Additive in Aerospace
The what, why & how of Additive in Aerospace
Over the years, the Aerospace industry has always been one of the first adopters of new manufacturing technology and techniques. This is in part due to the constant drive to push the capabilities of aircraft in a highly competitive field.
It is therefore no surprise that Additive Manufacturing in Aerospace has seen such widespread adoption because of its ability to create components that have a very high strength-to-weight ratio, a factor that has a direct impact on fuel efficiency and aircraft performance.
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Additive Manufacturing in Aerospace
Over the years, the Aerospace industry has always been one of the first adopters of new manufacturing technology and techniques. This is in part due to the constant drive to push the capabilities of aircraft in a highly competitive field. It is therefore no surprise that Additive Manufacturing in Aerospace has seen such widespread adoption because of its ability to create components that have a very high strength-to-weight ratio, a factor that has a direct impact on fuel efficiency and aircraft performance.
How is Additive Manufacturing being used in Aerospace?
Additive Manufacturing is quietly seeping into every major and minor Aerospace company. The large behemoths like NASA, General Electric, Boeing and Airbus have been using Additive for decades but the limitations of the technology relegated its use primarily for prototyping and testing. In the last decade the technological advancement of Additive technologies, materials and techniques have made it possible to begin manufacturing metal parts for commercial use.
Additive Manufacturing systems used in Aerospace
There are many different types of Additive Manufacturing techniques and technologies on the market with new types arriving every year, however due to the critical nature of aircraft and spacecraft, the machines that make these parts need to be the top of the line, capable of repeatedly producing parts that are in tolerance and maintain consistent quality.
Electron Beam Melting (EBM)
Instead of using a laser beam to melt the particles, EBM uses a concentrated beam of electrons. The EBM process takes place inside a vacuum to prevent the electron beam from colliding with gas molecules. Manufacturing inside a vacuum also has the added benefit of eliminating the effect of oxidation on reactive materials like titanium. EBM can also be used in fused deposition where the metal is fed in the form of a wire filament.
Direct Metal Laser Sintering (DMLS)
This is one of the more common metal Additive Manufacturing technologies and uses a laser to melt the powder into the final form. The build chamber is not under a vacuum. Parts made using this technique are denser and stronger than cast components and can go from concept to part much faster than a typical casting process.
Additive applications in the Aerospace Industry
Rapid prototyping has long been one of the key benefits of Additive Manufacturing. This is due mainly to the speed at which a prototype can be taken from concept to physical prototype. These prototypes help engineers uncover any potential pitfalls in their designs that would not typically be evident by looking at CAD models.
High fidelity sample prototypes also provide a way to introduce the concept of a product to investors or non-technical team members. A physical model has a greater impact than a rendering on a computer screen.
Furthermore, the use of surrogates allows engineers to print out a key component in an assembly to act as a temporary placeholder while the real part is still being manufactured. This allows the rest of the relevant assembly work to be continued and highlights any potential problems.
Complex lightweight designs
One of the most impressive abilities of Additive Manufacturing (AM) is the creation of parts that would be impossible to make on traditional CNC lathes and mills. This is possible because AM builds up parts layer by layer. The unfused powder behaves as a support for the areas already fused; this works particularly well for large overhangs and internal voids. These complex organic designs are not just for looks but arise from using topological optimisation techniques and generative design to create parts that only have material where the highest critical loads are experienced. The parts thus take on organic and abnormal-looking shapes because they are not limited to the constraints of traditional machines. This is uniquely beneficial to the Aerospace industry where parts need to be made as light as possible without sacrificing structural integrity.
On demand parts and spares
The military relies heavily on its spares and getting these spares across the world to various military bases is a large logistical operation. Spares are often needed urgently and, despite the US militaries’ mastery of logistics, there is still a time delay in receiving critical spares. AM allows parts to be printed on demand and then flown to wherever they are needed. This drastically reduces the need to keep large inventory stores and has the added benefit of custom parts fit for purpose.
Why Additive Manufacturing is changing the Aerospace industry
Additive Manufacturing in Aerospace is changing the way in which parts are designed, manufactured and assembled. This industry is uniquely positioned to gain the largest benefit from the technology because of the typically low production volumes required, and the types of technologies traditionally used like metal casting and CNC machining. The end result of the adoption of this tech is lighter, more fuel-efficient aircraft with easy to maintain components and lower inventory requirements.
Cost of Manufacture
For any commercial enterprise the fundamental goal is to reduce costs and increase profit. This is no different in the Aerospace industry, and Additive Manufacturing has many cost advantages when compared to traditional manufacturing technologies.
