Precision machining Revolutionising surface quality: Kern Micro HD enables high-precision mould inserts at Vema

Source: Kern Microtechnik Reading Time: 6 min

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At Vema, the production of high-precision mould inserts with polished surfaces forms the key foundation for the success of the downstream plastic injection moulding shop. What in 2021 still required several process steps and final manual work, has since 2022 been possible in a single clamping operation without manual rework thanks to the Kern Micro HD high-end machining centre, equipped with an MHT medium distributor.

Roughing (B04a) and finishing or polishing can always be done in one clamping with the Kern Micro HD.
Roughing (B04a) and finishing or polishing can always be done in one clamping with the Kern Micro HD.
(Source: Kern Microtechnik)

When modern vehicles say “let there be light”, it is not uncommon to find high-end lenses from Vema behind them. This is because the medium-sized family business produces these lenses in a wide variety of forms for leading car manufacturers. In addition, other demanding industries such as sanitary and medical technology are among the large customer base of the company headquartered in Krauchenwies, Germany.

Vema is a full-range supplier which, when it was founded a good 40 years ago, was already committed to a number of principles that are still valid today. Master toolmaker Werner Veser, managing director and one of the founders, explains: “My founding partner Josef Macho and I were in agreement from the very beginning. Firstly, we offer consulting, tool/mould making and plastic injection moulding from a single source. Secondly, we offer precision at the highest level. That proved to be absolutely right at the time and is still a guarantor of our company's success”.

So what began in 1982 as a two-man operation in a garage is now a family business with 75 employees, which repositioned itself in 2012 when the founder's son Christian Veser joined the company.

Together with his father, the industrial engineer implemented the construction of new greenfield halls, introduced digital processes and ensured maximum energy efficiency in his company through various measures. “We have installed photovoltaics on all halls and use the waste heat from our machines to heat water, to name just a few examples,” says Christian Veser, adding: “But we also invest in modern technologies in all other respects.” For example, an ultrasonic cleaning system helps to keep the 600 or so self-managed moulding tools clean and ready for use.

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Kern Micro HD fulfils a long-cherished dream

With another investment, Werner Veser fulfilled a long-cherished dream in 2022, as he recounts with a smile: “I have been looking at Kern machining centres at trade fairs for 20 years, but could not bring myself to buy them because of the not exactly favourable prices. Now I've recalculated together with my son, and we're sure that the investment in our high-end Kern Micro HD five-axis centre is worth it.”

The decisive factor, he says, is above all the extremely high-quality results in terms of surface quality and accuracy that can be achieved with the Kern Micro HD. An example illustrates why these criteria are so important. Vema produces plastic lenses for leading car manufacturers that are used in headlights or other lighting units in the interior and exterior. On the one hand, expensive plastics with a high transmission value (light transmittance) of 95 percent are needed to ensure that the light falls in and goes out optimally. On the other hand, perfect surfaces are needed — especially in headlight lenses.

To reproduce these surfaces in the plastic is only possible with mould inserts that are highly precise and offer the highest surface quality, especially in the relevant areas. A requirement that until a year ago could only be met by manual polishing.

One hundred percent polishing quality straight from the machine

The senior boss was never really happy with the earlier processes: “Apart from the fact that I don't know anyone who likes to polish by hand, some places on our moulds are difficult to access, so it didn't always fit at first go.” In addition, when polishing, it is important to create polished sharp edges between the lenses to ensure a perfect beam of light when used in vehicles later on. Another challenge that sometimes requires repeated reworking. “Since we have been using the Kern Micro HD with the MHT medium distributor, these problems no longer exist. Now perfect components in polished surface quality always come directly from the machine, without any rework. This has allowed us to reduce throughput times by 20 to 30 percent — with better quality.”

Before Kern was awarded the contract, Werner Veser and his employee Luca Bornhorst — a prospective master toolmaker — compared many suppliers. But: “No one was able to produce our desired sample workpieces with comparable surface quality as Kern”, says Bornhorst. The Micro HD is also unique in terms of the precision that can be achieved. “After the first 'test shots' on our plastic injection moulding machines, it naturally happens that the results do not fit exactly.” In some places, the plastic is slightly too thin or too thick. Ergo, individual areas of the moulds have to be reworked in order to pass the elaborate tests in the light laboratory. “We are talking about one or two hundredths of a millimetre on the moulded part. So we clamp the mould again and re-mill it. With our core, it's accurate to the µm. In the end, it's always right, one hundred percent,” says the future master craftsman happily.

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Veser adds that the control of the machine was also important to him. All the milling machines in the company have a Heidenhain control system. This means that every employee is able to operate the milling machines. This brings planning security to the company.

Kern Micro HD and MHT medium distributor harmonise perfectly

So after numerous tests and comparisons, the decision for a Micro HD was already in the final stretch. There was only one important criterion that Kern had not yet been able to fulfil: the integration of the MHT medium distributor. Vema had already had very good experience with this minimum quantity lubrication system in the past and did not want to do without its advantages in the future. In addition to increasing the service life of the milling tools, the medium distributor also has a significant effect on the achievable surface qualities. Not to mention the company's green footprint. After all, it does not require any emulsion or machining oils in toolmaking.

The basis of MHT's minimum quantity lubrication system, which functions technically and physically differently from conventional minimum quantity lubrication systems, is a precisely fitting nozzle body with which each tool holder is equipped. A red sleeve equipped with 16 small air nozzles does not rotate during the milling process and thus ensures that the air, which is slightly mixed with aerosols and expelled at a pressure of six bar, is drawn over the entire tool and permanently ensures optimum lubrication and cooling on all cutting edges. At the same time, all chips are blown off efficiently.

For Kern and MHT, this was reason enough to stick their heads together and work on a solution. Vema boss Werner Veser remembers and is still impressed by the good cooperation: “Both companies are extremely innovative and always open to new technologies. Accordingly, the joint work went well.” Despite some technical challenges — especially with the automated mould change — the technicians from Kern and MHT managed to develop a solution that works perfectly.

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Unmanned operation in three shifts

Since the Kern Micro HD produces all mould inserts as well as the required copper electrodes in one clamping and in reliable quality, automation has also found its way into this area. Previously, due to the lack of basic accuracy and reproducibility of the milling machines, the toolmakers always had to work their way to the correct dimension, with a correspondingly high reject rate. “Autonomous production was therefore out of the question,” Werner Veser confirms: “Today it's different.”

The internal tool and workpiece changing cabinet with 90 tools and 30 workpieces not only makes it possible to machine complex moulds — some of which have a running time of 60 hours — day and night. The Micro HD also produces many small components in 24/7 operation. Should the 30 workpiece blanks no longer be sufficient in the future, a solution has also been prepared for this. Because the high-end machining centre already has an automatic door to which an external workpiece changer can simply be docked.