Towards In-situ Monitoring of Additively Manufactured Parts Using Nonlinear Resonant Acoustic Spectroscopy

Additive manufacturing (AM) is rapidly reshaping the manufacturing landscape due to its ability to produce light weight components, complex parts with minimal waste and reduced manufacturing time. However, AM parts may contain various process defects such as porosity, lack of fusion and cracks limiting their industrial applications. The quality of the AM parts needs to be ensured for successful application in various critical industries such as aerospace and biomedical. While nondestructive testing (NDT) is an efficient tool for quality control and process monitoring of the AM parts, existing NDT techniques have limitations. This study investigates the feasibility of using nonlinear resonant acoustic spectroscopy (NRAS) for real-time process control of additively manufactured parts. NRAS is a resonance-based nonlinear acoustic technique widely used to measure the nonlinear hysteretic parameter (𝛼𝛼) of a test material. In NRAS, the test material is excited about its resonance frequency and the linear shift in the resonance frequency with the increasing driving voltage amplitude is measured as the hysteretic nonlinearity. We propose a NRAS test setup for process control of AM parts while they are still attached to the build plate. Several cylindrical AM specimens are tested to measure the hysteretic nonlinearity with and without the build plate for comparison. We observe a systematic decrease in the measured nonlinearity when the specimens are tested on the build plate, which we attribute to the low nonlinearity of the build plate. Despite the observed difference, the measured nonlinearity of the specimens with and without the build plate is highly correlated. With further investigations, the proposed test setup can be potentially used for process monitoring of AM parts in situ.