Measuring the Effects of Post-Processing on Final Quality in 3D Printing
ZEISS 3D ManuFACT
From lightweight, high-strength structures to hyper-realistic prototypes, 3D printing has found its way into a variety of applications. This process of additive manufacturing (AM) is becoming more common in high-volume production of designs with moderately complex geometries.
A successful AM build, however, requires various post-processing treatments that can influence the dimensional characteristics of the end-use part and have a significant impact on the overall yield. It is, therefore, necessary to understand and ensure dimensional accuracy and optimal material properties through analysis of parts across all post-printing steps.
Impact of Heat Treatment
A critical post-process treatment for a 3D-printed part is annealing, a heat treatment process originally developed for metallurgy. This heat-treating process alters the material’s physical (and sometimes chemical) properties and can make a 3D printed part stronger by reducing stresses and increasing the operating temperature of the print.
As Timothy W. Simpson, Paul Morrow Professor of Engineering Design & Manufacturing, Pennsylvania State University, explains: “In many cases, this step also requires an environmentally controlled furnace with the ability to regulate the temperature and cool-down schedule. Heat treatment may affect the dimensions of the parts, so most people prefer to heat-treat parts before they machine/finish them.”
Although this can strengthen the part and increase its stiffness, internal stresses may result that end up acting like perforated lines that are more likely to fatigue or crack under pressure.
The Problems that Arise from Post-Processing Treatments
Even before heat treatment, with powder-bed AM, residual gas porosity and lack-of-fusion defects can cause a significant detriment to fatigue life of as-built components. However, even if a part is well within tolerance in an as-built state, significant distortions may occur following not just heat treatment but the removal of the part from the build plate.
High residual thermal stresses that develop during the building process can drastically affect the form, size and position of holes and features of a part. Consequently, the mechanical performance of a 3D-printed part may suffer as a result of:
- Undesired shape distortion
- Detachment from support structures
- Crack formation
Finally, a part will need to be removed from the build plate and cleaned. Good adhesion of a print to a build plate is vital during the AM process, as the first layer adheres to the plate and everything that follows builds on this surface.
A print being properly placed and oriented on a build plate can greatly reduce aesthetic impact of support material on the final print. A loose part can result in a failed print, and there’s always a chance a build plate leaves behind excess material or marks, diminishing accuracy and appearance.
Afterwards the part must be removed, as described by Timothy W. Simpson:
“Most companies use wire EDM to remove parts from the build plate, however many machine shops are starting to use a bandsaw (see Figure 2) because it is faster and the bottoms of the parts must be finished anyway. Keep in mind that materials such as Inconel strain-harden as they are worked, making it difficult to remove them from the build plate with just a bandsaw.”
Each of the three steps of post-process treatment can affect the microstructure and mechanical properties of a part. In order to ensure the part does not have any defects, it should be scanned, measured and inspected for quality:
- As built
- After heat treatment
- When removed from the build plate and cleaned
Solutions – Scanning for Final Quality
ZEISS 3D ManuFACT has significant expertise combined with unique metrology technology, allowing detailed monitoring of the three post-process steps. ZEISS offers measurement and inspection solutions for each of these stages and across multiple AM applications.
“Companies receive a volume model of the entire component within a few minutes and can then easily compare these actual data with the target data from the CAD model,” says Dr. Marcin Bauzau, Director of New Technology & Innovation, Carl Zeiss Industrial Metrology. “This information can be also verified across post-printing steps, allowing analysis of parts in ‘as build’ state, then heat treated state, and finally removed from the build plate.”
Correlating obtained information across each of the process steps can significantly improve overall part performance. To better understand the influence of those processes on final quality, a CMM or optical 3D scanner can be used.
Coordinate Measuring Machine (CMM)
Description: Shop floor CMMs can be used as a quick check of the part’s dimensional condition across all three post-process steps: as built, heat-treated, removed and cleaned. Tactile measuring machines allow consistent measurement across many surface finish conditions and metrology of deeper holes and cavities, providing valuable information regardless of part density or finish.
- Products: The ZEISS DuraMax HTG is a compact shop floor CMM that allows investigation of post-build processes, showing any influences on dimensional accuracy of finished parts.
Description: 3D scanning offers the ability for high-speed, highdensity data collection. It can capture data of the entire external surface by generating high density data, allowing you to analyze form, size and location of features as well as the whole part.
- Products: The ZEISS COMET 3D scanner offers a high measuring speed, quickly showing any post-build process influences on the dimensional accuracy of a finished part.
Additive manufacturing is not a magical process that results in a part springing wholly into existence. There is a long and winding road to guaranteeing the repeatability and reliability of a 3D-printed part, including after heat treatment.
With ZEISS 3D ManuFACT, productivity is increased as your manufacturing and assembly is supported by this integrated process. Our ZEISS technologies, including CMMs and optical 3D scanners, provide knowledge and certainty across all process steps, from powder to performance.