Abstract Microinjection moulding of high-aspect-ratio microstructures is important for the fabrication of various microsystem components。 Successful microinjection moulding technologies may depend on accurate understanding of the cavity filling process of a polymer melt and a reasonable prediction of the filling degree in a microchannel。 To date, there has been a lack of adequate investigations of the filling process in injection moulding for microcantilever structures。 In this study, the microinjection moulding of microcantilevers was performed with dynamic mould temperature control and cavity pressure measurement。 The influences of injection flow rate, peak cavity pressure, melt temperature, and mould temperature on the filling length were observed。 A simple, onedimensional analytical model was developed that describes the relationship of the four process parameters with the filling length。 The measured cavity pressure profiles were applied to the numerical analyses。 The   model   was   validated   by   comparison   with   both 76186

experimental measurements and simulation results and showed acceptable agreement among the processing parameters。 The development of the cavity pressure and the temperature transition of the melt in the microchannels had a critical influence on the filling process。 The increase in the mould temperature over the glass  transition temperature during a filling stage using the mould temperature control system was the most effective way to maximize the filling length。 The combination of the theoretical model and cavity pressure measurements can be used to predict the filling length and design the injection mould for high-aspect-ratio microstructures。

Keywords Injection moulding 。 Microstructure 。 Microcantilever 。 Highaspect ratio 。 Filling

1 Introduction

University, 237, Sangidaehak-ro, Siheung-si, Gyeonggi-do 429-793, South Korea e-mail: wkim@kpu。ac。kr

Injection moulding is the most suitable manufacturing process for plastic parts because of its low costs and mass production capabilities。 It can meet the increasingly stringent requirements for shape complexity, high precision, and varied product applications。 In recent years, injection moulding has been explored for the fabrication of micro/nanoscale parts and surface structures in the fields of microfluidics, microsensors, microoptics, and other microsystem technologies。 Mass production of micro/nanoscale features by the injection moulding techniques has become increasingly popular across a number of industries such as health care, display/lightning, solar energy, and automotive [1–3]。文献综述

Microcantilevers are one of the key elements in microsensors (e。g。 biochemical sensors, calorimetry

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sensors, humidity sensors, accelerometers, and atomic force microscopes) because they are sensitive to small changes in mass and temperature。 Thus,  static deflection and dynamic vibration frequencies change by surface reactions, such as stress and load [4]。 Injection- moulded polymer microcantilevers have definite advantages, including low cost, disposability, and availability of perse polymer materials。 Injectionmoulded microcantilever beams of 2 to 40 μm thick were produced, and the moulded microcantilevers showed performances almost equal to those of silicon- based microcantilevers [5, 6]。 More recently, surface- patterned microcantilever arrays were manufactured by nanoimprinting as well as microinjection moulding [7, 8]。

Polymeric microcantilever structures with high aspect ratios can be fabricated by filling the polymer melt into microchannel cavities。 As the cross-sectional area decreases, the filling length becomes limited because the melt cools and solidifies quickly in the cavities。 This is caused by the increased surface-to- volume ratio and is common for other microscale parts。 The filling process in microinjection moulding is more complex because heat transfer at the melt-mould wall interface, wall slip and surface tension effect, and the compressibility of the melt are reported to be different from those for conventional injection moulding [9–14]。