Raw material cost is by far the largest contributor to the cost of manufacture. Power and labour are a relatively small percentage of the cost despite lasers being very inefficient in converting mains power to usable heat for manufacture. The cost to produce an AM part is made up of 4 main components as listed:
- Raw material cost
- Depreciation cost
- Power cost
- Labour cost
As the deposition rate of AM increases the total cost decreases. At a certain point increased deposition rate does not change the cost of manufacture; this is because the faster the deposition rate the closer the cost of manufacture gets to the raw material cost – which is fixed. The other cost components like labour and power are so low that they do not significantly reduce the overall cost if optimised. It is therefore important that the machines have a high deposition rate
Despite the raw material being more expensive, Aerospace applications still enjoy cost reduction when using Additive Manufacturing.
Aerospace equipment is highly complex, and this complexity results in many moving parts. Additive Manufacturing can reduce the total inventory in any manufacturing plant due to two main reasons:
- Components can be made as one homogeneous structure and do not need to be made from multiple different components that then need to be assembled post manufacture. The reason why Additive Manufacturing can reduce the overall part count is because it is not restricted by traditional machine limitations. Complex internal chambers can be made that would be impossible with subtractive manufacturing and even with cast components.
- Due to the flexibility of Additive Manufacturing, parts can be made on demand when and where they are needed. All that is required is the CAD model and any factory with a metal Additive Manfacturing system. The part can then be printed on demand. It does not have to be held in inventory. The reason why parts are normally kept in inventory is because they have such long lead times and if a part is needed urgently this will create serious delays, whereas AM parts can be made in a matter of a few days or even hours depending on their complexity and size.
In the Aerospace industry there is a term known as ‘buy to fly’. This refers to the amount of raw material that is scrapped during manufacturing. More specifically, the buy to fly ratio is calculated by dividing the weight of the raw material by the weight of the final component. In a typical component manufactured using subtractive machining technology the buy to fly ratio is anywhere between 6:1 and 30:1. In some cases as much as 98% of the raw material is scrapped. A ratio of close to one is achievable with AM. This is especially true if the unused powder can be recycled.
Flight to weight ratios
Passenger aircraft can gain large benefits from reduction in weight, this is due in part to their considerable time spent in flight where every kilogram saved during manufacture results in large quantities of fuel saved over the lifespan of the aircraft. The manufacturer who can offer a better operational cost will have a clear advantage.
New developments have resulted in the creation of a meta-material that can effectively reduce noise while maintaining a high percentage of airflow. An ideal application would be the aircrafts exhaust which produces high levels of noise pollution. Despite this technology still being in very early development, it would not have been possible without AM and it’s ability to manufacture parts that mimic theoretically optimal designs.
Additive Manufacturing Aerospace parts
NASA has been testing the manufacture of a rocket engine, with the valves, fuel injector and many other key components being produced with Additive Manufacturing technologies. The combustion chamber is the only major component that is not yet produced additively.
Rolls Royce is producing the Advance3 demonstrator engine with the aim of using as many Additive parts as possible to improve the overall fuel efficiency.
SpaceX is a champion of new technological development, anything that can improve their overall efficiency is brought into the fold. The SuperDraco engine used on their crew dragon spacecraft is a prime example of this as it’s engine chamber is metal printed using a DMLS printer.
General Electric is one of the leaders in using Additive Manufacturing in their engines and are developing the Leap engine to make use of a large proportion of printed components. Their leap engine uses a fuel nozzle that would be impossible to manufacture with traditional technology.
Liebherr is aggressively pursuing the conversion to Additive Manufacturing for many of their components such as their nose landing gear brackets manufactured for the Airbus A350 XWB. Another example is their high pressure hydraulic valve block, the first primary flight control hydraulic component used in a commercial aircraft, a major step in the Aerospace industry.
Which Aerospace parts can now be produced additively?
Listed below are some of the major examples of additive metal manufacturing of Aerospace parts. Companies like General Electric are clearly the ones driving metal Additive Manufacturing adoption.
The Boeing T25 compressor inlet temperature sensor casing is made from a cobalt chrome alloy and was the first part to be certified by the FAA for use in a commercial jet engine.
General Electric is currently building up a production line to print 35,000 to 45,000 fuel nozzles for the Leap jet engines per year. This engine contains 19 additively manufactured fuel nozzles and is undergoing flight tests. These parts simply cannot be made with traditional manufacturing techniques because of all the internal passages and geometries required to create an optimally performing part.
General Electric has also developed a power door opening system bracket which is used to open the fan compartment during maintenance operations. These brackets are to be manufactured commercially for the Genx–2B airline engines which are used to power the Boeing 747-8 airliners. The brackets are made from a cobalt chrome alloy.
