Page 25 - 3D Metal Printing Fall 2018

Fig. 2—AM concepts promote laminar flow through the valve.
valve from the “inside out” and consider the functional component of the design first, and the manufacturing or production method second.
Conventional design methodology, and most product-development processes, require the involvement of manufacturing engineers at the very early stages of design and throughout the design process. Designing for AM provides increased design freedoms and opens the doorway for innovation by allowing focus on func- tionality, not manufacturability. However, AM is not completely devoid of traditional processes and some post-processing may still be required. With respect to the design concepts developed in this project, these processes included grinding and polishing of the ball’s outer surface to achieve a suitable finish and create a tight seal.
Adapting for AM
Adapting design methodology for AM requires consideration of print setup, part removal and post-processing, all part of
this project’s evolution.
During print setup, identifying prop-
er support-material placement is crit- ical to the quality of the build. Bray’s ball-valve models needed slight adjustments to ensure sufficient adhesion to the build plate, as well as suitable support throughout the height of the build. Build orientation also was considered and carefully selected to reduce required sup- ports and maximize build effi- ciency. Finally, the overall layout
of parts on the build platform,
assigned to minimize heat-transfer
effects of nearby parts, optimized build times and avoided part drag during the re- coat process (Fig. 3).
Another critical consideration, part removal may require a slight adaptation in AM design. Unlike some plastic printers that create dissolvable or breakaway sup- port material, metal-AM components typ- ically are “welded” to a build plate, requiring physical removal. Renishaw accomplishes this through locator buttons 3D printed directly on the build platform, indicating precisely where to separate the print using a wire EDM. Furthermore, Bray’s ball valves require the addition of surplus geometry into the design in order to assist with accurate part removal. Removal of excess powder is another consideration for AM designers, especially when dealing with internal lattice-like structures aimed at reducing weight.
Typically, parts produced by a metal 3D printer require some level of post-pro- cessing that can range from simple sup- port removal to complex CNC machining. Again, Bray’s 3D-printed ball valves required polishing and grinding to achieve an acceptable surface finish for creating a tight seal. Two main design adaptations were required to enable this post-pro- cessing operation. First, excess material needed to be added to the outer diameter, similar to adding machining stock to a sand casting. Second, securing these com-
ponents during grinding and polishing required custom fixtures. Due to the com- plex flow-bore geometry of these valve balls, a simple cylindrical expanding man- drel no longer would suffice. The solution: 3D print the required custom mandrels as well. Bray and Renishaw did that, apply- ing the same design and AM principles to the mandrels as were applied to the valve balls themselves.
Maximizing Performance
Metal 3D printers offer a unique ben- efit: the ability to produce functional end- use parts that are heated, cooled, machined, pressurized and tested in the same manner as a part produced by tra- ditional metalforming methods (sand casting, investment casting, forging, etc.). Weeks, even months, can be saved in the product-development process by con- ducting prototype qualification on metal- AM components. In order to realize this benefit, Bray assembled the AM compo- nents into standard ball valves and sub- jected them to prototype validation test- ing—specifically flow-coefficient and cavitation-index evaluation. The test results, partially shown in Fig. 4, con- firmed the added performance benefits on one of the design concepts. The smooth-transition ball resulted in a 62- percent increase of flow capacity through
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Fig. 3—In 3D printing the valves, layout of parts on the build system minimized heat-transfer effects of nearby parts and optimized build times.