LEAPS AND BOUNDS: GEAR HOBBING AT WORLD RECORD SPEED

Dry or wet machining? This decision must be made by the customer and is application-based. The same logic applies to the choice of automation and auxiliary equipment. The new generation of K160 gear hobbing machines from Koepfer Verzahnungsmaschinen GmbH & Co. KG (Villingen-Schwenningen, Germany) used for the high-speed machining of gears up to module 2.5 does not make that choice any easier. However, where machining times are concerned, the main objective is always the same: as fast as possible.

The basic prerequisites for fast chip-to-chip times are high spindle speeds for the cutter and work axes. These features allow the machine to take advantage of high cutting speeds. But to make the manufacturing process truly efficient, you also have to reduce the times for loading, unloading, setting and programming to their absolute minimum.

Over the last few years, users of this system appear to have these factors well under control. Considering the fact that only eight or ten years ago the machining of armature shafts took 20 to 25 seconds, this machine has achieved a world best of 8 to 10 seconds for some years now. The dry, high-speed hobbing of planetary gears or the high-speed gear cutting on armature shafts using the ?fly-hobbing? process are as much a part of the reason for its success as is the possibility to use the tangential hobbing process to generate the gear teeth on worm wheels.

The greatest time saving, however, could be the optional work piece loading concept, where the parts are loaded through the spindle. This concept has now evolved to the next level with further development and fine-tuning. Armin Wacker, vice president of sales and marketing at Koepfer, sees this development as a real quantum leap and a measurable time saving. ?Our equipment already gives us the fastest manufacturing time for shafts in the world. This new concept, in which the workpieces are literally ?shot? through the spindle, almost completely eliminates idle/changeover times and allows us to reduce the machining time for a shaft by yet another two seconds. In other words, we have made the leap from eight to six seconds?

The new concept also includes a brand new shifting hob head with a maximum hob shift of 160 mm and new software with dialogue programming facility. Programming has been greatly simplified ? even for operators that lack special qualification ? by the BWO control with conversational dialogue, full colour touch panel, and one MB of memory. The combination of new software and drive technology allows the customer to achieve a level of precision that has previously only been possible with grinding.

Such quality also makes this machine tool a viable proposition for machining components with special safety requirements, including those for the aerospace industry. As mentioned earlier, chip-to-chip times are mainly dependent on spindle speeds and cutting speeds. In its standard version, this machine has a work spindle speed of 1,000 rpm and a maximum cutting spindle speed of 5,000 rpm. The latter can, without problem, be increased to 12,000 rpm wherever the application requires.

This provides a power reserve that, according to Wacker, serves a valuable purpose. ?On the one hand, we are not maxing out any of our machines, as we not only want to but must ensure they always suit the prevailing customer requirements. On the other hand, tooling manufacturers have ? over the last few years ? made enormous strides with, for example, coating processes. The much greater wear resistance of today?s tool alloys allows us to increase spindle speeds and cutting speeds. 5,000 rpm is already pretty fast, but we have to be able to increase that, when necessary.?

STANDARD VERSION SETS NEW BENCHMARK
With the standard work spindle speed the user can produce armature shafts with 4 teeth, using a 24 mm hob at a cutting speed of 300 m/min. The standard machine is rated at a maximum workpiece length of 30 mm and a maximum hobbing length of 200 mm. A long-bed version of this system, with a maximum hobbing length of 480 mm and a maximum work piece length of 600 mm, is also available.

The standard machine can be equipped with a variety of different Koepfer automation systems. First, there is the integrated gantry loader with flexible work piece magazines, chain loader and conveyor belt storage section. A rotating twin-gripper offers shortest loading and unloading times. Optionally, a high capacity re-circulating storage system allows the machine to be run a number of hours and is quick and easy to reset ? accommodating both gears and shaft- or pinion-type components. Using a special metering hopper with multiple feeder rails, the work pieces can be loaded diagonally, which considerably increases the autonomy of the machine.

Also available as an option is an auxiliary tool that can be used for deburring operations (via deburring disc or rotating tool) as a vibration dampener, as a holder for the sensor that allows the automatic timing of workpieces with hardened gear teeth, or for special purpose applications such as live deburring tools. The flexibility of this machine tool continues to show when the machine is integrated into a production cell that includes gear hobbing, washing, measuring, etc.

All in all, the K160 gear hobbing machine sets the new standard for the future. It is easy to calculate the amount of savings that will accrue as a consequence of a two-second time saving per armature shaft, of which a million are produced every year.

Koepfer Verzahnungsmaschinen GmbH & Co. KG, DEU ? 78120 Furtwangen, Villingen-Schwenningen, Germany, +49 (0) 7723 655-128, www.koepfer.com.