Clinch nuts vs tapped extrusions sheet metal 1

[travisr34]

I am currently designing a sheet metal chassis out of 18 gauge steel for use in the electronics industry. I was looking at using either clinch nuts or tapped extrusions to fasten parts together. Clinch nuts I am very familiar with, tapped extruded holes I am not. The main concern here is cost. I want to do the cheapest option. From a structural stand point I am sure either will work. Not a lot of forces or loading involved in an electronic chassis. The part will be stamped. However I believe a tapped extrusion will still add a few extra process to my piece. These process seem highly automated compared to clinch nut installation. But labor in certain countries is also very cheap. Does anyone have any experience with tapped extrusions? Can to share your experiences with me? Do the threads come out okay? Was there any cost savings vs clinch nuts?

Thank you

 

[MikeHalloran]

I've used tapped extruded holes in PC-compatible chassis made of steel.
I more or less copied what IBM and its cloners did.
Showed a cross section with a tubular extrusion roughly twice the thread OD, with a ragged distal end.
Specified express tapping with a minimum full thread of roughly two diameters in length. (impossible to measure, but not hard to eyeball)

Side note: PC chassis screws are almost universally made of carbon steel, nickel plated, because it's near impossible to retrieve a stainless screw from the bowels of a computer, but a small magnet will handily pick up a carbon steel screw. We had the screws custom made, with hex/flange/Phillips heads, $1200 for the minimum order of 25,000, which sounds like a lot but it didn't fill a big coffee can. Now they're a commodity, and probably much cheaper. Pretty much any PC-compatible bracket you could imagine is also available as a commodity now, too.

Our own prototype sheet metal shop had no particular difficulty doing the extruding, given a reasonable tolerance and a few test articles. Express tapping goes really quick, especially if you have an auto-reversing tapping head.

Your usual suppliers should have no great difficulty doing it, and it should be much cheaper than clinch nuts.



Mike Halloran
Pembroke Pines, FL, USA

 

[ornerynorsk]

Installing a clinch nut vs pierce/extrude & tap is about a horse apiece when considering semi-automated labor. Personally, I greatly prefer the extruded method because there's nothing to come loose in the final assembly. Extruded threads also eliminate component cost. Most turret presses and laser/punch machines can be fitted with the tapping head as one of the turret positions, which makes it an obvious advantage with a more modernized shop.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[CoryPad]

Extruded holes in the chassis should be cheaper. You could even use thread forming fasteners and avoid tapping costs. Beware that extruded holes usually have larger dimensional variation than a formed nut.

 

[ornerynorsk]

Thanks Corypad for clarifying that. Yes, threadforming is the usual convention in an extruded "tapped" hole. I've not seen cut threads used except once in aluminum of substantial thickness.

It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.

 

[ajack1]

Have you considered using Dayton punch and die? Basically it just replaces a piercing punch and dies no extra stages required in a press tool. These are used extensively in white goods manufacture, might be worth a look.

 

[berkshire]

AJack1
I think this tool is generically referred to as a thread form die. Mate and several other CNC turret press tooling companies produce these as well as Dayton, you have to specify the thread form you want.
This is used instead of the punch, extrude, then tapped hole, which tends to slow down a CNC turret press as it taps the hole.
B.E.

You are judged not by what you know, but by what you can do.