Evaluating Powder Structures Prior to the 3D Printing Process
ZEISS 3D ManuFACT
Additive manufacturing (AM), the 3D printing process, is increasingly important in the production of complex, high-value, critical parts with potential applications in the medical technology, aerospace and automotive industries.
Using AM in the industrial production chain to create consistent and predictable properties, however, requires an in-depth understanding of your input materials.
Powder is the Building Block
AM processes build parts one thin layer at a time. The most common form of metal 3D printing begins with laser powder-bed fusion (PBF). “The design freedoms enabled by laser PBF,” says Timothy W. Simpson, Paul Morrow Professor of Engineering Design & Manufacturing at Pennsylvania State University, “can be exploited to lightweight components, to build intricate lattice structures for more efficient material usage, to consolidate multi-component assemblies and to optimize a part’s shape for functionality.”
Such parts include:
- Medical implants (orthopedic, cardiac, dental and craniomaxillofacial)
- Medical devices (surgical instruments, dental restorations and external prosthetics)
- Automotive parts (bellow pieces, ducting, mounting brackets)
- Jet engine parts (housings, heat exchangers, turbine blade molds)
The quality of the part, however, begins with the quality of the powder. Poor powder can produce defects in the resulting part relating to:
- Residual stress
- Suboptimal surface finish
- Compromised throughput
How material properties ultimately produce quality parts is a complex process. To attain pre-production validation, you need to inspect the metal powder before starting the process.
Which properties are important to defining a robust powder specification? Powder size and form and, the size distribution of individual powder particles, influence how the powder is compacted. This affects the density of the build and can result in defects visible later in the printing process.
Size Distribution – Increasing the Density of a Printed Part
According to “Characterization of Metal Powders Used for Additive Manufacturing,” published in the Journal of Research of the National Institute of Standards and Technology (NIST), “metal powders used in AM are assumed to be nominally spherical, and have a particle size distribution that is designed to facilitate good packing behavior, such that the final manufactured part has good mechanical properties and is fully dense.”
“Particle size distribution has a direct effect on flowability and the potential to provide a uniform powder bed density,” says Micromeritics Instrument Corporation. Spherical particles improve the flowability of the powder and the density, and a wider particle size distribution allows fine particles to fill spaces between larger particles, resulting in higher density. If there isn’t sufficient flowability of powders, the possibility of defects later in the process becomes more likely.
3D ManuFACT from ZEISS offers holistic inspection verification that helps to detect those defects in powder quality prior to an AM build. A combination of Light Microscopes (LM), Scanning Electron Microscopes (SEM) and X-ray Computed Tomography (CT) are used for this initial process, focusing on powder and material characterization.
Powder Structure Analysis Technologies
Light Microscopes (LM)
Description: Optical microscopes offer the possibility of quick powder sampling and reliable analysis of particle size distribution.
Application: Dr. Robert Zarnetta, Head of Field of Business Industrial Microscopy Solutions at ZEISS: “Companies often characterize powder with our light and electron microscopes. This is an important issue for quality assurance, because the PBF process requires the use of powders with very strict specifications in terms of size, shape and material properties. As our experience shows, deviations from these parameters have a great impact on the quality of the final product.”
- The ZEISS Smartzoom 5 digital microscope is the tool of choice for capturing powder structures prior to the construction process.
- The ZEISS Axio Observer inverted optical microscope system uses dedicated software modules to conduct material analysis and detailed inspection of build patterns and cross sections of, for example, non-metallic inclusions and grain sizes.
Scanning Electron Microscopes (SEM)
Description: Powder particles are fairly small in size, typically ranging from a few micrometers to tens of microns in diameter. SEMs offer nanometer-level resolution and the ability to examine batch or each individual particle to help engineers better understand the build ingredients for additive manufacturing.
Application: Dr. Zarnetta: “Our scanning electron microscopes are used by companies to check whether the powder contains oxidized particles, which could cause problems when melting in the 3D printer, or analyze the recycled powders, if they still can be used for high quality builds.”
- The ZEISS Sigma and EVO SEMs enable micro structural crystallographic characterization and powder analysis that ensure sharp surface details can be obtained at low beam energies on sensitive powders and particles.
X-ray Computed Tomography (CT)
Description: High-resolution X-ray CT provides detailed analysis of particle shape, size and volume distribution. The analysis of shape in relation to powder bed compactness helps to determine proper process parameters and to shorten optimal print recipe development.
Application: Dr. Zarnetta: “Detected abnormalities in the powder at macro scale can then be investigated at the micro level with pinpoint localization transferred to an electron microscope or X-ray computed tomography, enabling hassle-free nanometer range analysis. This helps customers to evaluate the powder quality faster and prevent material-related defects in the build stage.”
- The ZEISS Xradia Versa is a highresolution X-ray CT system that supports detailed analysis of powders, surfaces and structures with voxel size down to 70 nanometers.
A staged quality process in AM can help you prevent defects in a part’s final dimensional characteristics, saving you time and money.
ZEISS 3D ManuFACT enables end-users to evaluate and measure quality across the manufacturing process. High-quality industrial metrology equipment, such as microscopes and CT systems, can help you determine if the quality prior to the execution of downstream processes, such as heat treatment and removal of components from the build plate, will pose any problems.