Stretch forming dies are unique to each section of an aircraft’s fuselage. Since many are needed, the sheer volume of dies can pose a storage problem, with stacks of heavy dies taking up valuable space and requiring much labor to move, organize, and mount on the press.
Additive manufacturing (AM) – 3D printing – offers a solution.
Akron, Ohio-based Additive Engineering Solutions (AES) LLC has applied its ability to 3D print large-size composites to create lighter stretch forming dies with modular, interchangeable components for Spirit AeroSystems.
We recently asked Spirit AerosSystems’ Advanced Product Development & Research Engineer Matthew Guile and AES Vice President & Co-Founder Andrew Bader to share some details about the project.
Aerospace Manufacturing and Design (AM&D): How is the tooling used?
Matt Guile (MG): The tool is used as a die for stretch forming body frames. Body frames are the ribs of a fuselage and are found about every 20". A stretch press grips an aluminum extrusion and plastically deforms it across a die. This die matches the contour of the fuselage at a given location and gives the frame the shape it needs. AM&D: What prompted the need for a composite insert? MG: Despite the shape of the fuselage only changing slightly every 20", a unique die is needed to form that contour. The result is a parking lot full of hard tools. Along with the high cost of these dies, there’s no easy way to store, transport, and get them on and off the stretch press. These issues are compounded as production rates increase. Research and development (R&D) saw an opportunity to develop a modular tooling method to remedy these issues. For the material, composite thermoplastics have an excellent strength-to-weight ratio, which allowed us to design smaller, lightweight tools.
AM&D: How is the new solution like or different from stretching on a metal tool?
MG: The unique aspect of a stretch form tool is the forming surface, which the aluminum extrusion is stretched across. The rest of the tool is mostly the same from die to die. A traditional stretch form die is a bulky monolithic tool with one forming surface. Alternatively, the modular tooling approach has an interchangeable forming surface. With our modular tool, a forming insert is mated to a universal base to make up a complete tool. The forming insert is a lightweight, smaller component that features the forming surface. The universal base stays mounted on the stretch press and provides rigidity and alignment for the forming insert. Instead of changing the entire die, the forming insert is simply changed out. Reducing the weight of the insert eliminates the use of forklifts and overhead cranes. Reducing its size also minimizes the storage footprint. Additionally, large format AM provides the means to produce a forming insert faster and less expensively than any other method.
AM&D: What were the origins of the project?
MG: Spirit tried before to find a better tooling strategy for this challenge. However, previous efforts were either cost prohibitive or impractical to implement. The idea of a modular tool came to mind in 2018 as large-format AM was becoming further developed and increasingly popular.
AM&D: What makes this project a good fit for large format AM?
Andrew Bader (AB): The shape and design of the tool was perfect for large format additive manufacturing (LFAM) because of its large radius or half-moon shape. Determining whether something is a good fit for LFAM depends on the geometry of what we need to print. Some designs that are very flat in nature without a lot of curvature or deep projections usually aren’t the best fit for LFAM. While we still may be able to physically print it, it usually won’t make economic sense if you can simply buy something such as 3" thick aluminum plate stock and machine it quickly. In this case, however, to get a traditional tool into a half-moon shape you can bump-form thick metal to a near-net shape and machine it, but this process is expensive and not a lot of people do it. Or, you have to buy a large, rectangular block of material and machine away a lot of that material. With LFAM, we could print the shape to near-net dimensions, which made our tool manufacturing process much more efficient, faster, and with a lot less waste involved.
AM&D: Was this the first time AES worked with Spirit?
AB: AES has been working with Spirit since 2017 and has completed about a half-dozen different style tooling projects.
AM&D: What specs did the tooling have to meet?
MG: The design objectives were to create a forming insert light enough so that two mechanics can manipulate it, quickly mate it to the universal base, and form a good part under standard conditions. Spirit’s process modeling team performed a computer simulation of the forming process and determined the insert needed to withstand loads of more than 5,000psi. The required dimensional tolerance was ±0.010" across the full insert, which was 144" (12ft) in its longest dimension.
AM&D: Which company designed the tool?
MG: Spirit designed the end-use tool, while AES was responsible for a near-net as-printed design that would be later machined down to the final geometry. (Near-net print is shown on the magazine’s cover photo.) Composite thermoplastics have a high strength to weight ratio, which allows the insert to be as light as possible. An overhead crane is no longer needed to change out dies, increasing shop efficiency. The storage footprint for tooling is minimized also. AB: The material used in the tool is fiber-filled polycarbonate. Spirit provided AES the tool design with some input from AES, but we had to make a special as-printed design to 3D print it to a near-net shape that would yield the most successful print for machining.
AM&D: How many parts per tool can be made?
MG: The fatigue life of the tool is still being evaluated. Initial forming trials successfully stretched a low-volume run of body frames prior to heat treatment, where the aluminum was in a soft, ductile state. Further trials stretched a full production run of 40 frames after heat treatment, where the aluminum was significantly harder and the load on the tool significantly higher. The tool was scanned before and after the trials. No significant deformation or wear was observed.
AM&D: These molds are composite being used to form aluminum parts – it’s unusual to form metal with plastic, correct?
AB: This project is a great example of using 3D printed thermoplastic tooling to provide a solution that wouldn’t have worked well through traditional manufacturing. First, we’re using LFAM to make a near-net tool off the printer, which creates a faster and more efficient tool-making process, with better economics and lead time than traditional tooling processes. Second, we’re demonstrating the usefulness and robustness of thermoplastics as a viable tooling material choice. Another benefit is the reduced weight. AM&D: Will Spirit try to leverage this new technology in other areas? MG: Aerospace manufacturing is notorious for high quantities of complex and large tools. Spirit’s Research and Technology team has identified right life tooling as a distinctive capability that Spirit believes will define the aircraft of tomorrow. AM is critical to solving tooling challenges for commercial and defense programs of the future.