ID (Inside Diameter) Threads Shrinking due to Heat Treatment and Weld

[CMfgT]

Not sure if this is the right area to post this question, but our facility makes a number of cylindrical pins and shafts with I.D. Threads. After we tap the threads many parts will be induction heat treated or welded in an assembly. A number of times we will shrink the threads with the heat being applied and the threads will not gage. This will result in a rework op to retap and gage. Then we run into the issue of the no go going after being retapped. Does any one have a better solution to this.

All I see is we can do two things:
1.Drill and tap after Heat Treat or weld, but the parts will be to hard and break taps, or the weldment will be difficult to fixture to tap threads.

2. Plug the hole with a bolt or some material to keep the I.D. Hole from sucking the heat towards it and shrinking.

#2 is what I was hoping to hear some success with. I just don't want to get a bunch of bolts stuck in the I.D. It seems like we have the worst luck with 1/8-27 NPSF threads.

Sorry for the ramble, just a big quality / waste for us and would like to at least see if others are experiencing the same problem.

Thanks,

 

[bobdoering]

Re: ID Threads Shrinking due to HT and Weld

Not sure if this is the right area to post this question, but our facility makes a number of cylindrical pins and shafts with I.D. Threads. After we tap the threads many parts will be induction heat treated or welded in an assembly.

Do the threads need to be heat treated - or are they affected by adjacent areas being heat treated?

 

[CMfgT]

Re: ID Threads Shrinking due to HT and Weld

Do the threads need to be heat treated - or are they affected by adjacent areas being heat treated?

Both, the threads at weld are caused by adjacent heating of the process.

Heat Treat normally requires a certain depth to be hard, so no matter what the threads will be affected because even if your not intending to go as deep as the threads the heat will have to affect the threads in order to meet the depth spec. Make sense?

 

[bobdoering]

Re: ID Threads Shrinking due to HT and Weld

Both, the threads at weld are caused by adjacent heating of the process.

Heat Treat normally requires a certain depth to be hard, so no matter what the threads will be affected because even if your not intending to go as deep as the threads the heat will have to affect the threads in order to meet the depth spec. Make sense?

We had parts that needed heat treated, but the threads were to remain soft. There was a heat treat paste that was put on the threads to protect them (which would also minimize the dimensional distortion), then removed afterwords. Not sure if that approach is applicable or not.

 

[CMfgT]

Re: ID Threads Shrinking due to HT and Weld

We had parts that needed heat treated, but the threads were to remain soft. There was a heat treat paste that was put on the threads to protect them (which would also minimize the dimensional distortion), then removed afterwords. Not sure if that approach is applicable or not.

Two Questions:

1. Are you referring to ID Threads or OD Threads
2. If you are referring to a tap hole (ID Threads), then can you specify what paste you used and how did you remove it from the hole?

thanks

 

[JRKH]

Re: ID Threads Shrinking due to HT and Weld

The problem you are running into may not be threads shrinking but being deformed (out of round) I suspect this may be especially true in the welding area. This could at least partly account for the Oversize condition after retap.

Just two things that came to mind quickly.
What "H" size are your taps. You could try using a tap with a higher "H" value which will give a slightly larger thread and thus be more forgiving after heating.
Another thought is to use a thread forming tap for any retap operation. These will likely last longer since they are not "cutting" material, rather they will "Move" material so should be less likely to gage large after retap.

Peace
James

 

[bobdoering]

Re: ID Threads Shrinking due to HT and Weld

Two Questions:

1. Are you referring to ID Threads or OD Threads
2. If you are referring to a tap hole (ID Threads), then can you specify what paste you used and how did you remove it from the hole?

thanks

The specific application we had was OD threads. The material was removed with a hot caustic wash. The thread was about 1/4-20 or so. I do not recall the brand of material (it would be handy...) This might be a clue, though. Trust me, the removal is a trick - and for us the paste was specified by the customer. We had done hard turning, but not threads.

 

[rnsvasan]

Re: ID Threads Shrinking due to HT and Weld

Need some input such as, what is the wall thickness ? Is Fixture being used for induction heater is ok - I mean runout, centers, etc? what is the material - is there any thing to play with the chemistry ?. what is the shrinkage pattern you are getting so that to compensate in soft condition? I accept these aspects you might have studied. I recommend some fastereners personnel could suggest best method.

 

[John Martinez]

Re: ID Threads Shrinking due to HT and Weld

Both, the threads at weld are caused by adjacent heating of the process.

Heat Treat normally requires a certain depth to be hard, so no matter what the threads will be affected because even if your not intending to go as deep as the threads the heat will have to affect the threads in order to meet the depth spec. Make sense?

Have you thought about cutting the threads oversize, then trim after HT?

 

[Stijloor]

Re: ID Threads Shrinking due to HT and Weld

Have you thought about cutting the threads oversize, then trim after HT?

That will likely depend on the required hardness. Hardened material does not thread/tap/machine very well.

Stijloor.