Laser melting with metals is gaining importance in aircraft manufacturing because of the benefits of quicker throughput times, cost-effective components and heretofore unimaginable design freedom. A range of new benefits, though, are becoming apparent.
Leslie Langnau • Managing Editor
The new benefits coming to light include lightweight construction, bionics and a new approach to design. A bracket connector used in the Airbus A350 XWB is an example of these trends. It was honored as a finalist in the “2014 German Industry Innovation Award.” Previously the bracket was a milled part made of aluminum (Al); now it is a printed part made of titanium (Ti) and is significantly lighter than it used to be.
Questions were put to a panel of industry experts regarding the use of additive manufacturing in the aerospace industry. These experts were: Prof. Dr.-Ing. Claus Emmelmann, CEO, Laser Zentrum Nord, Hamburg; Frank Herzog, CEO, Concept Laser, Lichtenfels; and Peter Sander, Head of Emerging Technologies & Concepts, Airbus, Hamburg.
1. How does the use of additive manufacturing technologies, such as laser melting with metals and laser sintering of polymers, affect the design of structural elements used in aircraft?
Sander: Additive manufacturing in the form of laser melting with metals allows us to design completely new structures, which are more than 30% lighter than conventional designs using casting or milling processes. Another factor is that we can proceed directly from 3D designs to the printer, that is, the laser melting system. Usually tools are required to manufacture aircraft parts—this is now no longer the case for us. This saves money and shortens the time until the component is available for use by up to 75%. To cite an impressive statistic: Previously we budgeted around six months to develop a component—now, it‘s down to one month.
Emmelmann: The advantages for structural elements used in aircraft are obvious. The high degree of geometrical freedom of design enables more effective lightweight constructions compared to conventional approaches. For the brackets we‘re currently focusing on, this means a considerable weight reduction, which in turn translates into lower fuel consumption and the potential to increase the load capacity of aircraft. These represent important steps toward more sustainable solutions.
2. How does the additive process change project processes?
Emmelmann: Since tools are not required in the process, it‘s possible at an early stage to produce functional samples of components that are very close to being ready for series production without incurring the high cost of tools or other pre-production expenses. The sources of error can be identified early in the design process, which allows for optimization of processes within the project as a whole.
3. What are some of the effects that result from changing from milled or cast components to printed components?
Sander: Milling aircraft parts can produce up to 95% recyclable waste. With laser melting, we produce components with near-final contours, which results in waste of only around 5%. This makes the process especially attractive when valuable and expensive aircraft materials, such as titanium, are used. Compared to casting, another advantage is not requiring any foundry tools. Furthermore, additional safety considerations are associated with cast parts, such as cavities. Last but not least, they are heavier than printed components.
Herzog: Beyond reduced resource consumption, you also have the ability to determine the microstructure quality. Another fundamental quality feature is the ability to define the force distribution within the component, which is often impossible with conventional parts or is considerably more difficult to achieve. This is an important argument when it comes to safety-related components. Concept Lasers’s QM modules integrated into a system technology let users take advantage of real-time, inline quality control. In addition, process mapping is a key tool for ensuring quality. It makes reverse engineering possible and serves to seamlessly document the process. Environmentally, reduced energy and resource consumption are features of the laser melting process.
Emmelmann: Metal additive manufacturing generally reduces costs for small- to medium-sized unit quantities. For instance, the comparatively higher relative investment costs for casting molds are eliminated, as well as any costs for tools that may be required. Furthermore, laser additive manufacturing offers greater freedom of design, since undercuts and interior channels, (often used for cooling), can be implemented during manufacturing. Previously unimaginable geometries can be combined with functions. Moreover, the material properties are slightly different. Materials produced using laser additive manufacturing have greater rigidity, while at the same time, less ductility; however, this can be enhanced with the right heat treatment.
4. What potential applications do 3D printing techniques offer for aircraft manufacturing and structural elements used in aircraft?
Sander: Two areas need to be considered in this connection: process optimization, on one hand, and product design, on the other. For us, process optimization means that we no longer require any foundry, injection molding or pre-production tools. We can print components directly from the 3D design system. This reduces our throughput time by up to 75%, with considerably lower one-off expenses. For example, we installed several tons of test equipment in the first test aircraft. This required thousands of Flight Test Installation (FTI) brackets to be produced in small unit quantities.
Spare parts are an additional, exciting area. In the future we will be able to manufacture them close to where they‘re needed, without tools and on an “on demand” basis—instead of having to finance large warehouses to store rarely needed spare parts all around the world.
Since laser melting can manufacture very fine—even bone-like—porous structures, the aircraft parts of the future will look “bionic.” Nature has optimized functional and lightweight construction principles over millions of years, minimizing the amount of resources required in clever ways. Initial prototypes indicate great potential in this approach. The process is expected to launch a sort of paradigm shift in design and production.
Herzog: The use of multiple lasers will play a role in the future. By relying on “intelligent exposure strategies,” the laser can apply layers to a component in a strategic manner to produce custom characteristics in terms of structure, rigidity and surface quality. The quality and speed in this area offer considerable potential to aircraft manufacturers.
5. At what point does the technology reach its limits for safety relevant components?
Sander: Generally speaking, there are no compromises in aircraft construction, since safety is the prime concern. Especially when one considers that our products remain in the skies for up to 30 years. We still have to learn how best to take advantage of implementing the new geometrical freedom in component design. Toward that end, we will have to perform many structural tests and trials over the coming years. The result will be a novel “bionic” aircraft design.
