How are sheet metal enclosures closed with screws?

Question

I need to design an aluminum enclosure for some electronics, but I have no idea how to screw the different pieces together. I have settled for a folded box design with a top, but I can't figure out how the lid is supposed to be screwed with the rest.

By checking on metal enclosures I have access to, it seems that it is frequent to have a hole, kind of "punched" towards the inside, that is made to be exactly the right diameter to be tapped, allowing a screw to be screwed inside. However, I can't find any info about how that is actually done, and in details : which tools are required, what sizes the holes need to be for the formed cylinder to be the right diameter for tapping...

I have been checking on self-tapping metal screws too, but could not find very good references specifying the required diameter of the hole for the screw to tap correctly, and the correct sheet metal thickness required to ensure the screw won't snap out of the sheet due to having not enough fillets fitted inside the hole. Or are rivet nuts something that could be considered using for this application ?

So which technologies are available for this purpose, available without expensive tooling (hydraulic presses...), especially for 2mm aluminum sheets ?

P.S. : I have never worked with sheet metal and could not really find much info on the internet nor have any people around me with some experience about sheet metal enclosures.

Answer 1

If the enclosure is going to be opened and closed periodically and you wish to have longer life integrity for this action, consider an alternative method to sheet metal screws.

Self-tapping screws can be found in self-drilling form but that aspect makes the longevity of the fastener even more reduced if repeatedly cycled.

Your consideration of using rivnuts is a far better choice. The threaded portion remains within the flange at the top opening (or front, as the case may be) while the cover need only to have matching holes of the correct diameter for the machine screws or bolts to pass.

Rivnut tools are far less expensive than when I first learned of them, as are the individual rivnuts. Repeated open and close cycles will not be a problem. Ensure that the rivnut is well seated and do not over-torque the fastener (causing the rivnut to spin) and you should find it a suitable solution.

One determines the fastener size desired then uses that information to find the appropriately threaded rivnut, which will be followed by a reference to the hole size to drill to accept the rivnut.

One last caution: determine the appropriate pulling force/limit, as it is far too easy to apply sufficient force to pull the threads from the rivnut, creating a failure point. My first inexpensive tool required "that's about right" for determining the force to be applied, while the replacement tool has a travel stop preventing the tool from closing too far.

Amazon has a number of tool sets which can also include the rivnuts. One can also search for a DIY rivunt setting tool, which is effectively a compatibly sized bolt with a pressure sleeve and a couple of nuts. If you have only a few dozen to embed, it may be more cost effective to replace dollars/euros/what-have-you with elbow grease. Oh, yeah, apply lube to moving parts of any tool you create and make your life that much easier.