Technical Paper: PIM International, Vol.1 No. 3 September 2007, pages 56-58, 1969 words

Authors: L. Merz, S. Rath and B. Zeep

Forschungszentrum Karlsruhe GmbH, Institute for Materials Research III, Postfach 3640, 76021 Karlsruhe, Germany

Abstract

In the last few years micro system technology has gained increasing attraction. Within this time powder injection moulding (PIM) has established itself as a suitable production process for micro parts made of advanced materials. Starting with ceramics and stainless steels, now also cemented carbides can be used for these purposes. First results of feedstock development with different tungsten carbide powders, different amounts of cobalt as binder metal, rheological investigations, injection moulding of micro parts, sintering experiments, hot isostatic pressing and examination of micro structures were carried out.

Introduction

The economic production of micro mechanical systems does not only require large numbers of components, there is also a need for time and cost effectiveness and for net shape fabrication as finishing of parts in sub millimetre scale is very cost intensive or even impossible. Therefore, reduction or even prevention of finishing is an important objective of the current research in micro parts production. Especially for parts with high wear resistance, e.g. parts made of cemented carbides, micro powder injection moulding (Micro PIM) represents a process for future mass production of components or even integrated systems with reduced or without finishing [1-5].

Due to their small size, micro parts are usually injection moulded on a substrate plate and have to be separated manually, afterwards. Compared to that the production of isolated micro parts is far more efficient. Because of their small size micro parts require good surface quality as well as high dimensional accuracy, especially when interacting with each other. This is only realised with small grain sizes after sintering and therefore feedstocks made of powders with small particle sizes are required [6,7]. Additionally, a mould insert of high quality and low surface roughness is necessary for injection moulding [8].

For complete form filling and damage free demoulding in combination with decreasing size of the moulded parts, tailored binders are used for feedstock production [9]. Besides a tool concept for moulding and damage free demoulding, the debinding and sintering strategy is important to establish the complete process. An overview of the process chain is given, including feedstock development, mould insert production by millcutting, tool concept, mass fabrication, debinding and sintering. Results will be presented including injection moulded WC/Co gear wheels with diameters after sintering down to lt;750 µm.

Further sections of this article include:

- Feedstock development
- Powder injection moulding
- Debinding and sintering
- Conclusions and outlook
- References

Figures and Tables:

Fig. 1 Rheological data of the WC/12Co feedstock showing pseudo plastic behaviour up to high shear rates.

Fig. 2 Three plate mould for the production of micro gears with runner plate (large picture, right) and ejector plate with micro structured mould insert (large picture, left). Upper left: Mould insert in detail. Lower left: Injection moulded WC/12Co green parts.

Fig. 3 Injection moulded gear wheels made of WC/12Co (solid loading: 55 Vol.%; from left to right: green part as demoulded, chemically debound and sintered).

Fig. 4 Dilatometry of WC-12Co. Length of debound green part: 7mm; heating rate: 3 K/min; dwell temperature: 1500°C; dwell time: 60 min

Fig. 5 Optical microscopy image of a sintered WC-12Co microstructure: Porosity and particle size distribution

Fig. 6 SEM- image of a sintered WC-12Co microstructure