Additive Manufacturing for Microwave Vacuum Electron Device Cost Reduction
Navy STTR 2016.A - Topic N16A-T010
NAVSEA - Mr. Dean Putnam - dean.r.putnam@navy.mil
Opens: January 11, 2016 - Closes: February 17, 2016

N16A-T010 TITLE: Additive Manufacturing for Microwave Vacuum Electron Device Cost Reduction

TECHNOLOGY AREA(S): Battlespace, Electronics, Sensors

ACQUISITION PROGRAM: PEO IWS 2.0, SPY-1 Radar

OBJECTIVE: Develop additive manufacturing for key microwave vacuum device components that meets on-demand, flexible, and affordable manufacturing requirements.

DESCRIPTION: A majority of existing Navy radar, fire control, and electronic warfare (EW) systems, as well as some communications systems, employ microwave vacuum electron devices (for example, microwave tubes). Solid-state retrofitting of these systems is expensive and simply cannot be done in many cases. Therefore, to support these legacy systems, microwave tubes will remain in the Navy inventory for decades to come, although in slowly decreasing quantities. Microwave tubes offer unmatched performance but are expensive and the decreasing demand increases their per-unit cost. This is largely due to sporadic manufacturing, often in quantities insufficient to support continuous production. It is common for procurements of microwave tubes to involve quantities of a few dozen or less. The discontinuous and batch nature of production then ripples through the manufacturing supply chain, resulting in long lead times and added expense for key piece-parts.

Even under the best of circumstances, manufacturing of microwave tubes is a labor-intensive process requiring multiple steps that typically combine unique materials and manufacturing processes. For example, parts and sub-assemblies are typically brazed in sequential steps with the lowest level assembly receiving the highest braze temperature so that the part can survive succeeding braze cycles at progressively lower temperatures. The body of the tube must be impermeable to provide a perfect vacuum. Ceramic to metal seals are the industry norm with oxygen-free high-conductivity (OFHC) copper and high purity alumina predominating. Interior sub-assemblies often combine multiple, specialty metals (including refractory metals) which present unique manufacturing challenges (Ref. 1 and 2).

Furthermore, microwave tube manufacturing has inherent design and quality requirements specific to the industry. For example, the heat load encountered in most tubes presents not only thermal management challenges, but metal-to-metal and metal-to-ceramic joints must be designed to compensate for differing coefficients of thermal expansion. Ceramics often require complicated shapes, such as corrugation (to inhibit high voltage breakdown) and typically undergo complex plating processes in preparation for joining. Throughout the manufacturing process, the governing requirement is vacuum integrity. Materials selection, design, handling, machining, and fabrication are all performed with an eye to the final vacuum processing step that ultimately determines production yield, so crucial to overall cost.

The advent of additive manufacturing (commonly known as 3D printing) offers a possible solution to the expensive and discontinuous nature of microwave tube manufacturing, as well as offering potential manufacturing advantages not available with traditional machining (Ref. 3). The ability to produce parts as needed and reduce the waste of expensive materials would be a boon to the industry. Even greater advantage could be gained from the single-step production of complicated structures (such as resonant cavities) that typically require the brazing of multiple parts. Some relevant progress in this area has been made. For example, ceramic elements for microwave circuits (Ref. 4) and a proof-of-concept slow-wave structure have been recently fabricated (Ref. 3). However, the stringent requirements (e.g. tight mechanical tolerance, low surface roughness, and high-vacuum compatibility) particular to microwave tube production have so far inhibited the broad adoption of additive manufacturing methods by the industry. Consequently, innovative additive manufacturing technologies for microwave tube cost reduction are desired. Target values of 40%-70% cost reduction are considered reasonable (as compared to conventional machining of the same part), depending on the complexity of the parts chosen for demonstration.

The Navy needs an additive manufacturing method that must meet two key requirements. First, it must produce vacuum quality parts. Any process that leaves residual solvents, oils, binders, sacrificial materials, or other contaminants (metal or organic) which cannot be removed by cleaning or heat treatment (bake out) are useless to the industry. Likewise, the parts cannot be porous such that they trap residual gas. Second, it must have an acceptable process to produce parts of high mechanical accuracy, as many microwave tube circuits have critical dimensional tolerances approximately one thousandth of an inch. Other desirable features would include the ability to form parts in more than one metal, the ability to form complicated parts such as hollow cavities that cannot be machined out of one piece, and the ability to plate parts in-place. Desirable technologies for ceramic manufacturing would produce complicated ceramic shapes as well as have the ability to vary the ceramic material in order to produce ceramics with gradually varying loss characteristics. Common to all of these requirements is that the technology must produce parts in the metals and ceramics that are standard to the microwave vacuum devices industry.

