Main efforts during the investigation of the MIM process were concentrated on the filling phase of the process and the mould (insert) making. To improve the filling behaviour of micro-structures different modifications have to be made to the process, compared to conventional injection moulding. To avoid the so-called diesel effect, the burning of polymer by trapped and compressed air in blind holes, a vacuum system is attached to the machine. Especially with LIGA moulds the problems of trapped air increase due to the prismatic character of the inserts. Equipped with a seal and a vacuum pump, the cavity is sucked empty shortly before the regular injection of the polymer starts. Furthermore, to increase the time the polymer can flow into the cavity without freezing, an external heating system is attached to the machine, to inductively heat up the surface of the insert in a short time to improve filling. The commonly used technique of oil heating is far slower and much more energy consuming, because the whole mould has to be heated (and cooled) by oil. With the inductive heating, just the surface of the insert is heated up. Furthermore it is found that polishing the insert surface improves the demoulding behaviour of the micro structures. Far less structures were ripped off. In mould making conventional techniques achieved great progress during the last years, competing with techniques like UP milling. They can already be used for special parts in mould making (see demonstrator), but cannot yet achieve as small structures as the LIGA technique can do right now.
For polymer manufacturers, this technique opens up new opportunities and markets. The never-ending trend towards miniaturisation of (mainly electronic) devices requires techniques that allow micro-injection moulding of polymers. For producers of mass polymers such as PC or POM, these markets represent volumes that are by far too small for them to justify research in this area. For manufacturers of high-end engineering polymers such as PEEK, LCP or PPS these potential volumes however can be interesting enough to continue to work on this subject.
