In recent years, the world of aerospace — including commercial and satellite, spacecraft, unmanned aerial vehicles, and unmanned aerial vehicles (UAVs) — has undergone some dramatic changes. More and more companies are joining the space race, and many of them need innovative manufacturing technologies.
The ability of laser processing to increase productivity and keep costs low may play a key role in achieving this response in the aerospace industry. Laser processing, which involves cutting, welding, peening, and drilling, has become an integral part of aerospace manufacturing.
Lasers are used, for example, to make flaps for aircraft wings, wing fasteners, jet engine parts, and seat components, but also to repair turbines, clean or remove paint from parts, and prepare component surfaces for further processing. In recent years, laser additive manufacturing (AM) has also become increasingly popular in the field of space flight. In addition, the market wants to improve the traceability of aerospace components, and the demand for laser marking is also increasing.
Laser cutting and welding
Laser cutting is a fast, cost-effective, and accurate process that can be used to meet the demanding manufacturing requirements of the aerospace industry. Compared with traditional processing, laser cutting has the advantages of high precision, less material waste, fast processing speed, low cost and less equipment maintenance. In addition, it maximizes productivity because it makes any necessary changes to machining quickly and easily. Lasers can be used to produce wing fastener parts, fixture parts, end effector parts, tooling parts, etc. It is equally suitable for small components such as grafted oil gaskets and titanium bleed air manifolds, as well as larger components such as exhaust cones. It can machine a variety of aerospace materials, including aluminum, Hastelloy (nickel that has been alloyed with elements such as molybdenum and chromium), Inconel, Nitinol, Nitinol, stainless steel, tantalum, and titanium. Laser welding is also used in aerospace as an alternative to traditional joining methods such as adhesive bonding and mechanical fastening. For example, the use of laser-welded lightweight aluminum alloys and carbon fiber reinforced polymer (CFRP) in aircraft manufacturing is gaining prominence and is being used to replace riveting wherever possible. Technologies such as laser weaving welding have also been successful in fuel tank connection, improving connection efficiency and strength, reducing rework and saving a lot of costs. Other welding successes in aerospace include the attachment of cast cores of turbine blades to cover plates and the creation of new lightweight wing flaps that increase laminar flow control, minimize drag and optimize fuel efficiency. Laser welding has the potential to save costs, reduce the weight of components and improve the quality of welding compared to traditional methods, and several manufacturers in the market are even beginning to consider laser welding to produce fuselage parts.
Laser cleaning
Manufacturers in the aerospace field use laser cleaning to remove layers from metal and composite surfaces in preparation for processing, to remove coatings or corrosion, and to remove paint from large components or entire aircraft before repainting. During the cleaning process, the laser is absorbed and evaporated by the metal surface, thus realizing the ablation of the surface material, while having almost no effect on the inner material, and no incidental thermal damage to the component. Kilowatt-class pulsed fiber lasers are particularly suitable for rapid laser cleaning-they can clean a wide range of materials, including ceramics, composites, metals and plastics, with high efficiency and precision. In recent years, the use of composite materials in aircraft has increased, so has the need to attach metal to composite materials. In aerospace manufacturing, adhesives can be used to join these two different materials, and in order to establish a strong bond, both surfaces must be carefully prepared for machining before the adhesive is used. Laser cleaning is an ideal option because it creates a very tightly controlled, reproducible surface effect that enables consistent, predictable bonding. Traditionally, this would be done through destructive blasting techniques or the application of several chemicals. However, laser cleaning now offers a one-step approach that is not only more cost-effective and productive, but also has less environmental impact because there are no toxic chemicals or blasting materials required. The impact of laser cleaning on components is also much milder than traditional methods. Laser cleaning of metal and composite aircraft parts is also more advantageous than chemical stripping or blasting techniques when it comes to paint stripping. During its lifetime, an aircraft may be repainted 4-5 times, and it may take a week or more to remove the paint from the entire aircraft using conventional techniques. Laser cleaning, by contrast, can reduce this time to 3-4 days, depending on the size of the aircraft, and it also makes it easier for workers to access parts. In addition, when used for paint removal rather than chemical stripping or blasting, laser cleaning provides significant cost savings – thousands of pounds per aircraft, as hazardous waste is reduced by around 90% or more, reducing material handling requirements.
Laser shot peening/laser shock peening
Internal stresses in metal components can lead to metal fatigue failure of aircraft components, such as jet engine fan blades, which can cause damage or injury. This can be mitigated by a technique known as laser peening. In this process, laser pulses are directed into an area of high stress concentration, and each pulse ignites a tiny plasma explosion between the surface of the component and the water layer sprayed on top. The water layer limits the explosion, which causes the shock wave to penetrate the assembly and create compressive residual stress as its propagation area expands. These stresses improve the cracking potential and other forms of fatigue resistance of the metal. Compared with the traditional process, laser strengthening can prolong the service life of metal parts by 10-15 times. Laser shot peening (LSP) has been widely used in aerospace industry. For example, LSP Technologies and Airbus have jointly developed a portable laser hardening system that was recently tested and evaluated at Airbus' maintenance and repair facility in Toulouse, France. The Leopard laser peening system will extend fatigue life by inhibiting crack initiation, propagation caused by cyclic vibrational stress. The flexibility of fiber optic beam delivery and custom tools allow the system to laser areas that are difficult for aircraft to reach. According to the partners, the system is a breakthrough in laser hardening technology that will advance its use, including extending the life of jet engine blades and more.
