Abstract This paper focuses on tuning the micro injection moulding process parameters. In this study four process parameters namely, barrel temperature, mould temperature, holding pressure and injection speed were considered. In order to capture their behaviour a L16 Orthogonal Array with two levels for each parameter was employed to produce the design of a 15 mm x 20 mm x 1 mm microfluidic platform using Cyclic Olefin Copolymer (COC), a common polymer. The demoulding force was measured during the micro injection moulding process. The sixteen trials were repeated ten times to incorporate process variation, systematic and random noise in the experimental procedure. The results were analysed using Taguchi method to identify the influence of the process parameters upon the demoulding force and their sensitivity to noise. In addition, the results also indicated either the presence or absence of the two level interactions between these process parameters. This study has contributed to understanding the characteristics of these process parameters in terms of their main effects, interactions and sensitivity to noise and to tune them for their optimal performance.71221

Keywords: Micro injection moulding, design of experiments, orthogonal array, Taguchi analysis.

1. Introduction

There is rapid improvement in micro-engineering technologies which leads to an increasing trend towards product miniaturisation. Components and products in micro/meso scale are gaining importance significantly in areas like communication, IT, health care, automotive sectors and consumer goods. Moreover, the development of new miniaturized products including medical and biotechnology give microtechnologies an important role in facing the macro and nano worlds [1, 2]. Micro Injection Moulding (MIM) is a reliable replication technique and economic in producing a wide range of micro components such as micropumps, microgears, and optical grating element in large quantities. In all of these applications, the quality of the micro features found on the replicated parts is a factor which influences the reliability of the selected replication process. This depends greatly on their size, aspect ratio, and overall geometry [3].

The surface quality achievable and aspect ratio in replicating the micro features underline the important characteristic of any micro fabrication process and determine the  manufacturing restriction  of a  given process  or material

combination [4]. For example, the surface quality and edge definition must be carried out systematically. In addition, achieving a high aspect ratio to mould micro features is still difficult [5]. Thus, in micro injection moulding process it is very essential to understand the factors that affect the replication capabilities [4].

To improve the quality in replication process of micro injection moulding, many research groups have investigated different areas like processing, tooling innovation, materials and insert manufacture. Although the high setting of melt temperature, mould temperature and injection speed are considered as the best result for producing quality parts the consequences on high mould temperature introduces tool innovation for heating and cooling the tool [6]. Hence, process output decreases and the cost of the moulded parts increases.

Demoulding is one of the micro injection processes that affect the quality in replication. When a replicated part reaches a stable solid form inside the mould, a series of ejector pins will forcibly eject the part out from the replication tool. Suitable amount of force are needed to overcome the retarding forces which build up at the tool interface and component due to friction and adhesion. During development of tooling in

injection moulding designers endeavour to optimize replication tool to minimize the demoulding force and resultant stress on replicated parts.

Previous research on micro injection moulding has shown that a high mould temperature is most important in achieving good quality of replication part but it increases the cost and time. Hence, an appropriate determination of mould temperature is essential to improve quality and output, and reduce the cost. In this paper, a design of experiment is used to establish the parameter levels that affect the micro injection moulding in their replication capabilities. In this study, the following process parameters such as temperature of barrel, temperature of mould, holding pressure and injection speed into mould were considered. Demoulding force was used as the measured output for setting the level of process parameters. The twofold objectives of this study were: to investigate the level of main process parameters which affect the demoulding force in order to achieve a good quality in the replication of parts; and to understand the effect of process parameters on the micro injection moulding process.