Page 48 - MSAM-4-2

Materials Science in Additive Manufacturing Measuring the porosity of AM components

Since the individual specimens were analyzed several Archimedean process can potentially also be used for the
times under identical conditions using the measurement preliminary inspection of green parts in two-stage AM
methods examined, the repeatability, that is, the ability of processes to quickly and relatively accurately obtain initial
the measurement methods to produce consistent results, information on part density and porosity, which can then
can be assessed. High repeatability is characterized by low be used to decide whether the green parts can be further
standard deviations in the results of multiple repeated processed or directly rejected. This contributes to saving
measurements. It can be concluded from standard resources and increasing process quality.
deviations depicted in Figures 7, 10, 13, 16, 19, and 21 that
gas pycnometry and Archimedes’ method exhibit very 5. Conclusion
good repeatability, while micrograph analyses are subject In this work, gas pycnometry, gravimetric buoyancy
to comparatively high fluctuations. measurement according to Archimedes method, and
Ultimately, further criteria for selecting one method micrograph analysis were analyzed and compared
over the others should also be taken into account. Terris with each other as density measurement methods for
et al. recommend determination of method based on AM components. In this regard, the basics of density
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the type of sample (shape, size, destructible or not), the determination were worked out, and basic density and
desired results (type of density or porosity, position, trend porosity values were researched from the existing literature.
between the samples), the available material, and the time AM processes and designs for the production of test samples
were then defined, the printing systems parameterized and
available. The findings of the current study can also be used the samples manufactured. This was followed by a quality
to derive general statements on the application of density
and porosity measurement methods for individual additive assessment as well as density and porosity determination
process categories listed in Table 1. All AM processes of the test samples according to defined standard
specifications. First, FDM-printed components made
that already produce relatively dense components due to of 316L stainless steel filament were analyzed, whereby
the process can, in principle, be analyzed very precisely green parts were first examined after the printing process
using gas pycnometry or the Archimedes method. Due to and then the final components after a sintering process.
the low porosity and usually only a few open pores, the Furthermore, SLS and EBM components made of PA12 or
measurement results of both methods are comparable. titanium powder as well as ceramic components that were
In this case, the true density determined using the gas printed using the LCM process from a zirconium powder-
pycnometer corresponds approximately to the apparent loaded slurry, initially as green parts and after a sintering
density determined using Archimedes method. This usually step also as final ceramic components, were analyzed.
applies to the AM processes directed energy deposition,
material jetting, metal PBF, sheet lamination, and VPP. The results of this study supplement and expand the
AM processes, which tend to produce porous components state of the art in terms of component density and porosity
due to the nature of the process, a distinction should be of the specimens produced using the AM processes
made between true and apparent density during analysis. investigated. In addition, the results obtained in the
The true density should always be determined using gas present study can be generalized and recommendations
pycnometer measurements and the apparent density using for the measurement of porosity and density can be
the Archimedes method. As a rule, the true density will derived for other AM processes. Detailed measured values
always be somewhat higher and lead to less part porosity are presented, which are also determined and validated
than the apparent density values. This must ultimately be using three different measurement methods. Based on a
considered when characterizing the component to predict detailed comparison of the resulting density and porosity
the mechanical properties of a component as realistically results between the density measurement methods
as possible. This procedure applies to binder jetting, MEX, used and between the results of the individual printing
methods, the advantages of the individual measurement
polymer PBF, and VPP green parts.
methods for certain AM process categories and processing
The automated form of Archimedean density materials were identified. Gas pycnometry is best suited
measurement is generally very well suited to industrial for determining the true density of components and the
production practice in particular, as it is more economical Archimedes method for determining the apparent density.
than the other methods. The measurements are as accurate Gas pycnometry is recommended for all AM processes
as with the other measurement methods, but can be carried that already produce relatively dense components due to
out much faster and are also more reproducible, less prone the process. The Archimedes method is advantageous for
to errors, and easy to integrate into industrial process AM processes that tend to produce porous components.
chains thanks to increasing automation. The automated For these parts, a distinction must be made between true

Volume 4 Issue 2 (2025) 22 doi: 10.36922/MSAM025090010