Hardus Greyling of South Africa’s CSIR and Marius Vermeulen from Aerosud, talk about Aeroswift, an R&D project involving the development of one of the largest laser-based additive manufacturing (AM) machines in the world.
Through an R&D collaboration between aerospace company, Aerosud Innovation Centre (IC), and the Pretoria-based CSIR, Aeroswift was established to advance laser additive manufacturing technology in South Africa. “The official programme started in 2011 with funding from our Department of Science and Technology (DST) and the R&D partners,” begins Vermeulen.
“At the heart of the programme is to better beneficiate South Africa’s titanium resources, along with supporting an emerging high-value component manufacturing industry, locally and abroad,” he continues.
“We have been developing laser and additive manufacturing capabilities for many years at the CSIR,” adds Greyling. “We are currently commercialising direct energy deposition/laser metal deposition (DED/LMD) technology for weld repair applications in industry, including work for our local power utility, ESKOM. This system is designed to be mobile, so that repairs can be undertaken onsite such as, for instance, repairing large power station components,” he reveals.
Aerosud IC, on the other hand, is key partner in the development of AHRLAC, an advanced, high performance, reconnaissance, light aircraft designed as a versatile and rugged, multi-role manned platform. “To achieve lowest possible weight and extended component life, AHRLAC was designed with additive manufacturing in mind and, with the Aeroswift powder bed fusion system we have developed, we have already started manufacturing commercial parts for the AHRLAC: the throttle grips, the engine condition lever grip and some titanium ducting components,” says Vermeulen.
Aeroswift, he continues, is an R&D laser additive manufacturing platform that also serves as a prototype. “Ultimately, we aim to design purpose-built LAM machines to suit target applications – and while we are currently focused on titanium, this is not a machine limitation,” he notes.
DED/LMD versus PBF
Direct energy deposition using a laser power source, explains Greyling, involves depositing layers of metal powder on a fusion path and immediately fusing the powder at the focal point of a laser beam. The DED laser output and powder deliver systems are carried by a robot or multi-axis manipulator around the build area and gas shielding is needed to prevent oxidation and porosity along the weld path. “In general, the process is also used with plasma and TIG welding systems as heat sources, with wire o en replacing powder as the material consumable,” he says.
In contrast, powder bed fusion technology involves scraping a thin (50 to 100 μm) layer of powder onto a flat surface before using the focused laser ‘spot’ to fuse the first image onto that layer. “This is done in a purpose-built chamber on the base of a table. The table is lowered between each layer so that another layer of powder can be spread and fused, until the part has been fully manufactured,” Vermeulen explains.
When the part has been completed, therefore, there is a full ‘bucket’ of metal powder with a fused part inside of it. The unfused powder is then shaken off and collected for reuse; while the part is cut off its base supports and sent for finishing.
Powder bed fusion is, in fact, a relatively old technology used originally for prototyping in the thermoplastics industry. When used with a laser on high value metals such as titanium, stainless steels, aluminium, nickel- or cobalt/chromium- alloys, the technology offers significant advantages compared to machining and other manufacturing methods: for light- weighting, for example, complex lattice structures can be easily manufactured using any of the layering techniques of additive manufacturing.
Comparing PBF and DED technologies, Vermeulen says that powder bed technology currently offers higher accuracy, better build resolution, and smoother surfaces. “We can make complex parts to high accuracies with our Aeroswift machine,” he says.
Compared to precision-machined parts, small amounts of distortion will affect overall part dimensions, but this can often be managed and/or compensated for at build design stage and a quick final machining stage is often required, especially in high-tolerance areas of the part, to ensure the accuracy and surface finish required.
The DED process generally results in thicker walls and lower layer resolution – of about 500 μm. It is ideal for simpler geometries but it is, typically, faster. “A key advantage, however, is that laser- based DED systems can be used to fuse additions onto existing components.
“If a complex feature needs to be attached to a basic cylindrical form, for example, then the cylinder can first be accurately machined and the complexity added using an DED/LMD system,” says Greyling, adding that this is known as hybrid manufacturing.
The Aeroswift PBF system
The Aeroswift machine was designed to use big powder volumes, up to 2 000×600×600 mm, typically for manufacturing large aerospace components or batches of smaller components in titanium. “Aerospace is a business involving low volume, high value and high integrity applications, and additive manufacturing is ideal for supplying this industry’s needs. The process is also being successfully used in the medical profession for implants such as titanium lower- and upper-jaw reconstruction,” says Vermeulen.
The Aeroswift machine itself was designed, developed and constructed from the ground up … read more.