China3D printingNet May 7th,A research team at the Technical University of Munich (TUM) has developed a non-destructive method that uses neutron detection3D printingInternal stress in the part.Researchers at the energy technology company Siemens Energy3D printingTested their method on the lattice structure, the company’s3D printingThis method is used in gas turbine blades.
“Complex components with such a complex structure will not be able to be manufactured using traditional manufacturing methods (such as casting or milling),” said Dr. Tobias Fritsch of the German Federal Institute for Materials Research and Testing (BAM). “We want to see if we can use neutrons to detect internal stresses in this complex component.”
The lattice structure of the measurement position on the residual stress diffractometer STRESS-SPEC. Image courtesy of Tobias Fritsch / BAM.
3D printingNon-destructive testing of parts
Siemens Energy used nickel-chromium alloys to print a lattice structure of a few millimeters in size, and deliberately omitted the conventional heat treatment after printing.
The lattice is manufactured by laser powder bed fusion (LPBF), which gives the structure a complex geometry. However, during the printing process, the local heat input of the laser and the rapid cooling of the molten pool will cause residual stress in the material.
Although it can take time and therefore money, this stress can be eliminated through a heat treatment process. However, before this, residual stress can also damage the components during the production process, resulting in cracks or deformation.
Evaluation of the structural integrity of materials is mainly carried out through destructive or semi-destructive methods, which is not ideal for mass production of parts. Instead, neutron diffraction can non-destructively detect residual stress in bulk materials.
In order to use this method to test the internal stress of gas turbine components, Fritsch bombarded the part with neutrons from the research neutron source Hein Maier-Leibnitz (FRM II) and used the STRESS-SPEC neutron diffractometer. Then use the Python script to calculate the principal stress direction, and extract six independent stress components from the nine strain measurements at the same time. These measurements indicate the principal stress directions of the pillars and junctions of the lattice structure.
The lattice structure of the measurement position on the residual stress diffractometer STRESS-SPEC. Image courtesy of Tobias Fritsch / BAM.
Detect internal stress
Through their experiments, the team demonstrated a reliable procedure for using neutron diffraction to determine the residual stress in the lattice structure. But once they detect stress, the next step is to find a way to reduce it.
Fritsch said: “We know that we must modify the production process parameters to change the way the components are built during the printing process. During the melting process, the stronger the locality of the heat applied, the greater the internal stress generated. Therefore, we must print Distribute the heat as evenly as possible during the process.”
Looking to the future, the team will study the process with new components and modified printing parameters, and has collaborated with Siemens to plan to use Garching’s TUM neutron source for new measurements.
Dr. Tobias Fritsch uses the remote control to place the lattice structure in the correct measurement position in the residual stress diffractometer STRESS-SPEC, which is used to study the neutron source. Photography: Michael Hofmann / FRM II / TUM.
Non-destructive testing in AM
Although yes3D printingDestructive testing of parts is still the most common method of detecting stress and weakness, but there are other ways to develop non-destructive testing procedures.
For example, scientists at the National Institute of Standards and Technology (NIST) have developed a method that uses advanced probes and computer algorithms to accurately measure SLA 3D printingThe method of polymer hardening rate in the process.
Combining machine learning with CT scanning is another non-destructive technique, and researchers from the Tandon School of Engineering at New York University have applied this technique to reveal3D printingThe hole behind the composite material.
Elsewhere, Singapore’s National Additive Manufacturing Innovation Cluster (NAMIC) has partnered with Singapore’s National Metrology Center to develop standard guidelines for non-destructive testing of parts manufactured by powder bed fusion and binder injection.The research project was funded by standards developer ASTM International to encourage3D printingOne of the eight initiatives for internal standardization.
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