Extruded Hole in Steel Stamping

[jmarkus]

What is the appropriate method to determine the size (hole diameter, extrusion height) of an extruded hole meant to be used as a nut in a given thickness of material. Assuming it is tapped, and assuming a thread cutting screw is used?

Thanks,
Jeff

 

[TVP]

I am not aware of any standards for this practice. A couple of stamping references that I have give the following information:

1. Generally, the height of the extrusion is limited to approximately the stock thickness, meaning an overall height from tip of extrusion to the top of the original sheet thickness of ~ 2-3t. Obviously a 3t height extrusion will have more thinning than the 2t version.

2. Taking into account the unavoidable lead-in or pull-down radius, one can expect a full thread length approximately 1.5x the stock thickness.

The Steel Design Manual from AISI may have more information on this subject. You can obtain this document from the Auto Steel Partnership website using the following link:

http://www.a-sp.org/publications.htm

 

[mtdmetro]

We have encountered this problem also. What we did was to develop the hole size by drilling and then extruding the hole to get the right height. This can be done in a milling machine. We drilled a series of holes in the proper thickness of material. We then put the bottom extrusion plate in the vise of a mill and put the punch in the collet. We used a piece of rubber for the stripper and proceded to extude the sheetmetal sample. The results were recorded and the optimum hole size was used.
I hope this helps.