Origin of shrinkage, distortion and fracture of photopolymerized material

The influence of different laser power settings and layer pitches on the mechanical properties, microstructure and stability of parts built via ultraviolet (UV) laser scanning and subsequent post-curing under an intense UV light was investigated. It was observed that both UV power during scanning and the thickness of the layer have a strong influence on the mechanical properties and shape stability of the parts. Microstructural observation shows that two types of defects are generated during laser UV curing. The first type is the gas hole which is formed from air bubbles. It normally appears elliptical in shape. The second type is the cavity in which uncured resin can be found. Cavities can normally be observed at the upper last scanned layers of a cured specimen. They are associated with low laser power setting and/or large layer pitch. Measurements taken from the experiment indicate shrinkages appearing in two different directions.