Traditional manufacturing methods such as machining and injection molding necessitate working under design restrictions and limitations. But these rules don’t apply when using what is called direct digital manufacturing. DDM frees medical-device designers from traditional manufacturing constraints because it uses additive techniques to build up prototypes and functional parts of almost any complexity.

But how far does this freedom go? What can engineers and designers do with DDM, and what do they need to know? In certain jobs, the technique can free engineers to design the optimal part for the application. To get started on the road to DDM success, consider these helpful design tips:

• Forget about design for manufacturability (DFM). Remove your blinders and let your mind expand beyond what you have learned through years of education and practice. Ignore worries about form, fit, and manufacturability. When it comes to DDM parts, think “fast, low-cost, and practical.”

• Focus on function. Feel free to make parts as complex, intricate, and detailed as they need to be. Just go ahead and design parts that will provide the best performance possible. When it comes to prototypes, the only difference between the prototype and the production part is its intended use. This approach provides a low-risk, rapid-turn cycle that lets medical-device designers be creative and push the envelope. There is no penalty for design revisions late in the product-development cycle.

• Refine the design. DDM can be performed with various additive technologies, so it is important to have a good understanding of the one you will use. Each technique has different specs for wall thicknesses, tolerances, surface finishes, and material properties. When you cannot produce the needed part qualities using the additive process at your disposal, you must either outsource production or purchase a machine for in-house use. Fortunately, purchasing a machine often provides a fast ROI.

• Question tradition. For example, a part previously made of sheet metal may be an ideal candidate for DDM because the rationale for the original decision may no longer hold true. Sheet metal may have been selected as a practical, but not preferred, manufacturing method because of low production volumes and the high cost for injection molds. With DDM, a sheet metal enclosure can be converted to a sophisticated, stylized plastic part because there is no tooling to amortize over a small production run.

• Make it feature rich. Traditional manufacturing methods add costs with each feature because they must be machined into the part, mold, or die. In contrast, DDM costs are not affected by part complexity. So don’t simplify a design for reasons other than boosting product performance or improving aesthetic value.

• Rethink wall thickness. Many manufacturing methods have a narrow range of recommended wall thicknesses. For example, the sweet spot for injection molding is 0.40 to 0.80 in. When designing a part for DDM, the only consideration is to stay above the minimum wall thickness for the part to perform as specified.

Also, DDM makes it unnecessary to maintain a consistent wall thickness. To maximize strength while minimizing weight, consider making walls hollow. In the fused deposition modeling (FDM) process, this construction style is called “sparse fill.” A lattice structure can be skinned with bounding surfaces to yield the mechanical strength needed while decreasing material volume. Although volume reduction can range greatly, it’s typically around 60%. Hollowing-out features also reduces material cost and part-construction time.

• Consolidate or segment. Consider part consolidation. Rather than producing a multipiece subassembly, the entire unit might be consolidated into a single component. This eliminates assembly tasks and simplifies inventory management. Part consolidation can even sometimes overcome an overly tight tolerance spec. For example, a tight-tolerance interface can be avoided by consolidating mating parts.

Or, when advantageous, DDM also lets a single piece be divided into several components without a significant increase in cost.

• Fill the envelope. When feasible, use every nook and cranny of your product’s available space. Twist, turn, and contort the design to minimize the size of the product. Because machining and molding limitations are removed, you can think organically and let designs flow.

• Forget draft angles. When the design is complete, there is no need to invest time to adapt it to process-specific requirements like those common for machining or injection molding. For example, DDM relieves you from spending time to define parting lines, add draft angles, and determine how to incorporate them without changing form, fit, and function. Also, designers need not resolve undesirable sink marks, ejector marks, or knit lines.

Lastly, never stop redesigning. DDM doesn’t necessitate tooling or take much manpower, so a design is never “frozen.” It is perpetually fluid. Capitalize on this by continually refining designs to satisfy customers, maximize manufacturing efficiencies, and minimize production costs