NASA & UAB
NASA & UAB developed freezers that allow the transport and processing of experiments. They needed a new liner design to optimise the space and weight of the freezer and used an Aerospace- grade plastic to achieve this.
Jet Propulsion Laboratory NASA
Jet Propulsion Laboratory NASA has used an Aerospace plastic as an alternative to machining antenna arrays out of Astroquartz. These were used on the Cosmic-2 satellite that contained 30 of these antennae and were able to operate in the vacuum of space.
United Launch Alliance
The Atlas V environmental control system duct was printed from an Aerospace plastic and the part reduced from 140 pieces to only 16.
The Liebherr Primary flight control component has a valve block that is made from titanium powder that is fused together by lasers. This part was initially made from castings but due to Additive Manufacturing technology it was made 35% lighter with fewer parts while still maintaining the mechanical strength of the cast part. Liebherr is also working on a rudder actuator that contains a valve block, cylinder housing and reservoir all manufactured as one component where in the past these used to be made from multiple different parts.
Aurora Flight Sciences
This UAV is made from 34 parts of which 26 are Additively manufactured using FDM technology to print the main fuselage and main wing. This allowed the creation of structures that were both stiff and lightweight.
In general, the main disadvantages of many of the powders are their cost. Since the materials need to undergo a specialised and expensive process to create the powder, the cost will always be more than a billet of the same material until another method is developed.
Another issue is the characterisation of the material; most forged and cast metals have been extensively tested and characterised so that their mechanical properties are very well known. It cannot be assumed that the final part will have the same mechanical properties of the base material as different types of printing technology will result in different properties. The additive manufacture of steel and titanium alloy components will continue to grow in terms of adoption and applications.
This titanium alloy is the most common alloy used in industry and is ideally suited for Aerospace applications because of its high strength-to-weight ratio, its resistance to fatigue and high corrosion resistance to typical Aerospace chemicals.
This alloy is generally used in the medical industry for dental implants but has found uses in the Aerospace industry due to its high wear and corrosion resistance.
316L Stainless Steel
This grade of stainless steel is one of the most widely used grades of steel, it has very high corrosion resistance and good mechanical properties. This metal is also known to produce one of the smoothest surface finishes amongst the powdered metals.
Inconel is a well-known superalloy being used in the Aerospace industry. It has very high temperature resistance and can maintain its mechanical properties in extreme environments. It has high corrosion and creep resistance making it ideal for engine components. It is also difficult to machine this material using subtractive techniques, making it ideal for AM.
Used mainly for prototyping purposes but there has been a growing trend for manufacturing production components. It is cheaper than Titanium and can be post processed and machined without needing advanced machining techniques like those required for Inconel and Titanium. Special alloys like Scalmalloy are being developed specifically for AM.
Barriers to adoption
Despite the many advantages of Additive Manufacturing and the ever-growing list of parts that can be made with Additive Manufacturing there is still a large barrier to entry that limits many smaller companies from adopting the technologies required to produce flight-ready Aerospace components. The key reason is the cost of the machinery. Machines capable of producing Additive parts that are acceptable for Aerospace applications are expensive, not to mention the cost of the metal powder which is more expensive than normal metal billets.
The vast majority of AM components will need to be post processed on traditional machines but the amount of machining is limited to surface finishing and creating high tolerance features. This means that companies cannot get away with just a metal printer on their shop floor; a CNC machine will always be needed.
What’s next for Additive Manufacturing in Aerospace & Space?
The continuous advancement of Additive Manufacturing technology seems to be happening at an ever-increasing pace. There are various new start-ups bringing metal printing to a whole new tier of businesses, effectively democratising access to metal printing. This expanded access to the technology will further drive its adoption, which will in turn continue lowering the barriers to entry. A wider usage of the technology will result in better characterisation of the various materials and will allow the development of industry standards for these materials and techniques.
One of the most important advantages of Additive Manufacturing is its ability to simplify complex designs. Engines can have their total part count drastically reduced by printing homogeneous components. Not only does this reduce possible points of failure in an engine but it has the effect of significantly reducing overall weight, cost and manufacturing time. This is truly the next leap in manufacturing technology.
Embedded electronics and sensors within components are also achievable with companies like Boston Dynamics exploring the possibilities of printing components that already have channels for hydraulic fluid, electrical conduits and embedded sensors printed in place. This opens the door for parts that are completely manufactured in one step without any assembly required.
Launching large, delicate structures into space is always expensive, risky and sometimes impossible. However, if these parts can be manufactured in space then raw materials can be launched into orbit without worrying about space limitations or damaging delicate equipment. In-situ manufacture in space will allow the creation of huge structures that will pave the way for the eventual colonisation of the solar system in the next century.