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Evaluation of UV post-curing depth for homogenous cross-linking of stereolithography parts

Tristan Schlotthauer (Institute of Aircraft Design, University of Stuttgart, Stuttgart, Germany)
Jan Nitsche (Mercedes-Benz AG, Böblingen, Germany)
Peter Middendorf (Institute of Aircraft Design, University of Stuttgart, Stuttgart, Germany)

Rapid Prototyping Journal

ISSN: 1355-2546

Article publication date: 12 August 2021

Issue publication date: 18 November 2021




During post-processing of stereolithography photopolymers, the limited penetration depth of ultraviolet (UV) light can lead to inhomogeneous cross-linking. This is a major problem in part design for industrial applications as this creates uncertainty regarding the mechanical load capacity. Therefore, this paper aims to present an experimental method to measure the post-curing depth in stereolithography photopolymers.


Printed specimens made from urethane acrylate photopolymers are placed in a protective housing and are exposed on one side to UV light during post-processing. A depth profile of the hardness according to ASTM D2240 Shore D is determined alongside the specimens. UVA,-B and -C spectra are investigated and the dependence on exposure dose and pigmentation is studied. The results are directly linked to the mechanical properties via tensile tests and validated on an automotive trim part.


Exposure with a 405 nm light-emitting diode provides the deepest homogenous post-curing depth of 10.5 mm, which depends on the overall exposure dose and pigmentation. If the initially transparent photopolymer is colored with black pigments, post-curing depth is significantly reduced and no homogenous post-curing can be achieved. To obtain comparable mechanical properties by tensile tests, complete cross-linking of the specimen cross-section has to be ensured.

Research limitations/implications

The spatial resolution of the presented measurement method depends on the indenter size and sample hardness. As a result, the resolution of the used setup is limited in the area close to the edges of the specimen.


This paper shows that the spatially resolved hardness measurement provides more information on the post-curing influence than the evaluation of global mechanical properties. The presented method can be used to ensure homogenous cross-linking of stereolithography parts.



Declaration of competing interest: The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Funding acknowledgment: This research did not receive any specific grant from funding agencies in the public, commercial or not-for-profit sectors.


Schlotthauer, T., Nitsche, J. and Middendorf, P. (2021), "Evaluation of UV post-curing depth for homogenous cross-linking of stereolithography parts", Rapid Prototyping Journal, Vol. 27 No. 10, pp. 1910-1916.



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