Design of an endoscopic micro optical part for fabrication with micro two shot injection moulding

Abstract

Micro two shot injection moulding (µtwo shot IM) is a manufacturing process capable of simultaneously replicating two polymeric parts and assembling them; removing the requirement for costly micro assembly. Endoscopes are used in medical environments to observe areas that are otherwise unobservable. µTwo shot IM has the potential to simultaneously replicate and assemble polymer lenses for endoscope imaging and assembling them to their required housing. In view of this, this paper contributes a case study part for application of µtwo shot injection moulding in the fabrication of an endoscopic micro optical component. This paper covers several aspects involved in the design of such a part. This novel design concept consists of an optical component and a housing component moulded sequentially on top of each other using µtwo shot IM. The lens component consisted of three lenses with a common base moulded as the first shot. The second shot moulded on onto the optical component was the housing component incorporating an external thread for interchangeability. From a material selection exercise it was concluded that cyclic olefin copolymer (COC) shall be used as the optical material and polyoxymethylene (POM) shall be used as the housing material. One major concern in the design of such a part is the deformation of the optical material by the housing material due to softening via heat transfer. Simulations of such a scenario were carried out and it was indicated that the functionality of the optical material shall not be compromised