Post-cure shrinkage of photo-sensitive material used in laser lithography process

Shrinkage causes distortion and warpage due to the internal stresses built up during fabrication, and greatly influences the dimensional accuracy of a part. This paper presents an experimental study on the relationships between the key parameters of the laser lithography (LL) (or commonly known as Stereolithography) process and the resulting post-curing shrinkage due to thermal and ultraviolet (UV) exposure. The UV-sensitive material used in the experiment is an acrylic-based resin, namely SCR-310. The post-curing process causes partially-cured and uncured resin to be further polymerised and is necessary for the improvement of the final mechanical properties of the parts. In principle, a larger laser power or a smaller layer pitch will result in a smaller amount of partially-cured or uncured resin, with less shrinkage after post-curing. A better understanding of the behaviour and characterisation of the shrinkage process during thermal and UV treatments will help to reduce the post-cure distortion, and will lead to more accurate rapid prototypes produced by the LL process. The origin of shrinkage from photo-polymerisation is closely examined through the measurements along both the scanning and transversal directions.