Strong Triangle, Strong Products

Tool manufacturing is one of the industries that has been facing ever increasing demands for some time. With strong customer orientation, the durability and quality of the tools in particular take center stage in the promotion: “Both narrow tolerances and a long service life for the tools are required in equal measure,” emphasizes Managing Director Hans-Jürgen Kröger. “Ultimately, a precise, needs-based tool that works perfectly even after many years and thousands of production cycles forms the basis for an economical production process.” Requirements that Werkzeugbau Kröger must grapple with under deadline pressure day in, day out. That this is completed successfully is, not without pride, the verdict of Michael Sieve, who is in charge of technical purchasing and order processing at Kröger. Werkzeugbau Kröger GmbH has been on the market since 1998, “always available for our customers,” says Sieve regarding the necessary flexibility. Hand in hand with the customers and their designers, individual high-precision and high-quality injection molding tools are developed in Lohne. Starting with the development and construction of tools, the expertise of the 28-person team extends to testing services, prototype manufacture, and repair and modification work. The program is rounded out by contract manufacturing taken on for companies from the surrounding area.

Broad Market Position
The toolmaker’s client base includes companies from the automotive, construction, and food industries, as well as companies from the electrical, horticultural, or agricultural technology sectors. “For the automotive industry, which accounts for 70 percent of our order volume, we produce, for example, tools for Isofix holders, covers for toothed belts, interior components, or cylinder head covers,” explains Sieve. These kinds of tools, which are exclusively processed with tool steel, are built up to a size of 1,200 × 900 × 550 mm (X/Y/Z). In machining, four Hermle machines are used for this purpose – two of which are five-axis and two are three-axis. In the eroding segment, Kröger works with two vertical and two wire eroding machines. Production quality is assured by a measuring machine, among other things.

A Huge Difference
With Kröger’s market entry 21 years ago, Meyer + Münster became a supplier for the toolmaker. Since then, the dealer of tool and workpiece clamping technology, tools, and machine tools has established a close partnership with the toolmaker. Managing Director Hermann Meyer in particular knows all about production in Lohne and is aware of which technologies are required. This was also the setup seven years ago when Kröger purchased a new Hermle C40. With this milling machine, meaning a switch from SK 40 to HSK 63, new toolholders were also needed. Should we continue with shrink-fit holders here, which we worked with previously? A few things suggest not: “For shrinking specifically, we often wanted three or four hundredths but didn’t get it,” states Sieve. “At the same time, high retaining forces, high vibration dampening, and the durability of the holders were very important to us.” As if on demand, Meyer then arrived with the powRgrip. And even with a test device, which he usually provides to potential users for four or five weeks. Intensive system tests then followed during which concentricity, handling, and quality were meticulously examined. Those at Kröger were initially skeptical regarding compression: will it really hold? “It held. Really well, actually. Even when we went at full tilt,” says Sieve. “When comparing the shrink-fit and powRgrip holders, the surface in particular won us over. That was a tremendous difference.”

Seamless Use
On the basis of such results, the transition from shrink-fit to powRgrip holders was now consistently driven forward. “But you need to be aware that this kind of transition has consequences, such as for programming,” emphasizes Sieve. After all, Werkzeugbau Kröger continues to work with shrink-fit holders to a lesser extent. In order to flexibly select a machine on which manufacture should eventually take place, the toolholder can therefore not always be programmed. “But we must always respond quickly and flexibly to the wishes of our customers. This is an area of tension that must be faced up to,” says Sieve. “But we would not have done this had we not been completely satisfied with the powRgrip holders.”
Kröger has now long since ensured flexibility for machine use: powRgrip has been deployed on every machine today. “As a result of day-to-day business, this seamlessness in the system is very important to us,” emphasizes Sieve. In the meantime, almost the entire powRgrip product range is used. This means the PG colletholders as well as the PG collets, with which solid carbide tools from 0.6 to 16 mm in diameter are held. The special solution PG secuRgrip is also used, which ensures especially high extraction security for tools with Weldon surface. “Especially with trochoidal milling, secuRgrip is a fantastic thing,” of this, Sieve is certain. “The retaining forces are significantly higher than for other holders, the cutter is not removed, and we are quicker.” In the last year, the clamping unit has also been exchanged for the latest Rego-Fix model. With the PGU 9500, Kröger can now work from PG6 to PG32, and therefore from 0.2 to 25.4 mm. The decisive factor: with the slimmer holders, the toolmaker now gets even closer to its components. In any case, Sieve sees the fact that Rego-Fix does not rest during product development as a great advantage: “The powRgrip’s interference contour is always seen as a shortcoming. But the Swiss are constantly working on improvements here.” The fact that Rego-Fix also always has the toolmaker in mind during these kinds of developments is demonstrated with the example of the PG15 holder, for which a 12 mm collet is now offered. “With it, companies that produce small parts can work very close to the contour,” says Meyer. “Rego-Fix thereby takes account of the fact that many parts are becoming ever more complex, thin-walled, and delicate.”

Process Reliability, Accuracy, Flexibility
At Kröger, the powRgrip system is today a fundamental part of the production chain. There have also been clear advantages. “So not much can go wrong during clamping provided you observe due cleanliness,” says Sieve regarding the process reliability. With shrinking, things are different. In this case, you should not heat a holder for too long. But you cannot always exclude the fact that this will sometimes happen for 10 or 20 seconds more. Nobody then checks how the structure is subsequently conditioned, how great the concentricity is, or whether a holder is involved that should be withdrawn from circulation. And an hour later on the machine, you have three hundredths in the component.” With the powRgrip system, these uncertainties do not exist. Handling is simple and tool centering is always a given. If you observe the manufacturer’s recommendations, powRgrip works independently of the operator and, alongside process reliability, it ensures a high degree of flexibility. “Because unlike shrinking, where a holder is required for each diameter,” says Sieve, “you can use one powRgrip holder with different sleeves.”

Ensure Lasting High Quality
While many users of the Rego-Fix holders quantify a significant increase in tool life, this increase can only be expressed qualitatively at Kröger: “Because we have no series production and always process different parts,” explains Sieve. “But we can say that the service life is definitely longer.” The quality of the parts in particular has improved considerably. Although Kröger usually still erodes after milling, it gains immediate benefits from this: the effort required to achieve the final quality is significantly lower – when it comes to shaving and assembly, for example. “The closer we come to the result, the less shaving or assembly work we have to do afterwards. While we sometimes had to shave tools for three, four days before, today the machine is never occupied for more than a day.” Because Kröger is constantly under deadline pressure, this therefore completes another circle. Not least because powRgrip also relieves some of the pressure in the grinding area. Here in particular, various applications could be replaced by milling – to the same quality. “Ultimately, from the tool buyer’s point of view, the conclusion is that you regularly need to buy new holders for shrinking. The powRgrip holders, on the other hand, have almost no limitations in their use.” There is only one figure from the manufacturer here: Rego-Fix guarantees consistent accuracy for the holder beyond 2,000 clamping cycles.

Strong Products, Strong Triangle
For more than twenty years, the partnership between Werkzeugbau Kröger and Meyer + Münster has been characterized by trust. “For us, a big advantage of this cooperation is that we have a sales partner that represents very good brands. In addition to clamping technology, we also get excellent cutters, drills, and threading tools,” says Sieve with satisfaction. “This takes us forward as a toolmaker.” The triangle of user, manufacturer, and supplier therefore works. Only recently, another component has been added: the exchange of experiences in Switzerland that brings powRgrip users together who want to get to know the system and manufacturer Rego-Fix even better and improve their production efficiency.