According to the engineers, AM can produce complex-shaped metal components strong enough for structural applications. But developing complex geometries with fewer errors and distortions, as well as quality standards to test the manufactured items, has not kept pace with the technology.
"Multiscale Structure-Mechanical Property Investigation of Additive Manufactured Components for Development of a Reliable Qualification Method" has been funded US$300,000 by the National Science Foundation's Division of Civil, Mechanical and Manufacturing Innovation (CMMI) while "Automation Tools for Modeling AM Process of Complex Geometries in ABAQUS" was awarded aUS$150,000 Research for Additive Manufacturing in Pennsylvania (RAMP) grant, funded jointly by the Pennsylvania Department of Community and Economic Development's (DCED) "Discovered in PA, Developed in PA" program and America Makes (National Additive Manufacturing Innovation Institute).
The investigator for both grants is Albert To, PhD, associate professor of mechanical engineering and materials science. According to Dr To, AM is at a critical juncture in its evolution where both computer modelling and qualification methods need to be improved in order to reduce manufacturing time and costs while improve quality and product integrity.
Prone to errors
"Additive manufacturing continues to demonstrate its ability to manufacture very complex lattice structures and geometries, enabling us to build complex structures that would be difficult to replicate using traditional or "subtractive" manufacturing," he said. "However, these increasingly complex parts are very time-consuming to model and therefore more prone to errors. The RAMP grant will enable us to develop computer codes that first will automate the finite element simulation of certain AM process and material.
"By improving the modelling of these complex, sometimes microscopic structures, we can design the process path and/or part geometry to reduce residual stress that causes failure to the part during manufacturing."
Improving the modeling and simulation processes in additive manufacturing go hand-in-hand with developing new qualification methods that ensure the quality of a manufactured part or component. Dr To notes that additive manufacturing has advanced so rapidly that typical manufacturing standards have yet to catch up.
Microstructure understanding
"Traditional qualification standards are not adequate for additive manufacturing because AM parts are "built" by adding layer upon layer of powdered ceramics, metals and polymers, which therefore exhibit residual stresses and higher number of defects,” he explained. "For example, in aerospace manufacturing, a machined part is inspected for surface cracks, dimensional accuracy, and material composition. To develop qualification methods for AM components, we need a better understanding of the microstructure and its mechanical behavior."
Accomplishing this begins with the use of X-ray micro computerized tomography, or a CT scan. In conjunction with mechanical testing and computer simulation, this will enable the researchers to investigate at the microscopic level the mechanical effects of flaws and residual stress, and later develop a computer-based, non-destructive method that is rapid, reliable, and affordable, thereby greatly improving AM techniques and quality.
