Modern steering systems are based on exactly tuned interaction between precise mechanics and finely controllable hydraulics or powerful electronics. ZF Lenksysteme manufactures highly precise pinions for passenger car steering mechanisms at its Schwäbisch Gmünd site in Germany, and puts its trust in the Tendoturn hydraulic expansion holder from Schunk

An oversized spanner wrench is like a relic to Dionys Müller, NC programming and planning operator in the ‘K valve’ business unit at ZF Lenksysteme, manufacturer of steering mechanisms for passenger and utility vehicles.

He says: “We used to clamp our tool with this in the past. Precise tool presetting on the collet chucks is critical every time. During the clamping operation, the tool changes its position by a minimal amount – but still too much.

“The ER collet chucks securely clamped tools but the spanner wrench and excessive force caused problems. Today, tool presetting with Tendoturn from Schunk is child’s play.”

Tendoturn reduces rejects

At ZF Lenksysteme quality is paramount with a robot loading and unloading the Gildemeister CTX 400 series CNC universal lathe every 30 seconds. Steering pinions are machined from 16 MnCr5 and individually and automatically checked. There are no compromises with safety-related parts, like steering mechanisms. Schunk’s Tendoturn is used on the machines for turning and drilling. Design specification P7 is easily complied to, when boring out an M12 diameter without reworking.

Müller says: “Rejects have been drastically reduced by switching over to the hydraulic expansion holder from Schunk. In addition, we could increase the feed from 0.08 to 0.15mm. This way, we save around 50 per cent on machining time. At the same time, we also achieve a much better surface quality and profit from the prolonged service life of our tools.”

The pinions produced with Tendoturn are part of a complex steering system that can be found in various car designs from numerous manufacturers. As a joint venture between Robert Bosch and ZF Friedrichshafen AG, the company has over 9,000 employees at 18 production sites in 11 countries, and is thought to be one of the leaders in this field.

The higher price of the Schunk Tendoturn compared to an ER collet chuck is justified, as far as experts at ZF Lenksysteme in Schwäbisch Gmünd are concerned. The precision toolholder pays for itself in a short time and is said to ensure reliable performance and top class machining quality. Tendoturn VDI 30 and 40 are used in Schwäbisch Gmünd.

The hydraulically clamped precision tool holders from the Tendo range are said to ensure maximum vibration dampening with the user profiting from brilliant surfaces and from the prolonged service life of the used tools. The vibration dampening is said to drastically cut the possibility of the cutting edge of the tool breaking, thus reducing tooling costs.

When considering whether to retrofit a production system with a precision clamping device, time is a decisive factor. With Tendoturn hydraulic expansion holders, the tool is clamped with an Allen key, which is fully precise and still conceivably simple within a minimum amount of time and without a peripheral device. In addition to more reliable performance, set-up times are also reduced.