Material behaviour Polymer flow dynamics in microimpressions: An experimental approach T.V. Zhiltsova a, * , M.S.A. Oliveira a , J.A. Ferreira a , J.C. Vasco b , A.S. Pouzada c , A.J. Pontes c a Department of Mechanical Engineering, University of Aveiro, Portugal b Polytechnic Institute of Leiria/Institute for Polymers and Composites/I3N, University of Minho, Portugal c Institute for Polymers and Composites/I3N, Department of Polymer Engineering, University of Minho, Portugal article info Article history: Received 21 December 2012 Accepted 5 February 2013 Keywords: Microinjection moulding Monitoring Polymer dynamics DOE abstract The melt flow dynamics of acrylonitrile-butadiene-styrene (ABS) and polypropylene (PP) in a variable thickness microimpression was assessed by monitoring cavity temperature and pressure as relevant process parameters. A micromoulding block with a variable thickness cavity was designed, manufactured and instrumented with pressure and tem- perature sensors, acting as monitoring devices as well as flow position markers during filling. A full factorial design of experiment (DOE) was carried to optimize the filling of the microimpression. This study with ABS and PP suggests that mould temperature is the more important parameter for the entire micromoulding thickness range under analysis. Nevertheless, the influence of the melt temperature and the injection speed were found to depend on the micromoulding thickness and the polymer type. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Microinjection moulding (mIM) of thermoplastics is continuously growing in importance due to the possibility of obtaining quickly and inexpensively microcomponents in a variety of complex shapes and configurations. This trend has been enabled by the adaptation of injection moulding equipment and moulds, and miniaturization of the macro injection process, but still lacks a thorough un- derstanding of the underlying thermo-rheological pro- cesses at the microscale [1]. As Griffits and coworkers demonstrated, the reduced dimensions and high surface to volume ratios of microparts call for higher injection pres- sure and faster injection speed to avoid premature melt freezing and incomplete filling [2]. In the flow conditions associated with micromoulding, the polymer is subjected to excessive shear stresses, which are likely to promote polymer slippage over the mould wall and subsequent damage of the microcomponent [3] or abrasion of the moulding surface [4]. Many attempts have been performed to establish a cause-effect relationship between the injection moulding process conditions and the replication quality of the microparts. Preheating the mould tool above the glass transition temperature of polymer is reported by Liou and Chen [5] to promote filling and improve the overall part quality of poly(methyl methacrylate) (PMMA) microparts. The weld line strength of polypropylene (PP) micro-tensile specimens was improved when the mould was thermally controlled with a variotherm system [6]. Improvement of the microcomponents replication in a wide range of poly- mers was documented by Attia and Alcock [7] and Sha and coworkers [8] using the upper temperature limit recom- mended for conventional moulds. Meister and Drummer reported a study where the mechanical properties of polyamide micro moulded tensile bars were compared with those of milled micro tensile bars. The deterioration of * Corresponding author. Department of Mechanical Engineering, Campo Universitario de Santiago, 3810-193 Aveiro, Portugal. Tel.: þ351 234370830; fax: þ351 234 370 953. E-mail address: tvzhiltsova@ua.pt (T.V. Zhiltsova). Contents lists available at SciVerse ScienceDirect Polymer Testing journal homepage: www.elsevier.com/locate/polytest 0142-9418/$ – see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.polymertesting.2013.02.005 Polymer Testing 32 (2013) 567–574