Monitoring tools in advanced CNC centres: Reliable unmanned production

Messkomponenten

Precision work during the night shift

The Tuttlingen area is a centre for medical equipment specialists of all sizes and fields. At Günter Stoffel Medizintechnik GmbH in Wurmlingen, Germany, high-precision CNC processing and traditional craftsmanship are at the heart of the company’s success. Productivity is ensured by probes, laser measuring systems and tool setting probes from Blum-Novotest, which play an essential role in the unmanned production of extremely small components.

“All Stoffel instruments have ultra-high level of precision in common. Whether it’s the tiny spoons of biopsy forceps, whose edges must connect to within one-hundredth of a millimetre to be able to cut with precision, or tweezers with the tiniest of teeth at their tip – our job is to manufacture products with the accuracy necessary to ensure that the multi-part instruments can be assembled and function properly,” comments Dieter Stoffel, Managing Director. “With the exception of electropolishing, all production steps are performed in-house.” Parts produced on advanced CNC centres are deburred, adapted, polished and installed by hand.

An important factor for Stoffel is productivity. For this reason, the company invested in a five-axis milling machine from DMG MORI in 2021, along with a laser measuring system from BLUM and automation with a Fanuc robot, which inserts blanks and removes the finished parts. The new machine can work overnight or the whole weekend without human intervention. It is essential, however, that the tools be monitored during unmanned production to detect tool breakage, wear or damage to the tool cutting edges. This is the only way to prevent scrap production by means of automatic corrections or, for example, by replacement with a sister tool.

On the new machine, unlike on its predecessor, it is important not only to detect tool breakage but also to identify damage to the tool cutting edges. For this purpose, the production experts employ the LC50-DIGILOG laser measuring system from BLUM. This device can take thousands of the measurements per second. Consequently, it is capable of detecting changes in the geometry of the tool cutting edge, such as those caused by wear, even while the tool is turning at the operating RPM.

This is especially important considering that the tolerances aimed for are very tight and often less than one-hundredth of a millimetre. Stoffel products consist of multiple very small parts whose tolerances add up when they are assembled together. In addition, the parts are so small that they are very complicated to measure after production. Thus, the parts are assembled to determine whether they fit together geometrically. If not, the machine in Wurmlingen needs to be adjusted. Of course, this is not possible at night or on weekends. Still, Stoffel needs to know right away whether the parts are OK – and this is easiest to achieve by means of regular monitoring of the tool cutting edges using the laser measuring system.

To remove the tiny chips reliably, Stoffel works with large quantities of cooling lubricant – a fact that ‘the laser has got to deal with’. LC50-DIGILOG is able to take high-precision measurements anyway because the cutting edges, which are cleaned with air blow by the HPC air nozzle, can be measured at full machining speed, where the cooling lubricant is expelled from the rotating tool. In addition, LC50-DIGILOG can reliably differentiate between coolant and cutting edge on the basis of the large number of measured values and the plausibility checks that these make possible, thereby ruling out false measurements.

Stoffel has been working with Blum-Novotest in the field of production metrology for over ten years now. Consequently, the machine is installed with the new LC-Vision software for BLUM laser measuring systems and with the TC52 probe from BLUM. “The measuring tasks of the latter include monitoring of the fourth and fifth axes. The pivot point of the axes is measured and entered in the machine parameters to obtain optimal kinematics for swivel movements,” explains Dieter Stoffel. “Many factors depend on this measurement because if the pivot point of the axes does not match the coordinate system of the machine exactly, errors result on the workpiece during simultaneous or swivel processing. For this reason, this measurement is performed regularly on a measuring sphere installed in the machine – a process that, again, is only made possible by the BLUM measuring system.”