A complex component incorporating four long slots among other features was posing problems for Timo Lehmann, the CEO of Karlheinz Lehmann GmbH in Oberwolfach, Germany. The solution for the subcontract manufacturer was ultimately provided by a Citizen Cincom M32 turning centre and a TC76-DIGILOG touch probe from Blum-Novotest.


“Highly complex components are part and parcel of our business. But manufacturing a quick-coupler for a compressed air input was a tough nut to crack,” says Timo Lehmann of the challenges posed by a project for Parker Hannifin GmbH, a world leader in drive and control technology and pneumatics. “The key components are hardened and coated free cutting steel with threads, bores and four lightly tapered slots. The slots were the crucial point of the whole design.”  

The parallelism of the slots was only allowed to vary by 2μm from the reference values. Otherwise the fully automated machine that assembles the component unit at Parker-Hannifin, would abruptly stop.

Moreover, the quick-coupling would not work if the tolerance was exceeded. When assembled, the lightly tapered slots contain balls, which must not protrude too far, yet must also never be allowed to fall through the slot. Through this design, the Parker quick-couplers prevent the otherwise common snapping noise when detaching. It also allows single-hand operation. The task of measuring the slots is just as challenging as the production process.

The BLUM TC76-DIGILOG touch probe proved the only cost-effective means of verifying the design’s dimensional accuracy. Analogue measurement is always advantageous for assessing areas or lines. If a switching digital probe were to be used in the Lehmann application, a very large number of points on the slots would have to be measured in order to attain an adequate resolution. By contrast, the TC76-DIGILOG scans across the surface at a measuring speed of 2 m/min. As this is happening, the system generates an extremely large number of values (50,000 per second in fact) in a fraction of the time based on analogue data acquisition.

The TC76-DIGILOG has been running smoothly and efficiently in Lehmann’s production operations since February 2015. The sequence at the start of a production run has a reference part clamped onto the machine and the complete contour of the corresponding slot is scanned and recorded. The master profile is recorded and saved in the evaluation software. The subsequent production workpieces are measured and compared against the recorded profile and any that exceed the tolerance are discarded. As a result, the tight tolerances of the slot are reliably checked immediately after the cutting process in the lathe. In-machine measurement delivers enormous benefits. If it is run without a problem in the idle times, as in Parker Hannifin’s quick-coupler production, it is hard to beat. It allows 17 employee Lehmann to implement 100 percent checking with error trends being detected at an early stage by its evaluation software.

Incidentally, it doesn’t matter whether the TC76-DIGILOG is fitted in a grinding machine or a milling machine. And thanks to its increased scanning forces, it is even well suited to the unforgiving conditions in a lathe. The TC76-DIGILOG scans the part accurately and non-directionally, measuring with supreme precision thanks to the patented shark360 measuring mechanism. “Neither coolant nor viscous oils impair the reliability of the measurement data. With its higher scanning force, the touch probe simply pushes through the coolant,” adds David Cousins.

The Blum-Novotest/Citizen combination is also used for other large production lots from 10,000 to 30,000 pieces. The processed materials are wide-ranging from stainless steels, heat-treated steels and free cutting steel through to aluminium.

“Given that we were close to having to refuse the quick-coupler order from Parker Hannifin, we are delighted to have found such a powerful solution in the combination of Blum touch probe and Citizen Machine,” Timo Lehmann concludes with satisfaction.


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