Over-Grip Collet Scores with Cycle Time Reduction on Wiha Tools Screwdriver Bits

Andreas Stengele (left) and Eugen Belz examine the Masa Tool overgrip system, which is used to manufacture the bits for the Speed-E electrical screwing aid. Image: Yannick Schwab / Konradin

 Wiha: Family business with a high level of vertical integration

Founded 80 years ago as a small company by Willi Hahn, Wiha Werkzeuge is now a global company with production sites in Vietnam, Poland, Germany and Switzerland. In the second generation, his son Wilfried Hahn, who is still part of the management team today, built up a global company network that is currently managed by the founder's grandson, Wilhelm Hahn.

The Mönchweiler plant is the location for the company's VDE tools. The screwdrivers and bits that are manufactured here are usually coated with plastic to protect the user from electric shocks.

​According to Andreas Stengele, head of the Langdreher / Bits department at Wiha, the resulting very high demands on security and quality still justify production in the high-wage location of Germany. The plant, or the entire company, impresses with a high level of vertical integration.  Even the hardening process and the surface treatment take place on site. Only the electroplating is done externally.

Clamping technology specialist at the hand tool manufacturer

In production at the Mönchweiler location, Wiha relies on a total of 13 Swiss-type lathes from various manufacturers. The Schlenker company, which is based in nearby Villingen-Schwenningen, has made special modifications to some of the Swiss-made lathe machines and, for example, modified the mounting of the counter spindle.

The fine line of proper leadership

Bits for screwdrivers are a core product in Mönchweiler: Wiha produced 1.1 million of these components in 2018 from low-alloy spring tool steel, mostly in batches of around 5,000. The raw material is provided in hexagonal bars, each three meters in length.

During machining, very high concentricity and roundness requirements are placed on the parts. If this is not the case, the insulating plastic layer will be distributed unevenly during overmolding and the risk of breakdown when working with the screwing aid increases. Particularly in the area of ​​guide bushes on Swiss-type lathes, it is difficult to meet the requirements in terms of both concentricity and roundness. According to Andreas Stengele, this is due to the diameter of the material used: “We work in the diameter range of three to four millimeters, but we use much larger machines. Because the smaller machines offer neither the necessary tool positions nor the necessary performance. ”The hexagonal bars are clamped with the main collet and guided through a guide bush. If it is too narrow, the material will bend when it is fed. However, if it is too loose, concentricity and roundness will suffer. “That's why it's always a fine line how I adjust the guide bushing,” says the expert.

Conventional, adjustable guide bushes can be adjusted using a thread. Flexible guide bushes, on the other hand, such as those offered by Schlenker, adapt to the material. Eugen Belz, technical manager at Schlenker: “This is a pneumatic system that is controlled by the machine. There is a constant pressure on the guide bush, for example 2.5 bar. If the material becomes larger or smaller, the guide bush adapts to the changed conditions. "

The Masa Tool basic body and the associated Microconic collet on a Maier long lathe. Image: Yannick Schwab / Konradin

Reaching over for rear processing

In order to further optimize the bit production process and save cycle times, Schlenker has equipped the Swiss-type lathes with the Masa tool. The overgrip collet from the Masa makes it possible to overgrip turned parts with a diameter difference of up to four millimeters, regardless of the available path of the machine. This means that the subspindle can be viewed as a fully-fledged spindle. Depending on the geometry of the workpiece to be machined and the possibilities of the machine, this can lead to enormous savings in cycle times.

The Masa Tool Microconic systems consists of a base body and, in this case, an over-grip collet in T-design.

The use of this collet makes sense if the diameter to be clamped is smaller than the diameter to be overcome. This enables a concentricity of 5 μm.

The system is used in the subspindle and can be precisely set on the machine. For this purpose, Schlenker provided  the Masa Tool MicroGrad setting ring, whereby the closure of the microconic collet can be adjusted in steps of 0.02 mm. This setting is then held by the base body.

According to Andreas Stengele: “Normal collets are adjusted by feeling. With the Microconic system, I can define exactly how far you tighten it for the ideal tension." The closed system is made of spring steel and is very flexible. "We have been offering the system for over two years and have not yet seen a break," emphasizes Eugen Belz.

Minimize cycle and changeover times

Without the Microconic solution, processing would alternatively only be possible in two stages, which ties up more capacities and employees - because Wiha does not manufacture unmanned. “It's always about saving yourself the second or third step,” explains Daniel Schanne. The aim is to reduce lead times in order to get the product to the customer faster. In this way, more than a quarter of the cycle time could be saved in the small parts series.

The family business has also organized its production in such a way that ideally only one bar diameter is machined on a sliding head lathe and therefore only the profile to be milled changes. Since the rear side remains the same and is spanned at the front, the machines do not have to be converted, which is time-consuming. "In order to mill the most varied of screw profiles, you only have to change the milling cutter," says Daniel Schanne with satisfaction.

To view the original article click here.

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​This article originally appeared in MAV Innovations Forum

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