Baking up an Additive Manufacturing Delicacy

Baking is my favorite hobby, and it’s a lot more like engineering than you think. Baking requires both meticulous planning and process control – a journey where the end result is the sweet reward eagerly anticipated by my family (and me). My kids regularly ask for muffins, and trust they will hit the mark every time. Crafting the perfect double chocolate muffin involves strategic choices, variable controls and trade-offs…a lot like the gauntlet a seasoned project manager runs. From ingredient choices and mixing methods to refrigeration of the dough and baking time and temperature, each step is a crucial variable in the delicious equation. Achieving consistent flavor demands the use of high-quality ingredients in precise proportions, much like the critical steps in additive manufacturing. Environmental factors, such as humidity and elevation, act as unseen factors, influencing the batter’s rise. For every adept baker, the true assessment of the entire process comes when cracking open the baked goods to reveal perfection…the flawless execution of the underlying chemical reaction.

As I engage in the process of baking, it prompts me to contemplate the steps involved in the entire additive manufacturing (AM) process. With innovation progressing rapidly, it’s essential to step back and analyze the complete lifecycle of the process, extending beyond the mere act of printing. AM is often perceived as just the method of making a complex part faster, so we seldom acknowledge that it is more than act of manufacturing. The community needs to recognize the significance and understand every step of the AM lifecycle and their interactions, from the conceptual design to the final verification.

Figure 1. Major process steps in the iterative lifecycle for additively manufactured components.

However, with the excitement focused on printing technologies and rapid development activities we have seen, a crucial aspect seems to be overlooked – the entire process and how it ultimately plays into the critical role of flying qualified and certified parts. Cheap, complex shapes no longer suffice; what’s required are pedigree parts that can withstand the rigors of space exploration. Each print must be a testament to reliability, ensuring the safety of astronauts or the success of a Mars rover landing. It’s not enough to merely create a shape that meets some geometry; the detailed heat treatments and resulting microstructure must be linked to mechanical properties along with repeatability and reproducibility. Tensile properties at room temperature are straightforward and may be easy to meet, but what about fatigue at elevated temperatures, stress rupture, and fracture toughness? These are essential aspects that demand attention when processing AM pedigree parts that are safe for space flight.

Laser Powder Bed Fusion (L-PBF) GRCop-42 has enabled next generation propulsion concepts like NASA’s Rotating Detonation Rocket Engine testing (Courtesy: NASA)

Things we have observed in AM implementation in critical applications:

• What is the perfect recipe? It is not easy to define a manageable, systematic, and consistent approach to AM policy implementation. AM comes with the “local aspect.” The stand-alone operation and individual nature of AM automatically makes it process-sensitive. This brings the added scrutiny on investigating the potential failure modes. AM is also a rapidly evolving technology which means well-documented benchmarks and agreed upon standards have yet to emerge. Successful adopters of AM recognized this challenge and put increased emphasis on the build-to-build material quality as well as periodic review and confirmation. They also have enforced the discipline and systematic rigor throughout the entire value chain of AM, from design to part. They have defined the end goal: having the qualified, reliable, and predictable products that will perform. They then put the policy in writing, in the way of a qualification standard or specifications, so consistent decisions are made regarding qualification and certification of AM designs and hardware.
• You found the perfect oven. Now what? Having the most advanced oven is not going to serve you well in producing the product you need for your system. Feedstock material, the AM machine, post-processing operations, and the AM process is indelibly linked and should be defined, evaluated, and recorded to serve as the baseline AM material and process qualification. Once this is one complete, developing the material properties and their integration into the AM ecosystem for use in part design and implementation is manageable. This systems way of thinking naturally forces all the stakeholders (printer technicians, part designers, machine manufactures, material engineers, and program managers) to work together by having the clear communication channels built on trust.
• Who and how will these baked goods be judged? The end game is to demonstrate that you fulfill the specified requirements. In other words, you can stand behind the entire process — material, design, build and post processing, equipment, parts, and operators — and meet all the requirements to assure that the resultant product will perform as intended. This is a profound statement that one would make that ensure reliable systems. You must demonstrate that you have executed the task accurately, comprehending and documenting each step of the process. This is achieved through the collaboration of the entire industry. The AM industry has proven to be a tightly-knit community, with experts from end-users, machine manufacturers, heat treatment services, post-processing equipment companies, government agencies, and test labs convening in the same room to exchange insights and experiences.

It is important that we continue these conversations on the entire AM process lifecycle and understand each other’s inputs, outputs, and challenges. We may own one part of the process, but must integrate into the entire lifecycle. Our double chocolate muffins are going to be awfully bland if someone forgets to add the salt.

L-PBF Turbine demonstrator using NASA’s extreme temperature GRX-810 additively manufactured alloy with 1,000x improved creep

Paul Gradl, Principal Engineer and Subject Matter Expert at NASA Marshall Space Flight Center (MSFC) will be participating at the upcoming Additive Manufacturing Strategies business summit in New York, February 6 to 8, 2024. Gradl will be giving a talk titled “Space Exploration Using AM.”