Additive Manufacturing
AM, sometimes referred to as 3D printing, offers a vast improvement in manufacturing technology with its ability to produce complex designs on demand. These designs include very intricate internal channels and elaborate lattices, providing superior strength to the product and greater single-piece functionality, while substantially reducing weight as compared to traditional subtractive manufacturing methods.
Although traditional subtractive manufacturing processes such as CNC machining may be more suited to higher volumes and can be less expensive per part than AM, they work by removing material from a larger block to achieve the final desired form. These traditional processes, therefore, can lead to a significant waste of material and, importantly, they lack key and revolutionary abilities that AM can offer such as the creation of hollow and porous products, the incorporation of two or more additional materials, and fast prototyping.
Particle Size
Particle Shape
Density
Bulk density of a powder is heavily influenced by physical properties of the particles but also by the quantity of air entrained within the bed. Bulk density can be important in establishing material specifications and complements other assessments of powder flowability and bed formation.
Envelope density is based on the geometric volume of a sample and is useful for evaluating the end-product as it can accurately measure intricate and irregular volumes. When combined with true density measurements, porosity can be quickly and easily determined.
Porosity
For example, artificial bone implants need to match the surrounding bone porosities or porosity may simply be specified in the design to achieve lightweight products with the desired mechanical strength.
Mercury intrusion is a proven technique for quantifying porosity characteristics of powders and formed product. This technique is based on the intrusion of mercury into a porous structure under stringently controlled pressures.
As well as offering speed, accuracy, and a wide measurement range, mercury porosimetry enables numerous properties to be assessed such as pore size distribution, total pore volume, total pore surface area, median pore diameter, bulk and skeletal density, and percentage porosity.
Surface Area
The specific surface area of a powdered material can be measured by gas adsorption using the well-established BET method. For this technique (typically) nitrogen gas is physisorbed at cryogenic temperatures and the quantity needed to form a monolayer on the surface determined by applying the BET method to the collected isotherm data.
Powder Flow
Whether sintering powder densely packed into a mold or localized fusing layer-by-layer, the process will be sensitive to the flow properties and bulk behavior of the feedstock. Poor flow properties can lead to inconsistent density and non-uniform layering, fouling, blockages, and downtime – all of which result in low productivity and poor product quality.
Traditional techniques for quantifying flow, such as Angle of Repose and Hall Flow measurements are often acknowledged as being too insensitive to identify subtle differences between powders that can affect performance in an AM machine.
Powder rheology provides a comprehensive, multivariate assessment of dynamic, bulk and shear characteristics of feedstocks generating process relevant data that can be used to define materials suited to a process supporting process optimization and lifecycle management of powders.
Environmental Stability
Surface Topography
SEM can also be used to analyze the raw material powders used in AM, for example, to detect agglomerations, assess surface roughness, and quantify the ratio of spherical to irregular shaped particles; all of which impact powder flowability and sintering.
Additional Resources
https://www.materialstoday.com/measuring-the-critical-attributes-of-am-powders