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Materials Science in Additive Manufacturing Measuring the porosity of AM components

process in which an ultraviolet (UV)-sensitive polymer resin different AM components made of metal (titanium printed
is used as a printing material and cured layer by layer using using PBF and stainless steel printed using MEX), ceramic
UV light. The fourth process chosen was lithography-based (ZrO produced using VPP), and plastic (PA12 produced
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ceramic manufacturing (LCM) as a representative of the using PBF) with regard to their part density and porosity
VPP processes, which can produce ceramic components, for using automated measurement methods and processes has
example, from zirconium oxide, by light-curing a ceramic- not yet been carried out. In addition, AM ceramic and metal
loaded slurry and then debinding and sintering the green green parts (composites) produced using VPP and MEX,
body. 5 respectively, are also analyzed, and thus the accuracy and
All components manufactured using the respective AM reproducibility of the respective measurement methods are
processes have characteristic properties that make them evaluated at an early stage of a multi-stage AM production
suitable for applications of varying complexity. The applications process. This is the subject of the present work. As a result
range from low-stress prototypes to final components that are of the investigations, conclusions are then drawn about the
sometimes exposed to high loads. With increasing stress on preferred density measurement methods for various AM
AM components, it is important to be able to evaluate the processes.
manufacturing quality of the structures. The density and 2. State of the art
porosity of AM components are of great interest here, as they
have a strong influence on the mechanical properties and are In the state-of-the-art, basic principles of pores and
the most economical to analyze. Porosity in this case is the porosities, as well as densities of components, are first
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presence of a defect in the form of a pore or cavity or a lack explained. Furthermore, special measurement methods
of solid material in the fractions of a component. A certain are considered. Current research on the density and
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degree of porosity cannot be avoided in any AM process, porosity of AM components, which were determined using
meaning that internal pores are always present in every AM the analysis methods investigated in this study, are then
component. 6,10-12 According to the ASTM, porosity in AM discussed. Data from other literature are of comparative
can be categorized into two main types: apparent porosity significance to the results of this study.
(unintentionally occurring defects in the structure and/or 2.1. Principle of open and closed pores
surface of AM material) and artificial porosity (intentionally
created and controlled to enable a specific performance or Many parts do not consist entirely of a solid component but
function). The apparent porosity has a negative influence on have cavities, capillaries, and inclusions. According to Otto
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the mechanical component properties and the corresponding et al., these cavities can be filled with air or any single-
pores often act as nuclei for fatigue cracks. 10,12,14,15 Heavily phase or multiphase liquid and consist of several areas,
stressed components should therefore have the lowest possible so-called pores. According to ISO 15901-1, these pores
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apparent porosity and be completely sealed to minimize are in turn divided into closed and open pores. According
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the probability of failure during operation. For certain to Klobes and Munro, this classification is based on how
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biomedical implants, on the other hand, a certain degree of accessible they are to an external fluid (Figure 1). Closed
(artificial) porosity is desired, for example, to promote better pores are inaccessible to an external fluid and are also
osseointegration with biological tissue. 7,11,16
Various non-destructive methods such as the Archimedes
method, gas pycnometry, and X-ray computed tomography
(CT), as well as destructive methods such as micrograph
analysis or mercury intrusion (Hg intrusion), are suitable for
investigating and quantifying the porosity of AM components
and its effects on the mechanical component properties. All
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of these methods are based on the detection of microstructural
defects and pores in the components and, in some cases,
on the analysis of porosity distribution. Furthermore, all
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methods have specific measurement characteristics or manual
influences that affect the measurements to a certain extent and
thus lead to deviations between the measurement results. In
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addition, some processes are very complex, time-consuming,
or, as in the case of Hg intrusion, pose environmental and
health risks due to the use of toxic substances. An extensive Figure 1. Schematic representation of closed (A) and open (B-D) pores
comparison of the individual measurement methods for and the surface roughness (E) of a component (based on Klobes et al. )
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Volume 4 Issue 2 (2025) 3 doi: 10.36922/MSAM025090010