Article
Effect of Post-Process Curing and Washing Time on Mechanical
Properties of mSLA Printouts
Bartłomiej Nowacki
1
, Paweł Kowol
1
, Mateusz Kozioł
2,
* , Piotr Olesik
2
, Jakub Wieczorek
2
and Krzysztof Wacławiak
2
Citation: Nowacki, B.; Kowol, P.;
Kozioł, M.; Olesik, P.; Wieczorek, J.;
Wacławiak, K. Effect of Post-Process
Curing and Washing Time on
Mechanical Properties of mSLA
Printouts. Materials 2021, 14, 4856.
https://doi.org/10.3390/ma14174856
Academic Editors: Arkadiusz Gola,
Izabela Nielsen and Patrik Grznár
Received: 31 July 2021
Accepted: 25 August 2021
Published: 26 August 2021
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1
Faculty of Electrical Engineering, Silesian University of Technology, ul. Bolesława Krzywoustego 2,
44-100 Gliwice, Poland; bartnow218@student.polsl.pl (B.N.); pawel.kowol@polsl.pl (P.K.)
2
Faculty of Materials Engineering, Silesian University of Technology, ul. Krasi ´nskiego 8,
40-019 Katowice, Poland; piotr.olesik@polsl.pl (P.O.); jakub.wieczorek@polsl.pl (J.W.);
krzysztof.waclawiak@polsl.pl (K.W.)
* Correspondence: mateusz.koziol@polsl.pl; Tel.: +48-32-603-4369
Abstract:
The article discusses the influence of the post-process on the mechanical properties of
elements produced with the use of the mask stereolithography (mSLA) method. Printed samples
were subjected to the following post-process steps: Washing and post-curing, at various times. Then,
static tensile and static bending tests were carried out, as well as Shore D hardness measurements for
the inner and surface part of the sample, as well as profilographometric analysis of the surface. The
post-curing time has been found to strongly affect the tensile and bending strength of printouts, and to
improve their surface quality. Washing has an ambiguous effect on the strength of the printouts, but,
in the end, it was found that extended washing slightly reduces the strength. Washing significantly
affects the quality of the printout surface. A washing time that is too short results in a surface that
strongly resembles the printing process, with high roughness. Increasing the washing time to 10 min
lowers the roughness by one order of magnitude. Post-curing has also been shown to be beneficial for
the cured sample with the application of shielding water. This approach results in an improvement
in the flexural strength of the printouts. In general, the obtained research results indicate that, for
printouts with cross-sectional dimensions of several mm, the optimal washing time is no more than
10 min and the post-curing time is at least 30 min.
Keywords:
3D printing; mask stereolithography; post-process; mechanical properties; hardness;
profilographometry
1. Introduction
Stereolithography (SLA) is historically the first used additive manufacturing (AM)
process [
1
,
2
]. This technique is characterized by the smallest number of process parameters.
It guarantees an excellent quality of the print surface compared to other AM techniques. It
consists in hardening the photopolymer in a liquid state, with the use of ultraviolet (UV)
light. The polymerization process consists of twostages. Initially, gelation occurs, which is
the process of creating an infinite molecular network [
3
,
4
]. Then, the vitrification process
begins, i.e., a gradual thermoreversible process of the formation of a glassy material [
5
,
6
].
The printed “green” element consists of the following two phases: gel and sol. The
printout is anisotropic, due to the additive nature of the process [
2
,
5
]. A problem occurs
in reaching the inner areas of the printout, by UV rays, which is necessary to cure the
sol phase. A properly long exposure time leads to polymerization of unlit areas, due to
a chain reaction that is maintained by the large amounts of photoinitiators added to the
resins that are used in SLA technology [
5
]. Initially, a UV laser light source was used for
curing the polymers. In recent years, however, devices using light electric diodes (LED)
have appeared. Devices of this type use LED matrices to harden the appropriate tracks
in the resin, producing a properly pathed layer. This technique is referred to as mask
Materials 2021, 14, 4856. https://doi.org/10.3390/ma14174856 https://www.mdpi.com/journal/materials
