applications. Its use is being ... bed fusion process, electron beam melting. (EBM), in which lasers are ... A similar p
Nickel alloy use in additive manufacturing
Additive manufacturing (3D printing) is rapidly expanding. Originally restricted to the production of plastic artifacts, it can now be used to print whole jet engines, turbine blades, and aircraft parts, medical implants and other applications. Its use is being extended to food, human organs and even, so it is said, to entire houses! This article takes a look at what is happening in the fairly new field of 3D printing of nickel alloys and superalloys. By James Chater
Lasers fusing metal powder. Photo: Siemens.
[ Nickel alloys ] Introductory Additive manufacturing (AM) is entering the mainstream. For years companies have been pioneering the various techniques of AM and many have got as far as using it for prototyping, while holding off from AM mass production for the time being. Now companies are starting to take the plunge and integrate AM into their mass production.
GE’s main competitor, Siemens, is also very interested in 3D manufacturing. It is investing in a number of 3D printing start-ups, the most significant to date being the UK firm Materials Solutions, and it aims to incorporate their technology into their gas turbine manufacturing process. Materials Solutions develops both highperformance materials and laser printing processes, working with Inconel, titanium, stainless steel and other materials on machines supplied by EOS. Its customers include large aerospace and energy companies, the likes of Rolls-Royce, ITS and Sumitomo Precision Products.
Fuel nozzle for the LEAP aircraft engine being developed by CFM International, a 50/50 joint company of GE and Snecma (Safran) of France. The nozzle is made by GE. Additive manufacturing is used on its elaborate interior.
Engineers at Monash University made this jet engine using the SLS process.
Techniques of 3D printing
Investments A clear leader among the large companies is GE, which is already using 3D technology to manufacture the elaborate interior of the fuel nozzles for its LEAP aircraft engines. More recently, the FAA recently cleared GE’s first 3D-printed part for a commercial jet engine, a sensor housing. Now MTU Aero Engines is 3D-printing the boroscope bosses for the A320neo engine, made by Pratt & Whitney (see photo).
Borescope bosses for the PurePower® PW1100G-JM engine – the Pratt & Whitney engine to power the A320neo – are made by selective laser melting (SLM). The lowpressure turbine for this turbofan engine will be the first ever to come equipped with borescope bosses produced by additive manufacturing processes. The bosses form part of the turbine case and allow the blading to be inspected using a borescope. Photo: MTU Aero Engines.
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This short pipe section connects two parts of a gas turbine. The fluid transition from round to square is easier to achieve with 3D printing than with conventional methods. Photo: Siemens. So much for individual aircraft components; but what about whole engines? Engineers at Australia’s Monash University claim to have produced the world’s first 3D-printed jet engine, using the selective laser sintering (SLS) process. The university is collaborating with companies such as Airbus, Boeing and Raytheon to develop new components with 3D printing. Meanwhile, GE has revealed it has completed a multi-year project to print a working jet engine. The engine, which admittedly is small enough to fit into a backpack, was printed using at DMLM technique (see box). The printer, which can handle several different special metals and alloys, was supplied by EOS.
There are many techniques of 3D printing, but not all are equally suitable to the printing of metals, let alone nickel alloys. The most relevant process where stainless steels or nickel alloys are concerned is powder bed fusion, where energy sinters regions of a powder bed. One version of this technique is direct metal laser melting (DMLM). A similar method is direct metal laser sintering (DMLS), the difference being that sintering does not fully melt the powder but heats it to the point that its molecular structure changes. There is some confusion, with the terms DMLM and DMLS sometimes being used interchangeably. As a general rule, melting is better than sintering if you are working with one material, whereas sintering is to be preferred for alloys, because of the different melting points of the alloying elements. Arcam has introduced another powder bed fusion process, electron beam melting (EBM), in which lasers are replaced by electronic beams. A similar process is Sciaky’s Electron Beam Additive Manufacturing (EBAM). A less common type is direct energy deposition, where thermal energy, usually in the form of a laser, fuses the powder as it is being deposited. www.stainless-steel-world.net
[ Nickel alloys ] Several companies are investing to take advantage of the aerospace boom and the rapidly advancing 3D printing techniques for special alloys. Alcoa will spend $22 million on hot isostatic pressing (HIP) at its facility in Whitehall, Michigan. This will improve the strength of both the 3D-printed and cast parts it produces. ATI is also expanding its capacity for nickel-based superalloy powder in response to increasing demand for materials used in the 3D printing of aircraft parts.
Materials AM techniques have gradually extended to include various types of stainless steels, maraging steels (17-19% nickel), pure titanium, titanium alloys, pure nickel, nickel alloys and several other special materials. Among superalloys, the most frequently encountered in AM processes are Inconel 718 and 625. Alloy 718 is especially favoured for aerospace parts and gas turbines, two areas in which the advantages of AM are especially significant. Alloy 625 is used in the aerospace, chemical and energy markets, with applications including gas turbine blades, filtration and separation, heat exchanger and moulding processes. Other nickel-containing materials being produced for 3D printing include Hastelloy X, Kovar (a Fe-Ni-Co alloy used in lighting) and Invar 36. EOS has developed a new alloy, NickelAlloy HX, specifically for 3D printing. This Ni-CrFe-Mo alloy resists temperatures up to 1,200C. It is used in the combustion heads of Siemens gas turbines. Nitinol, a Ti-Ni alloy, is also used in 3D printing. This extraordinarily bendy
Guardians of Time by Manfred Kielnhofer, 3D-printed polished nickel steel by Shapeways, 2014. material is much sought after for catheter wires and stents. Because it is so difficult to machine, 3D printing opens up entirely new possibilities in the field of medical products.
The difference Nickel-alloy based powders have a different microstructure than nickel-alloys made using conventional methods. This makes them stronger, better-performing and more durable. The increased hardness means that thinner walls can be
used, making the components lighter and more compact, important characteristics if fuel savings and other efficiencies are to be achieved. To maximize the benefits of 3D printing, however, it is essential to know it from the inside out, i.e. to understand the properties of the materials used. This is the idea behind a project launched by the Defense Advanced Research Projects Agency (DARPA), called Open Manufacturing, which aims to gain greater understanding of the physics and parameters of 3D printing. In conclusion, we may expect manufacture and 3D printing technology to feed off one another in a virtual circle. As industries such as aerospace, chemicals, nuclear power and medicine develop, so 3D printing will advance, which will in turn lead to new breakthroughs in these industries.
Did you know?
With a building volume of 400 x 400 x 400mm, the EOS M 400 allows the production of large metal parts on an industrial scale directly from CAD data. www.stainless-steel-world.net
Plans are afoot to manufacture metals in space, benefiting from the technical advantages of low gravity and the absence of oxygen. In particular, Deep Space Industries is developing a way to use gas to extract the nickel from asteroids and deposit it into 3D shapes. The technique would work with or without gravity. Stainless Steel World October 2015
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