“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 manufac- ture 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 Navy. Te layer-build component resulted in part-count reduction and elimination of postproduction assembly costs and time while still being able to meet all of the engineering design requirements.


EBM vs. Laser Melting Tis Electron Beam Melting fabrication process is gener-


ally a higher quality alternative to laser melting manufac- turing 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. Te high temperatures used during EBM (700° C for titanium and up to 1000° C for other materials includ- ing nickel-based superalloys) leave parts stress-free aſter cooling, eliminating the need for separate post-build thermal treatments to develop full titanium mechanical properties. Further, 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 oſten the best material for certain


aircraſt applications, the metal’s high costs, design chal- lenges, and lengthy time-to-design have oſten prevented its use. Consequently whenever possible engineers have selected machined or investment cast aluminum as an alternative ma- terial (with appropriate design modifications to adjust for the metal’s lower strength), or heavier steels when aluminum was not a satisfactory replacement. With additive EBM technology, engineers can reconsider using titanium all over the aircraſt, given the cost and schedule benefits of the process.


A Look at 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 techni- cians lay out the required part in the virtual build space. Temporary features may be added to provide physical support to the part as it takes shape during the build. The products formation begins after the chamber is heated to build temperature, when the first layer of powder (typically 50–70 µm thick) is spread over the start plate by an internal rake. All of the material in the first layer is sintered to the


Mesh structure used for removing excess weight.


start plate and when melted in place becomes part of the finished assembly. Aſter 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. Te “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 pres- sures and elevated temperatures heal any internal micropores, thereby greatly increasing product fatigue life. Aſter 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 op- erations aſter fabrication, is usually three weeks aſter receipt of order (ARO). In addition to 6Al-4V titanium, CalRAM can also print


commercially pure titanium, cobalt-chrome steel, gamma tita- nium aluminide, and nickel-based superalloys including Alloy 625 and Alloy 718. Te 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.✈


Aerospace & Defense Manufacturing 2014 153


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