How do you make cheap enclosures (for production)

[Yansi]

Jeezus... absolutely none of the cheap enclosures are from stainless steel. Stainless is expensive. There is no need for it (unless designing stuff for specific corrosive or food handling enviroments).

They are the most basic DC01 grade steel sheets.  Mostly powder coated fully, or just one side, rest of the surface being zinc plated.

[Saimoun]

Ok thanks.

[Fire Doger]

Stainless steel doesn't "stain". As you can see in most of gear teardown on EEVblog Dave is looking for rust (and usually finds a little), no-one is using stainless for enclosure.

You can avoid rust if they don't have sharp edges (ask manufacturer for it).
Sharp edges will take more time / material to cover and usually have none or very thin layer of protecting coating that's why they rust.

[Cerebus]

Fair enough, you guys kept speaking about bent sheet metal - I thought the material was stainless steel, it is what most of the manufacturers we looked at suggested for bent sheet metal. What is the material, then?

I think they saw you coming.    I'd avoid anybody who blindly suggested stainless to you without you having given them a good reason to suggest it and I suspect you didn't. It's an inherently more expensive material and harder to work with than plain old mild steel which is what is probably most appropriate for your use. Kind of smells of 'sharp' business practices to me.

If something like the Behringer case you linked to is what you want, then you're looking for simple mild steel, perhaps a passivated version of mild steel such as Zintec, finished by powder coating.

The cheapest way to manufacture cases like this, once you get beyond a certain minimum quantity, is for someone to create a set of stamping dies that will cut, out of cheap flat sheet metal, the outline of your flat case parts, including punching any connector, control, ventilation, and even screw holes in one operation. That's followed by a few simple bending operations, optionally some spot welds where corners fold over and then powder coating. Probably followed by silk screening to get any labelling you need. That will get you the minimum per case material and manufacturing costs, but with the NRE cost of the dies as an upfront cost. The exact quantity breakpoint where this becomes the cheapest option is going to depend on the complexity of the case (number and type of holes etc.).

At the other end, quantity wise, any competent machine shop that does sheet metal work will be able to fabricate individual cases by cutting out sheet metal stock, drilling and punching out individual holes, and folding the flat parts on a box and pan folder. Your cost per case will be much higher, but there aren't any NRE costs.

Cases made from die stamped parts are likely to be more consistent than individually fabricated cases.

Powder coating costs will roughly be the same at both ends of the scale. Screen printing costs will also be similar at both ends of the scale with the caveat that there's some setup costs to any screen printing run, which makes long runs cheaper per unit.

Anything that involves 'proper' machining operations such as drilling or milling individual holes and openings, to modify existing stock cases is going to be more expensive because those operations have to happen to each and every case you have made. It's cheaper overall below a certain minimum number, but once you get to a certain number then it's better to invest all that 'proper' machining into manufacturing dies rather than individual cases.

The same logic applies to the dies for making custom aluminium die cast or extruded cases. Those are an inherently more expensive option, both for dies and basic manufacturing, and for the fact that you're unlikely to get a finished case without doing some further machining to the, already custom, case for those processes. If you start with stock cast or extruded cases, then the per case machining costs are all unavoidable and therefore higher still.

[Saimoun]

Thank you Cerebus that really helps a lot

And @Fire Dodger thanks that's a good tip we will try avoiding sharp edges, sounds difficult though to avoid it where the metal plate ends (for ex where the two pieces of a U-shape case meet)?

We are definitely a lot smarter than we were before this topic - so that's good. And also convinced custom is the way forward then - it is also a lot more fun than spending hours trying to find an already existing box to modify

I have a lot of audio devices similar to the one we want to make at home which we looked at - and to be honest that's all we saw: L-shape or U-shape metal case, or extruded aluminium. The aluminium ones are usually made of one round aluminium piece covering top, bottom and two of the sides, leaving the front and back side for connectors/pots, these often covered by a flat metal plate.

This one f.x. : https://www.thomann.de/gb/art_headamp_4.htm - the round metal is one aluminium piece which has a way for the 2 PCBs to slide into (no screws needed) and has built-in thread for screws for the front and back panels, as well as a way for these nice rubber sides (clearly custom as well) to slide onto it. The front and back plates seem a lot heavier so I would definitely guess there are steel.