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Materials Science in Additive Manufacturing Measuring the porosity of AM components

loading was 45% by volume. The components were prepared according to Archimedes’ principle and is often used with
using Autodesk Netfabb and the process parameters set on special measurement setups and manual measurement
the printer are listed in Table 5. Three print jobs were carried procedures. It is suitable for determining the apparent density
out in which all components of a design were produced. of a component and for determining its open porosity. As
After printing, green parts were available, which were first with gas pycnometry, gravimetric measurement according to
washed in isopropanol and analyzed for density and porosity. Archimedes’s principle also attempts to reduce the influence
One green part of each design was then subjected to a sintering of the air trapped in the components. Due to capillary effects
process. The sintering process was carried out in-house according and the larger molecules of water compared to helium, only
to a Lithoz specification. A sintering furnace (Nabertherm larger open pores in the surface layers of the components
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GmbH, Lilienthal, Germany) was used for sintering, which can be infiltrated. This means that the air still trapped in the
could automatically run the predefined sintering ramps. component pores leads to buoyancy, which in turn influences
the density measurement. The measured density is generally
3.2. Density and porosity measurement lower than that measured with gas pycnometry. However, the
measurements are highly dependent on the measurement
3.2.1. Gas pycnometry procedure and the human influence factor.
The gas pycnometer measurements were carried out using Due to a high degree of automation, the automated
an Ultrapyc 5000 gas pycnometer (Anton Paar GmbH, Graz, Density L measuring system used virtually eliminates
Austria) and helium. With this measurement, the true density the human influence factor during measurement.
of component samples (or the material density of powder) Furthermore, environmental parameters such as air
can almost be determined by volume. The open porosity of pressure and temperature are recorded through sensors
a sample can also be measured. For this purpose, a sample is and included in the density determination using integrated
placed in a primary container with a calibrated and precisely software and correlation equations. This enables the fully
known volume at atmospheric pressure. This container is automated measuring system to achieve a very high
then filled with helium up to a certain pressure P1. The gas measuring accuracy of up to 0.001 g/cm³.
is then expanded to a defined pressure P2 in another empty
expansion vessel with a known volume at atmospheric In this study, each sample was measured three times
pressure. The pycnometer measures the volume of displaced automatically. Except for the PA12 samples, all samples were
gas from the primary container at pressure P1 to the expansion measured in distilled water with 0.2% BYK-DYNWET 800
container up to pressure P2. The change in pressure enables N surfactant (BYK-Chemie GmbH, Wesel, Germany). The
the sample volume to be determined. The helium is forced PA12 samples were measured in ethanol ≥99.5% to avoid
into the pores and channels of the component by pressure and floating of the lightweight plastic components. Air pressure,
displaces the air normally contained therein. Only completely air temperature, and fluid temperature were recorded by
closed pores and pores with a diameter of <1 nm cannot be sensors for each measurement and considered in the density
flushed by the helium and continue to contain air, which leads calculation. Between the individual measurements, the
to measurement uncertainties in the density determination. samples were dried to evaporate the water trapped in the open
However, these are very low with helium gas pycnometry. The pores and thus not falsify the subsequent measurements.
density and porosity of the component can then be calculated
using the mass of the tested sample, which was determined 3.2.3. Micrograph analysis of cross-sections
using a balance before the analysis, and the determined sample For micrograph analyses, the component samples were
volume. For the investigations in this work, five consecutive separated, embedded in KEM 90 epoxy resin (ATM Qness
measurements were carried out for each component sample GmbH, Mammelzen, Germany), ground (grit 1200 to
in airtight containers to reduce the influence of measurement 4000), and polished with a diamond suspension (ATM
uncertainty. Qness). Two polished samples were created for each
printed component, one horizontal and one vertical to
3.2.2. Archimedes method the build direction. A BX51 light microscope (Olympus
The fully automated Density L system (Dimensionics GmbH, K.K., Shinjuku, Japan) was then used to generate the
Kessin, Germany) was used to measure density according to digital micrographs. For each micrograph, five measuring
Archimedes’ principle. During the measurement, the weight fields were examined at defined positions (Figure 5) with
and volume of a body in air and in a liquid are measured and a magnification of 33.5×. The component porosity was
the buoyancy force acting on the body immersed in the liquid then determined using the mean value of the individual
is equated with the weight of the amount of liquid displaced. measurement field porosities. In contrast to gas pycnometry
The method is also known as gravimetric density measurement and the Archimedes method, this method determines the

Volume 4 Issue 2 (2025) 8 doi: 10.36922/MSAM025090010