Micro Hardness of Screw Tip? 2

[mxracer17788]

I have a new prototype for a screw that doesn't seem to be performing as well as the competitors. They are self-drilling screws that are meant to drill into at least two panels of 18 gauge sheet steel. Normally, our self drilling screws have a #3 drill point at the end, but these have a sharp point, similar to a wood screw. During installation testing, the tip just spins on the metal and eventually wears out and becomes dull without driving into the material. Given almost identical material and geometry to our competitors, my assumption is that our heat treating processes are different. I want to mount both samples and check for micro hardness at the tip, but I'm wondering what the best technique to do this is. Obviously I wont be able to take readings right at the tip, and will need to take some material off. Any ideas on the best way to mount the screws to do this?

 

[mxracer17788]

Since the screws are short, one initial thought was to mount the screw lying horizontal, and grind away until I'm left with a perfect section view of the screw. Thoughts?

 

[redpicker]

Since the screws are short, one initial thought was to mount the screw lying horizontal, and grind away until I'm left with a perfect section view of the screw. Thoughts?

That's the way I would do it. I might grind the head off first, to help in mounting the screw horizontally.

rp

 

[mxracer17788]

Perfect, Thanks.

 

[TVP]

The following two links have some good information on metallographic preparation of fasteners:

http://www.buehler-asia.com/brochure/apps_support-tech-notes_vol1_issue1.pdf

http://www.struers.com/resources/elements/12/143764/Application_Notes_Fasteners_English.pdf

 

[Screwman1]

I have worked on a number of gimlet pointed designs the were "intended" to drill through double 18 gauge material and none of them are still in production. The problem with the gimlet design is the mechanism of material removal; there isn't one. So you either have to rely on end load or frictional heating to pierce the sheets and neither of those will work consistently from lot to lot.
The way to mount the part is to cross cut the shank so that you have the tip, then make a mount of that with the shank parallel to the surface and then slowly work it back to the cross section that you need. If you need to learn how to mount fasteners you are going to have trouble with this project.