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This landing gear knuckle illustrates how electron beam melting (EBM) technology can be used to produce one of a kind parts rapidly without any tooling. Since the part is built layer-by-layer, the microstructure is completely uniform regardless of the whether a thick section or thin section is examined. This homogeneous microstructure translates into uniform, consistent mechanical behavior. The material possesses complete isotropy. Thermal shunts fabricated as the part is being built (visible on the part) are used to keep the temperature isothermal and are easily broken off after the part has been built. (All images:CalRAM)

3-D manufacturing of titanium components takes off

With such challenges as base closings, shrinking defense budgets, and sequestration, the worldwide maintenance, repair, and overhaul (MRO) sector is projected to experience a significant decline over the next few years.

According to Hal Chrisman, leading analyst and Vice President at aviation consultancy ICF SH&E, “it appears that defense operations and maintenance spending will drop nearly 8%.” He added “forecasting, which is especially critical in the aftermarket world, is very tricky this year.”

Underscoring this problem, international aerospace and defense consultants IHS stated in their report Overcoming MRO Supply Chain Dysfunction, “Look closely at the product life-cycle within the typical MRO organization and you’ll notice that 50% of open work orders are waiting for parts; 30% of in-house stock will never be used; 8% of SKUs are duplications; and, on average, employees spend 25% of the workday looking for parts."

Parts management becomes even more critical as the military fleet ages and consumes all available replacement parts. MRO operators must face difficult financial choices in controlling these costs: either replicate components such as those made from titanium from scratch through a lengthy and costly remanufacturing effort, or delay those expenses by cannibalizing other aircraft for “used” replacement parts, thereby decreasing the reliability of repaired aircraft while rendering some aircraft un-flyable.

Tool-less additive manufacturing

To address such issues, a cost-effective manufacturing technology is being applied to titanium parts manufacturing for the MRO, aviation, and defense industries. CalRAM fabricates 3-D, near-net-shape components by melting titanium (and other metal) powders one-layer at a time using an electron beam. Employing electron beam melting (EBM) machines built by Arcam, CalRAM’s tool-less additive manufacturing technology is said to "rapidly create solid titanium objects faster and with less cost than traditional methods."

Located in Simi Valley, just north of Los Angeles, CalRAM says it is the only independent AS9100C certified, EBM-based manufacturer in the U.S. Offering this technology to MROs and other suppliers in the aviation and aerospace industries, the company has been producing titanium components for airframe primes and gas turbine engine aircraft manufacturers for almost a decade.

During CalRAM’s manufacturing process, electron beam paths are defined by proprietary software that “slices” existing 3-D design models into a series of separate layers, much like the views in a modern CAT scan. Powder is spread on the “start plate” by a traversing rake in the build chamber and then sintered to the plate using heat from the electron beam.

After the layer is sintered to ensure a conductive path for the electrons, the beam passes over the surface a second time at higher energy to melt and consolidate material that will form the finished part. This process is repeated, layer-by-layer, until the entire part is complete. Since parts are formed directly in the powder bed, EBM is fast with maximum build times less than 60 hours. And because EBM requires absolutely no custom tooling, the company’s layer-build components can save 85 to 90% of the MRO operator’s cost for replacing titanium products.

The process is said to also save designers up to 90% of their development time by substantially compressing the “design-test-redesign” process as well. After receiving the customer’s CAD file, CalRAM can deliver a titanium component in about two weeks, making development hardware available for installation and testing in days instead of months. Further iterations, if required, follow the same path, significantly reducing a client’s time to market.

Speed and lower manufacturing costs are not the only benefits of CalRAM’s EBM manufacturing process. With additive manufacturing, “complexity is free.” To save weight and improve performance, engineers have almost complete geometric freedom to include otherwise impossible to fabricate elements such as holes, stiffeners, overhangs, and meshes in their designs.

Iso grid and lattice block structures are actually cheaper to manufacture than less complex designs because they use less material and therefore take less time to produce. In one example, the company built a warm air mixer for Northrop Grumman’s unmanned combat aerial system that is being developed for the U.S. Navy. The layer-build component resulted in part count reduction and elimination of post-production assembly costs and time while still being able to meet all of the engineering design requirements.

EBM advantages over laser melting

The EBM fabrication process CalRAM has implemented is generally a higher quality alternative to laser melting manufacturing for titanium components. Operating in a vacuum instead of an inert gas environment, EBM minimizes oxygen contamination of the titanium melt, leading to improved microstructure with excellent mechanical and physical properties.

The high temperatures used during EBM (700°C for titanium and up to 1000°C for other materials including nickel-based superalloys) leave parts stress-free after cooling, eliminating the need for separate post-build thermal treatments to develop full titanium mechanical properties.

Also, because of the higher energy of the electron beam compared to a laser (3 kW vs. 700 W), EBM is much faster than laser-based processing, producing material at rates up to five times that of laser methods.

Although titanium is often the best material for certain aircraft applications, the metal’s high costs, design challenges, and lengthy time-to-design have often prevented its use. Consequently whenever possible engineers have selected machined or investment cast aluminum as an alternative material (with appropriate design modifications to adjust for the metal’s lower strength), or heavier steels when aluminum was not a satisfactory replacement.

With additive technology EBM technology, engineers can reconsider using titanium over more the aircraft, given the cost and schedule benefits of the process.

More on the EBM process

The process starts with a customer’s CAD file. Following a series of proprietary design rules to ensure parts can be built successfully in the Arcam machine, CalRAM technicians lay out the required part in a virtual build space. Temporary features may be added to provide physical support to the part as it takes shape during the build.

The product's formation begins after the chamber is heated to build temperature, when the first layer of powder (typically 50–70 µ thick) is spread over the start plate by an internal rake. All of the material in the first layer is sintered to the start plate and when melted in place becomes part of the finished assembly.

After the melt layer is complete the start plate is lowered the thickness of a single layer, the rake distributes fresh powder and the cycle continues. When the part is complete the material is allowed to cool in the machine chamber.

The “brick” containing the parts is removed from the machine and sent to the powder recovery station where sintered powder is separated from the finished parts. When the parts are cleaned they are typically sent to a hot, isostatic press (HIP) facility, where the high pressures and elevated temperatures heal any internal micropores, thus increasing product fatigue life.

After HIPing, parts are either delivered to the customer or if required, sent out for additional finish machine operations such as grinding, drilling, spot machining, or chemical milling. Delivery time for parts that are HIPed, and don’t require additional finishing operations after fabrication, is usually three weeks after receipt of order.

In addition to 6Al-4V titanium, CalRAM can also “print” commercially pure titanium, cobalt-chrome steel, gamma titanium aluminide, and nickel-based super alloys including Alloy 625 and Alloy 718. The EBM industry has also conducted fabrication experiments with copper, Invar, and aluminum, so that these materials may be available for EBM fabrication in the future.

This article was written for Aerospace Engineering by Dave Ciscel, Director of Engineering and co-founder of CalRAM Inc.

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