Linear machining Trouble-free production leads to higher precision and better surfaces

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Dohlen & Krott Werkzeugbau in Baesweiler elevates its production of complex injection moulded parts to new levels of speed and precision with the Versa 645 linear machining centre from Fehlmann. After a rigorous benchmarking process, the company opted for the Swiss-made machine, citing its unmatched precision, energy efficiency, and compact footprint.

The main focus at Dohlen & Krott Werkzeugbau in Baesweiler is on highly complex, predominantly hardened injection moulded parts. Although a fully-fledged 5-axis machine was available for milling these components, it was difficult to achieve the required precision with it. Therefore, after an intensive benchmark, the decision was made in favour of the Versa 645 linear machining centre from Fehlmann. With success, because the components in question can now be produced much faster and more precisely.

The managing director of Dohlen & Krott Werkzeugbau, Ralf Kahlen, did not make it easy for himself. When the decision was made to invest in a new machining centre, an intensive benchmark was first carried out and, among others, the Fehlmann company in Switzerland was visited. The production depth, the quality, the availability of spare parts, but also the competence of the employees and the willingness to innovate convinced him. The tendency towards the Vrsa 645 linear, according to Ralf Kahlen, was already there beforehand: “The Fehlmann company had mentioned two well-known customers in Holland to me. I visited these companies and talked to the people in charge about their experience with these machining centres. The workpieces produced on them really impressed me. But also in comparison with the other machine manufacturers, my decision was made quickly. Our space is very limited. Any other machining centre would have been too big for the existing product portfolio. Irrespective of this, energy efficiency is also an issue for us. And then, of course, it was the precision that could not be achieved with any other machine.”

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The tolerances in Baesweiler are 5 µm, the surfaces Rz 0.8, without air conditioning. This is one of the reasons why the high-precision package option was chosen. A package that Alain Strebel, sales manager at Fehlmann, specifies as follows: “We still scrape the contact surfaces of the linear guides, have a geometric precision protocol and check the positioning accuracy in all axes according to ISO 230/2. For both measures, we then set ourselves even tighter tolerances.“ Peter Potjans, FE sales engineer for North Rhine-Westphalia at Fehlmann, adds: “We deliberately milled the test component for Dohlen & Krott several times without air conditioning. With the result that the results were continuously within the tolerances of +/- 3 µm.”

A good feeling also from an economic point of view

Dohlen & Krott is committed to milling anyway, because 98 percent of the components in the cavity area are polished. An EDM structure is not necessarily seen as an advantage. With the Versa 645 linear, which arrived in October 2022, it is now possible to deliver the components to the polisher with almost the final quality. Ralf Kahlen can confirm the advantages that Fehlmann describes for the Versa 645 linear. It starts with the work area, which is freely accessible from the front in any arrangement for set-up work and process monitoring. Automation can be connected without any problems.

In Baesweiler, the Versa 645 linear machining centre is already prepared for an Erowa automation system. Although the Versa 645 linear is also used for contract production (25 to 30 percent), the future automation will be used exclusively for the area of multiple cavities (up to 96 cavities). Now the linear drives also permit high acceleration and dynamics. However, dynamics only play a subordinate role at Dohlen & Krott, because in mould making they are not looking for the second. Ralf Kahlen: “If I have a good feeling about such an investment, it is not the second or the price that decides. In the end, I have to have my customers' products in mind. And if, as with the Fehlmann, I can produce the precision and quality quickly and without problems, that is also an economic advantage.” Another economic advantage is certainly the fact that a complete product range has now been transferred from another machine to the Versa 645 linear. Process reliability, on the other hand, was a high priority for Dohlen & Krott from the very beginning. Especially since a wide variety of materials are machined on the machining centre. This starts with M 330, extends to alloy and heavy metals, hardening up to HRC 62 and soon also titanium. For a correspondingly large set of moulds, the machine can run for two days. But even then, there have been no problems with precision so far.

Now the products in Baesweiler are the same as before the investment. However, the required precision and quality can be produced much faster and without problems. And not entirely unimportant in this context is the fact that the employees are also enthusiastic about the Versa 645 linear. Especially since the tolerances are becoming increasingly tighter.

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