Additive manufacturing has been described as "disruptive" and "game changing" more times than is probably a good idea. As more developments and innovations continue to come to light, familiar obstacles are illuminated just as many times as the technique is described as something akin to "revolutionary."
Researchers know that hard data is imperative for anyone engaged in actually pushing any technology forward. One method that requires quite a bit of quality assurance and performance quantification data is metal additive manufacturing. Most of the guidelines for metal AM are works in progress, but the potential for powder bed fusion to facilitate a significant shift from traditional manufacturing techniques to 3D printing techniques has a few obstacles.
The new NIST report focuses on "missing sections in current guidelines for powder bed fusion" by identifying "key unknowns". The potential of metal additive manufacturing lies in it's versatility, and the report illustrates a cohesive view which "systematically links process inputs to in-process phenomena that might either be measured or modeled and to the ultimate determinants of part quality such as material characteristics, dimensional accuracy and surface roughness."
Powder bed fusion is one of seven categories of additive manufacturing processes defined by the ATSM standard. In this method, top layer after top layer of metal particles on a bed of powder is melted and fused selectively. The powder is replaced after every layer and repeated until the designed part is finished. Medical implants, automotive parts and fuel nozzles for jets and many other components are already made this way.
As aerospace and automotive manufacturers explore ways to expand and advance current techniques, they need to first need to advance process control and reliability standards.
Conventional manufacturing methods often require machining portions from blanks of material, then joining those machined pieces together to make a customized part. Powder bed fusion is currently more time consuming, but additive manufacturing offers easier customization of complex shapes and features. This allows for design experimentation and leads to cost beneficial innovation. Designers can execute visions that would be incredibly complicated to machine using traditional techniques.
System performance and reliability issues have led to less than desirable part quality, a common concern across pretty much every sector of 3D printing. There are dimensional irregularities, form errors, voids in fused layers, high residual stress in the final parts, and a lack of understanding with respect to material properties.
"Robust process control through in-process sensing and real-time control can prevent or correct these problems, but achieving this solution requires detailed understanding of all of the many intricacies of powder bed fusion," according to the NIST researchers. When they review their previous work in the report, they cite a study which claims more than 50 factors influence just the melting process.
After they surveyed their previous research, the NIST team distilled 12 categories of "process parameters," 15 types of "process signatures," and six categories of "product qualities." The cause-and-effect relationships are then examined among variables in each of these categories.
"This cause-and-effect breakout can guide research to develop measurement and sensing capabilities as well as modeling and simulation tools—all with the aim of enabling better process control," says NIST mechanical engineer Brandon Lane, one of the report's authors.
In the report, you get a glimpse of the researchers next phase, where the NIST team plans to build an "additive manufacturing test bed for evaluating in-process measurement and control methods." According to the report, this tool will allow the research team to "observe melting and solidification of metal powders, integrate process metrology tools, and implement software interfaces and data acquisition for process measurements, as well as test control algorithms."
Download the free report, courtesy of NIST.
Source: NIST