Investigation into Additive Manufacturing for Controlling Thermal Expansion in Optical Applications

The design of components for the optical industry requires a consideration into the thermal expansion co-efficient of the materials used. Often the body material of an optical system exceeds the thermal expansion of the lens material. This can lead to lens decentre and misalignment. This thesis will investigate the use of additive manufacturing to tailor the thermal expansion co-efficient of the parts produced so that they match the thermal expansion co-efficient of the lens material. Several state-of-the-art additive manufacturing methods are investigated to achieve this. These include metal laser powder bed fusion, polymer fused deposition modelling, and continuous fibre re-enforced polymer fused deposition modelling. A method used to tailor the co-efficient of thermal expansion focuses on the design of the components, while another method focuses on the adjustment of the materials used. The design of an optical system features two metals with different thermal expansion co-efficients which work together to produce a different overall thermal expansion co-efficient similar to the lens material. Another method investigates the use of the low expansion invar alloy, and the controlled expansion aluminium - silicon alloy. Adjusting the elemental constituents by mixing the alloy powders with elemental powders has shown to successfully change the overall constituents of the printed alloy, opening up the avenue for tailoring thermal expansion in-situ with the build process. A promising method of controlling thermal expansion with polymers is shown by introducing inclusions into the polymer filament feedstock material. The introduction of carbon and glass fibres as well as metal and organic particles shows a remarkable ability to adjust the co-efficient of thermal expansion over a wide range. Using a fibre polymer printer, a composite can be printed with a layer of carbon, glass, or Kevlar fibre laid in a predetermined orientation. This method provides the widest range of thermal expansion control.