Successful partnership Micromilling on 384 component sections to an accuracy of 5 micrometres

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Jongen Werkzeugtechnik GmbH

MOLDINO Tool Engineering Europe GmbH

The tool and mould maker Quarder was asked to produce an injection-compression mould for the manufacture of a component in microfluid technology. However, the requirements were extensive, even for experts.

The toolmaking department at Erwin Quarder Systemtechnik in Espelkamp recently tackled a challenging project with intensive support from the machining tool experts at Moldino. It involved highly complex contour areas that required minute milling cutter diameters, machining to plus 5 micrometre accuracy - and that even on 384 measuring fields for a microfluidic disposable sample carrier called Spechip. In addition, there were extremely long machine runtimes. This injection-compression moulding tool is used to produce the Spechip from transparent plastic. Injection-compression moulding of plastic distributes the pressure on the melt particularly evenly. The component then has very low internal stresses in the solidified state, which is important for optical applications.

The 96 sample channels in the Spechip, each of which has four measuring chambers, can be used to automatically measure the particle concentration in liquids down to the molecular size. Because the Spechip method is based on UV light absorption measurement, the optical properties of the sample carrier are of great importance. According to Quarder, it is one thing to mill within such a small tolerance range, but to manage this at 384 different points was a real challenge for the specialists. In addition, due to the complexity and dimensions of the contour areas, the machining had to be carried out almost exclusively with very small milling diameters of less than 1 millimetre.

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After the construction of the injection-compression mould was complete, the first task was to find out how long this difficult machining process would take in total. A small test workpiece with only six sample channels plus the measuring fields was milled at the beginning. This was done firstly to demonstrate whether it would work at all, and secondly to be able to extrapolate the time needed to do this for the overall machining time. The test was successful right from the start, thanks in no small part to the support of Moldino. Shortly before the start of the Spechip project, Quarder began to increasingly build up HSC machining (high-speed machining) with a focus on high-precision hard milling. In this way, die-sinking EDM was also to be replaced to a large extent by milling.

Projections showed that Quarder had to allow for 200 to 300 hours for each half of the tool - in other words, an extremely long time. Because the company's own machine capacity was not to be tied up for so long by this project, inquiries were made with production service providers. Everyone who saw the component, however, was immediately sceptical. After all, it meant that a machine would be permanently occupied for one to two months. So it was decided to manufacture the Spechip mould in Espelkamp. This was done in blocks, however, so that the machine was available for other orders in the meantime.

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