This topic serves to increase mission capability by controlling life-cycle cost and reducing delays in the procurement of microwave tubes for critical and widely deployed Navy systems such as SPY-1, SPS-48, SPQ-9B and Nulka. Sustainment of legacy systems is a major challenge and few opportunities exist to introduce cost savings measures. This effort is a basic manufacturing technique that can reduce cost incrementally across many systems. The need for flexible manufacturing techniques will only grow as these legacy systems age and become harder to support. As it is, manufacturers see little incentive to invest in technology to support legacy systems now. However, this technology has broad appeal and is attractive for both existing and new military and commercial products.

PHASE I: The company will develop a concept for innovative additive manufacturing technology for microwave tubes that meets the requirements stated in the topic description. The company will demonstrate the feasibility of their concept in meeting Navy needs and will establish that the concept can be feasibly produced through sample testing, modelling, simulation, and analysis. In the Phase I Option, if awarded, the company will develop a capabilities description and a plan for development and demonstration of the technology in Phase II.

PHASE II: Based on the results of Phase I and the Phase II Statement of Work (SOW), the company will develop prototype additive manufacturing techniques and equipment for the production of microwave tube parts consistent with industry material standards and assembly practices as described in the description section. The prototype techniques and equipment will be evaluated to determine their capability in meeting the performance goals defined in the Phase II SOW and the Navy requirements for reduced cost microwave tube manufacturing. Performance will be demonstrated primarily through testing by the small business of industry-representative sample tube parts for mechanical and vacuum integrity over the required range of manufacturing and operating parameters, including braze, bake out, and vacuum exhaust cycles. Testing may be augmented by modeling and analytical methods. Evaluation results will be used to refine and deliver the prototype with an initial design that will meet Navy requirements. The company will prepare a Phase III plan to transition the technology for commercial use and to supply Navy needs.

PHASE III DUAL USE APPLICATIONS: The company will be expected to produce its additive manufacturing technology for microwave tubes and support the processes required for its successful transition to microwave tube-based systems (such as SPY-1) in the Navy. The company will develop and fully document the processes required to integrate the technology for use by industry according to the Phase III development plan. The technology will be evaluated to determine its effectiveness in specialty production of microwave tube parts. This may require the company to license their processes to other manufacturers for actual production. The US domestic microwave tube industry supplies commercial as well as military markets and technologies that reduce process costs typically benefit all product lines. Since this topic seeks to develop a fundamental manufacturing technology and not a specific military application, the potential for commercial application is assured. The potential commercial market is essentially stable, should the technology prove effective.

REFERENCES:

1. Rosebury, Fred. Handbook of Electron Tube and Vacuum Techniques (American Vacuum Society Classics edition). New York; American Institute of Physics, 1993; http://www.gbv.de/dms/hebis-mainz/toc/084071397.pdf

2. Kohl, Walter H.; Handbook of Materials and Techniques for Vacuum Devices (American Vacuum Society Classics edition). New York; American Institute of Physics, 1995; http://www.google.com/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=2&ved=0CCYQFjAB&url=http%3A%2F%2Fwww.springer.com%2FproductFlyer_978-1-56396-387-2.pdf%3FSGWID%3D0-0-1297-30739452-0&ei=qsKaVZ2mNML9yQSk_43YBA&usg=AFQjCNHN3SMHF-O7FgZg8oFzyx15Gs0_Yw

3. Anderson, James, et al. "Fabrication of 35 GHz Folded Waveguide TWT Circuit Using Rapid Prototype Techniques." 39th Int. Conf. Infrared, Millimeter, and Terahertz Waves (IRMMW-THz), Tucson, AZ, 14-19 Sep. 2014; http://ieeexplore.ieee.org/xpl/articleDetails.jsp?reload=true&tp=&arnumber=6956205&openedRefinements%3D*%26filter%3DAND(AND(NOT(4283010803))%2CAND(NOT(4283010803)))%26pageNumber%3D8%26rowsPerPage%3D50%26queryText%3D(microfabrication+techniques)

4. Marchives, Yoann, et al. "Wide-band Dielectric Filter at C-band Manufactured by Stereolithography." Proceedings of the 44th European Microwave Conference." 6-9 Oct. 2014: pp. 187-190; http://ieeexplore.ieee.org/xpl/login.jsp?tp=&arnumber=6986401&url=h

KEYWORDS: Vacuum electron device; microwave tubes; microwave vacuum devices; additive manufacturing; 3D printing; refractory metals

TPOC-1: Larry Dressman

Phone: 812-854-4804

Email: lawrence.dressman@navy.mil

TPOC-2: Bryan Mitsdarffer

Phone: 812-854-5264

Email: bryan.mitsdarffer@navy.mil

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