SBAER
Hot Rolled
- Joined
- Aug 21, 2006
- Location
- Kitchener, on canada
Hi
We make the gears for our first prototype by wire EDM and that works pretty well. When we need to make the first run of 20 gearboxes we get the gears hobbed by a local shop that specializes in this type of work. Gear noise is a big issue for these gearboxes, we are trying to make the quietest gearboxes possible but still limiting ourselves to AGMA Class 9 tolerances. We don't fully understand how all the individual tolerances that make an AGMA 9 gear an AGMA 9 gear affect the noise of the gear train over its intended speed range.
There is one gear set in the current gearbox under development that is excessively noisy in one direction but not in the other direction. We can change the direction that the objectionable noise occurs in by flipping the gear over (pinion orientation does not affect noise). The whole lot of 20 gears has the same issue to some degree of the other, some are very quiet in one direction but really loud in the other, others are not as quiet in the good direction but also not as loud in the other. The gears are 4140HT, nitrided after hobbing. We have a shadowgraph that allows us to compare the generated gear profile to the CAD (theoretical) profile, but the 10:1 magnification is not high enough to conclusively highlight any anomaly (the gear has a module of 2.25). If we look at flanks of the gear that has run for a couple of hours under a microscope we see a different wear pattern on one flank vs the other. See pictures below
I have uploaded a video with sound if you are curious enough
My question is; what could have gone wrong in the hobbing process to cause this? Is this worn equipment, badely sharpened hob, sloppy setup or something else?
We make the gears for our first prototype by wire EDM and that works pretty well. When we need to make the first run of 20 gearboxes we get the gears hobbed by a local shop that specializes in this type of work. Gear noise is a big issue for these gearboxes, we are trying to make the quietest gearboxes possible but still limiting ourselves to AGMA Class 9 tolerances. We don't fully understand how all the individual tolerances that make an AGMA 9 gear an AGMA 9 gear affect the noise of the gear train over its intended speed range.
There is one gear set in the current gearbox under development that is excessively noisy in one direction but not in the other direction. We can change the direction that the objectionable noise occurs in by flipping the gear over (pinion orientation does not affect noise). The whole lot of 20 gears has the same issue to some degree of the other, some are very quiet in one direction but really loud in the other, others are not as quiet in the good direction but also not as loud in the other. The gears are 4140HT, nitrided after hobbing. We have a shadowgraph that allows us to compare the generated gear profile to the CAD (theoretical) profile, but the 10:1 magnification is not high enough to conclusively highlight any anomaly (the gear has a module of 2.25). If we look at flanks of the gear that has run for a couple of hours under a microscope we see a different wear pattern on one flank vs the other. See pictures below
I have uploaded a video with sound if you are curious enough
Relating Sound and Wear Pattern_1.mp4
drive.google.com
My question is; what could have gone wrong in the hobbing process to cause this? Is this worn equipment, badely sharpened hob, sloppy setup or something else?