DLR Develops Automated Production Line for Resin Transfer Molding (RTM)

 

 

According to Composites World magazine in January 2016, the Lightweight Production Technology Center of the German Aerospace Research Institute (DLR) has developed an automated production line called EVo, which can produce 100,000 complex composite parts per year.

 

EVo was originally designed to manufacture aircraft frames and stringers. Work began in 2009, when the next generation Airbus A320 was planning to use carbon fiber reinforced composites. How to achieve an annual production of 500 aircraft using manual layup was a challenge for Airbus. Each aircraft has 200 fuselage bulkheads, and 500 aircraft per year means that 100,000 bulkheads must be produced per year, so an automated process production line must be developed.

 

The DLR research team initially intended to select a supplier to make an integrated production line, but ultimately chose six independent part splicing production lines, namely: prepreg preparation, preforming, precision trimming, RTM (resin transfer molding), ovens and software. These suppliers can work in harmony by establishing a standard.

 

The prepreg preparation module rolls the fabrics and then sends them to an automatic cutting machine, which cuts different materials and prepreg layup layouts according to the digital cutting file. The cut prepreg is stored on a shelf system that is sorted by a robot, which places it on a transport table and transports it to the preforming area. A camera system on the roof of the workshop provides information for the robot.

 

Automated Cutting and Laying Modules on the EVo RTM Automated Production Line

 

The next module uses a vacuum film to pressurize the stacked prepregs and extract air from under the laminate, while activating the powder epoxy binder on the material through infrared heating. The results show that the preforms handled by this robot are relatively stable during the trimming process.

 

The precision trimming module trims the stable preforms to a near-zero excess preform, which makes EVo more powerful. This step prevents the resin in the preform from wandering and forming “dry spots”. It is particularly important that the composite parts do not open because milling the cured parts will expose the fibers to moisture, which can form micro cracks in the resin. All edges must be sealed and placed back in the autoclave.

 

Precision Finishing Module on EVo RTM Automated Line

 

The robot places the near-thin preform into the 4-part RTM mold, the outer mold with all the heating channels, and the preform on the inner mold/core mold. The core mold is closed and placed in the RTM press. All frames look similar, but the actual geometry is different, so each set of molds is required to handle different parts. In addition, the process requires a specific resin, which cures in more than 90 minutes, so after closing the mold, the mold is moved to the press and baked for post-curing. EVo can inject and cure different parts at once.

 

The first test piece is a 2m long V-shaped curved frame with varying thickness and curvature along the length. In reality, no part is like this, but the test is to collect all possible problems, so all the characteristics are put on one part, which people call the part “Frankenframe”. The EVo line can process parts with dimensions of 2.5m×2m×40cm (height) in a target time of 30-40 minutes. If a faster curing resin is used, the time can be greatly reduced. It is also possible to improve the precision trimming area to enable foam milling to produce sandwich parts, and to use diaphragms to cure the parts.