Printing up performance07 March 2019

Additive manufacturing (AM) technologies offer a wide range of benefits for short run products, prototyping and high-end superalloy components. Now, having built a foothold in niche products, AM is set to break out of its traditional mould

Additive manufacturing (AM) technology, also known as 3D printing, is at the forefront of a trend that is revolutionising product design and production. Emerging as a new industrial tool for producing complex metal components quickly and cheaply, AM offers a host of benefits.

The process is relatively straightforward. A 3D model, in CAD (computer-aided design), of an object is digitally sliced into layers a few tens of microns thick. Then the AM machine builds it back up again by laying down molten material, or melting powder selectivley. The pattern of the object steadily builds with each melting pass and each layer of powder. For metal AM, high-powered lasers or electron beams are used to melt the powered material, which typically consist of titanium and nickel high-temperature superalloys for high-performance parts in the medical, aerospace or automotive industry.

Described variously as direct metal laser sintering, laser powder bed fusion and selective laser melting, products produced through AM are fully dense and possess the material qualities of the parent material.

Lead time on component availability can be cut by up to 75%, in some cases as much as a reported 90%, using AM, while multiple design iterations for new product research and development become far quicker and less costly. Smaller, faster and cost-effective production offers an opportunity for the development of concepts like zero-inventory, on-demand spares and mass customisation.

Perhaps most significantly, freedom from conventional forging, casting and welding techniques has allowed engineers to embrace radical new designs not possible before the advent of AM.

Powering AM development

In the few decades since its 1995 development at the Fraunhofer Institute, in Aachen, Germany, AM’s appeal has exploded, and machines are now becoming more established in service. According to the ‘Additive Manufacturing with Metal Powders 2018’ report from industry analysis firm SmarTech, AM sector revenues resulting from hardware, materials, and software grew 24% in 2017 to exceed $1 billion for the first time. There is an increasingly positive long-term outlook, with sector revenues expected to reach $9.3 billion by 2027.

Among the many companies investing and scaling the technology are the Tier One gas turbine supply majors like US-based GE and European giant Siemens. The high-temperature, high-pressure operating conditions found within a gas turbine make materials properties critical to their operation and it’s no surprise that power generation is one of the sectors that is pioneering the commercialisation of AM technology.

Components operating under the harshest conditions found at the heart of a gas turbine, such as blades and burners, are already being produced with AM. These components are delivering higher performance with lower weight, and improved operational properties such as better thermal management and fluid mixing.

In some cases these components are already being delivered at scale. For example, a GE Aviation installation in the US with 40 AM machines has produced more than 30,000 jet engine fuel nozzle tips over a three-year period since operations began. Prior to the use of AM, the 20 elements that comprised the unit would be welded together. With AM, the fuel nozzle tip was reduced to a single piece, which also proved to be some 25% lighter.

Phil Hatherley, general manager of Siemens-owned business Materials Solutions, explains: “It is possible to make components that are just impossible to manufacture in any other way. We’re making a combustion component for Siemens’ next-generation turbine, the 9000 HL, there’s just no other way you’d be able to do that.”

The drive for more efficient gas turbines with better part load efficiency and faster ramp rates is pushing manufacturers to explore the limits of AM. “It’s certainly one of the areas for this technology because of the alloys we’re using, the high-end superalloys, and the ever-present desire to get more efficient and to improve the environmental conditions.”

“Whether it’s a jet engine or a gas turbine, there’s this really strong focus on using manufacturing to get the most efficient combustion burner,” says Hatherley.

Certainly, the big players are putting their money where their mouth is. In February 2016, for instance, Siemens opened a new production facility for 3D printed components in Finspång, Sweden, and followed this with a new AM facility in Worcester which opened last autumn. It plans to increase the fleet of AM machines at the site from 15 to 50 over the next five years.

Achieving high-end performance

The unique capabilities of the AM process also allow novel internal geometries, for example cooling ducts, in those parts of the turbine that reach very high temperatures. As Hatherley says: “It’s quite amazing what we can do today and the geometries that are available to us. AM adds extra layers of opportunity.”

Indeed, by early 2017, Siemens was finishing its first full load engine tests for gas turbine blades completely produced using AM. Running AM blades at 13,000 rpm in an SGT-400 industrial gas turbine, the tests at the Siemens facility in Lincoln, UK, also saw the use of a new blade design with a completely revised internal cooling geometry, made possible with AM.

