Left: Before a redesign, this washing rotor for a centrifuge had 32 parts. Inset: After a redesign and laser-sintering, it had three parts.

Starting any medical design project with a traditional design-for-manufacturability (DFM) checklist can handicap innovation. When the limits of traditional manufacturing technology— casting, milling or turning—are factored in—the form, function, and quality of the finished product can be affected.

Engineers designing with laser-sintering in mind, however, are freed from such constraints and instead can focus on such matters as how to achieve the best flow rate and how to achieve desired design results with the least amount of material. Product designers still need to prove out the fundamentals of load, durability, and performance using finite element analysis (FEA), but now they also can envision geometries that satisfy those requirements while consolidating and integrating parts into elegant, simple designs that serve the entire system’s functionality, not just its manufacturability.

For high-volume production runs, cost-effectiveness is still best served in many cases by applying design-for-manufacture strategies and using traditional manufacturing methods. But for physical prototyping, manufacturing limited production lots, or engineering patient-specific products, additive manufacturing technologies such as laser-sintering are increasingly providing better answers.

Less is more

Form may follow function, but with laser-sintering, form also can enhance function and other attributes, as illustrated by the washing rotor example (above) from Hettich (America), Alpharetta, GA, a maker of centrifuges.

Human heart with exterior blood vessels in red and blue. Image: American Heart Association.

Using laser-sintering as the driver for a functional integration project, the company was able to reduce the number of parts in this component from 32 to three without tooling. How? By thinking way outside the box: design engineers realized that the multiple parts of the centrifuge’s core could actually be thought of as a single system that could be sintered out of plastic in just two pieces (the third part was a metal ring). By employing additive manufacturing they were able to do away with the need for several tools and a special steel-injection pipe requiring costly deburring. The finished product had better integrated functions, reduced assembly costs, and improved performance.

Realizing the economies of production to be gained with laser sintering, Hettich is now using it on other products. The company can respond more quickly to customers’ individual design requirements, make variations in materials at minimal costs, and produce limited production runs “on demand” as their markets dictate.

Designing as nature intended

Much as embryonic cell layers grow and differentiate into a complete human body, laser-sintered materials are built into a finished product in a way that seems almost organic.

Conventional cooling channels drilled into a mold (unspecified product).

A human parallel can help illustrate the vision-expanding freedom of design that comes with additive manufacturing: think about how the body lays out its network of blood vessels to nourish every organ. Picture the heart, embraced by arteries and veins (see image above) that closely follow its exterior shape to furnish it with a continuously circulating supply of freshly oxygenated blood.

Now envision the injection- or blow-mold designer trying to draw heat away from a newly formed component using cooling channels. Traditional manufacturing would call for circular channels drilled straight into the mold block from several directions at right angles (see images at right). But designers with additive manufacturing in their arsenal can build oval conformal cooling channels right into a laser-sintered mold. Precisely enveloping the product’s shape from 360 degrees—in much the same way as the exterior blood vessels of the heart—these will bring cooling liquid close to the mold surface quickly and evenly.

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