Additive manufacturing is taking hold in aerospace sector

Yet for some large manufacturers, additive manufacturing (as 3D printing is also known) has been firmly under their wing for many years. For the aerospace sector, where small reductions in weight can equal large savings in fuel costs, the potential for lightweight, cheaply-made components is transforming the industry.

A case in point is Pratt & Whitney, the US-based aerospace manufacturer, which has created the first working aero-engine to use additively manufactured parts. The PurePower PW1500G, contained 24, from simple brackets to more complex central engine components designed to withstand high temperatures. The PurePower engine powered a Bombardier CSeries plane successfully through its test flight last year and is scheduled to enter into service in 2015.

The concept of additive manufacturing, which involves using lasers to fix layers of powdered metal into a digital mould, has been around for 30 years under various guises. Stereolithography, where layers of material are cured by a UV light, was first commercialised in the US during the late 1980s. During the 1990s other 3D printing methods, such as laser sintering and materials deposition, were developed as rapid prototyping became commonplace. Then in the early 2000s, when engineers began to realise that the technologies being developed could be applied to manufacturing, the term additive layer manufacturing (ALM) was coined.

Building the Geared Turbofan Engine

P&W’s Geared Turbofan (GTF) engine is a game-changer for the industry. It is the first series of Pratt & Whitney engines to use powder-bed additive manufacturing and now has more than 5,000 engine orders and commitments, including options.

GTF engines use a reduction gearbox to connect the fan at the front end of the engine to the low-pressure shaft. The cooling mechanism allows the turbines to run at higher speeds than found with conventional turbofans. Advanced cooling technologies are built in to prevent damage to the metal components. Overall, this leads to reduced fuel consumption of as much as 16 per cent and a 75 per cent reduction in noise footprint.

Seeking the advantage

The first obvious saving is time. Designs can be made in a fraction of the time taken using traditional techniques, and changed at the touch of a button. Lead times are also shortened because powdered materials can be bought on spec rather than the one or two years needed to purchase large billets of titanium.

Another benefit is the minimal waste involved and therefore the reduction in costs. ALM reduces consumption of raw materials by up to 50 per cent compared with traditional techniques such as forging or casting. Given the costs involved with aerospace-grade metals, these are significant savings. ALM is also more precise and adaptable than traditional methods and can be used to produce detailed designs such as complex geometric features on parts, for example.

The weight savings on components are also huge. The buy-to-fly ratio (the ratio between the weight of the raw material used to make a part and the weight of the finalised part) can be up to 20:1 can be reduced to less than 2:1 using ALM.

P&W has used this technology to make more than 100,000 parts and prototypes; including casting patterns, tooling, and test rig hardware. More than 2,000 additive manufactured metal prototypes have been made to support developmental engine programs.

Achieving aerospace material qualities

P&W is using the titanium and nickel alloys it already uses on its engines, tailoring the additive manufacturing process to create properties consistent with current materials.

This involves a number of key steps. First, an engineer prepares a build file. A 3D CAD design is created for each part and then split into layers about 0.1mm thick. This is then grown in a bed of metal powder. This powder is melted by a laser or electron beam following the shape highlighted by the initial CAD design.

The chamber space is then lowered and concealed with another coat of powder and this process is then repeated. When the components are grown, any left-over powder is cleared from the component and re-used to make another part.

ALM does have limitations. Scale can be an issue as one thing casting techniques do well is produce high volumes cheaply. As technology investment continues however, the efficiency and cost savings of ALM are becoming broader.

Training and investment

The additive manufacturing industry is now at the stage where investment from the likes of P&W is driving the next generation of technology. To this end, a $4.5m Pratt & Whitney Additive Manufacturing Innovation Center opened in 2013, in partnership with the University of Connecticut. P&W invests $3.5m a year there over the next three years, training a new generation of engineers in additive manufacturing research and development.

The facility is one of a small number in the US to work with metals rather than plastics, using highly sought-after electron beam melting machines. In addition, Pratt & Whitney is also working on additive manufacturing in collaboration with Penn State’s Applied Research Lab, North Carolina State University and the University of Texas at El Paso.

The future is additive

ALM will revolutionise the aerospace industry in the future due to its cost-savings and flexibility. At the University of Connecticut research centre they are looking into how to improve and optimise the ALM process for specific parts and alloys. Parameters being looked at include the powder size, the powder purity, the number of times the powder can be used before it is cleaned, the process parameters of power input, and the speed of the laser.

Pratt & Whitney views ALM through a wide lens but expects the technology to play an increasingly broad role in its manufacturing process, supporting the overall goal to make products that are greener and more efficient for customers.