ridge National Laboratory (ORNL) indicates that new methods of joining might soon be available as well.
According to the release, the new method uses a laser “to replace the practice of preparing the surface of the materials by hand using abrasive pads, grit blasting and environmentally harmful solvents. Using a laser to remove layers of material from surfaces prior to bonding improves the performance of the joints and provides a path toward automation for high-volume use.”
The process was developed by a team led by Adrian Sabau of the US Department of Energy.
“Our technique is vastly superior to the conventional surface preparation methods,” Sabau said. “Combined with the potentially dramatic reduction in the cost of carbon fibre polymer composites, this represents an important step toward increasing the use of this lightweight high-strength material in automobiles, which could reduce the weight of cars and trucks by 750 lbs.”
The new process also works on aluminum, according to the release from ORNL. The surface treatment of both aluminum and carbon fibre is essential to the joining process and directly affects the bond quality. In the case of aluminum, the surface often contains oils or other contaminants introduced during the production process. Carbon fibre surfaces are typically molded. Getting the part out of the mold requires a mold release agent, and this release agent can make joining difficult unless it is thoroughly removed.
“These surface contaminants affect surface energies and the quality of adhesion, so it is critical that they are removed,” said Sabau, adding that the laser also penetrates into the top resin layer, leaving individual carbon fibres exposed for direct bonding to the adhesive and increasing the surface area for better adhesion.
Test results of single-lap shear joints showed showed strength and maximum load were increased by 15 and 16 percent. Displacement at maximum load was increased by 100 percent. The researchers also reported that joints made with laser-structured surfaces can absorb approximately 200 percent more energy than the conventionally prepared baseline joints.
The process also doubles the ability of the joints to absorb energy. This has obvious implications for increasing safety in the event of a crash.
OEM parts manufacturer Magna International is a project partner in the research. Tim Skszek heads up government partnerships in the NAFTA region for the company. He also expressed enthusiasm for the initial results.
“The results are most encouraging, enabling the automated processing of a multi-material carbon fibre-aluminum joint,” Skszek said. “With this work, we were able to focus on addressing the gaps in technology and commercial use, and we look forward to applying these findings to products.”
Other members of the research team are Claus Daniel, Dave Warren, Donald Erdman III, Jian Chen and John Henry of ORNL and Mary Caruso Dailey of 3M.
You can see a demonstration of the process in the video below.