Gear manufacturing by Power Skiving takes the traditional approach: After a cutter has reached its maximum wear, the operator changes the cutter, adjusts the cutter data, cuts the next workpiece, transfers it to the inspection room, waits for the first part inspection, and – if necessary – corrects the process by adjusting the machine parameters before proceeding with serial production.
Because Power Skiving is much faster than the shaping process, cutter changes usually happen several times per day and require more frequent operator action. Additionally, this procedure requires resources for cutter management and handling used cutters, sending used cutters to refurbishing (resharpening and recoating), returning cutters into the production flow and on the machine(s). Furthermore, there is a great cutter inventory required to bridge the time cutters are out for refurbishing. Note that while “one-way” wafer cutters for gear shaping process have been in use for some time, such cutters do not offer benefits to today’s Power Skiving process. The more frequent cutter changes of the much faster Power Skiving Process do not lend themselves to a Wafer Concept.
The Revolutionary Idea: On-Board Cutter Sharpening
By adding the capability of resharpening cutters on the Power Skiving machine, Gleason has taken a evolutionary step forward in raising the economy and quality of Power Skiving applications. This new development enhances Power Skiving results in virtually every significant area.
The fully-integrated, on-board sharpening unit is available for the vertical series of Gleason Power Skiving Machines up to 600 mm in diameter. The cutter face can now be resharpened fully automatically in the machine after it has cut a certain number of gears — without any operator involvement. The cutter geometry is adjusted automatically, considering the removed stock and the serial production is continued without further interruption. Recoating the cutting face is not required because the original coating on the flanks sufficiently protects the cutter teeth.
The frequency of cutter changes is greatly reduced: A single cutter can stay on the machine for several days or weeks before it is completely used. The time used in the past by the operator for a cutter change is instead used for three to four automatic cutter grinding cycles with a reduced stock removal per grinding cycle to keep the cutter constantly sharp for a high and constant gear quality.
Additional time is saved since first-part inspection and machine corrections after cutter change are no longer necessary because the same cutter stays in production. This also minimizes cost and required capacity in the inspection room.
Cutter management and handling logistics for ordering new cutters in time to ensure a continuous production is also greatly reduced. Required cutter inventory is much less as well, because there is no longer the need to circulate cutters through an external re-furbishing cycle.
For all Applications
Integrated cutter resharpening can be applied to spur and helical step sharpened cutters. The process can be integrated in all soft-cutting processes using HSS or carbide cutters and to the hard skiving process as well where carbide cutters are mandatory. An inexpensive standard grinding wheel technology is used. The grinding wheels don’t need to be dressed as they remain sharp due to a self-sharpening effect from the grinding process. When carbide cutters are used for soft or hard skiving, the savings from avoiding the external refurbishing are even higher. Also, the danger of damaging expensive carbide cutters by manual handling is greatly reduced as the cutters stay much longer in the process without being touched. The productivity of the Power Skiving process is not jeopardized by having no coating on the cutter face because re-sharpening now happens more frequently compared to the cutter life of the current process with external cutter re-furbishing.
Closing the Loop
The new on-board cutter sharpening process works seamlessly with Gleason’s Closed Loop system to exchange data directly with the gear metrology machine for automatic profile corrections on the production machine. The machining process is supported by dedicated technology software to calculate the process and provide designs for required tools and workholding. For an even more comprehensive picture, Power Skiving tool design can be verified within KISSsoft’s gear and transmission design software. Together with KISSsoft, Gleason offers a comprehensive suite of software solutions to make Power Skiving simple and reliable, with a complete Closed Loop from design to the optimum, application-tailored gear.
Entering New Frontiers
Typical applications for Power Skiving are internal ring gears, spur and helical gears in soft and hardened state, used in: automotive, light and heavy trucks, agriculture and construction equipment, aircraft and robotics, as well as many other industrial applications, typically served by job shops. Now, Power Skiving becomes increasingly employed in the hard finishing of higher quality gears in electro-mobility and robotic applications. Gleason Power Skiving machines with integrated cutter resharpening ideally support these requirements for quieter and more precise gears, with lower direct and indirect tool cost.
Conclusion
For the past decade, Gleason has been building Power Skiving machines at its Gleason-Pfauter facilities in Ludwigsburg, Germany. Today, the productivity and cost-per-piece benefits of Gleason’s Power Skiving process are widely recognized and make it a viable alternative to shaping and, in many cases, to other soft machining processes such as hobbing or broaching. As a result, the series of Gleason Power Skiving machines has grown to include different sizes for internal and external gear cutting and finishing, up to 800 mm in workpiece diameter. Today, with new integrated cutter resharpening, Gleason has added significantly to the Power Skiving capability.
