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Allowable Stresses Per AGMA 2001 Too Convservative?

SwaggingIt

SwaggingIt

Mechanical
Oct 31, 2014
24
I havent been a gear designer for a long time, but I'm following AGMA 2001 and my values are verified by KISSsoft. So because I havent been designing gears for long, I'm not sure how to deal with this situation:
Gear pair is 48 pitch with driver spinning at 1686 RPM worst case for only 4.44 hours at this max operating condition.
Material is 15-5 through hardened to 42 HRC (392 HB). I use table 9 in AGMA 2001 to determine Sat then apply the factors in the image to get my acceptable stress of 49.6 ksi. Shigley states that the endurance strength for steels is 0.5*Sy so this would be 72.5 ksi for 15-5. How do I reconcile what AGMA says versus what Shigley says? Is AGMA just too conservative when it comes to fine pitch high speed gears, so I should consider Shigley's endurance strength in these instances? But I would still use AGMA calculation for the bending stress number which is essentially applying the stress modifiers in the Shigley version.

Been spinning my wheels over this for a while now and just need the most logical way to defend my design to the customer. Thank you for any feedback!
P.S. the YM factor is because I'm expecting oscillation and this factor is "from" ISO 6336.

Sateff_ng2jy6.jpg
 
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Op
Please provide the required Torque and rpm
In and out. AGMA is proven calculations.
Why was 15-5 chosen
 
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Op
AGMA is conservative because it's used for Aerospace, and heavy industrial uses with high Torque and rpm values.
The material is chosen for contact stress,
Loads on gear tooth flanks, and bending fatigue.
Your application is medium high rpm.
But you gave no Torque values.
AGMA quality grade is based on many factors ,one being to minimize vibration, and tooth errors.
 
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Thanks for the feedback.
15-5 chosen because its what my company traditionally used for our gearboxes for relatively high strength, core ductility, and anti-corrosion.
Driver inputs are for max operating condition are ft-lb = 9.2 at 2686 RPM.
Gear ratio is 2.048:1.
For this specific application, we're not as concerned for flank life, primarily root life.
 
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Op
I don't make quick response so I took time to answer.
Yes a minimum fillet radii at root, is a must. Contact stress if not sufficient it will cause pitting and Crack propagation.
Tooth bending will cause failure at the root. Stay below the SN cycles. For the material chosen. For the required cycles.
Follow all the AGMA specifications for the previous mention. There are very good gear programs which I like to use now. To eliminate any calculation errors or missed
Effects, like contact ratio, contact stress, gear tooth bending, interference cause by incorrect gear teeth geometry,
Proper gear profile shifting, to enhance the pinion gear which fails first.
Tooth proportions strength of the pinion and proper gear ratio of the gear box to obtain correct Torque and rpm output.
 
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