Emmelmann: Currently, there are limits to surface quality. These limits are comparable to those evident in cast components, however. But the result is reduced fatigue strength, especially with titanium, which is a concern since it is essential for structural components in aircraft manufacturing, which are exposed to high stress. Downstream surface treatments, such as those using microwave radiation, can significantly increase fatigue strength when combined with proper heat treatment. Ultimately, values comparable to those of rolled material can be achieved when necessary.
6. What methods or instruments do you use to monitor and validate processes with LaserCUSING?
Sander: Concept Laser uses “Inline Process Monitoring” provided by its QMmeltpool QM Module. The system uses a camera and photo diode to monitor the process within a very small area of 1 x 1 mm². The process is then documented.
7. Does the additive manufacturing approach change the thinking around design in aircraft manufacturing?
Sander: The next generation of aircraft engineers will understand 3D printing and all the opportunities it brings in greater depth. Thinking around design and production is currently changing. I would also call it a paradigm shift. We should remember that resistance to new things is only slowly overcome. Our production engineers are currently well-trained in casting and milling, so we need new insight and experience. Last but not least, some advocacy work has to be done in the form of practical examples we can point to in aircraft manufacturing. In general, laser melting technology is capable of developing safety related components that are even better, lighter and more durable than the components available today.
Emmelmann: With projects already completed for Airbus, we have determined that the opportunities presented by laser additive manufacturing have fundamentally led to new ways of thinking and lightweight construction solutions. Especially with regard to structurally optimized components, which generally have a high degree of geometrical complexity, it is possible to implement the form in a very direct way to achieve a high degree of lightweight construction. In the past, compromises with lightweight construction have been necessary due to the restrictions of conventional manufacturing—restrictions we are now able to elegantly avoid.
8. What general changes have 3D strategies produced in aircraft manufacturing, in your opinion?
Sander: Initial studies show that the number of manufacturing steps necessary has been cut in half, since the process yields blanks with near-final contours. Welded components composed of multiple parts are also attractive, as they can now be manufactured in a single process without welding equipment. Additive 3D printing is enabling new, more rapid speeds for component development and the construction process, drastically shortening previous development timelines. The cost structure of our projects is also changing significantly. The new approach has allowed lightweight construction to develop further. And it is leading to new design perspectives, which will be evident in the different geometries used.
Emmelmann: Since we do not require any special tools or clamps for the additive manufacturing process, we can produce the component directly from the 3D CAD data. This time factor ensures that in many cases we can work considerably faster than with conventional manufacturing processes. Speaking of production costs: If the direct cost of manufacturing a milled component is compared with the cost of manufacturing the same component using laser additive manufacturing, the additive process is usually found to be less cost effective. However, when the components are redesigned and improved thanks to the new design possibilities, for example by making them lighter or with higher functional performance characteristics, there are already many examples of circumstances in which the use of additive manufacturing processes offers cost advantages.
9.What opportunities do you see for integrating various functions, such as cooling functions, into the components of the future?
Herzog: Laser melting is synonymous with functional integration and added value. Added value is evident in superior component quality. Close contour cooling in tool construction for injection molding is one such application that we‘ve initiated over the past decade. In aviation, these cooled elements can be used for electronic systems or hydraulic components. In terms of aircraft design, future components can strategically accommodate the force vectors.
Emmelmann: The capability of producing entire assemblies as a single piece and of integrating additional functions into a component are among the major advantages of laser additive manufacturing. Laser additive manufacturing will therefore continue to increase in importance, especially in areas in which we exploit the geometric freedom of design and functional integration capability. Yet the options enabled by this freedom of design should be taken into account early on in the design process in order to differentiate it from conventional production strategies. Currently, design and development often fail due to lack of knowledge of the capabilities of this production process on the part of engineers and production experts.
10. Aircraft manufacturing is characterized by long lifecycles and comparatively low batch sizes. What effects does this have on additive manufacturing strategies?
Emmelmann: The comparatively small unit quantities involved in aircraft manufacturing favor laser additive manufacturing techniques. The additive manufacturing process does not allow us to take advantage of any economies of scale, as is the case for other production methods. In concrete terms, this means that the unit costs change only very slightly as production volume increases. Conversely, conventional production methods, such as pressure casting, are more cost efficient for producing large unit quantities.
Herzog: I agree. The lot size aspect, along with safety considerations and durability constitute a special profile of requirements for aircraft manufacturing. The strengths of laser melting also lie here: no tools required, production-on-demand, rapid, cost-effective, high quality.
Sander: Let‘s consider two aspects, namely quality, which is ensured through inline process monitoring, as well as geometrical freedom, which is achieved through being able to dispense with the aids that form the contours of parts; these make aircraft components produced using 3D printing with metals better, lighter, more rapidly available and most importantly, safer—not to mention the cost advantages.
11. What components produced using additive manufacturing are conceivable in aircraft manufacturing over the next decade?
Sander: If development continues in a similar manner, I see no technical restrictions. The decision will then ultimately be based on cost-effectiveness and on the industrial availability of metal powders and high-speed machines.
Emmelmann: We won‘t be printing complete aircraft, even in ten years. But I‘m confident that in the future, laser additive manufacturing will be capable of producing increasingly larger and more complex components in a cost-effective manner. This will be possible thanks to the rapid pace at which the system technology is being further developed, and the increased productivity associated with such advances. I see great potential in particular for structural components with dimensions of up to 1 m, as well as for engine components.