Development of a novel electrophotographic additive layer manufacturing machine

Abstract

The aim of this research was to develop a low-cost, desktop Additive Layer Manufacturing (ALM) system. A review of commercial ALM systems, a number of which are also called 3D printers, has been undertaken with the intention of identifying a suitable technology to embody within a system demonstrating low-cost and desktop characteristics. The review resulted in a commercially unexploited powder deposition technology, electrophotography, being identified. The significant barriers to implementation of this technology were the limitation of build height in the Z-axis due to electric field depletion and the formation of part material fringing due to the non-uniform electric field present at the boundaries of printed artefacts. Initial trials were undertaken using a laser printing system to determine the printing characteristics of low-cost sacrificial and recyclable materials such as Mica, flour and sugar as well as an engineering polymer, Nylon 12. Mixed results were seen due to the large distribution of particle sizes and their tribocharging characteristics. The identified limiting phenomena were recreated and analysed in order to develop possible solutions, and further testing on the electrostatic behaviour and print acceptance of substrate transfer materials was undertaken with standard styrene co- polymer based toner. Consolidation techniques were investigated and powder layer transfer mechanisms were trialled, culminating in the development of the novel thermal transfer system, eliminating both the build height phenomena and artefact fringing issues. Development of a complete prototype system was undertaken, producing a compact desktop system with novel process architecture. The system functioned through the electrostatic deposition of a polymeric thermoplastic material onto the surface of a registered PTFE transfer substrate. The powder image present on the transfer substrate, was brought into close proximity to a build platform, where the powder layer was heated, consolidated and mechanically transferred using a single moving mechanism. Later concepts describe the novel continuous printing process, exhibiting high productivity while maintaining accuracy and resolution. This work demonstrates a significant step forwards in the apparatus for use in an electrophotographic ALM system. In doing so, solutions to fundamental electrostatic transfer problems, and a clear route for the further development of a commercial electrophotography ALM process have been demonstrated. The system conceptualised, designed and produced within this research holds much novel value and provides a basis and direction for further development.