Special Issue: Design for Additive Manufacturing: A Paradigm Shift in Design, Fabrication, and Qualification

Mechanical engineers design a wide variety of structures, devices, products, and systems. Through manufacturing classes and hands-on design/build projects, students learn all about the challenges of fabrication, the costs of production, and the importance of quality control. We educators reinforce these lessons by teaching students about “design for manufacturing” and the subsequent constraints that each manufacturing process places on how a part is designed, the surface finish that can be achieved, the tolerances that can be held, etc. We teach solid modeling and computer-aided design using conventional x, y, z coordinate systems with well-defined datum planes, and students learn design specification using standards for geometric dimensioning and tolerancing established for conventional manufacturing technology. Design tools and analysis methods have been developed based on years of experience and practice and provide engineers with the confidence they need to manufacture high-quality parts in high volumes.Additive manufacturing (AM) is changing all of that. Whereas other computer-controlled manufacturing technologies share a similar “digital thread” connecting part design to machine instruction, AM has many differentiating elements: (i) its layerwise approach enables unparalleled geometric complexity; (ii) the relatively simple process setup reduces the barrier to production and enables lights-out manufacturing; and (iii) low-cost systems are effectively democratizing manufacturing, enabling anyone to design and produce components at any location. As such, AM is redefining how we design, make, and qualify parts. For engineers, it liberates the designer by opening up the design space and removing many of the conventional manufacturing constraints. AM flips “design for manufacturing” on its head and provides “manufacturing for design,” allowing us to produce geometries that were previously impossible. Meanwhile, multimaterial AM systems allow designers to functionally grade material compositions to achieve unique product functionality, and multipart assemblies can now be additively manufactured as a single part. Moreover, the ability to fabricate parts layer-by-layer enables lightweight structures, internal cooling passages, and a host of other design benefits that increase product performance, reduce manufacturing lead-time, and shorten product-development time. AM is even changing the economics of production by reducing setup time, eliminating tooling costs, and enabling small batch runs of customized product offerings.If AM is so powerful, then why has not it proliferated more widely into industry? There are countless reasons for this, but the reason we tackle in this special issue is the lack of accepted designing for additive manufacturing (DfAM) knowledge, guidelines, methods, best practices, tools, and educational resources. Every AM process has its unique capabilities and nuances, which can change based on the material used during fabrication. Thus, the established “design guidelines” and “design rules” that we have for milling, casting, forging, stamping, etc. do not yet exist for the majority of AM processes despite their use to fabricate countless prototypes, models, and production-scale parts since their invention three decades ago. Plastic and polymer AM systems continue to advance and evolve to offer improved accuracy, speed, and material options, and the promise of metal AM processes has driven interest to astronomical propositions, which is further accelerating advancements in AM technology.Whereas AM enables extraordinary levels of part complexity, successful production of qualified parts using AM requires specialized knowledge and insight into the particular process(es) used for AM. In many cases, it is more difficult to design a part for AM than to fabricate it. Design is now the bottleneck for AM to achieve its full potential. Therefore, we set out to capture the state-of-the-art in DfAM in this special issue within the mechanical engineering design community and beyond. We received more than 60 submissions over the course of three months, of which 18 were selected for publication based on the journal's rigorous peer-review process. The 18 manuscripts included in this special issue highlight the latest advances and ongoing challenges in DfAM and collectively identify nearly limitless streams of future research in AM and DfAM.We organized the 18 manuscripts in the Special Issue into four categories: (1) part-design methods and specification challenges in AM, (2) multimaterial design methods for AM, (3) process planning considerations for AM, and (4) novel applications of design for AM. In the first category, we have four papers ranging from a contribution from researchers at the National Institute of Standards and Technology (NIST), outlining the challenges designers face when specifying and tolerancing parts made with AM, to papers delving into methods for optimizing part topologies and consolidating parts to take advantage of the design freedoms enabled by AM. In the second category, we have five papers that investigate multimaterial challenges in AM, with many highlighting the lack of design methods and computational tools for analyzing such structures. In the third category, we have three papers that address a critical step that mechanical engineers often overlook or ignore in AM, namely, how to orient and fabricate parts to achieve specific tolerances or performance. Finally, in the fourth category, we have four research papers and two technical briefs that highlight the range of applications for AM and the opportunities to rethink our current paradigm for design, fabrication, and qualification.