Sharp-edged mills for sleekly cut shapes

"The carbide grades which were used in tool and mould making were standard grades which were also employed in other areas of machining," explains Josef Giessler, Head of Development for rotating tools at Walter, as he looks back over tool evolution. "These cutting materials still had a high content of cobalt (10 per cent), and could be used for hardness grades of up to around 52 HRC." This describes the way things were at the start of the 1990s.

At that time, the Walter competence brand Prototyp presented the first solid carbide range of mills specially designed for mould makers. Mills for tool steel or hard machining accounted for the largest part of the spectrum, with a smaller group of special versions for graphite and copper electrodes rounding off the range.  Harder or "ultra" It wasn't long, the head of development went on to explain, before the tools of the first generation were no longer up to the job of meeting user requirements. As early as the mid 90s, the trend in materials was already heading towards hardness grades of around 60 HRC. The development taking place in Zell am Harmersbach in the Black Forest at that time was running at full speed. The next range of mills for tool steel already used an ultra fine-grained carbide. Based on this development, Walter Prototyp launched the "Ultra" milling cutter family. The name of the product itself indicated the new and important substrate property.

There was a good reason why developers at that time were looking very closely at the substrate in particular. Josef Giessler: "Then as now, users were looking for universal tools which were equally suitable for both roughing and finishing. To meet this requirement, tools which are both tough and hard are necessary. This combination of properties is best provided by ultra fine grain substrates. Their development in the 90s represented an enormous step forward."

Great steps forward in development are usually followed by optimisation, as was also the case here. The specialists at Walter Prototyp discovered ways of improving the substrates even further in terms of grain size and composition. The current solid carbide end mills for tool and mould making from the Proto?max? Ultra range already use a carbide grade from the fourth generation. But it wasn't just that the materials became harder. Degrees of accuracy were also increased. Tolerances of one hundredth of a millimetre are now quite usual, and sometimes the requirements are even higher. Users therefore demanded extremely high degrees of accuracy in concentricity. These are now higher than they still were 15 to 20 years ago by a factor of four.

High levels of production quality can only be achieved if the tool outlasts the component which is to be milled. A tool change during machining, especially during finishing, is absolutely the worst case scenario for every mould maker. The developers therefore made adjustments to all adjusting screws for the tool life and apart from looking at the substrate, modifications were principally made to the shape of the cutting edges and to the coatings.

In this way, over time a package emerged with optimally coordinated features: the radius copy mills of the Proto?max?Ultra family. Proto?max? now represents a maximum in machining performance. With a new TAS coating on a TiAlN base and special microgeometry, the mills are suitable for hardened materials of up to 70 HRC. An extremely small diametre of 0.1mm is also a new arrival in the Walter range. Twenty years ago, 1mm was already considered extremely small.

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