In-Situ Fringe Pattern Profilometry for Feed-Forward Process Control

In Phase I the research team demonstrated a superior in situ profilometry sensor, based on fringe pattern projection, which quickly measures the whole build plate. In this data, significant process phenomena are accurately measured and easily identified, such as spreading defects, rogue particles that have been sintered to the part’s surface, distortion, surface roughness variation, and virtually any geometric feature. Of particular importance is the measurement of powder layer condensation and uniformity. This data serves as input to a model that generates feedforward information to adjust process parameters, resulting in better prediction and control of key material properties such as residual stress and density. In Phase II the team will further improve the sensor and test the feedforward model. After fine-tuning the modelling capability for stress and distortion, mechanical testing will be conducted to validate model performance and determine the effect of defects (measured with the profilometry) on mechanical performance. The result will be real-time determination of part quality by a modelling tool that integrates profilometry-detected defects into the performance predictions. This novel data will then be used to feed and validate a fast-feedback look-up table (generated by inverting the feedforward model), for layer-to-layer laser parameter adjustment during builds. Next, a new design of the profilometry sensor will be completed to make it very compact (a few inches) so it can easily be added to OEM AM machines. Then the research team will implement a new sensing technique (with the same hardware) to record video-rate, measurements, at nanometer precision, of thermal expansion and shrinking during the melting process, thereby facilitating novel and powerful analysis of residual stress and/or delamination formation. Finally, the research team will demonstrate the whole sensor/modelling package on a NASA geometry of interest. More »