Technology Today

2015 Issue 1

Additive Manufacturing at Raytheon

Many traditional part manufacturing processes are subtractive in nature where material is removed to create the final object. They typically require creation of new tools and fixtures which adds developmentcost and cycle time and ultimately drives how we design and build products. Additive Manufacturing (AM) is a term applied to a group of manufacturing processes that create objects by adding material, usually plastic or metal, in multiple thin layers where needed to form the final shape. Also referred to as 3D printing, AM offers unique benefits over traditional subtractive manufacturing methods and is shifting the paradigm from designing what we can build to building what we can design.

Some of the key advantages of this technology are:

  • A reduction in early production cost and cycle time, making AM ideal for prototypes and small lots and enabling early rapid design iterations.
  • The ability to create complex geometries and material combinations that are not possible using conventional manufacturing, potentialy allowing new higher performance, lower cost and weight products.
  • The ability to customize parts during production runs with minimal additional cost.

AM technology is decades old but has only recently matured to a point where significant numbers of deliverable parts are now being produced using AM. With potential growth in virtually every manufacturing sector, the global market reached $1.6 billion in 2013 from $1.1 billion in 2012 and had a compound annual growth rate of 44 percent with greater than 20 percent growth in each of the previous three years.1There are many different AM types with three of the most common methods shown in Figure 1. Nearly all of the AM processes share the ability to build parts layer by layer, whether the base material used is a metallic powder or a plastic filament and whether the printer uses a laser or other material consolidation method. There are many variations of the AM processes shown in Figure 1, typically with only minor differences. For example, powder based fusion (PBF) variations include direct metal laser melting (DMLM), where metal powder is used, laser sintering (LS) for plastic powders, and electron beam melting (EBM), where an electron beam is used in place of a laser.

Figure 1. Three common additive manufacturing methods

Raytheon applies AM throughout the product development cycles, including model and demonstrator development for early concept studies, tool and fixture production for product assembly and integration, early prototype development for evaluation and field test, rapid early production cycle support and obsolete part replacement. Raytheon investments in new areas of AM research such as printed electronics and thermal management enable designs that were not previously possible with traditional manufacturing techniques. The next four sections highlight AM applications.

Manufacturing Tools and Fixtures

AM enables rapid development and manufacture of manufacturing aids, tools, assembly fixtures, potting molds, paint masks, product guards, testing devices and inspection fixtures. The unique shapes of these manufacturing devices make them well suited for AM, and the fixtures can be easily and quickly modified as the product design evolves. Fixtures are generated directly from computer-aided design (CAD) models and allow for complexity that would previously be very expensive with long cycle times by standard tooling methods. There are also AM materials with static dissipative properties for making devices that have applications where an electrostatic discharge (ESD) damages products, impairs their performance or causes an explosion. Figure 2 shows examples of additively manufactured tools and fixtures:

  1. Custom detailed mask boots are fabricated directly from the CAD models and replace time consuming manual tape masking for paint.
  2. Custom semi-rigid cable bending fixtures created directly from the CAD model ensuredrawing specifications are met.
  3. Press-fit fixtures for gasketed electromagnetic interference (EMI) window installation are rapidly iterated to the final design, significantly reducing fixture costs.
  4. Custom ESD holding fixture fabricated directly from the CAD model to ensure repeatable alignment.

Figure 1. Three common additive manufacturing methods

Unmanned Underwater Vehicles

From concept models to deliverable systems, Raytheon utilizes AM in the development of unmanned underwater vehicles (UUVs). In particular, LS, is used by design teams to rapidly prototype functional vehicles and develop tooling and fixtures used during assembly, integration and test. LS allows designers to quickly iterate through complex geometries that would have been cost and schedule prohibitive under traditional manufacturing processes. AM technologies also allow engineers to merge complex structures to reduce part counts, eliminate hardware, and simplify assembly versus conventional manufacturing methods. Though UUV parts built with LS from thermoplastic based powders can be less robust when compared to metal based counterparts, especially parts associated with the vehicle’s hull, Raytheon engineers have addressed these structural challenges by integrating threedimensional lattice structures into the original part geometries. The result is a part with highly complex lattice geometries built in a single step by a single AM manufacturing process. The part is lighter weight but still structurally equivalent to the conventionally manufactured version (see Figure 3).

