Leitz Precision CMM Ensures Accuracy of Gear Grinding Machines

Reishauer AG is a company with a long tradition in the gear industry. Reishauer’s products range from tooth profile grinding machines, to diamond and CBN tools, which the company exports to industrial states throughout the world. Teeth on gears with a diameter of 150 mm to 1,000 mm are given their final super-accurate grind on Reishauer’s highly precise machines, therefore it is critical that the inner workings of Reishauer’s grinding machines run as smooth as clockwork.

With approximately 11,000 measuring devices—from small calipers and gear measuring machines to 3-D coordinate measuring machines (CMM)—Reishauer is in full control of the quality of its products. That is why, at the Wallisellen factory in Zurich, the quality assurance department has relied on Leitz for the inspection of their machine components for more than 20 years.

“It all began with length measuring machines and measuring microscopes,” says Renato Righes, a QS engineer with Reishauer, regarding the development of metrology at Reishauer. “That was in the 1980s. Up to then we measured everything in separate steps. There were no closed processes. Twenty-two years ago we took the step to three-dimensional measuring with a Leitz coordinate measuring machine. That made everything much simpler.”

Parts that fulfill key functions in gear grinding machines still call for precise CMMs. The latest addition to the inspection room at Reishauer is a Leitz PMM-C Ultra, which has been in the factory since June 2008 and is replacing a 22-year old Leitz CMM. With a measuring range of 1,200 x 1,000 x 700 mm, an accuracy of 0.4 + L/1,000 µm and its compatibility with QUINDOS metrology software, the PMM-C Ultra is the solution for measuring rotary and cubic parts from production. All parts that form the core of the machine and ensure the functionality of the grinding machine must be 100-percent documented and are inspected with the CMM. These parts include shafts, final drives, or grinding spindles (parts with tolerances of less than 10 microns). Monitoring of measuring equipment is also carried out by the PMM-C Ultra.

“With us, quality always comes way out in front,” says Righes. “In other words, the quality of every individual part in a gear grinding machine must be 100 percent, so that the grinding machine can produce the expected quality in the future. Some customers grind their gear wheels in the micron accuracy range. Rotary machines in the printing industry have to operate at high speeds and cannot tolerate circumferential defects or imbalances. Therefore every gear wheel must be a perfect fit. The working spindles in our gear grinding machines have to be positioned to within a micron. It is important that the shafts work exactly in sync with one another. With us, tolerances of a micron or half a micron are the order of the day. We need a suitable coordinate measuring machine that can work quickly and precisely. Our requirements for throughput and accuracy of the machine have further increased over past years. There are other companies offering these systems, but in the end we had to conclude: If we wish to record values down to a micron, we have to be working to an accuracy of one tenth of that figure in the quality assurance department. And that is best achieved with the PMM-C Ultra.”

Figure 2: The Leitz PMM-C Ultra, which is available to the Reishauer AG Metrology Team in the climate-controlled inspection room, is used to inspect rotary parts of gear grinding machines, which are subject to tolerances of 10 microns.

The company also owns a Leitz PMM C, with a measuring range of 2,400 x 1,200 x 700 mm and an accuracy of 0.9 + L/800 µm, that has been measuring parts on the production floor for three years. This CMM is slightly less accurate than the PMM-C Ultra. But that isn’t a problem given its function as production floor CMM intended to measure tool carriers or bearing points on which the bearings of the gear grinding machines run larger components that don’t require as much accuracy. A tool carrier can, for example, have a length of 1,300 mm.

As with the PMM-C Ultra in the inspection room, the PMM C marked a further milestone in the shared history of Reishauer and Leitz, a Hexagon Metrology company. Reishauer’s first Leitz machine was part of the Leitz PMM-C product family but had a more limited range than the newer model, which lead the company to purchase the newer model.

“The actual requirements for the new measuring machine included not only higher speed and accuracy but also the ability to place the machine directly in the production facilities,” explains Righes. “A user-friendly interface and simple configuration were further requirements. The ability to integrate a rotary table was also important. We manufacture many rotary parts that we are not able to inspect using a conventional probe system, a star probe for example. The many other parts in our repertoire also include a vertical shaft that has top and bottom external diameters of 240 mm and 650 mm respectively. In the lower section there is also an additional diameter of 210 mm, which runs concentrically with the top diameter. The rotary table in this case is the only logical solution to achieve all angles.”

The software support team at Hexagon Metrology works closely with Reishauer’s metrology technicians. “We spent a week at Wetzlar, Switzerland, with Leitz to become familiar with the new version of QUINDOS 7, which runs on both coordinate measuring machines,” says Righes. “Now we can exploit the full potential of the software. When we need software support, Hexagon Metrology always comes up with a super instructor. That is fantastic. We have the instructor come to us when questions arise, an arrangement that we have always found extremely cost-effective. This lively exchange of ideas between us and Hexagon Metrology has already resulted in many programs which have been adopted by us and even other users of QUINDOS.”

The outlook for the gear grinding machine market is favorable, due to the redevelopment of the automobile industry. The sector is striving to introduce smaller, more efficient engines. At the same time these engines must also be set up to achieve their highest levels of efficiency. To optimize the power chain, a large number of gear wheels are required, which in turn boosts the market for gear grinding machines. Reishauer AG is also experiencing a helpful tail wind from the promising wind power industry. The company hopes to gain further sales from this sector, where the accuracy of gear wheels is essential—accuracy that can be reliably and quickly measured at Reishauer AG.

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