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Building blocks

There is growing use of 3D printing for cabin components but there are still some issues to be resolved. Ian Harbison investigates
 

Scott Sevcik, Vice Preisdent of Manufacturing Solutions at Stratasys, says his company has been involved with Airbus since prior to 2014, when its Fused Deposition Modelling (FDM) process was qualified for the A350. It was initially used as required to resolve supply chain problems and so avoid delays. In the years since,  Airbus has distributed specifications to their supply chain for serial production parts and, in 2017, his company started the series manufacture of multiple part numbers. This year, Airbus shared that cosmetic FDM parts have been introduced for Finnair A320 interiors.

 

Another important step this year has been the signing in February of a Joint Venture Agreement with SIA Engineering Company (SIAEC) a to establish an additive manufacturing service centre to produce plastic aircraft cabin interior parts as well as tooling for MRO providers. This followed the signing of an MoU in April 2017. Under the agreement, SIAEC will have a 60% equity stake in the joint venture, with Stratasys holding the remaining 40%. SIAEC will offer design, engineering, certification support and part production to customers worldwide including airlines, MRO providers and OEMs.

 

FDM uses a filament of ULTEM 9085 or other thermoplastic resin that is fed through a heated head and exits, under high pressure, as a fine thread of semi-molten plastic. In a heated chamber, this extrusion process lays down a continuous bead of plastic to form a layer. This process is repeated until the complete part emerges. After that, soaking in a tank removes any soluble supports that might be fitted to hold the piece in place during the process, or rigid breakaway supports can be removed with simple hand tools. FDM can produce visible layer lines on side walls and ‘tool paths’ on top and bottom surfaces. These have to be removed before painting.

 

One advantage of the process is that it can use materials that are fully certified to meet aerospace requirements. In the case of ULTEM 9085, this includes a high strength-to-weight ratio, high thermal and chemical resistance, and flame, smoke and toxicity (FST) ratings. Certified ULTEM also has documented traceability from filament back to a raw material lot number.

 

The company’s other 3D printing process is called PolyJet. This features a carriage – with four or more print heads and ultraviolet (UV) lamps – that moves across the work space, depositing tiny droplets of photopolymers, materials that solidify when exposed to UV light. After printing a thin layer of material, the process repeats until a complete 3D object is formed. He says this has now been extended to include droplets that contain a carbon fibre. Under robotic control, the alignment of the fibre can be adjusted in every bead to build up a reinforced structure. PolyJet uses a gel-like support material that can be simply removed with a water jet. It also produces a surface that needs only a little wet-sanding and polishing for a smooth, glossy surface that is ready for any process, including electroplating for a mirror-like finish.

 

Both systems utilise CAD/CAM data of the planned component to originate the forming process.

 

Last year, Hong Kong-based Western Tool & Mold (WTM) purchased the Fortus 900mc Aircraft Interiors Certification Solution (AICS). WTM is using the Stratasys technology to 3D print aircraft cabin parts with complex geometries and low quantity demand such as first class overhead bins and lavatory components. By 3D printing these parts directly from CAD designs, bypassing metal manufacturing processes, parts can be test printed early in the design process and modified if necessary, reducing manufacturing costs.

 

Collin Wilkerson, Managing Director, WTM, says: "Adding AICS to Stratasys FDM and PolyJet-based 3D Printing Solutions not only gives us the opportunity to provide repeatable, certified aircraft parts to Tier 1 and Tier 2 aircraft parts suppliers but also the accompanying documentation process is now automated – making it easier to meet evolving industry quality standards while freeing up more time to invest in production."

 

Sevcik explains that the Aircraft Interiors Certification Solution has been developed in response to the needs of the industry. While 3D printing can provide real benefits through manufacturing, performance and supply chain improvements, certification of aircraft parts is currently a challenging business. The primary reason is a lack of an established certification roadmap and qualified materials.

 

Companies may be experienced with the technology but not critical aspects as they relate to aircraft certification. The result is a lack of specific guidelines and specifications needed to satisfy the certification communities. Others may be familiar with the certification process but, if seen from a traditional manufacturing perspective, cannot translate the critical elements to the 3D printing world. Also lacking is a database of material properties that engineers can use to design and develop aircraft parts using the process.

 

The absence of material property data means aircraft companies are left to develop this information on their own, a process that can be extremely expensive and time consuming. Consequently, companies that develop their own data typically view it as proprietary information, which isn’t shared with the broader aerospace community. This creates an environment where all industry participants are forced to create their own data and processes, resulting in variability and a lack of material and process standards.

 

In fairness, the ability to replicate proprietary parts could be seen as leading to counterfeiting or piracy, so there will need to be some protection of the CAD data and IP, perhaps through licencing agreements.

 

It is in response to these industry limitations that Stratasys developed AICS. The first element is the Material Specification, which was audited by major aerospace OEMs in addition to Wichita State University’s National Institute for Aviation Research (NIAR) and the FAA. 

 

The Process Specification controls the entire workflow from material handling through part removal, inspection and delivery for installation using ULTEM 9085 resin. It also provides the information needed to ensure the Fortus 900mc operates within specification for achieving and maintaining printer qualification. This document was the result of several years of parameter isolation and validation to strike a balance between unlimited design freedom and stable, repeatable part production. Both of these documents provide the specifications and guidance necessary to attain consistent results and allow documented traceability from the part back to the raw material production lot. >>


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