Metal forming allows aerospace engineers to fashion a wide range of small and large aircraft structural parts and airframe components. Mónica Carranza Sáenz, coordinator of the EU-funded Rib-ON project, notes that despite the potential of this process, “when it comes to forming aluminium sheets at room temperature, they demonstrate low formability and springback, namely, they tend to return to their original shape. Increasing the temperature would significantly help tackle these challenges and produce highly precise parts with a complex geometry.”
Shaping metal parts at high temperatures
Hot stamping is a promising technology for high-volume and competitive production of primary and secondary aircraft structural parts. “Combining hot stamping with high-performance aluminium alloys offers a wealth of benefits, such as more curved shapes, tighter tolerances and reduced weight, while retaining the strength of the final component,” adds Carranza Sáenz. Through the Rib-ON project, Spain-based company Batz and project partner AZTERLAN successfully developed a modular, low-cost stamping die for manufacturing different wing rib geometries based on high-performance aluminium alloys. This advanced stamping die enabled engineers to manufacture aluminium ribs of different shapes and lengths. Prior to its development, researchers conducted simulations to define the type and proper configuration of the stamping die components. A simple configuration comprising a punch, a matrix and a blank holder was selected for the hot stamping tool. The metal forming process also incorporated a cold-forming stage to counterbalance possible spring-back. This cold-forming stage can also be omitted, as part tolerances achieved by hot forming are high enough. Tribological tests were performed to analyse the friction and wear of several material and coating combinations at different temperatures. Ultimately, GGG70-L – a type of ductile cast iron with high tensile strength – proved to be the most cost-effective material for die manufacturing.
Lower material and heat treatment costs
“Using this type of cast iron – a raw material – in hot stamping dies manufacturing helped cut material costs by 80 % compared to the commonly used forged steels (alloys of carbon and iron). Manufacturing costs were also decreased by using simple cooling circuits in the die, thanks to the long cycle time allowed by the small batch production,” notes Carranza Sáenz. Due to small batches, the need for die coating can be eliminated, as the cast iron demonstrated the lowest level of galling – a type of wear that causes a metal to adhere to another metal – at typical temperatures for short productions. Stamping dies are an important factor in the final cost of structural parts. Low costs undoubtedly facilitate their wide adoption by the aerospace industry. The BATZ hot stamping die proved suitable for manufacturing wing ribs, ensuring a high level of precision, tight tolerances and repeatability for complex geometries.
Rib-ON, hot stamping, stamping die, wing rib, aircraft, tolerance, aluminium, structural parts, cast iron, aerospace, metal casting