WOLFTEN’s Spherical Powders
Spherical powders, use and applications
Spherical powders are commonly used in 3D printing and metal injection molding (MIM) Metal injection makes a homogeneous mixture with binders, which allows a high dimensional accuracy, however the properties of the end product are determined by both – the characteristics of the metal powder and the process of 3D printing. Size distribution and morphology have a great influence on accurate reproducibility of components. Other important factors are density, compressibility, chemical composition and sintering ability.
One of the key aspects of 3D printing using metal powders is that the particles are spherical. Proper particle size distribution is important, because is allows them to be well packed, resulting in a dense product with desired mechanical characteristics.
piping in heat exchangers
liquid fuel rockets
elements of hydraulic systems
hip and knee implants
Production methods of spherical metal powders
The process starts with feedstock alloy is melted in a vacuum furnace. Why vacuum? Because it allows monitoring the amount of interstitial elements in the melt. The furnace is mounted above the atomizer to allow direct discharge of the material into the chamber. Then, free falling melt is being sprayed with high pressure nitrogen or argon. That allows is to crystallize into spherical powder particles and protects against oxidation and contamination. To some extent, the particle size can be altered by changing the amount of gas sprayed onto the melt. In case of highly reactive materials, such as Ti6Al4V, there is a high risk of contamination coming from the atmosphere or crucibles. That is why, such alloys are atomized using rods. Alloy rod is put through a induction rod, which melts it. With this method, the material is not in contact with crucibles. This method is called Electrode Induction Gas Atomization (EIGA)
With this method, the material enters the atomization chamber in form of wire, which is then melted using plasma torches and immediately sprayed with inert gas. This results in highly spherical powder particles and fine size distribution (0-200 μm). A slight modification of this method is Plasma Rotating Electrode Process (PREP), which uses rods instead of wire. Fast rotating rod enters the chamber and is melted by the plasma torches in inert gas atmosphere. Discharged melt then solidifies before reaching the chamber’s walls. With this method one can achieve even finer particles (0-100 μm). Titanium alloy spherical powders are made using this methodology.