Swiss company Polymeca AG enjoys an excellent reputation in its sector for precision machining. At its headquarters in Heerbrugg, Switzerland, the company manufactures, among other things, axis systems for theodolites with a precision of up to 0.001 millimeters. "To achieve such low tolerances in automated grinding centers, we have to use advanced process metrology, In cooperation with Jenoptik's Swiss Industrial Metrology Division in Peseux, Polymeca is now able to combine exceptional machining precision with highly efficient mass production.
Grinding axis systems for theodolites is one of the most demanding grinding tasks. The accuracy of GPS angle measuring instruments depends directly on the precision of the pivoting and tilting axes. Polymeca AG has been producing such high-precision axis systems on conventional grinding machines for over 20 years. The traditional company has now entered a new era in terms of the precision and reliability of these processes. Innovative production, consisting of four fully-automated precision grinding machines for internal and external machining, with the option of grinding up to three assemblies per pairing operation, has paved the way for incredibly efficient and, consequently, more profitable production. "Thanks to our investment of four million Swiss francs in advanced production facilities and logistics, we were able to halve lead times, increase capacity by 35% and reduce stock value by 20%".Petschnig sums up the results of this modernization. The most significant improvement brought about by the new production line is the effective process reliability achieved in high-volume production. This guarantees machining accuracy down to 0.001 millimeters, even during unmanned periods, such as weekends. This was made possible by the new generation of MOVOLINE dimensional measuring instruments, offered by Jenoptik's Industrial Metrology division. Directly integrated into the production facility, this technology ensures automatic trend correction and thus controls the axis grinding process, guaranteeing the high level of automation.
The highest Swiss precision, in partnership
Pivoting and tilting axes are given their final shape, down to the micrometer, in the four precision grinding centers. The machines are loaded with 960 blanks on transport pallets, enabling them to achieve these results even during periods of unmanned operation. These pallets are designed to store the parts after pairing. Specially developed grippers pick up the parts to be paired and feed them to the three pre-process measuring devices installed on a rotary table. At the same time as the internal diameter of the female part is measured, the axis groups are transferred to the grinding machine and ground. Hommel-Movomatic measuring systems are used to monitor the machining process. The measurement results for each internal diameter are transmitted directly to the axis machining centers. This unique example of three-stage grinding ensures that the axes adapt exactly to the part's three spans. The axes are ground in a single pass to an accuracy of up to ±0.0005 millimetre. The parts are then laser-marked and shipped as a set.
Comprehensive process metrology from a single source
This exceptional precision in a fully automated mass production environment is ensured by the principle of measurement before (pre-process), during (in-process) and after machining (post-process).
First of all, pre-process measurements determine the exact theoretical values for axis machining. These measurements are carried out using high-precision HOMMEL-MOVOMATIC pneumatic measuring rings supplied by Jenoptik's Industrial Metrology Division. They enable flexible, cost-effective measurement of inside diameters, even at high frequencies.
For in-process measurements, HOMMEL-MOVOMATIC DM200 diameter measuring heads and HOMMEL-MOVOMATIC DP200 positioning measuring heads are integrated into the machining equipment. These instruments enable reliable measurement of outside diameters, as well as passive axial positioning, even under the most difficult machining conditions. This reduces external influences on the grinding process to a minimum, and guarantees high manufacturing precision.
Immediately after the grinding operation, post-process measurements are carried out in the grinding machine using the same measuring devices. This is where ovality checks and new length measurements are carried out. This operation is used for quality control, statistical process monitoring and "This is mainly for readjustment in relation to trend correction, with the aim of compensating for thermal influences, grinding wheel abrasion, etc."adds Petschnig. He also sees another advantage: " Combining in-process and post-process measurements using the same measuring device eliminates the need for an additional final inspection station, and increases efficiency, as no part handling is required."
HOMMEL-MOVOMATIC SZ400 control units are modern solutions that meet the most demanding requirements in terms of operation and visualization of all measurement results.
Digital technology for high process reliability
"In fact, we've always used industrial dimensional measurement from HOMMEL-ETAMIC or HOMMEL-MOVOMATIC, now offered by Jenoptik under the MOVOLINE product line".says Petschnig. "With the new generation of in-process measuring systems, which we use in our production network, we were also won over by modern digital technology, which is not offered by any other manufacturer." Petschnig considers digital data transmission to be a significant advantage over analog systems, since measurement results are transferred without interference, regardless of cable length, even under the most difficult conditions. What's more, Fielbus fieldbus technology reduces the number of connecting cables required, which in turn reduces investment in the installation and maintenance of measurement components, and thus overall production costs. In addition to the digital transmission of measurement data, the new generation of measuring heads also offers a much more compact design. This makes it possible to implement measurement configurations such as those used in Polymeca's grinding centers. Depending on the axis dimensions to be machined, up to five in-process measuring heads for diameter measurement and one positioning measuring head can be installed, all in a very tight space.
"At first, no one believed that, thanks to this measuring principle from Jenoptik's HOMMEL-MOVOMATIC, we were able to achieve this unrivalled machining accuracy of down to one micrometer in a fully automated series production environment. However, we prove it every day, 24 hours a day, 7 days a week "Petschnig sums up with satisfaction.
Learn more: https://www.jenoptik.com/fr_metrologie-industrielle-Hommel-Etamic