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part is often the deciding design factor for choice of material and manufacturing process use. Also, the uncompromised need for safety in air travel adds a long list of complex requirements, even for the simplest part. To consistently produce parts with identical and understood properties, the material and the process used to form it must be understood to a very high level. This complicated aerospace manufacturing context, which blends low-volume economics with acute weight sensitivity and the need for highly controlled materials and manufacturing processes, has led to the development of knowledge within The Boeing Company required to safely transition AM from the laboratory and model shop onto the factory floor.

To begin to understand the foundation of requirements placed on a commercial aircraft part, one can look to the U.S. Federal Aviation Regulations, which must be met before a Type Certification can be issued for a given aircraft series, required for entry into service with an airline (Federal Aviation Administration, 2011). While this set of regulations is very extensive and detailed, the single most pertinent language within the context of an AM review can be found in Title 14, Section 25, Subpart D, Subsection 25.605: “The suitability and durability of materials used for parts, the failure of which could adversely affect safety, must (a) Be established on the basis of experience or tests; (b) Conform to approved specifications (such as industry or military specifications, or Technical Standard Orders) that ensure their having the strength and other properties assumed in the design data; and (c) Take into account the effects of environmental conditions, such as temperature and humidity, expected in service.” This brief but clear requirement is one of many that leads to the incredible safety record of commercial air transportation and also provides the impetus to rigorously study new fabrication methods such as SLS. Each A&D manufacturer will have internal specifications or will look to established standards organizations for data that allow accurate design of components from a given material, based on minimum allowable performance. Examples of material performance factors that are considered for even the simplest of components include specific strengths, fatigue, creep, use temperature, survival temperature, several tests of flammability, smoke release and toxicity, electric conductivity, multiple chemical sensitivities, radiation sensitivity, appearance, processing sustainability, and cost.

USE OF ADDITIVE MANUFACTURING IN AEROSPACE

Within Boeing, both military (Hauge and Wooten, 2006) and commercial (Lyons et al., 2009) programs use SLS to produce lightweight, highly integrated systems and payload components, as seen in Figure 1, that eliminate non recurring tooling costs and provide for life-cycle production flexibility. Since the first implementations on Boeing aircraft, the use of SLS has grown organically within a large number of programs. This is primarily due to its ability to produce thermoplastic parts that are lightweight, nonporous, thin-walled, and highly complex



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