Micro and nano structuring of sapphire for Micro Injection process investigation ICOMM 2014 No.53 S. Bigot 1 , F. Lacan 1 , H. Hirshy 1 , P. V. Petkov 1 , M. Babenko 2 , G. G. Castro 2 , J. Sweeney 2 , H. Ugail 3 and B.Whiteside 2 1 Institute of Mechanical and Manufacturing Engineering, Cardiff School of Engineering, Cardiff University, UK 2 Polymer IRC, School of Engineering, Design and Technology, University of Bradford, UK 3 Centre for Visual Computing, School of Computing, Informatics and Media, University of Bradford, UK Abstract The work presented in this paper contributes to a wider research objective aiming at gaining a better understanding of the injection moulding process at microscales. More specifically, it contributes to the development of a new modelling approach combining experimental observation and mathematical modelling to characterise thermal contact resistance that results from the imperfections present on the surfaces when two surfaces are brought in contact. Thus, this paper describes micro and nano structuring technologies (Focus Ion beam and Laser Ablation) used to structure sapphire inserts that are used as ”windows” in the injection moulding process, allowing thermal measurements with a high speed thermal camera whilst sapphire structures are filled with polymer melt. Keywords: Sapphire, Focus Ion Beam, Laser Ablation, Injection Moulding, micro and nano structuring. 1. Introduction The computer simulation of polymer processes has advanced significantly in recent years. This has been accompanied by improved understanding of the mechanical behaviour of melts, and the success of proprietary simulation software products. However, there is one particular area in which knowledge and understanding is in a primitive state that greatly limits the predictive power of simulations. This concerns the interface between the polymer and the process tooling, often a metal/polymer melt interface. Here, heat transfer is a highly significant issue, as polymer melt contacting a metal surface is generally cooled, and the rate of cooling can have a significant influence on both the flow characteristics and morphology development during the process. These effects are particularly relevant to thin- walled moulding and moulding of microscale features and geometries, where the surface area to volume ratio of the components far exceeds those typically encountered in conventional moulding. This paper takes part in a wider investigation aiming at producing an accurate predictive model of the phenomenon mentioned above. A truly predictive simulation of melt processing would incorporate a verified model of the polymer/tool surface interaction. An overview of the proposed modelling methodology, which uses a combination of experimental observation and mathematical modelling to characterise thermal contact resistance that results from the imperfections present on the surfaces when two surfaces are brought in contact, is given in a previous publication [ 1]. Of particular significance is the mould surface topography at a microscopic level. In practice, tool surfaces are of variable and complex topography, and it is necessary to use surface models that are statistically representative, based on observation of actual mould surfaces. 2. On-going investigation details Detailed measurements of temperature fields associated with the contacting melt surface are now possible using a high speed infra-red (IR) camera together with an instrumented micromoulding machine [2]. Thus, the ongoing investigation [1] aims at studying the effect of tool surface by introducing tailored surface topographies on the inside of a sapphire window incorporated into an injection moulding tool. Experimental works are investigating cooling behaviour of polymer melts using an optimised injection mould tool design mounted on a Battenfeld Microsystem 50 micro injection moulding machine. The design is modular to allow the study of a range of cavity thicknesses and single crystal sapphire inserts patterned with a range of microscale surface structures. Sapphire has been chosen due to the following reasons: - Sapphire is robust enough to be employed in the high pressure/high temperature environment characteristic of moulding processes. - Sapphire’s heat transfer coefficient and specific heat capacity are close to that of typical tool steels providing an experimental environment which is directly relevant to industrial processes. - Sapphire transmission varies within 0.17 to 6.5 μm making it ideal for infrared measurements and leaving thermal fields virtually unaffected.