cONTROLLING INTERNAL SPLINE GROWTH IN 8620 FORGING
cONTROLLING INTERNAL SPLINE GROWTH IN 8620 FORGING
(OP)
We are having a 8620 gear forging which we are gear cutting prior to heat treatment. Then we are cutting internal splines to ANSI class 5 and then sending it for carburise and hardening to 57-60 Rc.
The perfectly OK spline is increasing in size by almost 0.005" between pins. We purchased the broach to 0.002" smaller but again we are geeting the same results.
I think that the heat treatment needs to be improved. SO need inputs as to which microstructure is suitable for lowest distortion without affecting the mechanical properties. Will the plug quenching help to reduce the distortion in splined bore? If so does it require any soecial fixturing? How is it done?
The perfectly OK spline is increasing in size by almost 0.005" between pins. We purchased the broach to 0.002" smaller but again we are geeting the same results.
I think that the heat treatment needs to be improved. SO need inputs as to which microstructure is suitable for lowest distortion without affecting the mechanical properties. Will the plug quenching help to reduce the distortion in splined bore? If so does it require any soecial fixturing? How is it done?





RE: cONTROLLING INTERNAL SPLINE GROWTH IN 8620 FORGING
RE: cONTROLLING INTERNAL SPLINE GROWTH IN 8620 FORGING
The forging has a hub dia 1.75". Gear width at teeth is 1.015" and in the hub area it is 0.88 and in the remaining area 0.515.
Gear data is not important in this case but it is 72 T, 12 DP, 20 deg PA, 15 deg hellical gear.
I checked the gear hardness at teeth and near bore it is 57-58 HRc.
RE: cONTROLLING INTERNAL SPLINE GROWTH IN 8620 FORGING
How is the forging treated prior to machining?
It probably should be annealed from forging and normalized prior to marching.
What is the hardness of the forging as received?
RE: cONTROLLING INTERNAL SPLINE GROWTH IN 8620 FORGING
In case decide to anneal ,which annealing process you recommend? Is it full annealing or stress releif annealing?
The hardness is not really specified on the forging dwg. But it should be around 20 HRC, Since it is forged and normalised. But I will find out.
RE: cONTROLLING INTERNAL SPLINE GROWTH IN 8620 FORGING
Anneal @ 1600°F; Furnace cool @ 30°F per hour to 1150°F, then air cool to RT
Normalize @ 1675°F; air cool to Rt.
I'm digging for may data on carburizing 8620 and the dimension changes expected and how to minimize them. You have two conditions, carburizing and HT, that are additive causing you problem.
Someone with a better reference set than I have jump in and help gearman1234. My reference material is in an unstructured stack of boxes.
How are you carburizing , salt bath or atmosphere?
RE: cONTROLLING INTERNAL SPLINE GROWTH IN 8620 FORGING
www.eng-tips.com/gviewthread.cfm/lev2/16/lev3/58/pid/406/qid/68845
RE: cONTROLLING INTERNAL SPLINE GROWTH IN 8620 FORGING
Here is a web site for further review;
www.geartechnology.com/mag/archive/ferrit.htm
RE: cONTROLLING INTERNAL SPLINE GROWTH IN 8620 FORGING
RE: cONTROLLING INTERNAL SPLINE GROWTH IN 8620 FORGING
RE: cONTROLLING INTERNAL SPLINE GROWTH IN 8620 FORGING
After carburize, if you reduce temperature and hold between the upper critical and lower critical temperature and then quench, it will stabilize the distortion. However this will tend to produce grain-boundary carbide network if you hold too long in the carbide forming temperature range. If your gear teeth are only modrately stressed in service, this should not be a problem. But if the teeth are substatially stressed it is a problem.
Jesus is THE life,
Leonard