Myth 1: Complexity is Free.
National Institute of Standards and Technology
Complex components such as those using lattice structures or those that combine multiple part features are possible. However, the designer must know when and how they should create a complex design and in what applications it will provide the greatest value. Complexity can increase design time and post-processing, and overall the time it takes the designers to integrate all the complex features into a part. Sometimes keeping things simple has its benefit, but knowing when to take advantage of design complexity is key.
The figure shows an example of a complex lattice structure that could be incorporated into lightweight aircraft structures or could enhance bone ingrowth into medical implant for bone reconstruction.
Myth 2: Variety is free.
U.S. Food and Drug Administration/Michael J. Ermath
In AM you aren’t just changing the part model, but the build model as well. Changes to the part design may place additional restrictions upon the part orientation, support structures, and post-processing operation such as heat treatment, surface finishing, final machining and inspection.
National and international professional organizations are developing standards to assist in the certification of materials and process and to streamline the certification of each individual parts. The hope is that standards will accelerate the process, but also make sure parts made from different printers or by different processes are meeting the same specifications and quality. AM can offer features that can improve patient’s recovery and the need for additional steps in surgery. A pelvic component of a hip joint replacement shown here features a porous surface structure. This is designed to allow for bone ingrowth into the component and to alleviate the need for bone cement.
Myth 3: No assembly required.
NASA Glen Research Center Lewis Field
AM machine capacities are increasing, but many parts are larger than what current AM systems can produce, requiring two AM piece parts to be fabricated, finished, and welded together. A fully “assembled” design may impede powder removal, or access to surfaces and features with critical post processing or service/repair requirements. This 3D-printed rocket engine fuel turbo pump (FTP) has 45% fewer parts than the Space Shuttle Main Engine FTP, but still requires precision fabrication, post-processing, and assembly. 3D printing metal for aircraft applications offer benefits to improve the “buy-to-fly” ratio—the ratio of purchased materials to that which ends up in the fabricated component flying in the aircraft. This is achieved by designing lightweight structures and reducing costly waste material. The benefit of printing metal to space applications is taken beyond the stratosphere, into orbit, when escaping the gravity well of earth.
As with medical applications, 3D printing is well-suited to space applications requiring costly materials (such as super alloys for rocket nozzles) and complex lattice structures (e.g., for lightweight components). Low production numbers and the ability to respond to the rapid pace of this new race to space also favor the use of this agile technology. 3D printing has already contributed to reducing the cost of launching a satellite into orbit by more than an order of magnitude. Given its current trajectory we may soon need to define the term “moonshot.”
Myth 5: Unlimited design space.
NASA, MSFC, Paul Gradl, AIAA 2018
Not that myth four (the myth of zero lead-time) isn’t important, but it’s hard to portray visually, so we’ll skip to myth 5. The figure below shows typical build box dimensions for powder bed type AM metal systems as compared to large rocket nozzle dimensions. Not only is the designed space a limiting factor but the complexity also becomes an issue for large nozzles. AM processes developed to overcome these constraints use metal wire feed, laser, electron beam, electric arcs, robotics, and large CNC-based motion systems.
Myths 6-8: AM uses less material; creates less waste; powder is 100% recyclable; no jigs, fixtures, people, or skill are required.
Cpl. Joseph Sorci, U.S. Marine Corps
Less waste and material reuse is possible, but the latter may need to be mixed with virgin powder to preserve the alloy chemistry. There is a waste stream of sieved powder particles or removed support structure that could may be recycled or may be contaminated, affecting the recycle value. In addition, you must consider the cost of any inert gases, removed support structure, and limited lifetime hardware such as build plates. If you are thinking less materials means more cost savings, some powders are four times the cost of its wrought counterpart.
Not only are supports required during the build, but they also may be necessary to use in place of fixtures and jigs during post-processing such as heat treating or machining to hold or meet tolerances and finshes. And of course printing requires skill and people. While some printers are made to be as user-friendly as possible there are always tips, tricks, and maintenance that will require knowledge of the materials, the process, and the specific equipment. Also, people in general are involved from the design to post-processing.
Myth 9: Infinite types of materials, multi-materials, in-situ alloying, and metallic glass.
While more AM materials are being offered commercially, the number of AM materials and metal alloys are quite limited. Many commercial materials are specifically designed for the process being used such as casting alloys, free machining stainless steels, and specialty weld filler metals. We are more likely to see many more colors of 3D printing polymer filament before we see a wide range of certified super-alloys specifically designed for AM metal fabrication. Despite this, there is a lot of innovation happening. This image is of NASA successfully hot-fire testing a 3D-printed copper combustion chamber liner with an E-Beam Free Form Fabrication manufactured nickel-alloy jacket.
Myth 11: AM will disrupt manufacturing.
NASA/Made in Space
We’ll skip myth 10: one-step processing—basically, an extrapolation of not needing skill or people. If 3D printing was so simple, and a one-step process, everyone would be doing it. Many metal AM processed parts not only require post-processing, some of those processes are traditional milling, drilling, and tapping. Myth 11 might be arguable, especially to the author of the Pan-Industrial Revolution. However, saying that AM will disrupt manufacturing is a myth hasn’t stopped industries from dreaming of what could be. This figure shows an artist’s rendering of space-based additive manufacturing system to produce structures, including lengthy beams and struts.