injection moulding

W. Michaeli (a), F. Klaiber (a), S. Scholz (b)

(a) Institute of Plastics Processing, RWTH Aachen University, Aachen, Germany
(b) The Manufacturing Engineering Centre, Cardiff University, Cardiff, CF24 3AA, UK

Abstract

Telecommunication, information and medical industries have a high growth potential. A key technology for those industries is the replication of microstructures. Precise microstructured parts with functional surfaces can be produced economically by injection moulding. The whole process chain (thermal mould condition, moulding, demoulding, measurement and analysis) must be analysed carefully to ensure the highest precision and reliability. To enable the precise production of such structures fundamental studies were conducted at the Institute of Plastics Processing (IKV). The studies considered several polymers (PMMA, POM) on the one side and various test structures on the other side. In addition an innovative external inductive heating unit was analysed and implemented into the process to heat the cavity surface efficiently. Using this technique cavity surface temperature increase rates of up to 60 K/s have been achieved. A pyrometer was implemented for contact less instant temperature measurement, and controller was used to realise preset cavity temperatures by regulating the inductor power. With the dynamic inductive heating system the moulding accuracy of the microstructures could be increased drastically. The final step of the process chain comprises of the measurement and analysis of the microstructured moulded parts. To analyse the microscopic deviation between the mould cavity and the surface of the moulded part scanning electron microscopy (SEM) and white light interferometry (WLI) was used.

C.A. Griffiths, S.S. Dimov, E.B. Brousseau
Manufacturing Engineering Centre, Cardiff University, CF24 3AA, UK

Abstract

To increase productivity and thus reduce the unit cost, often micro moulding tools incorporate multiple cavities. For this a runner design must be selected, the main function of the runner system is to facilitate the flow of molten material from the injection nozzle into the mould cavity. Therefore, the micro injection filling process depends on the optimum design of runner systems. In this context, the paper reports an experimental study that investigates the flow behaviour of the polymer melts in micro cavities with a particular focus on the relationship between the filling of micro parts and the size of the runner system. In particular, the runner size effects on the micro injection moulding process were investigated. The filling performance of spiral-like micro cavities was studied as a function of runner size in combination with melt temperature, mould temperature, injection speed and holding pressure time employing the design of experiment approach. In addition, the results were analysed further to identify the effects of the runner