Damage Detection in Direct Metal Laser Sintered Parts Using Vibration Mode Shapes

WCU Author/Contributor (non-WCU co-authors, if there are any, appear on document)
James Philip Walker (Creator)
Institution
Western Carolina University (WCU )
Web Site: http://library.wcu.edu/
Advisor
Sudhir Kaul

Abstract: Direct metal laser sintering (DMLS) is an additive manufacturing process that can be used to manufacture complex parts that are difficult or impractical to produce using traditional methods. However, this relatively new technology does not have the same base of knowledge as other processes. This makes it challenging to design parts that need to be manufactured using DMLS since many aspects related to this method are not fully comprehended.This study investigates the use of vibrational mode shapes as a possible means of detecting damage in parts that are manufactured from DMLS. Using vibration-based damage detection is a common testing technique due to the non-destructive nature of the test. The damage detection method chosen for this study involves the use of vibrational mode shape curvatures since the change in mode shape curvature has a unique pattern at the damage location. The parts that have been used for this study were printed from the EOS M 290 machine using 316L Stainless Steel. A notch is introduced into the geometry of several parts and damage is further propagated by sawing a slot at the end of the notch. A Polytec PSV-400 Laser Doppler Vibrometer has been used to identify the vibration mode shapes, these mode shapes are then compared to the mode shapes attributed to undamaged parts. Mode shapes have been analyzed using the wavelet transform as well as a curvature damage index.This study also investigates the possible effect of varying part densities on damage propagation. The properties of DMLS parts that increase cost efficiency and productivity, such as layer thickness and hatch distance, inversely affect the density of parts. Damaged parts are printed with varying process parameters and the mode shapes of damaged parts are compared to one another as well as the undamaged parts. The questions that this study seeks to answer are: Can damage of DMLS parts be detected from the mode shapes measured with a laser vibrometer? Can these mode shapes be used to predict or locate damage in parts? Do mode shapes of damaged parts differ with process parameters associated with the selective laser sintering process?Results indicate that damage can be successfully detected in the parts analyzed in this study. Additionally, it is observed that other unknown anomalies that are similar to damage can also be successfully detected. However, varying process parameters do not seem to exhibit any influence on damage detection.

Additional Information

Publication
Thesis
Language: English
Date: 2019
Keywords
Additive Manufacturing, Damage Detection, Direct Metal Laser Sintering, Laser Vibrometer, Mode Shapes, Non-Destructive Testing

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