• Evaluation of heat transfer at the cavity-polymer interface in microinjection moulding based on experimental and simulation study

      Babenko, Maksims; Sweeney, John; Petkov, P.; Lacan, F.; Bigot, S.; Whiteside, Benjamin R. (2018-02-05)
      In polymer melt processing, the heat transfer coefficient (HTC) determines the heat flux across the interface of the polymer melt and the mould wall. The HTC is a dominant parameter in cooling simulations especially for microinjection moulding, where the high surface to volume ratio of the part results in very rapid cooling. Moreover, the cooling rate can have a significant influence on internal structure, morphology and resulting physical properties. HTC values are therefore important and yet are not well quantified. To measure HTC in micromoulding, we have developed an experimental setup consisting of a special mould, and an ultra-high speed thermal camera in combination with a range of windows. The windows were laser machined on their inside surfaces to produce a range of surface topographies. Cooling curves were obtained for two materials at different processing conditions, the processing variables explored being melt and mould temperature, injection speed, packing pressure and surface topography. The finite element package Moldflow was used to simulate the experiments and to find the HTC values that best fitted the cooling curves, so that HTC is known as a function of the process variables explored. These results are presented and statistically analysed. An increase in HTC from the standard value of 2500 W/m2C to values in the region 7700 W/m2C was required to accurately model the observations.
    • Micro and nano structuring of sapphire for micro injection process investigation,

      Bigot, S.; Lacan, F.; Hirshy, H.; Petkov, P.V.; Babenko, Maksims; Gonzalez Castro, Gabriela; Sweeney, John; Ugail, Hassan; Whiteside, Benjamin R. (2014)
      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.