Why 3D Printing is Still More Alchemy than Science
While it continues to reshape the future of manufacturing, 3D printing, or additive manufacturing, is still less than miraculous. There are real performance and reliability issues in processes, like powder bed fusion (PBF), that result in inconsistent part quality. Some of the things that can go wrong are dimensional and form errors, unwanted voids in the fused layers, delamination, and high residual stress in the final parts. These are not the types of defects you want to discover in automotive or aerospace components.
Science and industry have had centuries to learn how metals behave and 100 years to understand plastics. In contrast, it was only in 1986 that stereolithography, the first additive manufacturing technology, moved from Dr. Charles Hull’s lab to commercialization. It was not until 2009 that the ASTM Committee on Additive Manufacturing Technologies Industry Standards was formed to start reducing variability in process, material, product, and language. While there has been a good deal of scientific research in the last few decades, material properties like hardness and strength resulting from phenomena like the melting process in PBF are still not well understood.
Now, the National Institute for Standards and Technology (NIST) is stepping into the picture and is beginning by pulling together all the research on PBF from around the world. The newly released report, “Measurement Science Needs for Real-time Control of Additive Manufacturing Powder Bed Fusion Processes,” summarizes the published relationships of process inputs, like energy and material, to in-process phenomena and the products that result.
The NIST team organized the data they found in more than 165 published studies into 12 categories of process parameters that determine the rate of energy delivered to the surface of the powder, and what happens as that energy interacts with it. They isolated 15 types of process signatures—what happens in the powder heating, melting, and solidification processes during the build. Then there are 6 categories of geometrical, mechanical and physical qualities of the end product. The report also includes charts of the known cause-and-effect relationships among variables in each of the three categories. As these are better understood, in-process sensing and real-time control technologies for powder bed fusion can be developed for the additive manufacturing industry.
Using the report as a guide, the researchers want to study these relationships further to identify what factors determine part qualities such as material characteristics, dimensional accuracy and surface roughness. Academic and industry research can also use it as a blueprint for organized discovery of the scientific principles underlying additive manufacturing processes.
What’s next? NIST plans a test bed for evaluating its in-process measurement and control methods. The researchers at NIST want to see what’s really going on when metal powders are melted and solidified, and what are the possible process metrology tools that can be integrated into the process. Then they will need to develop algorithms and software that will make sense of the data acquired by new tools.
These fundamentals can’t continue to be skipped over if the promise of 3D printing is to be realized. Manufacturers asking “What has the government done for me lately?” can be assured that NIST is facilitating basic technology advances that will benefit everyone seeking to profit from the 3D printing revolution.
Click here to download the full report, “Measurement Science Needs for Real-time Control of Additive Manufacturing Powder Bed Fusion Processes.”
Karen Wilhelm has worked in the manufacturing industry for 25 years, and blogs at Lean Reflections, which has been named as one of the top ten lean blogs on the web.
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