Siberian Federal University: Russian Researchers on Strategy of Additive Manufacturing for Large Parts from Light Alloys
Scientists from Siberian Federal University within Priority 2030 program develop an additive technology for Digital Multi-Arc Deposition (DMAD) to produce geometrically complex parts by controlled build-up of aluminium alloy layers.
Additive technologies are the hottest trend all over the world, since they facilitate the manufacture of metal alloys products for the aerospace, shipbuilding, and automotive industries. The production of complex-shaped parts using a three-dimensional computer model and sequential metal deposition can significantly reduce costs. In contrast to traditional manufacturing, when a significant part of the metal is wasted during machining, additive manufacturing is resource-saving. What is more, additive technologies can be used in space orbit within the Made in Space concept, which implies manufacturing products for orbital stations and planetary bases.
“Additive technologies that use metal wire rather than powder are gaining popularity. Now, large-sized products from aluminium alloys are made in small batches, mainly from solid billets or large-sized forgings using machining. This is irrational, since the significant part of a work piece up to 60-80% is simply cut off. It is possible to reduce material waste by several times using the technology of direct energy and material supply — the so-called wire and arc additive manufacturing (WAAM). There are three variants of the layout scheme of equipment for this technology: based on robots, and console, portal or computerized machine tools (CNC) with parallel kinematics. Unlike powder technology, this one is best suited for space conditions,” — noted Nikolay Dovzhenko, Doctor of Engineering, professor at the Department of Mechanical Engineering, Polytechnic School, SibFU.
As explained by the researchers, problems that occur during additive manufacturing of aluminium alloy products, such as porosity or poor mechanical properties, can be overcome using WAAM with controlled energy costs. It is also advantageous to use adapted alloys, including crossover (for example, from space debris components) or functionality graded ones. Accordingly, the WAAM technology strives to reduce heat input and increase the rate of layer-by-layer metal deposition — it becomes multi-electrode and multi-arc.
“SibFU scientists solve the fundamental problems of DMAD additive technology. The technology is based on three-dimensional modelling of a future product. New equipment and a programmable algorithm are being created, which helps to gradually build up layers and control metal transfer. This makes it possible to reduce the heat supply to the formed layer of a product and maintain a high rate of deposition,” added Nikolay Dovzhenko.
A feature of the DMAD technology is the use of two or more electrode wires, including wires from different alloys. It helps to create a combined arc from transferred and non-transferred arcs. It is non-transferred arcs between the electrodes that help to form the volume of the transferred metal. It allows to significantly increase the efficiency of the process by redirecting most of the heat to the supplied electrode material and by reducing the heat input to the formed elements of the product.
The first experiments conducted at the Polytechnic School showed that the technology is able to provide a two- or even three-fold increase in productivity compared to the traditional method using a single wire. The DMAD technology significantly increases the deposition rate — a part with a complex geometry is formed faster due to the intensive build-up of the metal. However, in comparison with the single-wire technology, the process of forming and transferring molten metal droplets is more complex. The point is in the modes of supplying two or more wires, including wires of different chemical composition. It is necessary to optimize these modes for the further development of this technology and its industrial application.
SibFU scientists say that the university has already developed highly efficient processes to manufacture electrode wires from aluminium alloys (including new ones sparingly alloyed with scandium) by casting into a magnetic mold and a combined continuous casting-extrolling process.