Aerospace parts require materials with certain critical properties like high strength-to-weight ratios, that can function effectively in exceptionally high temperatures. The aerospace industry always demands cutting edge technology, and is now benefitting from advances in additive manufacturing using selective laser melting processes.

Additive manufacturing, commonly known as 3D metal printing, allows for the manufacture of complex shapes from light metals with high mechanical strength. This unique material combination yields parts with a high strength to weight ratio along with good corrosion and fatigue resistance.

One of the most popular powder-based materials is the titanium alloy Ti-6Al-4V, which has found its way into both aerospace and medical applications. Titanium is already widely used in aircraft manufacture to prevent fatigue cracks or in structural parts like the frames of cockpit windows. Applications of titanium alloys are even more widely used in military aircraft, helicopters and spacecraft due to their high performance and unique properties, particularly weight reduction.

Selective laser melting machines are regarded as the most versatile additive manufacturing technology because the system can process a wide spectrum of materials that include aluminium, titanium, iron, nickel, cobalt, copper-based alloys and their composites. Choosing the appropriate material depends on a number of factors that essentially depend on the part requirements and process parameters.

For example, optimised parameters that meet the minimum mechanical property requirements of a part can be achieved by focusing on optimising the machine parameters to build a fully dense part. However, this has the effect of lengthening the build time. By focusing on optimising the heat cycles, the build time will be quicker, though this will depend not just on the machine parameters but on the material being used.

In the manufacture of titanium alloys in 3D metal printing machines, the formation phase and mechanical properties can be controlled by process parameter optimisation. In general, in the manufacture of complex parts, laser power control is extremely desirable, and it is in this area – of exploring parameter optimisation – that the technology manufacturer SLM Solutions is working with a number of companies in the aerospace sector.

SLM Solutions machines equipped with multi-beam laser systems and bi-directional powder applications offer the advantage of shortening production time – an attractive option recognised by Rolls Royce which recently added an SLM500 quad laser machines to help develop its additive manufacturing capability for aerospace components. In November 2019, BEAMIT, one of the largest additive manufacturing suppliers in Europe, also acquired an SLM500, adding to its existing bank of eight selective laser melting machines to specifically develop high-speed parameters using the aluminium alloys Al2024X and Al6061.

Typology optimisation is defined as a mathematical method that optimises material layout within a given design space, with load specifications, boundary constraints and conditions, with the goal of maximising the performance of the system. Some selective laser melting machines provide open parameters so that different applications can be adjusted to meet specific requirements. With laser systems, the higher the laser power is, the faster the melting time is, a function of multi-laser systems, but as the build comprises a layering process, careful management of the laser beam power is needed to avoid porosity or fusion defects in the component. Lowering the beam energy will take longer to process the component, but may be necessary to generate parts with very small geometric features. Process optimisation plays a key role in securing the benefits of 3D printed metal components with small, accurate features; internal channels; lattices and similar features that reduce overall weight; honeycomb structures; and complex heat exchange structures.

Early in 2019 a UK-based spaceflight company, Orbex, used an SLM800 large-format metal additive manufacturing system featuring a 260mm x 500mm powder bed that can build parts 800mm tall. Unique parameters optimised the particular geometry required, allowing the engine to be built in a single piece using a special nickel alloy creating a structure 30% lighter and 20% more efficient than any other launch vehicle in its category.

Using biomimetic (founded in nature) design principles, CellCore – a design company in Germany – incorporated a lattice structure in its development of a monolithic thrust chamber for the aerospace industry. The lattice structure both improved cooling and increased stability, as well as achieving a reduction in weight. CellCore chose to use IN718, a precipitation hardening nickel-chromium alloy with exceptional tensile, fatigue, creep and breaking strength up to 700 degrees Celsius suitable for a rocket propulsion engine.

Recently, Honeywell Aerospace, a user of additive manufacturing technologies with expertise across various platforms and applications, has commenced working with SLM Solutions in qualification of aluminium builds using increased layer thicknesses of 60 to 90 microns. Honeywell will begin with the standard set of aluminium parameters supplied by SLM Solutions, to further develop advanced parameter sets for quad-laser systems, with the aim of applying them in serial-production.

Additive manufacturing is advancing at a rapid pace, drawn on by the aerospace and automotive sectors. SLM Solutions has not just focused on process parameters to achieve more effective builds, but has focused on the development of selective laser melting technology itself. In 2017 a partnership between Divergent and SLM Solutions saw the creation of multi-laser machines that offer all the benefits of 3D metal printing with faster and improved manufacturing capability that will be affordable and provide greater efficiency.

At the Formnext 2019 additive manufacturing technology exhitibiton in Germany, Divergent displayed a suspension and chassis structure built using the whole suite of SLM Solutions laser machines. The next step is to purchase five pre-production machines from SLM Solutions to integrate into the Divergent facility in Los Angeles, California, and then to accelerate development and increase time to market. As envisaged by Divergent CEO Kevin Czinger, the company plans to acquire 20 of SLM Solutions’s next-generation systems to be able to roll-out product on demand.

Selective laser melting is finding its way into the aerospace industry through innovative and exciting developments, while seemingly charging its way into the automotive industry at the same time. Fortunately, one industry group will leverage from the other, such is the power of additive manufacturing using selective laser melting.