Metal powder atomization for additive manufacturing

The powder atomization plant includes the induction furnace, the atomization unit and the cyclones. It is designed for the complete process to take place in an inert atmosphere. This enables temperature measurements, sample taking and material feeding to be performed without causing any atmospheric variations. The melting procedure starts when the input material is melted down in the furnace under vacuum atmosphere in the vessel. After melt treatment and reaching the superheating temperature, the liquid metal is poured to the pre-heated tundish. The atomizing nozzle is arranged below the tundish. The metal runs through the so called closed-coupled-nozzle, undergoing atomization in the atomization tower by means of inert gas. From there the resulting powder is conveyed to the cyclone unit, separated from the inert gas and collected in containers. Then the metal powder is screened into the target fractions for different markets.

In our new developed continuous production prozess, two large vacuum induction melting (VIM) furnaces continuously hold liquid melt, which is atomized successively through the nozzle. The nozzles can be exchanged during operation. Melting is run under vacuum like in the conventional VIGA process. In addition to the VIM route, where pure scrap is used as feedstock, the new process can also work with an existing liquid metal supply. A metallurgical route with basic scrap as feedstock is also possible.

By the operation of the anti-satellite system as a modular unit of the powder atomization plant, the satellite formation is significantly reduced. Satellites are small particles that stick to a larger particles thus forming an undesired particle defect. With the anti-satellite technology, an external gas flow is generated and injected into the atomizing tower from above. This creates a secondary gas flow from the top down in the process chamber, which suppresses the rising of fine particles in the process chamber. Without using the anti-satellite system fine solidified particles would be picked up by a recirculation stream in the dead area between the wall of the tower and the spray cone. The rising particles would be pulled into the atomization zone, crating satellites by hitting larger solidifying particles.

SMS group offers a hot gas system for their VIGA plant as an option. The hot gas system enables the atomization to be done with pre-heated inert gas. In case of argon the gas can be heated up to 450 °C by the hot gas system. Atomizing with higher gas temperatures brings several benefits in terms of the process and the product quality. By using hot gas the yield of fine particle fractions is increased. The preheated gas lowers the cooling rate of the particles, extending the time for the particles to break down into finer particles. Furthermore the process stability is increased with the hot gas system by lowering the difference in temperature between gas and melt.