Aero engines benefit from additive manufacturing processes

4 min read

If one were to choose an industry sector whose acceptance of additive manufacturing would seem to signal its arrival as a fully-fledged production technology, aerospace would probably be top of the list.

This is because its safety-critical nature makes it understandably risk-averse and relatively slow to adopt new technologies. Thus, to become accepted, a process must be proven thoroughly and under the most rigorous tests possible. Thus, the qualification of both laser and Electron Beam Melting (EBM) processes in September 2012 for use on aero engines represented a highly significant step forward for additive manufacturing. One of the first companies to capitalise on this is Italian aerospace manufacturer Avio, which is now manufacturing turbine blades in Titanium Aluminide (TiAl). TiAl has a density of 50% compared to current alloys, but it is rarely used in engines due to being very difficult and expensive to cast. Avio, however, has shown that blades of different configurations and sizes can be manufactured in TiAl by using EBM. EBM is a type of additive manufacturing for metal parts. It is often classified as a rapid manufacturing method. The technology manufactures parts by melting metal powder layer by layer with an electron beam in a high vacuum. Unlike some metal sintering techniques, the parts are fully dense, void-free, and extremely strong. This solid freeform fabrication method produces fully dense metal parts directly from metal powder with characteristics of the target material. The EBM machine reads data from a 3D CAD model and lays down successive layers of powdered material. These layers are melted together utilizing a computer controlled electron beam. In this way it builds up the parts. The process takes place under vacuum, which makes it suited to manufacture parts in reactive materials with a high affinity for oxygen, e.g. titanium. No additional treatment The melted material is from a pure alloy in powder form of the final material to be fabricated (no filler). For that reason the electron beam technology doesn't require additional thermal treatment to obtain the full mechanical properties of the parts. That aspect allows classification of EBM with selective laser melting (SLM) where competing technologies like SLS and DMLS require thermal treatment after fabrication. Comparatively to SLM and DMLS, EBM has a generally superior build rate because of its higher energy density and scanning method. The EBM process operates at an elevated temperature, typically between 700 and 1 000 °C, producing parts that are virtually free from residual stress, and eliminating the need for heat treatment after the build. The melt rate is up to 80 cm3/h., Minimum layer thickness: 0.05 millimetres (0.0020 in). Tolerance capability: +/- 0.2 mm. Additive manufacturing offers a number of benefits to the aerospace industry. Not the least of these is the fact that in the aeronautical sector, what is known as the 'buy-to-fly' ratio – or the weight of raw material required to make one kilogram of finished product – can reach as high as 15 or 20:1 for many flying components due to complex geometries adding a lot of cost. The EBM process, by contrast offers an opportunity to produce lightweight titanium components with a Buy-to-Fly ratio close to 1. E-manufacturing processes are based on a completely different paradigm. Any component, three-dimensional by definition, can be seen as the 'stacking up' of 'bi-dimensional' layers, each only a few microns thick. The manufacturing process begins with distributing the base-material powder. The first layer is created by melting the powder through a source of energy (either a laser or an electron beam) which initially draws the contour and then melts the interior. After the first layer is finished, the platform on which the product is being built is covered with new powder which, when melted, will become the second layer. The process is repeated until the whole three-dimensional product is completed. This is why e-manufacturing is often referred to as 'additive manufacturing'. No complex tools are needed: everything takes place under the strict control of a software programme. The fact that fewer tools are needed leads to greater speed, lower costs, and ease of repeatability. There are also a number of other advantages, such as greater freedom: freedom of geometry, freedom of choosing complex materials, freedom from the constant manning of machinery, and freedom to change a design during development, without impacting on cost and timings. Additive Manufacturing offers huge potential cost savings in production for the aerospace industry. It also enables designers to create completely new and innovative lightweight designs using advanced lattice structures. Additive Manufacturing is particularly useful where production volumes are relatively low, part geometries are complex, materials used are expensive or difficult to process by conventional means. What is more, e-manufacturing is a more environmentally-friendly manufacturing process: no materials are wasted, it creates less pollution and consumes less energy. Indeed recent comparison between e-manufacturing and traditional technologies on a titanium component weighing one kilogram saw 95% less titanium used, 90% less greenhouse gas emissions and 90% less energy consumption. These are the reasons why Avio believes in e-manufacturing and has invested in the process since 2007. As the first company in the sector to have personnel, machinery, processes, software and materials fit for reliable and repeatable production, it is also the first company to produce turbine blades in titanium aluminide (TiAl) using additive manufacturing – currently being used in the GenX engine powering Boeing's 787 Dreamliner. In 2013, Avio will unveil its new plant in Cameri (Novara province), Avio's Centre of Excellence for all e-manufacturing technologies. This will entail 2,000 square metres of advanced technologies located only a few metres from the Italian Air Force's major logistical centre. This year, Avio will begin serialised production of aeroengine components, demonstrating how it can create 'power from powder'. This process has taken place with the help of machine manufacturer Arcam, which developed the unique EBM additive manufacturing process with its ability to provide a combination of high productivity, excellent material properties, high resolution and good surface finish. Arcam's A2 machine is described by the company as "the ultimate solution for Additive Manufacturing for the Aerospace and Defence industries", being specifically designed for manufacturing of large complex metal parts from a range of different materials. A robust production platform, The Arcam A2 is is delivered with two interchangeable build tanks, one for wide builds and one for tall builds. It also comes complete with MultiBeam parameter themes and the latest and most modern software, the EBM Control 3.2.