Page 14 - 3D Metal Printing Spring 2016

3D INSIGHTS IN METAL PRINTING BY TERRY WOHLERS AND IAN CAMPBELL
Pushing the Design Boundaries with Metal AM
Greater design freedom is recog- nized as one of
the key benefits of using additive manufacturing (AM) for the final produc- tion of parts. Reducing the need for tooling and being able to more freely add and subtract materi- al means that parts can be made with more geo- metric features than when manufacturing them with conventional processes, and with much greater complexity. This has been exploited in many ways, with value added to the product in one or more ways.
Fig. 1—Optomized engine cylinder head, courtesy of FIT
TERRY WOHLERS
race-car’s cylinder head that met performance requirements while also minimizing weight. The resulting part exemplifies how designing for AM maximizes geometric freedom to enable enhanced performance.
Design Opportunities
A key feature of the 3D-printed cylinder head is gas-flow optimization. The design of the com- bustion chamber, intake tract and exhaust tract can be shape-optimized using computational fluid dynamics (CFD). CFD can be used to opti-
Value can arrive from reduced lifecycle costs, improved aes- thetics, better ergonomics and enhanced performance. A pow- erful example of enhanced performance using powder-bed fusion of aluminum: an automotive-engine cylinder head, additively manufactured by the German company FIT (Fig. 1). Cylinder heads must exhibit minimal friction, to optimize gas flow (intake and exhaust), water flow (for cooling) and vibra- tion damping. And, the parts are load-bearing so they must be strong.
FIT was tasked with designing an improved version of a
Terry Wohlers is president of Wohlers Associates, Inc., an independent consulting firm based in Fort Collins, CO; 970/225-0086, www.wohlersassocaites.com. The firm provides technical and strategic consulting on the rapid-product-development and additive-manufacturing industries. Wohlers is a principal author of the Wohlers Report, a publication that provides data on all facets of additive manufacturing, including business, product, market, echnology and application.
Ian Campbell is an associate consultant with Wohlers Associates, and an associate professor in computer-aided product design at Loughborough University in the UK. He has been working in the field of additive manufacturing since 1993.
mize fluid flow, to remove heat from the combustion chamber and exhaust tracts.
Importantly, the need to compromise an optimized design, due to manufacturing requirements, is much less with AM when compared to casting, which requires draft angle on the casting patterns. AM allows the optimization of coolant circu- lation, a key advantage over casting. With AM, the water jackets and passage ways for coolant can include a lattice framework of complex structures (Fig. 2). This results in increased surface area and, therefore, improved heat conduction. In the case of the cylinder head, the surface area increased from 128 to 1585 sq. in. Depending on the exact configuration of the lattice structure, it also may help to create turbulent flow, another aid to cooling. This can give the added benefit of using a smaller water pump, which reduces power loss from the engine.
AM also helped FIT optimize the weight of the cylinder head. With the key functional features defined, engineers developed the main body of the head by increasing material thickness around the volumetric shapes. Extra material added strength to the part and served to dampen vibration. The
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