MRI monitoring and non-destructive quality measurement of polymeric patterns manufactured via stereolithography

The use of Magnetic Resonance Imaging (MRI) for monitoring, studying and performing output quality measurements of the acrylate-based polymeric patterns manufactured using stereolithography (SL) was introduced in this work. The effects of build parameters and humid environment on sample homogeneity, distribution of crosslink density, stability and defect formation were examined. The spatial resolution of the method was found to be sufficient to identify patterns according to the build parameters used and to detect specific hatch-predicted crosslink density variations. Qualitative information obtained using MRI visualisation was supplemented by quantitative measurements of Nuclear Magnetic Resonance (NMR) relaxation times and 1H NMR spectra. NMR spectroscopy confirmed the identity of the chemical composition among the patterns and showed that the crosslink density variation observed via spatially resolved T2-profiles stems from the difference of the build parameters. Different types of defects in the samples were observed and classified; some defects originated from local matrix continuity failures (partially cured resin trapping within the polymer or bubbles formation), while other defects were found in the form of bulk layering. MRI visualisation coupled with relaxometry and 1H spectroscopy of patterns during their interaction with humidity allowed tracking water distribution inside the sample and observing effects of swelling, fracturing and chemical decomposition. It was found that the initial inhomogeneous structure of the specimen has a crucial role in subsequent fracturing due to non-uniform expansion of the swollen parts. As a result, the approach presented in this work improves the output quality control and current testing techniques, provides insight how physical properties of the 3D parts are affected by different technical parameters, and eventually can help the use of SL technologies for a variety of applications.