Applied Metrology in Additive Manufacturing

Abstract

The fabrication of products by additively building them layer by layer promises exciting possibilities, including realisation of Industry 4.0, sustainability, local manufacturing and a measurement dataset which describes every voxel of the produced part. Measurement methodologies, which can measure such a dataset and interpret the result, are therefore needed. A cost-effective additive manufacturing technique, which can help with the worldwide plastic pollution problem, is Fused Filament Fabrication. This is an open source concept and ideal for adoption by developing economies. Measurement approaches are needed, though, to develop this technology beyond a rapid prototyping and modelling tool, to a functional production solution. This thesis develops cost effective, accessible solutions to improve the material feed mechanism, which is one of the most critical process components. A detailed review of the process steps is given first, which also contributes to this still rapidly developing field. This review includes the motion tool chain, from the stepper motor actuation to the firmware implementation to realise motor control. The feedstock materials and the liquefier design are also presented. Five methods for optimisation of the process are developed and experimentally tested. This includes the optical monitoring of the feed mechanism, which can measure the volumetric flow rate, a method to measure the exit flow rate, a pressure sensor to measure the liquefier state, single print optimisation with design of experiments and a link between the in-process and post process measured data. This is taken further by presenting the Vapour Deposition Fabrication concept, which is like the Dynamic Stencil Lithography process, but realised with a configuration based on the Fused Filament Fabrication electronics and firmware. The design and construction of the first Vapour Deposition Fabrication micro-printer are presented. This thesis finds that rate material addition in additive manufacturing is an important process variable, which needs to be monitored with indirect methods. Furthermore, standardisation is important for additive manufacturing, and this includes how G-codes are interpreted by the printer firmware. Finally, many process parameters must be optimised, and the single print optimisation method shown here is an example method, which can form part of a complete printer development, qualification and conformance solution.