SECTION TITLE
ADDITIVE MANUFACTURING
Electroforming reduces the time spent ‘in tank’
environments which they are subjected to, can be catastrophically damaging to aerospace components, particularly in desert and storm conditions, where sand, water and other debris can cause severe and premature wear and damage to the blades. In addition to weather, bird aircraft strike hazards (BASH) also pose a threat to composite blades becoming damaged from a collision. While the number of major accidents involving civil aircraft is quite low, 65% of bird strikes still cause damage to the aircraft.
AEROSPACE LIP SKINS Traditionally created by spin forming using aluminium alloys, lip skins, like rotor blades, need to be able to operate in harsh environments and developed to tight tolerances. Metal-spinning is a forming process in which a blank of material is rotated on a spinning machine similar to a lathe. Te blank of material is clamped onto a spin-forming mandrel and rotated by servo-controlled motors and drives. During rotation, heat is applied to the material by a gas torch affixed to a robotic armature and a roller on the spinning machine makes contact with the part blank, forcing the part blank to flow over the spin-
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forming mandrel surface. Te spun formed part requires considerable post processing steps to finish the part, including heat treating for stress relief, burnishing and machining. Te parts are also produced in a full-circumference, single piece. Operators may require the lip skin to be in multiple sections to allow for removal, and replacement of damaged sections during the life cycle. Tis can add further machining and stress relief steps to assure that the segments do not deform or spring back for installation onto the nacelle. Doncasters already produces a one-piece inlet lip skin for a production turboprop engine. Te electroformed process was adopted to replace a multi-piece sheet metal design that was mechanically fastened to the engine nacelle. Te electroformed lip skin precisely fits the contour of the nacelle and proved to be more cost-effective for the part production and subsequent installation.
Although this has proved successful for
many years, the Doncasters R&D team has identified major benefits of switching to the electroforming process.
Te first benefit is cost savings. Generally speaking, the process of electroforming is more cost-effective than aluminium
spinning. Tis is predominantly down to the reduced process steps, part count, reduction and elimination in post machining and processing of the surface, automation (and low labour costs), and defined time ‘in tank’. Metallurgical improvement is another benefit. Nickel cobalt has much better erosion properties than alternative metals. For example, its tensile strength is three times higher than stainless steel, while its hardness is more than 13% higher than titanium 6AI-4V. It has a much better strength to weight ratio and is corrosion resistant.
THE PROCESS Like all additive manufacturing processes, electroforming builds 3D objects by adding layer-upon-layer of a material. In this instance, it produces metal parts by electro-deposition of metal over a mandrel. It’s crucial that the area is prepared, to eliminate the risk of contamination, which could adversely affect the part quality and ultimately lead to scrapping the part. Te first stage of the process sees metallic pellets introduced into a precisely controlled bath that dissolve in the electroforming solution by passing current through anodes,
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