The finite element analysis of melt flow behaviour in micro-injection moulding C A Griffiths*, S S Dimov, E B Brousseau, and M S Packianather Manufacturing Engineering Centre, Cardiff University, Cardiff, UK The manuscript was received on 26 July 2007 and was accepted after revision for publication on 12 May 2008. DOI: 10.1243/09544054JEM965 Abstract: Micro-injection moulding as a replication method is one of the key technologies for micromanufacture. The understanding of process constraints for a selected production route is essential both at the design stage and during mass production. In this research, an existing finite element analysis system is used to verify the effects of four process parameters: the melt and mould temperatures, injection speed, and part thickness. Special attention is paid to the melt flow sensitivity when filling microchannels, particularly the factors affecting the shear rate, pressure, and temperature. In particular, the simulation model was used to investi- gate the flow behaviour of two polymer materials, polypropylene and acrylonitrile butadiene styrene, by varying the process parameters. Then, the results of this investigation were com- pared with those reported in an experimental study. Conclusions are made about the accuracy and sensitivity of the proposed simulation model. Keywords: micro-injection moulding, finite element analysis, viscosity, process parameters, response surface methodology 1 INTRODUCTION With the rapid development of micro-engineering technologies there is an increasing trend towards product miniaturization. The development of new microdevices is highly dependent on manufacturing systems that can reliably and economically produce microcomponents in large quantities. In this context, micro-injection moulding of polymer materials is one of the key technologies for micromanufacturing. Components manufactured by micro-injection moulding fall into one of the following two cate- gories. Type A consists of components with overall sizes of less than 1 mm while type B components have larger overall dimensions but incorporate microfeatures with sizes typically less than 200 mm [1]. Feature sizes and aspect ratios achievable in replicating microcomponents are the most important characteristics of any microfabrication process and determine the manufacturing constraints for a given process–material combination. Therefore, it is not surprising that the critical dimensions of various products are mainly associated with the aspect ratios in relation to feature sizes of microstructures [2, 3]. Consequently, it is important to study the factors that affect the replication capabilities of the micro- injection moulding process. For effective processing of microparts the polymer viscosity is a factor of significant importance. The balance between keeping the polymer temperature sufficiently high to fill the cavity and ensuring at the same time that it does not fluctuate above a critical point is essential for achieving a stable process. Exist- ing research in micro-injection moulding has found that high melt and mould temperatures and high injection speeds facilitate the filling of microcavities with high aspect ratios [4]. However, high process settings can lead to a temperature-related melt frac- ture of polymers resulting from the increase in the shear stress. In addition, part quality can be affected by slip–stick. This phenomenon of polymer chains alternately anchoring and debonding from tool sur- faces was found to be dependent on the molecular weight of the polymer and the surface quality of moulding cavities [5–7]. In this context, the beha- viour of pressurized polymer materials in contact with tool surfaces, particularly microchannels, could *Corresponding author: Manufacturing Engineering Centre, Cardiff University, Queens Building, Newport Road, Cardiff CF24 2AA, UK. email: griffithsca1@cf.ac.uk JEM965 Ó IMechE 2008 Proc. IMechE Vol. 222 Part B: J. Engineering Manufacture 1107