Laser drilling
Modern aero-engines have about half a million holes, about 100 times as many as engines built in the 1980s. At the same time, aircraft manufacturers are producing more and more other parts with a lot of drilling for riveting and screwing. Therefore, laser drilling has great market potential in the aviation field, because it provides a precise, repeatable, fast and cost-effective process. For example, new high-power femtosecond laser systems are being developed for efficient and precise micro-drilling in large titanium HLFC (Hybrid Laminar Flow Control) panels that will be mounted on wing or tail stabilizers. These panels draw air through small holes, which reduces frictional resistance and reduces fuel consumption. Because laser drilling is contact-free, the material being machined does not need to be fixed in the same way as with conventional tools. Another advantage of being contact-free is that there is no tool wear, which represents a particular advantage in the operation of drilling CFRP assemblies. Due to its hardness, CFRP components can cause significant wear on conventional tools. Laser drilling can also be done at very high speeds, so excessive damage from heat does not harm the material being processed.
Additive manufacturing
Laser additive manufacturing (AM) has also seen rapid growth in the aerospace industry. In this technique, a laser melts successive layers of powder to build the shape. A California-based rocket company even recently ordered two 12-laser beam 3D printers to make its space missions more economical and efficient by making lighter, faster and stronger space components. While many projects are still in the testing phase, laser additive manufacturing has been used successfully on two Mars missions. NASA's Curiosity rover, which landed in August 2012, was the first mission to carry a 3D-printed part to Mars. This is the ceramic component within the Mars Sample Analysis (SAM) instrument, part of an ongoing test program to investigate the reliability of additive manufacturing techniques. Meanwhile, NASA's Perseverance probe, which landed on Mars in February 2021, contains 11 metal parts made with laser additives. Five of the components are in Perseverance's Planetary Instrument for X-ray Petrochemistry (PIXL), which is looking for signs of microbial fossil life on Mars. These components need to be so light that traditional forging, molding and cutting techniques cannot be produced. NASA has also been experimenting with the use of laser additives to make rocket parts. In one study, the combustion chamber of a rocket engine was made of a copper alloy. This continued evolution of laser additive manufacturing has resulted in the component being manufactured at approximately half the cost and in one-sixth the time required for conventional machining, joining, and assembly. Because the copper alloys used are highly reflective to infrared lasers, NASA is now investigating how green or blue lasers can improve efficiency and productivity. Although the application of additive manufacturing in aerospace is still in its early stages, it is expected to grow in the next 20 years.
Laser texturing
Laser texturing is also a very new application in the aerospace industry. In this process, ultrafast lasers are used to create micro-nanostructures on the surface of aircraft through a technique called direct laser interference pattern (DLIP), which is used to create a natural "lotus effect" that creates nanostructures that help prevent surface contamination and ice accumulation on aircraft. Innovative optics splits a powerful, ultrafast laser pulse into several partial beams, which are then combined on the surface being machined. When viewed under a microscope, the resulting microstructure resembles a microscopic "hall" composed of "pillars" or ripples. The distance between the "pillars" is roughly between 150 nm and 30 μm — this structure means that the water droplets no longer wet the surface and stick to it because they don't have enough grip on the surface. The benefits of this material for aircraft include: increased rejection of water, ice and insects. These can stick to the surface of the aircraft and increase the ability of the aircraft to resist wind, thus increasing fuel consumption. Applying this laser texture will reduce the need for toxic chemical treatments currently applied to aircraft surfaces to avoid icing. It is known to age and break easily over time. In addition, laser structures produced with the DLIP method can last for years and cause no environmental problems.
Laser detection and stress control
In addition to the above functions, the combination of laser and ultrasound can be used for the detection and stress control of complex metal structures. High-energy pulse laser is used to act on the surface of the measured object, and the local temperature of the surface changes, which causes the thermal expansion of the surface layer of the measured object, and excites ultrasonic waves, which will carry useful information of the surface and interior of the material. The ultrasonic signal is received by the detector, and the data processing and analysis are carried out to judge whether the measured object has defects. In addition, because the laser ultrasound has the characteristics of high time resolution and spatial resolution, and can generate ultrasonic waves with rich waveforms and wide frequency band, the laser ultrasound can remove all tensile stress at any designated part of the part through switching and adjusting laser excitation parameters, and form a compressive stress strengthening layer with a certain thickness under the condition of not damaging the surface integrity and not heating up. At that same time, the stress value can be adjust and controlled to the range require by the design, and the anti-fatigue and anti-cracking performances of local positions can be obviously optimize.
