An enclosure is the most common sheet metal assembly there is, and it is where the whole vocabulary of fabrication design shows up at once: bend relief, flange length, hardware selection, finishing and earthing. Getting it right is mostly a matter of deciding early how it comes apart, because that decides nearly everything else.
How it comes apart decides the design
A folded box with a removable lid is the cheapest construction. A frame with panels is more expensive and better for large or serviceable equipment. A clamshell suits handheld products. Decide this first, because it decides where the joints are, where the fasteners go, how the earthing path runs and how the thing is assembled on a bench.
Hardware rather than tapped holes
Self clinching nuts and studs pressed into the sheet give a strong thread with no distortion, and they are cheaper than welding a nut or tapping thin material. Respect the manufacturer's minimum distance from an edge and the specified hole size, both of which are commonly ignored and both of which cause pull out. Captive hardware on removable panels stops screws being lost in service.
Earthing, coating and the contradiction between them
Powder coating and anodising both insulate, so an enclosure that relies on panel to panel contact for its earth will not have one after finishing. The answers are masking the contact areas, using paint piercing washers, or running a dedicated earth strap between panels. Whichever you choose, it belongs on the drawing rather than being left to assembly.
Ingress protection and where it actually leaks
A gasket needs a flat continuous sealing surface and a compression that is even all the way round, which means enough fasteners and enough flange stiffness. Most enclosures leak at the corners of a folded flange, at cable entries and around panel mounted components. Design the seal as a continuous path and choose components with their own rated seals rather than trying to seal around them.
Questions people ask about sheet metal enclosure design
What is the cheapest enclosure construction?
A folded box with a removable lid, made from one thickness with one bend radius, using pressed in hardware rather than welded or tapped threads.
How do I get threads into thin sheet?
Self clinching nuts or studs pressed into the sheet. Respect the manufacturer's edge distance and hole size, which are the usual causes of failure.
Why does my earthed enclosure not conduct?
Because powder coating and anodising insulate. Contact areas must be masked, paint piercing washers used, or a dedicated earth strap fitted.
Where do enclosures usually leak?
At folded flange corners, at cable entries and around panel mounted components. Design the seal as a continuous path and use components with their own rated seals.