Metal Additive Manufacturing (AM) is a fascinating technology that has gained acceptance over the past several years. Metal AM has found a foothold in the aerospace and automotive industries, and it’s beginning to expand into other trades as well. While plastic 3D printing has been around for over 30 years, metal AM is relatively young, but the potential growth is substantial.
Valve manufacturing is a traditionally conservative industry, but the emergence of severe service valves, smart monitoring systems and highly engineered control products have pushed the industry into the future. Metal AM is just another avenue in which valve manufacturing continues to transform into a more progressive industry. Bray partnered with Renishaw, a manufacturer of metal 3D printers, to explore the possible solutions that metal AM may be able to offer valve manufacturers. Does this technology have a viable application in the valve realm, or is it simply a solution looking for a problem?
Brainstorming exercises for this project produced a plethora of ideas from the simple to the complex. Eventually, Bray settled on a modified version of a V-port ball valve (Figure 1).
V-port control valve technology offers exceptional characterized control, increased linear response and fast response times. These precision cut balls match the control performance of globe valves while offering the economy, reduced size and weight, and features of ball valves including higher flow capacity.
Currently manufactured via wire EDM (electric discharge machining) these balls are highly customizable, but also have their limitations. Bray identified a potential to further increase the flow capacity of this product through AM, and potentially decrease the cavitation potential at the same time.
To achieve this, two design concepts were engineered that could only be manufactured through 3D printing. These design concepts eliminated abrupt interruptions in the flow path that were a consequence of traditional manufacturing methods, thus promoting laminar flow through the valve (Figure 2).
The “smooth transition” ball creates a smooth transition between the full port opening side of the ball and the v-port side, a feature that was not possible through standard CNC machining. The “honeycomb” ball attempts to straighten the flow through several internal pathways.
Designing for Additive Manufacturing (D4AM)
The design process for additive manufactured parts is contradictory to the design process for traditionally machined components. When no longer limited by traditional manufacturing methods (e.g., mill, lathe, CNC) it’s possible to think about a 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. D4AM provides increased design freedoms and opens the doorway for extraordinary innovation by allowing focus on functionality and not manufacturability.
However, in some cases, 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 diameter to achieve a suitable surface finish to create a tight seal.
Adapting for Additive Manufacturing (A4AM)
While D4AM can bring about some novel concepts, it is not without unique challenges. Adapting design methodology for AM requires a consideration of print setup, part removal and post-processing. All three of these considerations were fully realized during the evolution of this project.
During print setup, identifying proper support material placement is critical to the quality of the build. The 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 was also considered and carefully selected to reduced required supports and maximize build efficiency. Finally, the overall layout of parts on the build platform was assigned to minimize heat transfer effects of nearby parts, optimize build times and avoid part drag during the re-coat process (Figure 3).
Part removal is another critical consideration that may require a slight adaptation in AM design. Unlike some plastic printers that have dissolvable or break-away support material, metal AM components are typically “welded” to a build plate and require physical removal. Renishaw accomplishes this through locator buttons 3D-printed directly on the build platform that indicate precisely where to separate the print using a wire EDM. Furthermore, Bray’s ball valves required surplus geometry to be added 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 will still require some level of post-processing that can range from simple support removal to complex CNC machining. These 3D-printed ball valves required polishing and grinding to achieve an acceptable surface finish for creating a tight seal. There were two main design adaptations that were required to enable this post processing operation.
First, excess material needed to be added to the outer diameter, similar to adding machining stock to a sand casting. Second, custom fixtures needed to be created to properly secure these components during grinding and polishing. A simple cylindrical expanding mandrel would no longer suffice, due to the complex flow-bore geometry of these valve balls. The solution to this problem: 3D-print the required custom mandrels as well. The same D4AM and A4AM principles were applied to the mandrels as to the valve balls themselves.
Metal 3D printers offer a benefit that is unique compared to plastic 3D printers: the ability to produce functional end-use parts that can be heated, cooled, machined, pressurized and tested in the same manner as a part produced by traditional metal-forming methods (sand casting, investment casting, forging, etc.). Weeks, maybe even months, can be saved in the product development process by conducting prototype qualification on metal AM components.
To realize this benefit, the AM components were assembled into standard ball valves and subjected them to prototype validation testing, specifically, flow coefficient (Cv) and cavitation index (Ct) evaluation. Test results confirmed the added performance benefits on one of the design concepts. The “smooth transition” ball resulted in a 62% increase of flow capacity (Cv) through the valve at full opening, as compared to the standard v-port ball valve. Additionally, this valve also exhibited better cavitation performance.
The honeycomb ball did demonstrate an increased flow capacity (Cv) at full opening of about 4%, but that trend was not consistent through the full stroke of the valve. The cavitation performance of this valve was indecisive as improvements were noted, but not consistently throughout the valve stroke.
Metal additive manufacturing is no longer a technology reserved for academic research facilities and extremely specialized industries. This technology has been available to general manufacturing companies for many years now and is likely underutilized. Specific to the valve industry, metal AM creates a pathway toward innovative solutions to common performance desires such as higher flow capacities and decrease cavitation likelihood, as demonstrated through this case study. More generally, metal AM can dramatically reduce functional prototype lead times and speed up the product development process resulting in faster time-to-market for new products.
If proper design for additive manufacturing and adapt for additive manufacturing principles are applied, the valve industry can experience thriving innovation resulting in performance gains once thought impossible.