Problem solved - Saarstahl AG uses Blum Touch Probe TC76

Impressive by its Outstanding Quality
 
The theory suggested the measurement of the carbide rings would be relatively simple within the machine but the production technicians of Saarstahl quickly discovered it to be much more difficult in practice. They quickly decided they needed Blum measuring technology to simplify the measurement operation.
 
In spring 2008 they took delivery of their new turn-grinding center from EMAG. The VSC 400 DS had a special task: besides the combined turn-grinding machining of carbide roll rings it should also carry out measuring operations and thus optimise the production process. By means of an integrated measuring system the workpieces should be measured between the different manufacturing steps and so the tools should be checked indirectly. The diameter on the carbide ring is collected with a probe system, compared with the target data and then turned automatically to the correct diameter. If the diameter is finished, the calibre position and depth are measured, then remeasured after preturning, turned to size and then the dimensions should be accurate. So far theory!

Calibres in File

„In the beginning we underestimated measurement as we had no previous experience of this approach“, explains Michael Molter, staff member technical services of Saarstahl/Neunkirchen. The circumferential grooves on the carbide ring together with the grooves of the ring of the counter-roll are the profile of the roll product, called calibre. The carbide ring has two calibres and can be mounted on both sides. Therefore from each front side there must be the same distance to the center line of the calibre, otherwise there will be an offset. At Saarstahl the carbide rings are used on wire rod mill 32. They are mounted into 10 finishing blocks whereas each block has two carbide rings. The calibres of the carbide rings must form one line so that wires with Ø 8.5 – 25 mm, with a tolerance of ± 0.15 mm can be produced. Carbide rings with appropriate calibres are available for the different dimensions. To ensure that production is within the required tolerance the carbide rings are periodically turned by Saarstahl.

Difficult Measuring Task

In earlier times every carbide ring was measured offline after machining, i.e. at a measuring place with an electronic height measuring device. This complex task should now be taken over by the new turn-grinding center. A probe system for machine-integrated measurement was therefore supplied by EMAG. On outside diameter and front sides of the roll rings measurement was relatively straight forward, calibres, however, have different forms consisting of radii and chamfers. To collect the precise position of the calibres trigger contacts must be carried out on this complex geometry.

The first probe supplied from a different supplier provided only moderate repeatability - which was a real problem - lobing measuring characteristics at different deflection forces (lobing effect). I.e. depending on which radial angle orientation the probe triggered and which type of calibre was measured, the different measuring forces had negative influence on the measuring results. The staff therefore defined empirically a correction value for each calibre, incorporated it into the following measurement and checked the values offline on the measuring place. Andreas Braun, Manager roll machining and crane handling at Saarstahl: „The worst word of the year was: to gain experience! We determined these values in painstaking attention to detail. Then the probe system was accidentally destroyed and replaced by a new one of the same manufacturer. Both probe systems had such big tolerances that our staff had to re-define the correction values. They had to interpolate the data to get the approximate target values. To get experience our manufacturing technicians needed about two or three weeks. 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. „It had no in-process quality“, explains Michael Molter.
 
Problem solved
 
Due to the heavy problems a design engineer from EMAG proposed an alternative, the probe system TC76, a compact cable system by the measuring specialists Blum-Novotest in Ravensburg. This system was especially developed to measure workpieces and tools in turning and grinding machines. No sooner that the system was mounted all measuring inaccuracies had disappeared. Uwe Fischer, sales engineer at Blum-Novotest explains: „Inside of the TC76 is the new patented measuring mechanism “Shark 360” with modified face gear. This face gear 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 measuring mechanism. By means of the homogeneous trigger characteristics measurements on different calibres as appearing every day at Saarstahl can be carried out in µm.“

High In-Process Quality

Another advantage appreciated by the staff of Saarstahl is the no-wear trigger signal generation of the Blum probe. Differing from the systems applied first, the TC76 generates an optoelectronic signal by shading a miniature light barrier in the inside of the probe and not according to the tripod principle which means the interruption of a mechanical contact wearing by and by.
Since March 2008 the TC76 is integrated into the turn-grinding center. The probe system measures reliably and Michael Molter can now abandon time-consuming correction value collection. The values are repeatable and random checks of the carbide rings are performed on the measuring place. So, finally the requested in-process quality was guaranteed.

Better and Faster

Due to the considerably higher measuring speed with the probe system by Blum (up to 2 m/min) the measuring times were reduced which shortened the total measuring process by 40 percent. For machining of the carbide rings several measuring operations are necessary so that the reduced measuring time became evident. Intermediate measurements will be necessary as the tools are wearing – and one never can be sure how long they will survive. The probe checks the tools indirectly via workpiece measurement so that the manual inter-mediate 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, measured offline, reset and re-machined. With the new EMAG machine the complete ring can be turned in one setting. If e.g. a cutting plate has wear and the probe displays that the tolerance of 2/100 is exceeded the turn-grinding machine compensates this wear automatically and turns to the correct size. Measurement is carried out before each final cut and the tool is corrected correspondingly. Random checks on the measuring place are for quality control only.

High In-Process Quality

The staff of Saarstahl AG can rely on the probe – in midsummer in baking heat as well as in winter in cool environment it provides reliable values. They had no introduction or training period; according to Andreas Braun the program was installed and since then the probe provides its data. Neither maintenance nor contact to the Blum service department was necessary up to now – the probe is working perfectly.
Andreas Braun: „All what the probe does, is done very well. If you see how it works you cannot imagine the problems we had before…“.





Saarstahl AG

Saarstahl AG with their locations in Völklingen, Burbach and Neunkirchen as well as their „Roheisengesellschaft Saar“ in Dillingen belongs to the most import manufacturers of „long products“ worldwide. The traditional company is specialised on the production of wire rods, steel rods and semifinished parts in different qualities as well as contour forgings. Their customers belong to automotive industries and their sub-suppliers, construction industries, energy engine industries, aerospace industries, general mechanical engineering industries as well as other steel-working industries.
www.saarstahl.com





Editors´s notes:

Established in 1968 and based in Ravensburg, Germany, Blum-Novotest GmbH is recognized worldwide as a developer of leading-edge measuring and testing technology for international machine tools, aerospace and automotive industries. The family firm has more than 260 employees working in Germany, Great Britain, Italy, France, USA, China, Japan, Taiwan, Singapore and Korea. Together with skilled dealers (due to their technical competence called "system integrators") and regional sales offices they guarantee comprehensive service for thousands of Blum systems applied all over the world.




For further information:
 
Blum-Novotest GmbH
Production Metrology
Postfach 1202
D-88182 Ravensburg
Germany

Tel:  + 49 (0) 751 6008-0
Fax: + 49 (0) 751 6008-156
E-Mail: vk@blum-novotest.com
Web: www.blum-novotest.com