Additive Manufacturing (AM) offers designers creative freedom that opens up new doors in metal production, while its cost efficiency provides greater value to end customers than conventional subtractive and formative methods.
At present, am materials in metals is mostly employed for prototyping and limited production purposes, though its usage is quickly expanding into volume industrial production as well as high-end customized products.
1. Particle Size
Beyond chemistry, metal AM powders must also possess physical characteristics necessary to excel in an AM process. Key bulk properties for success in additive manufacturing processes are packing density and flowability – consistent packing density is important to maintaining consistent quality levels with minimal flaw levels in components, while reliable flowability is necessary in powder bed fusion and directed energy deposition processes.
Attributes such as particle size distribution and morphology play a large part in determining a material’s ability to flow, such as laser diffraction are key tools for characterising AM metal powders’ fluidity characteristics quickly, precisely and with high resolution measurements. Automated analytical imaging provides additional advantages with its shape classification feature which gives statistically relevant data sets about particles’ characteristics such as sphericity or elongation.
This allows for a comprehensive investigation of how powder morphology impacts powder behaviour, such as flowability and packing characteristics. As an example, in laser powder bed fusion an AlSi alloy was tested using this approach to demonstrate the influence of Al2O3 (Alumina oxide) on flowability and packing characteristics.
2. Density
Metal AM has evolved beyond prototyping into manufacturing, placing more importance on powder properties. Matching the AM process and choosing an alloy with uniform distribution across layers are keys, but so too is particle morphology and flowability.
Spherical powder particles tend to pack more efficiently than irregular ones, creating greater bulk density and providing greater freedom of movement. This can help improve surface finish quality while decreasing secondary processing needs; their narrow particle size distribution and spherical shape also facilitate simple handling, while minimising segregation during transport and storage.
Dynamic powder flow testing provides an objective way to assess powder characteristics while in motion and provides an extremely sensitive interpretation of how they affect AM machine performance. A recent study using laser powder bed fusion (L-PBF), for instance, used dynamic flow tests of two aluminium alloy powders with similar chemical composition and grade to evaluate their performance on an L-PBF machine.
3. Thermal Conductivity
Metal AM processing techniques are continually transforming, so powder producers must adapt accordingly. One effective approach would be to develop a consistent high-quality powder production process which produces extra clean and spherical powder every batch, giving producers flexibility in selecting an optimal powder based on each process’s individual characteristics.
This understanding will be especially relevant when developing standards for metal AM. These regulations will necessitate an enhanced knowledge of how powders flow, melt, fuse and solidify together during AM processing for more accurate models of performance such as apparent thermal conductivity.
Studies were performed to compare a typical atomized powder with the new and improved Toyo aluminum alloy powder for AM. The results demonstrated that the Toyo sample had more uniform particle morphology, size distribution, and surface oxidation levels compared with its counterpart; this allowed more efficient packing between particles as well as creating a cohesive lattice structure within the powder for more efficient packing of particles within it for lower contact resistance and higher effective thermal conductivity.
4. Strength
Metal AM has become an increasingly popular technique for quickly producing prototype and limited production parts. The process entails localized laser- or electron beam fusion bonding of multiple thin layers of aluminum alloy powders into an assembled part.
Quality atomized aluminum plays an essential role in mechanical properties like strength and ductility. For optimal results, it must be free from impurities like iron (Fe) and silicon (Si).
Sieve analysis or laser diffraction are popular methods of measuring this purity; however, neither approach reveals how atomized aluminum particles are distributed within their granular medium – an essential aspect that impacts powder spreadability when manufacturing aluminum powder using AM processes.
Flow characteristics of powdered materials can also be gauged using Hausner ratios or tap density (or “fluff density”)23. High tap densities are necessary to achieve quality recoating and melt pool continuity while Hausner ratios above 1.5 indicate favorable flow properties.
