Issues with Internal HEX Wrenching Features on thread-rolled parts

[MindCollizion]

I am not sure if this would be the best section to post this to, but I'm looking for help in determining where we are in error during the manufacturing/verification process of an internal HEX wrenching feature being broached into a cylindrical thread-rolled feature of the part.
We've been running into a lot of issues related to non-conformance of this feature (inspected by a HEX GO/NOGO ASME B18.3 Gages) once the thread-rolling process has been performed around it. We have attempted to swap the order in which the processes are performed (broaching before thread rolling, thread rolling before broaching) but the issue remains because of the size of the part itself (typically 0.094" and 0.078" NOM Socket size), so it's usually an issue for these smaller parts. It seems that the pressure of the rolling process affects the dimension of the HEX feature, making it non-conforming when it was acceptable beforehand.

Has anyone run into a similar problem or has any advice as to how I can proceed with determining the necessary changes to our manufacturing process?
Thanks in advance for your help, any info is truly appreciated.

 

[wmpy]

So, the thread rolling is closing up the broached hole? You said that you tried broaching after thread rolling. What was the problem with that method?

We thread roll parts that we've broached and don't have a problem, but I think it matters how close the broached size is to the threaded size. For reference, we regularly roll 5/16-24 threads on parts with a 5/32 internal hex and 7/16-20 threads on parts with a 3/16 hex.

I would start by making sure that your are not over-rolling your threads. Too much pressure caused by over-rolling could close up the hole. If you're not sure, try decreasing your blank diameter until the major diameter becomes too small.

I'm not sure what machines you're using, but it might be possible to put a close-fitting hex plug in the broached hole so that the material can't close up when rolling. This might not be practical for all applications.

You could also just accept that the hole will close up and start with a larger broached hole. Custom sized broaches are easily available. If your current process if producing broached holes that are .003" smaller than your desired size, you can order a broach that is .003" larger and hope it moves the same amount and in a consistent manner.

 

[Triaged]

You don't mention the thread size that goes with what hex size. Is the wall very thin? Are you drilling after thread rolling?