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Additive manufacturing — aka 3D printing — holds great promise for aerospace, capable of creating parts that are as strong as anything produced using traditional manufacturing techniques, but at a fraction of the weight. That’s one reason why Santa Cruz, California-based Joby Aviation has incorporated structural additive titanium components into the design of its S4, the five-seat eVTOL air taxi it hopes to certify by the end of 2023.
However, certifying these parts poses unique challenges, as Joby additive lead Sean McCluskey explained in a recent webinar sponsored by Dassault Systèmes. Here, too, Joby is blazing a trail as it races to become not only the first eVTOL developer to achieve Federal Aviation Administration (FAA) certification of a practical air taxi, but also “the first organization in history to attempt certification of multiple safety-critical structural additive titanium components with the FAA,” McCluskey said.
One of the chief obstacles to certifying safety-critical additive parts is that most 3D printers are intended for prototyping, not highly controlled production. In a standard framework, said McCluskey, a computer-aided design (CAD) tool is used to create a design that is exported as an open filetype. This is then processed through a mesh tool, a build prep tool, and a build execution tool where various parameters are injected, still using an open filetype.
“What I mean by open filetype is that file can be opened, edited, and saved again, with no record instrinsic to the file that it was adjusted,” McCluskey said. Obviously, that’s not ideal for the production of a safety-critical part, where even minor adjustments to parameters can have catastrophic consequences.
According to McCluskey, aerospace companies that have certified non-safety-critical parts have generally done so by implementing controls at each stage of the process, “which means either they’re password-protected, or they’re supported by some sort of training program, operating procedures, or some other methodology tied into the quality system at each point,” he said. “But you still have that open filetype issue. . . . You can try and solve that with a really good PLM [product lifecycle management] system, but there’s always the risk that the file type itself does not know if and when it’s been changed.”
To overcome this problem, Joby has collaborated with Dassault Systèmes to develop an immutable filetype similar to the solutions used in the financial technology space.
First, the part is designed and all of the controlled parameters are injected in Dassault’s full-suite 3DEXPERIENCE platform.
“Once this file is exported, it can’t be changed,” McCluskey said. “If someone does attempt to change it, the file itself knows that it’s been changed, and has values encoded in the file checksums and the like to ensure that the file is always revision controlled intrinsically. You’re not relying on a third-party software or on an additional quality suite to do that — it’s built into the file itself.”
This file is then loaded into Joby’s proprietary build execution tool, which bypasses the manufacturer’s software on a 3D printer to control the machine directly. “The filetype actually commands which pre-configured machine state is used. And the very valuable implication of this is that if a machine is not capable of printing a part in a controlled way, the file will reject that machine,” McCluskey noted.
Besides security, the filetype developed by Joby and Dassault has some additional advantages for the laser powder bed fusion technology that Joby is using. Unlike many filetypes currently used in metal additive manufacturing, this one has layer rules — specifying parameters for each layer of the build — and scan rules, for “each time the laser moves from point A to point B,” McCluskey said. “The control is at an incredibly granular level.”
The solution has also been designed with an eye to the future, he pointed out.
“If we’re going to spend all of this time, effort, energy and money to build this system, we must also add capability for the future so we don’t have to redo it every couple of years when the technology gets better and better,” he said.
“The proposed solution . . . allows for both auditable qualification and significantly expanded architecture. We can handle architecture that is completely different from what we have today, as long as the fundamentals of additive — the idea that you take a 3D object, slice it into layers, and those layers have subcomponents — remains the same.”