AS ISO ASTM 52907:2021 – Additive manufacturing- Feed stock materials – Methods to characterize metal powders.
4.7 Morphology
Powder morphology is strongly linked to the process used to produce the powder: as stated and illustrated in EN 1274. Particle morphology shall be described using the vocabulary defined in ISO 3252 or ASTM B243 (see Annex A for examples).
NOTE 1 Powder morphology is considered to be a useful property br comparing and controlling diFferent lots of powders over time,
In addition, qualitative image comparison and/or quantitative criteria can be subjected to a prior customer/supplier agreement e.g. a quantitative shape factor defined as the maximum Feret’s diameter divided by minimum Feret’s diameter, etc.
NOTE 2 The preferred method using SEM Is secondary electron imaging.
Quantitative values shall be determined by automatic or semi-automatic methods with the number of analysed particles being included in the report.
NOTE 3 A standard method for spreadahillty is under development within ISO/TC 261 and ASTM F 42. Information on spreadability can be found in ASTM 07891.
4.8 Flowability
Powder Ilowahillty isa function of multiple factors, particularly the following:
— powder size distribution,
— cohesive strength by adsorbed water on the particles’ surfaces from condensed. i.e. presence of agglomerating forces such as capillary bridges formed by adsorbed water on particles’ surfaces from condensed atmospheric vapour, electromagnetic forces in ferromagnetic materials, or Van der Waals bonds.
— inter-particles friction, affected mostly by particles surface roughness’ and morphology of the particle surfaces.
As moisture content Is a key factor in determining flowability. where drying is required or prohibited by the customer/supplier agreement or the selected flowability standard method (see list below), this shall be performed in accordance with the conditions specified in a standard operating procedure.
Flowability should be determined using one of the methods specified below:
— ISO 4490 or ASTM B213 (results reported In s/SO g).
— ASTM 8964 using a Carney funnel (results reported in s/iSO g or s/200 g).
— ISO 13517 using a Gustavsson funnel (results reported in s/50 g),
— ISO 4324,
The flowability test report shall include the initial powder condition, i.e. stationary or moving powder.
NOTE I Flowability measured by the aforementioned standards is not necessarily correlated to spreadability.
NOTE 2 The requirement of a powder for additive manufacturing to be able to flow Is relevant with regard to AM-systems that use piping and/or nozzle to deliver powder, and to mechanical devices to create thin layers necessary to control the manufacturing process. Other techniques, for example rotating cylinder, can be used to fulfil both requirements, whereas the funnel techniques are primarily able to assess powder flowability with regard to piping and/or nozzle requirements.
NOTE 3 Various indices e.g. Index describing cohesive forces between powder particles, for instance avalanche angles) and ratios (e.g. Hausner ratio) can be calculated to evaluate the I lowability of the non-freely flowing powder. Those Indices and ratios cannot replace the flowability measurement.
4.9 Contamination
Contamination of the powder lot shall be determined by examining a representative sample of the powder. Powder sampling shall be performed according to 4.3. Powder testing shall be performed by examining at least 625 mm2 (25 mm 25 mm) of a closely packed layer of powder at 20*. or by an alternative testing practice, subjected to a prior customer/supplier agreement. As agreed by customer/supplier, no foreign material containing morphology or chemistry outside of specification shall be visible under these test conditions.
NOTE In addition, EDX mapping can be used to detect cross contamination with another metallic powder.
4,10 Packaging, handling and storage
4.10.1 General
Powder contamination from any form of foreign material (e.g. desiccant bag) shall be avoided during handling, packaging and storage.
4.10.2 Packaging and handling
The powder should be climatized (temperature) before introduced to the machine.
It required by the customer, powder containers can be tilled by inert gas (argon or nitrogen) to provide protective atmosphere. Powder traceability shall be secured. The label shall include the following:
— the name and the address of the supplier,
— the reference of powder lot,
— quantity of the packaging unit,
— the packaging description, including the packaging, the nature of the shielding gas and the desiccant hag if relevant.
— the product description, including standard and/or trade/common name.
— the safety notice according to local regulation, which can include pictogram(s).