Multiple-Wheel Profifile Grinding  

The use of multiple-wheel profifile grinding offers several possibilities to  increase the performance or the workpiece quality. In a case where the teeth have no  special profifile modififications, four instead of two flflanks can be ground simultaneously  in roughing and fifinishing operations, which will reduce the grinding time by a factor of  two. Just as well, it is possible to reduce the risk of burn signifificantly without impacting  the productivity when compared to conventional profifile grinding. Therefore, just the two  external wheels are grinding and the middle one is not touching the teeth. This affects  a smaller contact angle between the grinding wheels and the tooth flflanks. Schlattmeier  describes the risk of grinding burn as becoming lower the smaller the contact angle  gets. The reverse conclusion allows an increase of the specifific material removal rate at  the same burning risk when grinding with just the external wheels; thus the cycle time  will be reduced.

Adaptive Grinding Technology 

Another important aspect in reducing main grinding time is to avoid so-called “air  grinding.” If using the conventional technology as described above, the maximum  amount of stock is subdivided into a certain number of strokes, which will be passed  through with the programmed axial feed speed. But due to hardening distortions, the  amount of stock is not constant over the tooth flflanks and around the gear, resulting in a  considerable amount of stroke length not grinding the gear.

To avoid this unproductive air grinding, an acoustic emission sensor technique is  used to detect whether the grinding wheel has contact with the workpiece. In case the  wheel is running without contact, the axial feed speed is increased to a maximum  speed, effecting time savings. Additionally, the dressing intervals can be increased as  well. Instead of dressing the wheel after a certain number of strokes, the wheel is  dressed after a certain amount of effectively ground stroke length. This is reducing  dressing time as well as tool cost, i.e., grinding wheel and dresser. The adaptive  technology allows time savings up to 33%. So the more critical the hardening  distortions, the more effective the adaptive technology.

Power Dressing 

The reduction of dressing time is another important aspect for productivity  improvement. When mounting a new grinding wheel, the shape does not fifit to the  required profifile and thus has to be dressed.

To avoid this ineffective dressing volume, Gleason has developed the so-called  “power dressing” method. Instead of dressing pass-by- pass, parallel to the target  profifile, the dresser works in the radial direction. Therefore, the raw profifile of the wheel  is programmed to the machine, which allows starting the dressing cycle just outside the  wheel and in feeding in the radial direction until the target profifile is reached. The effect  is that the processed volume (blue) is almost the same as the real dressed volume,  representing the high efficiency of this method.

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