A researcher at the Council for Scientific and Industrial Research (CSIR) is busy working on what is called “thermal stress management” for metal parts produced using additive manufacturing (AM – more popularly known as 3D printing). The CSIR hosts and operates one of the biggest, if not still the biggest, AM machine in the world, designated Aeroswift.
The form of AM used in the Aeroswift is called powder bed fusion-selective laser melting. That is, powder is laid down and then melted by a laser, the part being built up, layer by layer.
“With additive manufacturing, we start with nothing,” pointed out CSIR Materials Engineering MSc candidate Londiwe Motibane. “We build what we want, layer by layer.”
The process involves high temperatures and these can cause defects, most seriously cracking or de-lamInation, in metal parts while they are being made. This is what is meant by thermal stress. Lesser defects can be dealt with by “post-processing”, but this procedure cannot remedy cracks and de-lamination.
To reduce the incidence of this problem, Aeroswift pre-heats the metal powder it uses, up to 200 °C. Motibane is looking at using even higher temperatures, but the problem is that pre-heating can affect the qualities of the metals being used — for example, it could increase brittleness. She was working to avoid this.
AM has many advantages. It allows the manufacture of complex geometries which cannot be done with conventional (or “subtractive”) manufacturing. It can allow a faster manufacturing process. And it results in less waste, thereby reducing costs.
The Aeroswift machine is a “process developmental platform”, she explained. It was built from the ground up in South Africa, using a mix of commercial and locally-developed components. It was developed jointly with private-sector aerospace company Aerosud and funded by the then Department of Science and Technology (now the Department of Science and Innovation). It can manufacture parts with dimensions of up to 600 mm x 600 mm x 2 000 mm.
Aeroswift is part of the country’s National Beneficiation Strategy. It serves to support South Africa’s emerging high value component manufacturing capability and the realisation of the Fourth Industrial Revolution in the country. South Africa has another major AM research and development centre, in the Free State, which is focused on biomedical applications.
Motibane’s presentation was part of an event by the CSIR to mark Women’s Month, by highlighting some of the work being done by its women researchers.