Concept for In-process Measurement of Residual Stress in AM Processes by Analysis of Structure-Borne Sound

Process-induced residual stress is a major challenge in today's additive manufacturing (AM) processes, such as powder bed fusion by laser beam melting of metal. After the AM process, the exact stress state is usually unknown, and parts often require heat treatment to relieve residual stress. In-process measurement of residual stress is currently not possible. This paper presents a concept to derive the measurement of the residual stress by analyzing the structure-borne sound induced during the AM process. The first step of the concept is to integrate a device into a build plate to set a defined mechanical load during the manufacturing process. Then, samples can be fabricated on this build plate in several steps. By applying mechanical load with the device, the stress state in the samples can be changed between the fabrication steps. During this stepwise fabrication process, the structure-borne sound signal is recorded. Subsequently, the correlation between the stress states and the acoustic process emissions is analyzed using FFT, STFT and cross-spectral analyses. The overall goal is to establish a model to determine residual stress in AM components by evaluating the acoustic process emissions.