Gear Production
Issue link: http://gear.epubxp.com/i/155418
F E AT U R E A Breakthrough Development Until now, gear production has been restricted by three severe limitations. It usually required dedicated tooling such as a gear hob or special form tool suitable for only one size gear. It required single-purpose, dedicated gearproducing machines with suffcient torque and rigidity for the application. Special programming and operator skills were also generally required. InvoMilling overcomes all three of these limitations. It uses a standard, multi-purpose turn-mill machine; disk-shaped milling cutters with standard carbide inserts; and easy-to-learn conversational programming routines. Most shops implementing this process will have to make additional investments to acquire InvoMilling capability. For example, shops considering the acquisition of a new multitasking machine might fnd the option of adding gear production using this process a compelling incentive to invest in a DMG/Mori Seiki NT turnmill center. (Currently, DMG/Mori Seiki is the only builder licensed to use this process.) However, Nitin Chaphalkar, manager of advanced solution development at DMG/Mori Seiki, notes that multitasking machines are capable of not only InvoMilling, but also traditional hobbing and InvoMilling requires one of three sizes of disk cutters specially designed for the process. Each cutter covers all gear sizes within its range. For example, the CoroMill 161 shown here produces gears from module 2 through 4. Other cutters cover the range to module 12. All three sizes of the disk cutters use the appropriate off-the-shelf coated carbide inserts. 18—GEAR Production Supplement gashing processes. "This fact means that users of multitasking machines now have the choice of several effective ways to make gears," he says. The name InvoMilling represents a new concept in involute milling that is an alternative to the specialized hobbing process. It is a combination of slot milling and multi-axis turnmilling. Simultaneous motion of the X and B axes or with the Y and B axes enables the milling cutter to follow an involute path. Simply changing the tool path results in unlimited gear shapes producible with the same cutter. Sandvik Coromant has developed three disk cutter sizes (CoroMill 161, CoroMill 162 size 4 and CoroMill 162 size 6) to cover the range from module 2 to 12 or 12 to 2 DP (diametral pitch). Gears with any helix angle—both involute and noninvolute profles—can be produced with the same tools. Multi-Purpose Flexibility Eliminating the need to stock individual hobbing tools, which are costly and involve a long leadtime to acquire various gear sizes, is one of the important advantages of this process. "A gear manufacturer usually has a large inventory of dedicated tools. There's one hob or gasher for each diametrical pitch size of gear. Even with a huge inventory, it still may not be enough," Nicklas Bylund, InvoMilling project leader at Sandvik, says. "You have to place an order when you don't have the right tool. If you have InvoMilling, three tools will cover you from DP2 to 12, so much less tool inventory is required—that's revolutionary." When gear-cutting cycle times are compared between hobbing and InvoMilling, hobbing is sometimes faster, depending on the size of the gear and number of teeth. However, the overall effciency, fexibility and economy of InvoMilling clearly favor this process for gear production in smaller batches. "With InvoMilling, the actual cycle time for the gear part is comparable to a HSS hob, but you need to calculate the whole time from the hob being ordered to being delivered, which can be months," Dr. Bylund explains. "With InvoMilling in place on a multitasking machine, you can just program it and