The parts also have lower cost, reduced development cycles and reduced lead times compared to conventionally manufactured UUV parts. As a result, UUV design and build times have been reduced from months to weeks allowing for quicker design iterations and faster system development.

Figure 3. An additively manufactured UUV

Missile Production

An early opportunity for Raytheon to use AM for functional parts came in 2007 during the Excalibur Increment Ib program. Excalibur is a precision guided munition and the traditional titanium manufacturing methods typically used for the tail-fin assembly, including mold design and fabrication for the metal cast process, would take too long to produce the minimum number of parts required for flight testing to meet the desired early development production cycle. As an alternative, the EBM AM process was evaluated and chosen to quickly manufacture a fully dense titanium tail-fin assembly. With EBM, part manufacture and final machining of critical interfaces was accomplished in almost an order of magnitude less time than using the conventional manufacturing approach, significantly reducing cycle time and eliminating the cost of expensive casting molds. These additively manufactured parts were used in early engineering flight tests (see Figure 4). While customer requirements resulted in incorporating an alternative base configuration, the additively manufactured parts contributed to a substantial program savings during initial product development.

Additionally, additively manufactured production parts have been used as both structural and nonstructural components in other munition demonstations. For one program during prototyping and low rate production, the housings for the control actuation system (a structural component) was manufactured by LS and the guidance electronic unit (GEU) mounts (nonstructural) were stereolithographically fabricated. Similarly, for another program, the harness guides are manufactured using the LS process. These nonstructural flight components are very lightweight and low cost in low volumes.

Figure 4. The titanium tail-fin assembly for the Excalibur munition was additively

Thermal Solutions

Raytheon also uses AM to develop new and improved thermal management solutions for electronics packaging. The designs leverage the inherent advantages of aluminum powder bed fusion techniques such as direct metal laser sintering. Among the advantages of using AM are greatly decreased cycle time, improved thermal performance and the ability to combine multiple parts and scale existing designs. In addition, the designer of a thermal management solution is no longer constrained to designs that must be manufactured using traditional machining techniques. In fact, most CAD-designed topologies can be successfully built with an additive approach; this is not true for conventional manufacturing. The result is that AM provides the engineer enhanced design flexibility to optimize a system’s thermal management performance.

Many traditional cold walls used as part of a thermal management solution utilize a vacuum brazing approach to assemble multiple complex pieces. Vacuum brazing has a small vendor supply base, long cycle times, and the potential for leak paths to occur at braze joints. AM eliminates these concerns by combining the multiple parts that would be brazed together into a single component (see Figure 5).

Figure 5. Cold plate assembly (top left), traditional manufactured multipart cold wall (bottom

Building a vacuum brazed cold wall unit takes months, whereas with AM, an equivalent-functioning part can be built in less than a week. This greatly reduced lead time enables not only multiple design cycles but further refinements to the design based upon first article results. Also, considering all the precision fabricated parts, purchased fin stock sections and miscellaneous other parts needed for the brazed design, an additive approach can provide greater than a 90 percent reduction in part counts. The lower part count contributes directly to a reduced Supply Chain effort and streamlined logistics for long term product sustainability.

Summary

AM is a constantly evolving field with more applications and materials being developed daily. The processes are maturing to a point where widespread production adoption will start to occur. Raytheon is committed to additive manufacturing and its key advantages:

  • The ability to customize tools and parts during production runs with minimal costs.
  • A reduction in early production cost and cycle time — enabling early rapid design iterations.
  • An enabler to complex geometries not possible using conventional manufacturing — enabling potential higher performance, lower cost and lower-weight products.

Raytheon has already leveraged AM for tooling, prototyping and early production, and the full potential of AM is currently being explored to enhance new aerospace and defense system designs.

1Wohlers, Terry et al. “Wohlers Report 2014”, ISBN 978-0-9913332-0-2, 2014

Jeff Shubrooks,
Jack Graham,
Curtis Carlsten,
Teresa Clement and
Dave Brandt

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