For hard-finishing of high-precision gear teeth, users have set the bar high: Coolants need to effectively contribute toward achieving high performance in terms of safety, precision and machining speed. Participants learned how to reliably achieve this in the workshop “Development trends in gear teeth grinding” held at the Fraunhofer-Institute for Machine Tools and Forming Technology (IWU) on 11 November 2014. At the event, Meinhard Kiehl, Director of Marketing and Product Management at Rhenus Lub GmbH & Co KG, presented the latest findings to companies from the metalworking industry as well as suppliers. The renowned research institute invited interested parties to Chemnitz to promote a practical discussion of current challenges and perspectives regarding demanding gear teeth grinding processes. “The technical requirements for gear teeth grinding have significantly increased”, reported Meinhard Kiehl. “High-tech applications for gears — such as electromobility, downsizing especially in mobile applications or noise-optimized engines — require even more precisely ground gear teeth with narrow tolerance limits”. At least as important, however, is that production is as economical as possible. For users in the metalworking industry, this means: They need to increase the machining volume for gear teeth grinding, optimise workpiece precision and reliably prevent typical machining risks such as burning. This will only be possible, however, if production is optimised overall and the correct coolant is selected.
Success through attention to detail
Lubricant expert Meinhard Kiehl advises: “Focus more on supposedly minor factors such as selecting and using the correct grinding oil. For the demanding hard-finishing of gear teeth in particular, this can be the key to achieving higher performance”. During the machining process, the coolant used for gear teeth grinding must fulfil an extremely wide variety of functions: It must dissipate heat effectively, reduce friction, wash away grinding abrasion and metal chips reliably, decrease grinding wheel and tool wear, improve workpiece quality, prevent burning and improve the reliability of production overall — and all of this under a wide variety of operating conditions. To compensate effectively for any tolerances during the individual machining processes, modern grinding oils have a performance reserve.
Neat oil and its functions
When selecting the fluid, machining criteria such as the grinding process used or the grinding wheel type are just as important as the material used. Flushing properties, foaming behaviour and flashpoint are technical and safety-related properties of the lubricant that further narrow the range of suitable products. In actual practice, well-known gear teeth manufacturers rely above all today on low-emission, low-viscosity neat oils for demanding grinding operations. Meinhard Kiehl: “Low viscosity oils remove process heat considerably better during machining, which is beneficial especially for processes with a high machining volume — such as gear teeth grinding. In addition, coolants with a lower viscosity exhibit better flushing properties, significantly increase the sedimentation rate of the metal chips or abrasion and are characterized by a high filtering capability and good air separation”.
Fluid management is the final piece of the puzzle in any machining process
“With all of these considerations however, it is important to always view the lubricant holistically in the context of the overall process”, the lubricant expert additionally advises the workshop participants in Chemnitz. “As a process partner for industry, we provide our customers not only with specific product advice, but assist them with a comprehensive fluid management system—rhenus lubrineering—with carefully targeted measures at every stage that lubricant is used”. The technical staff at Rhenus Lub can rely on their years of experience as well as on highly developed products that have been tested in practice and approved by leading machine manufacturers. One example is the zinc-free high-performance grinding oil rhenus CXS. Thanks to the alternative base oil, the grinding oil exhibits considerably higher evaporation resistance despite a low viscosity of 10 mm2/s at 40 degrees Celsius — while retaining optimal machining performance. The benefits for the user are tangible: While conventional solvates exhibit an evaporation loss of 25.3 percent at 200 degrees Celsius, the evaporation loss with this special oil, based on rhenus CXS, is only 14 percent. In practice, the grinding oil exhibits very good flushing and cooling properties and is also characterized by low oil mist and evaporation. Users can therefore reduce coolant usage for demanding gear teeth grinding operations, prevent burning and in this way minimise the risk of deflagration and fire.
You can find more information on the workshop at the Fraunhofer Institute at: www.iwu.fraunhofer.de