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Sensor technology ensures perfection

Process reliability has top priority for aviation supplier  Ziegler Feinwerktechnik. Due to the high cost intensity of the materials and small batch sizes, sound parts have to be produced reliably from the start – waste is taboo.  The only way to achieve this is by means of sophisticated measuring technology.

Ziegler Feinwerktechnik in Bermatingen by Lake Constance has supplied the aviation industry for over 30 years. The company specializes in the manufacture of sophisticated lathed and milled parts in aluminum alloys, magnesium, titanium, high-quality steels and also fiber-reinforced composite materials for use in fixed-wing aircraft and helicopters. Managed by three brothers who belong to the second generation of the founding family, the company currently employs a workforce of around 40.

“Reliability is the outstanding criterion for aviation. We have to meet these standards on a day-to-day basis,” explains Hubert Ziegler. Within the management trio he is mainly responsible for quality management. “With an average batch size of 35 parts, we produce 80 percent repeat parts.” This applies mainly to components for chassis, control elements for landing flaps and ailerons as well as casings for electronics units. Processing is mainly carried out on three and five-axis Mazak machining centers.

Wolfgang Ziegler describes what is special about this manufacturing process: “Due to the high cost-intensity of the materials and small batch sizes, sound parts have to be produced reliably from the start – waste is taboo. The only way to achieve this is by means of sophisticated measuring technology.” For this reason, the machining centers were fitted with Renishaw  touch probes OMP 40 and OMP60 as soon as they were purchased. “In aviation it’s not only that every thousandth of a millimeter counts, but process reliability is absolutely crucial. Every part has to meet the specifications so as to guarantee faultless operation.”

After mounting, the touch probe detects the precise mounting position. The CNC control system uses this data to correct the zero point. Generally several geometries are then processed, for example a central bore or a bezel. These determine the accuracy of further geometry details. This is where the great benefits of the Renishaw touch probes come into play. They are taken from the rack of the machine center and slotted into the main spindle like a tool. By probing three points, in a bore for example, the control system of the machine identifies the position to accuracies of less than 0.01 mm. The touch probes transfer their data optically to the OMI receiver module. This is located in the working area, usually above the main spindle, and is largely insensitive to cooling water and chippings. Based on the touch probe data, the CNC control system corrects the zero-point for processing further geometries.

As Hubert Ziegler explains, this means the company is able to reliably guarantee accuracies of between 0.01 to 0.02 mm on every machined work piece. This accuracy is enhanced by the fact that Ziegler’s touch probes always incorporate the influence of the machine on work piece precision. As Ziegler explains: “We err on the side of caution, especially when it comes to very close tolerances which are difficult to adhere to. Before machining we register geometrical deviations caused by machine axes or travel deviations deriving from temperature influences, i.e. thermal growth of the machine. Here again we use the Renishaw touch probe.”

The OMP40 probe is inserted for this purpose, with a probe sphere providing multidirectional calibration. This significantly increases precision of geometrical data recording in the working area, especially with five-axis machining centers. Peter Ziegler adds: “In addition to process stability, the touch probes also give us economic benefits. We can assume that the parts will be assessed as faultless on the machine. This frequently saves us running a 100 percent check on a coordinate measuring machine, thereby considerably cutting throughput times, increasing flexibility and reducing fixed capital. It minimizes the number of parts which have been fully processed but  not yet released.”  Compared to the increase in process reliability and the advantages it provides, the time required by measurement on the machine is negligible.

Tool measurement and breakage detection at the machining centers ranks as key factors in this high level of process stability. Here, Ziegler relies on Renishaw’s NC4 laser measurement systems. As Wolfgang Ziegler explains, extensive measurement cycles are programmed for virtually every NC program prior to machining. Every piece of the current NC program is inserted and measured by the NC4 laser beam first. The NC control system adopts the individual correction data. Peter Ziegler describes the advantages as follows: “The closer you move tool measurement to the processing station, the more reliably you can eliminate potential errors and inaccuracies. Measuring at the machine completely rules out any transfer errors in setting the tools and programming. This ensures optimum process reliability.”

The aviation supplier further enhances process reliability by subjecting tools to a breakage detection check. “Small, slim tools in particular are inspected by the Renishaw NC4 after every production step in the working area. This means we avoid damage that would otherwise result in expensive and time-consuming scrap, as well as protecting other tools, the machine and the work piece from subsequent damage. Since breakage detection is carried out automatically, the machine operator is relieved of strenuous supervision duties which would require utmost concentration.

What is more, intervention in rapid machining processes was not always fast enough to avoid subsequent damage,” says Wolfgang Ziegler. So by using the touch probes of the OMP product family and the Renishaw NC4 broken tool detection system, Ziegler is able to significantly reduce the costs and time loss caused by scrap. As Peter Ziegler explains, by consistent use of measuring technology in the working area of machining centers it is possible to almost completely eliminate waste created by incorrect mounting position, or by inaccurately measured or broken tools.

Programs can run unmanned
Customers in the aviation sector demand standardized documentation on quality and precision, and Ziegler has three coordinate measuring machines for this purpose. Here again the benefits of the Renishaw touch probes come into play.

The TP touch probes in combination with the PH10 rotation and swivel head have proved ideal for very irregularly shaped parts with numerous bores at random angles, for example. There are various systems, depending on the coordinate measuring machines and the components to be measured. For measuring in very deep bores, for example, it is possible to insert highly rigid extensions between the rotation/swivel head and the probe, as well as between the probe and the probe tip. The coordinate measuring machines have a rack system for automatic exchange of the probes and extensions required. This means that even extensive, lengthy measuring programs can run unmanned.

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