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.
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.
Wanfu Precision Co.,Ltd