Non normalised 5120h gears 2

[bluenewt8]

Hi,

Does anyone have any experience with removing the normailizing process for rough forging stock for gears (5120h material or something similar) prior to green operations (turning, deburring, hobbing, spline rolling etc).

A proposal has been put forward to remove the normalizing process and send gear rough stock directly to our factory after hot forging. Removal of normalization will give a significant cost saving and i am aware of other people who have done this in the past.

Is this advisable?
Would you expect to see any adverse effects in green end operations due to the fact the the non normalised stock will have a higher core hardness.

Thanks

 

[TVP]

Did you read the article from Gear Solutions that metengr recommended in the other thread you started? Normalizing homogenizes the microstructure across all areas of the forged blank. Without it, you can expect more variation in the following:

distortion after quenching (more distortion, potential quench cracks)
hardness after quenching (soft spots)
tool life in turning, hobbing, and spline rolling operations (reduced tool life in all of these)
surface roughness after machining operations

 

[dbooker630]

I also know of suppliers that skip the normalize operation becuase of their perceived machine tool's ability to handle the material. We could not do it with our machines. But as TVP noted, you run the risk of variation not only in quenching but also with tooth contact pattern and splines.

 

[tbuelna]

I would agree with TVP's comments. I assume your gear blanks are hot-forged. Stress relief and normalizing of the blanks gives a more dimensionally stable and metallurgically uniform starting point for the rest of the manufacturing operations. The stress relief & normalizing of blanks would be done in large batches, so unless the gear is for an application that is extremely cost/time sensitive I can't imagine your budget would not allow for it. The fact that you are using forged blanks would seem to indicate that quality and performance are of some importance.

Lastly, I would point out that industry guidelines, like those published by AGMA, highly recommend normalizing alloy steels prior to initial machining operations. And the guidelines used in aeropsace, such as AMS 2759, typically make it a mandatory step.

Regards,
Terry

 

[redpicker]

Removal of normalization will give a significant cost saving ...

I have to question this statement. The cost of normalizing is just not that great. For a 5 pound gear, you're looking at 25 cents or so. Considering the overall cost of the gear, that really isn't that significant. While I understand that if you are looking at 500,000 of these gears, that's $125,000, which may seem like a significant amount, but considering the cost of 500,000 gears is probably $5 million, that $125,000 isn't really that significant. If you compare that $125,000 to the sale price of those 500,000 gears, you will find it really is insignificant.

When you give further consideration to the cost of the additional problems, as is mentioned above, any savings goes away. Just an increase in scrap rate of 1% could cut that number by nearly half. When you consider the cost of the change can be considerably larger than just a increase in scrap rate (increase rework, missed deliveries, lower product quality), chaniging the process can be taking a pretty big chance for a somewhat small return.

rp