Comparison of SLOT and μ-CT investigation of 3D printed polymer parts for quality assurance

Additive manufacturing has developed rapidly during the last few years. This kind of production technique is growing up more and more in production processes: metal parts as well as polymers are impacted. Big companies are already using additive manufacturing every day for assorted parts. One big challenge for adapting additive manufacturing to serial production processes is mandatory quality assurance. On-the-fly-control during the process is important, and the final quality assurance of finalized parts is even more important for a reliable serial production. Specifically for complex structures, a 100% testing rate would be important for quality assurance. Currently there is a more or less destructive examination by ionizing irradiation or by invasive testing methods on samples only. This causes a large amount of rejects especially in the case of small batch production. Imaging techniques such as micro-computer tomography (μ-CT) and optical methods such as scanning laser optical tomography (SLOT) and optical coherence tomography (OCT) can be used for nondestructive quality assurance of, e.g., 3D printed polymer parts. SLOT and OCT are based on the respective spectral range of the specific object to volumetrically visualize additive manufactured 3D polymer parts. A comparison of SLOT and μ-CT shows the advantages and disadvantages of these imaging techniques with respect to the properties of polymers. While μ-CT offers a high resolution, it is at least a very expensive method for quality assurance and it might initiate the aging process of the polymer. SLOT, on the other hand, delivers more information on a piece of the costs of a μ-CT device. It shows the same nonconformities, but it needs some postprocessing on the collected imaging information. An additional advantage of SLOT over μ-CT is the number of contrast mechanisms. While μ-CT uses only absorption, SLOT addresses absorption, scattering, and autofluorescence. Furthermore, with the lower costs, there is the opportunity for quality assurance on 100% of printed polymer parts instead of samples. This is of particular interest for safety-related parts.