A passenger aircraft seat frame is a structural component uniquely designed for each aircraft configuration. Typically, they are constructed from a single billet. But was there a better way to manufacture that could also reduce costs?
Autodesk, a leader in 3-D design and engineering software, had been developing a different way of designing using generative design software, which automates design options based on specific criteria such as weight and strength to perfect and speed up the design process. The company’s research led to a unique lattice-like structure, and they contacted Aristo-Cast (Almont, Michigan), an investment caster with experience in prototyping and magnesium, to help carry out the design for an aerospace seat frame.
Through collaboration and sound casting principles, Aristo-Cast delivered final castings in four weeks that reduced weight by more than half compared to other lightweight frames on the market. Because of the benefits to the end-user and potential for casting growth in other applications for lightweighting, the aerospace seat frame has been named Casting of the Year by AFS and Metal Casting Design & Purchasing magazine.
Using the generatively designed model, Autodesk sought to take out as much material as possible without affecting the strength requirements needed. The result was a much lighter seat frame with material located only were needed. The new shape was a perfect fit for investment casting.
“The casting design showcases the ability to change lattice thicknesses to add strength where it is required,” noted one judge in the casting competition. “This concept can be used to tie sections of a casting together where strength is not so critical to reduce weight.”
Autodesk originally started developing its generative design software for 3-D printing of direct-to-metal parts. But metal printing is constrained by size, and the team began considering how to use the model for other manufacturing methods. Metalcasting was a natural choice because additive technology can be used to make the patterns and tooling.
To gain interest from aerospace and automotive customers, Autodesk sought to make samples of parts produced in the generatively-designed lattice structure and calculate the potential savings, which led to Aristo-Cast.
“I had been researching the casting space for a little over a year and it became clear Aristo-Cast was a pretty unique operation and experience with the level of complexity we were interested in,” said Andreas Bastian, principal research scientist for Autodesk. “They work with magnesium, which was very interesting to us because it is about 35% lighter than aluminum and can’t yet be printed, so that was an added value.”
Aristo-Cast is one of fewer than 10 investment casting facilities in the world that regularly casts magnesium. Although the lattice structure in aluminum will also achieve weight and costs savings, creating it in magnesium multiplies the savings significantly.
“Autodesk was looking for samples and we have learned a lot throughout the years about how to gate magnesium versus aluminum,” said Paul Leonard, vice president, Aristo-Cast. “Right away the gating for the seat frame worked.”
Traditionally, aerospace seat frames are made from aluminum using a few different techniques.
“The lightest ones currently on the market are CNC machined from a solid billet, meaning there is a lot of material wasted,” Harris said. “Some are cast or made from an assembly and cost less, but they are heavier.”
The size of the seat frame was too large for a metal printing buildbox, so this was a chance to see how the approach would work for 3-D printing patterns for metalcasting. Aristo-Cast has two 3-D printing machines with build boxes each large enough to print 30 of the seat frame patterns at a time. With 60 patterns printed at a time, Aristo-Cast can provide not just samples but production volumes, as well.
“Investment casting is bringing the best of both current techniques and giving us the high performance and light weight we’re looking for while only using the material we need,” said Andy Harris, a design consultant for Autodesk’s DMG group. “It enables the scale of production when a few thousand parts are needed and allows the strength of additive manufacturing to be applied to investment casting.”
After designing the seat frame, Autodesk provided the files to Aristo-Cast, which made some adjustments to the design in order to optimize it for the investment casting process:“The initial design was so thin in areas we couldn’t print the patterns,” Leonard said. “So we had to add thickness to certain sections.”
After the minor adjustment, Aristo-Cast successfully cast the unique seat frame.
Autodesk calculates that the weight reduction of the magnesium frame would achieve annual fuel savings of 63 tons for an Airbus A380 that holds 615 seats. Based on current costs for jet fuel, average annual savings per aircraft could be $103,324 and life of service savings (20 years) would be over $2 million per plane. A fleet of 100 aircrafts would achieve annual fuel savings of more than $206 million.
“There is a huge amount of excitement around these high-performance structures with metal printing, but we see an interesting opportunity for foundry markets to engage in using 3-D techniques for making patterns and molds,” Bastian said. “It shows we can realize the same value from direct metal printing with a technology like metalcasting that is very well understood, very familiar, and offers a huge portfolio of materials that in many cases are already qualified for aerospace. The foundry industry is in an exciting spot to capitalize on the advanced design technologies to realize tremendous value very quickly.”