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Gear Machining Made Easy: TNC Cycles for Skiving

Machining gears is still regarded by many machine tool operators as a true challenge and a realm reserved exclusively for specialists. Three new cycles of the Heidenhain TNC 640 for skiving and hobbing of straight, helical, and herringbone gear teeth are now altering this perception.

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With new cycles for the TNC 640 control, Heidenhain is enabling the easy programming of complex gears, such as for the skiving of internal gears.

These new cycles enable simple and economical machining of high-quality external and internal gears completely within a single setup. The Heidenhain software allows the two machining operations to be performed in both milling and turning mode.

Millions of Gears at Work

Millions of internal and external gears are constantly at work behind the scenes—including in every vehicle. From bikes to earthmovers and from pedal-powered drives aided by electric motors to powerful hydraulic drives for heavy-duty machinery, things get rolling only when the gears used in millions of hubs and transmissions mesh smoothly.

Yet gears are still often manufactured on special machine tools, a practice that requires time-intensive rechucking of the workpiece. Moreover, traditional gear manufacturing methods are very time consuming. Accordingly, machining in a single setup with the dynamic gear-machining cycles of a TNC-controlled machine can yield savings in time, effort, and cost.

Support for Complex Processes

The new cycle 287 “gear skiving” from the TNC 640 control supports users in programming complex processes required for skiving. The only parameters needed are the data for the gear geometry and the tools to be used. All other calculations, including those required for complicated synchronization of movements, are handled by the Heidenhain TNC 640. As a result, the production of internal gears turns into an easily mastered standard application.

Skiving is a method of manufacturing external gears and, above all, internal gears on machine tools equipped with synchronized spindles. In skiving, parts can be completely machined within a single setup. No special machines, and therefore no machine changeovers, are required in this operation. Users benefit from time savings and increased quality.

Moreover, the current popularity of skiving in manufacturing is due to its considerably higher efficiency and productivity compared with that of traditional gear shaping. New tool technologies and the dynamic motion control of the Heidenhain TNC 640 in double-spindle operation enable the complex processes involved in skiving. The only requirement is a machine tool that features a workpiece spindle with sufficiently high speed along with appropriately configured spindle synchronization.

Only a few parameters need to be entered for defining the gear geometry on Heidenhain’s TNC 640 control.

Well Suited for Complex Gears

With the same ease as skiving—through programming on the basis of the gear geometry and tool definition—the TNC 640 supports users with its cycle 286 “gear hobbing.” The gear hobbing process is especially well suited for machining external gears. The required synchronized movements of the tool spindle and workpiece spindle can be implemented either physically, through a mechanical linkage,or electronically, through a linkage in the control.

The advantages of skiving are based on the method’s high productivity. In addition, a wide variety of tooth forms, including complex ones, can be machined. This can be accomplished with an array of standard cutting tools, while any special tools needed can be manufactured with relative ease.

The basis for the new gear-machining cycles is cycle 285 “defining the gear.” As its name suggests, this cycle is used solely for the definition of the gear geometry. With this cycle, the geometry need be defined only once. This definition is then used in all of the required machining steps of the subsequent production process, including roughing and finishing.

Protection and Reliability

In addition to the benefit of easier programming, the new cycles provide further advantages in terms of machine, workpiece and tool protection as well as process reliability. For the avoidance of damage during unforeseen program interruptions, such as power outages, cycles 286 and 287 support optimized lift-off. These cycles automatically determine both the direction and the path of the tool’s retraction from the workpiece.

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