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Impressive by its outstanding quality

Impressive by its outstanding quality

Added to MTDCNC by Blum-Novotest on 02 June 2015

The measurement of carbide rings was supposed to be a relatively simple aspect of the production process at Saarstahl AG, Germany; however technicians quickly discovered the process more difficult in practice. The engineers quickly decided they needed measuring technology from Blum to simplify the measurement operation.

In spring, the company took delivery of its new turn/grind center from EMAG. The VSC 400DS had a special task, to combine turn/grind machining of carbide roll rings and carry out measuring operations to optimise the production process. By means of an integrated measuring system, the workpieces should be measured between manufacturing steps and the tools checked indirectly. The diameter on the carbide ring is collected with a probe system, compared with the target data and then turned to the correct diameter. If the diameter is finished, the calibre position and depth are measured, then re-measured after pre-turning, turned to size and then the dimensions should be accurate. That was the theory!

Saarstahl AG is a traditional company that specialises in the production of wire rods, steel rods and semi-finished parts plus contour forgings. Customers include the automotive, construction, energy, aerospace and general mechanical engineering industries.

''In the beginning we underestimated measurement as we had no previous experience of this approach'', explains Michael Molter, a technician at Saarstahl. The circumferential grooves on the carbide ring together with the ring grooves on the counter-roll are the profile of the roll product, called the calibre. The carbide ring has two calibres and can be mounted on both sides. Therefore each front side must be the same distance to the center line of the caliber, otherwise there will be an offset. The calibres of the carbide rings work with wires from Ø 8.5–25mm with a tolerance of ± 0.15mm. 

Difficult Measuring Task

Previously, every carbide ring was measured offline after machining at a measuring station with a height measuring device. This complex task should have been taken over by the new turn/grind center, credit to a probe system for machine integrated measurement supplied by EMAG. 

To collect the precise position of the calibers, trigger contacts must be carried out on the complex geometries. The first probe provided only moderate repeatability, which was a real problem that created lobing measuring characteristics with different deflection forces. The staff therefore defined a correction value for each caliber and incorporated it into the following measurement and checked the values offline at the measuring station. Andreas Braun, Roll Machining Manager at Saarstahl says: “The probe system was accidentally destroyed and replaced by a new one from the same manufacturer. Both probe systems had such wide tolerances that our staff had to re-define the correction values. They had to interpolate the data to get the approximate target values. Measurement with the electronic height measuring device on the measuring position failed, too. Sometimes the values were within the tolerance, sometimes outside of the tolerance. We had no in-process quality.”

Problem solved

Due to the extent of the problems, a design engineer from EMAG proposed an alternative from measuring specialists Blum-Novotest in Ravensburg, its TC76 probe system. The system was developed to measure workpieces and tools in turning and grinding machines, so no sooner had the system been mounted, all measuring inaccuracies disappeared. Uwe Fischer, sales engineer at Blum-Novotest explains: “Inside the TC76 is the new patented Shark 360 measuring mechanism with a face gear. This guarantees precise trigger contacts and forces in all directions. The probe has precise non-lobing touch characteristics even for measurements with torsion forces on the mechanism.”

Another advantage is the no-wear trigger signal generation of the Blum probe. The TC76 generates an optoelectronic signal by shading a miniature light barrier on the inside of the probe and not according to the tripod principle. 

Since being integrated into the turn-grinding center, the Blum probe system reliably measures and Michael Molter can now abandon time-consuming correctional alterations. The values are repeatable and random checks of the carbide rings are performed. So, finally the requested in-process quality was guaranteed. 

Better and Faster

The considerably higher measuring speed with the Blum probe (up to 2m/min) reduced the measuring process time by 40%. The probe checks the tools indirectly via workpiece measurement, so that the manual intermediate measurements are now automated. So, the TC76 and the new turn/grinding center are complementing each other perfectly. With the previous machining center the carbide ring had to be taken from the machine and measured offline, reset and re-machined. With the new EMAG machine the complete ring can be turned in one setting. If a cutting plate has wear and the probe displays that the tolerance is exceeded, the turn-grinding machine compensates this wear automatically and turns to the correct size. Measurement is carried out before the final cut and the tool is corrected correspondingly. 

The staff at Saarstahl AG can now rely on the probe in hot summer or cold winter weather with no deviations. Staff had no introduction or training period and according to Andreas Braun the program was installed and left to work. Neither maintenance nor contact to the Blum service department was necessary as the probe is working perfectly. 

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