Light Engines for VAT Photopolymerization

Mask Projection VAT Photopolymerization (MP VPP) is a type of Additive Manufacturing (AM) technology that uses light exposure to selectively harden liquid photopolymers and create Three-Dimensional (3D) objects. A Light Engine, also known as a photo projector, controls the curing process by producing, shaping, and projecting light in or near the Ultraviolet (UV) spectrum onto the photosensitive resin.

Commercial MP VPP products are easily accessible in the market, but their composition is often kept confidential, hindering research. Some researchers have begun developing customized MP VPP equipment and materials as a solution. However, while highly valuable, these investigations usually overlook the manufacturing process's central element, i.e., the Light Engine.

It is essential to gain more knowledge in MP VPP photo projectors. Learning about Light Engines can enable the development of custom projection systems, enhance the control of the manufacturing process, and permit the discovery of novel ways to fabricate 3D objects via MP VPP.

This dissertation aims to shed some light on the field of MP VPP projectors by presenting the development and characterization of a custom MP VPP Light Engine and providing a handbook for researchers to build their own.

The custom photo projector meets most requirements and costs nearly three times less than a similar product. The Light Engine fulfils the target specifications relative to its distortion, throw ratio, exposure time and irradiance control, peak wavelength, irradiance levels, uniformity, and dimensional accuracy of the manufactured samples. However, more time and suitable equipment would be necessary to evaluate the photo projector contrast ratio and lateral resolution adequately. Finally, the constituents of the Light Engine are approximately 34'000 DKK, almost three times less than a comparable commercial device, costing around 96'000 DKK.

Building a working Light Engine has enabled the development of two innovations. The first is a waveguide that acts as a light shaping component. This waveguide is highly customizable, compact, and cost-effective. It generates a uniform, rectangular light distribution at the photo projector image plane. The second component is a new method to cure photopolymers. This approach uses pulsed exposure and has shown promising results by exhibiting improvement in surface uniformity and an increased curing degree in manufactured samples. The work presented in this dissertation facilitates the construction of photo projectors, ultimately strengthening knowledge on the topic, enhancing the control of the manufacturing process, and expanding the range of possibilities.