Vat Photopolymerization Process Chain

Macarena Mendez Ribo*

*Corresponding author for this work

    Research output: Book/ReportPh.D. thesis

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    Mask-projection vat photopolymerization (MP VPP) is an additive manufacturing (AM) process that uses ultraviolet radiation to selectively cure liquid photopolymer in a layer-by-layer fashion. The combination of precise optical control and fast reaction chemistry enables MP VPP) to build complex 3D objects with microscale resolution at speeds unmatched by other AM technologies. This ability to produce custom, precise parts at low cost has propelled VPP) in various medical industries including general orthopedics, dental implants, and hearing aids. More recent advances in resolution continue to drive VPP) presence in microfabrication applications like microfluidics, microelectromechanical systems, and metamaterials.

    Despite being the first AM technology, patented and commercialized in the late 1980s, VPP) growth has been hampered frequently by proprietary restrictions. Today, these restrictions often limit user access to machine controls, which prevents a full understanding of the process and slows technological evolution.

    The aim of this dissertation is to break this barrier through the development of an open architecture vat photopolymerization platform— a machine that grants full access to the user. This is accomplished by exploring the physical and digital subsystems that comprise VPP), both in theory and experiment. Each subsystem is characterized and scrutinized experimentally to enhance performance. Success of the resulting platform is demonstrated at several stages by the manufacture of parts for application in soft-tooling, microfilters, and microstructured functional surfaces including demonstration of a reliable minimum pixel pitch of 7.56 μm.

    The open architecture MP VPP) platform allows for control of all components and parameters. Accordingly, when a new material or unique part feature is posed, a series of calibration and testing methods are necessary to achieve optimal build results. In this work, two calibration methods are proposed, selection of which depends on the desired part feature size. For macroscale features, a parametric study reveals how to uniformly cure samples. Microscale features are found to be particularly sensitive to the amplitude of radiation applied, so a second method is proposed which adapts the radiation to the needs of each layer in the geometry. This is achieved by generating and projecting grayscale images to realize layers with optimum, homogeneous crosslinking.

    The final step of the process chain involves post processing, which is often overlooked in literature and even by commercial VPP) machine manufacturers. Special attention is placed on the cleaning and drying stages, where the importance of matching material and solvent selection is highlighted. Finally, a solvent recovery method and prototype are described which led to a patent application. The method aims to solve a problem of toxic waste generation by solvent recycling and waste neutralization.
    Original languageEnglish
    Place of PublicationKgs. Lyngby
    PublisherTechnical University of Denmark
    Number of pages214
    ISBN (Print)978-87-7475-631-6
    Publication statusPublished - 2020


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