Manufactured in Worcester, AM turbine blades are made of polycrystalline nickel superalloy powder, allowing them to endure the high rotational forces of the turbine’s operation, surrounded by gas at 1,250°C and cooled by air at over 400°C. The blade design provides improved cooling features that can increase overall efficiency, Siemens says. The company’s first 3D-printed component for a heavy-duty gas turbine has been in commercial service since mid- 2016.

GE, too, is offering improved turbine performance with an upgrade package featuring AM components. Vattenfall Wärme Berlin, a subsidiary of Swedish utility Vattenfall, is set to be the lead commercial operator of the MXL2 package with a project at its Heizkraftwerk Berlin-Mitte district heating plant announced last June. The new MXL2 features first-stage turbine vanes and heat shields, produced by GE’s Additive Manufacturing Works (AMW). GE notes that the significant amount of cooling air these parts traditionally require impacts on the performance of the engine. Again, AM allows advanced designs that reduce the cooling air requirement, improving the turbine’s overall performance.

Following the upgrade of the existing GT13E2 gas turbine, electrical output from the plant is expected to increase by 21% and heat generation by about 4 MW. GE says the use of AM technology within the MXL2 package could help gas plant power producers with GT13E2 machines save up to $2 million in fuel annually.

Building volume & cutting costs

At a small-scale level, AM can produce replacements for obsolete parts, such as the steering box of a 1918 Ruston Hornsby motor car.

Although AM does have considerable advantages in typically high-end or bespoke manufacture, a more widespread technology breakout will require a shift in the perception from being a prototyping technology to a viable option for serial production.

Certainly, companies like Siemens and GE anticipate the production of thousands of AM parts over the coming years. However, while taking out some of the manufacturing steps, like braizing or welding for example, volume remains a challenge at today’s relatively high cost for AM components.

As Hatherley explains: “Because it is still quite a costly technology, if you’re making low numbers or prototypes, then it makes sense, because you don’t have the cost of developing a tooling suite for say casting or forging. If you’re making thousands of units of a product, then it becomes more of an economic business case to invest in that tooling.”

He explores the anticipated limits placed on AM: “I would expect to see more AM processes enter the aerospace base. For automotive, it’ll be a long time before you see it on a basic model saloon car, but there are potential applications in prototyping and in the high-end car market. Currently, though AM is certainly a proven and established technology, it’s not suitable for volume manufacturing at the moment.”

Nonetheless, though AM is still fairly specialised today, volumes are increasing, and prices are dropping. Looking ahead, perhaps five or 10 years, AM production looks set to become more comparable to traditional manufacturing techniques.

Hatherley says: “What we’re focused on is that industrialisation portion of AM, taking it out of the lab and turning into a fully-fledged industrialised manufacturing process. Driving that cost down but keeping the quality high.

“It’s not a mainstay manufacturing process for the jet engine today: there’s an awful lot of analysis and testing going on, but I believe it will get there. It’s not for every component; that just doesn’t make sense. Just because you can print a fork doesn’t mean you should. But it’s amazing how much 3D printing is used already around the world and in various industries, be it dental and medical, as well as automotive and aerospace.”

Future trends for AM

With greater industrialisation, even in the short-term, AM is forecast to emerge as one of a number of manufacturing techniques for metal components, just like welding. Says Hatherley: “Within the three- to five-year time frame we are going to see AM as just another tool in the manufacturers’ armoury, along with forging, casting and other production processes, and considered in just the same way, depending on what part you need.”

While AM may only now be getting into its stride, other appealing avenues are already emerging for advanced materials and AM. As Hatherley explains: “While high nickel superalloys are already being used in AM manufacturing for gas turbines, for instance, AM is also creating opportunities for the use of novel materials that could not be fashioned through traditional techniques.”

While most AM processes use conventional alloys that have a significant market volume, there is growing emphasis on the development of new materials with particularly desirable properties that are suitable for AM.

Although such developments are typically at a lower technology readiness levels (TRL), depending on market volume and how widespread they are in their application, there are likely to be more opportunities for alternative materials as the use of AM grows.

“There is more knowledge of, and confidence in, AM technology capabilities. At Siemens we’ve got over 110,000 hours of engine experience using AM components, so we have confidence with turbine blades, for example. That brings designers and engineers more confidence to use it and see other applications,” says Hatherley.

He adds: “As more designers understand what can be done, they will start designing products that, because of the benefits to the final component, can only be manufactured using AM. Designers are starting to grasp what AM can bring to the party. The 3D printing arena is a leap.”

Along with digitisation and the industrial internet, AM is widely tipped as one of the key levers in realising the fourth industrial revolution. And, while it is very unlikely that every product will feature AM components in years to come, there is plenty to suggest a steadily growing proportion of products will.

David Appleyard

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