Micro injection moulding : process monitoring and optimisation

The advances in micro engineering and especially micro products and micro components with functional micro and nano structures / features are directly dependent on the advances in manufacturing technologies for their scale up production. Micro injection moulding is one of the key technologies for cost affective serial production of micro components. In this thesis, the process capabilities and constraints of this technology were studied systematically. More specifically, new tool making process chains and various process factors affecting the micro injection moulding process were investigated. The manufacturing capabilities of this technology were further analysed by investigating the filling behaviour of micro cavities, the influence of air in micro cavities and the forces occurring during the demoulding stage. Chapter 2 of this thesis reviews the slate of the art in micro tooling and micro injection moulding. In Chapter 3 an advanced condition monitoring system was developed to better understand the behaviour of the injection moulding process. In particular, cavity pressure sensors were utilised to analyse interdependences between process conditions and key characteristics of cavity pressure curves. Chapter 4 investigates the influence and effects of air inside micro cavities. A design of experiments’ study was carried out to identify process settings for achieving an optimum filling of micro cavities In particular the flow length inside the cavity was investigated to judge about the process performance. Next, the demoulding stage of the injection moulding cycle was studied in Chapter 5. In particular, ejection forces were analysed to investigate the influence of different process settings on demoulding behaviour of polymer parts. This is especially important in order to avoid any part damage during demoulding. In Chapter 6 micro stereolithography was used to fabricate mould inserts for micro injection moulding. Experiments were carried out with such mould inserts, and the tool life in relation to process settings for both the manufacture of the inserts and their replication performance, was studied systematically. Finally, Chapter 7 summarises the main conclusions and contributions to knowledge of this research. Also, future research directions in the area of micro injection moulding are proposed and briefly discussed The main findings of this research can be summarised as follows: • Indirect measurement methods can be utilised to monitor cavity pressure conditions in micro injection moulding and it was shown that Pmax, Pwork and Prate were dependent on the materials and processing conditions. • The performance of the u-IM process can be improved by understanding the effects of V1 and air evacuation on Qmax, Q, and the part flow length. High u-IM process settings and a limited venting through the primary split line have a significant impact on the filling performance. The u-IM process performance can be improved by incorporating secondary vents and by applying vacuum methods for air evacuation. • Pmax, Pwork and Fe max were dependent on the processing conditions and there is a direct correlation between cavity pressure and demoulding force. The position of the pressure sensors is important, but the readings of both sensors correlate. The holding pressure has the highest impact on the maximum demoulding forces. Rapid tooling can be applied successfully in u-IM and offers a faster, cheaper and highly flexible manufacturing route for producing prototypes in the final material. Only the uSL inserts produced with a layer thickness of 20 um (less undercuts) survived during the demoulding stage. The best results were achieved with PP, followed by PC. ABS polymer parts couldn’t be replicated successfully.EThOS - Electronic Theses Online ServiceGBUnited Kingdo