Tapping 304 ss Thin Walled Holes. 1

[ozarks]

I have a small 304ss part that I must thread (tap) on a production basis. The part is stamped out of .050" thick 304ss with a punched thru extrusion that has sidewalls about .100" high. The I.D. of the extrusion is .284" dia. and it gets tapped with a 5/16-32 UNEF-3B L.H. thread. The .284" dia is textbook for the 5/16-32 UNEF.

Due to the work hardening ability of the 304ss tapping is very difficult and sometimes requires (3) passes with the tap. I am thinking about annealing the stamping prior to tapping in an attempt to reduce surface stresses.

I am presently using spiral flute plug taps. One concern brought to my attention is the possibility the sidewalls of the emboss may be elastically stretching as the tap drives thru and "snapping" back after the tap is removed, thereby not cutting the threads as clean as needed.

Any advice on how to optimize this process would be appreciated.

In the ozarks....

 

[MikeHalloran]

Support the o.d. of the emboss by placing a round die over it while tapping.



Mike Halloran
Pembroke Pines, FL, USA

 

[MadMango]

Can you flow drill the material and use thread forming/rolling fasteners?

"Art without engineering is dreaming; Engineering without art is calculating."

Have you read faq731-376 to make the best use of Eng-Tips Forums?

 

[ozarks]

Thanks Mad Mango;


This specific component is used as a "bung" in a furnace assy. The mating (male thread) part is actually a brass nipple of, which explains the need for a low-pressure tight class-3 thread.


I truly appreciate your response.

In the Ozarks...

 

[MortenDK]

http://www.flowdrill.com/

Just adding a link to help finding tools.
It is possible to roll a tread after flowdrill, I've had some parts made this way in AISI304L, 1mm thick, M3 tread. The screws goes in fine, but I shall not be able to say about the low-pressure tightness as our need was just to fix a screw without a nut insert;
I am very impressed by the flowdrill result.
regards.


Morten K. Thillemann

 

[wellman]

If you have 3 axis available. Thread milling works very well in this type of material. Programming isn't all that complicated.

 

[griffengm]

Ozarks,
Would a PEM style insert work in this application? Is the fitting seeing liquid or gases? Could an O-ring on the fitting provide the seal and allow a bit more variation in the threads?

Just some thoughts.

Griffy