Enclosure Design
Nearly every enclosure we are asked to quote starts life as a welded box. It is the natural way to build a metal housing: cut the panels, weld the corners, and you have a stiff shell. But welding commits you to a design in a way bolting does not, and an increasing number of European OEMs are converting welded enclosures to bolted ones — not to save money on assembly, but because they need to get inside the machine.
This is a decision worth making deliberately rather than by default, because the trade-offs are not obvious and one of them — sealing — catches people out.
What welding actually buys you
A continuous weld gives you three things:
- Stiffness. A welded corner is a continuous joint. Under load the box behaves close to a monolithic shell.
- Inherent sealing. A continuous seam weld is a continuous barrier. For dust, water and — critically for acoustic enclosures — sound, this is the easiest way to get a leak-free shell.
- Low piece-part count. No fasteners, no gaskets, no tapped holes. Once the weldment is done, the enclosure is done.
For a sealed box that will never be opened, welding is genuinely the better answer. The trouble is that very few machine enclosures are never opened.
What welding costs you later
The cost only appears after the machine ships:
- Service access. If a pump, compressor or drive needs replacing, you are cutting the enclosure open and re-welding it — on site, in a customer’s plant, with a grinder.
- Shipping volume. A welded enclosure ships at its full assembled volume. On a large housing that is a serious freight cost, and it is why welded enclosures are usually crated rather than palletised.
- Design change. Once the weldment is tooled, geometry is frozen. If the machine layout changes, the enclosure is scrapped or modified by hand.
- Recycling and end-of-life. This is the quiet driver behind the shift. A bolted assembly can be separated into single materials at end of life; a welded, painted, foam-lined box largely cannot. For customers selling into the EU this is moving from a nice-to-have to a requirement.
What bolting buys you — and what it costs
| Welded | Bolted modular | |
|---|---|---|
| Service access | Cut and re-weld | Unbolt the panel |
| Design change | Geometry frozen | Individual panels re-cut |
| Shipping | Full volume, crated | Flat-pack possible |
| On-site work | None | Assembly required, with instructions |
| Piece-part count | Low | Higher — fasteners, gaskets, captive nuts |
| Stiffness | Highest | Good, if panels are folded with returns and braced |
| Sealing | Inherent | Must be designed in |
| End-of-life separation | Poor | Good |
How we make a bolted enclosure behave like a welded one
A bolted enclosure is not simply a welded design with the welds replaced by screws. It needs three things done deliberately:
1. Stiffness from geometry, not from weld
Welded boxes get stiffness from the joint. Bolted panels get it from folded returns — every panel edge is folded back on itself, which both stiffens the panel and gives a flat face for the fasteners to pull against. On larger panels we add internal bracing or a formed rib. A flat sheet screwed to an angle is a floppy assembly; a folded pan stiffened at the edges is not.
2. Fastening that survives repeated service
Self-tapping screws into sheet metal are the wrong answer on a serviceable panel — they lose grip after a few cycles. We use:
- PEM captive nuts or studs pressed into the panel, so a bolt goes into a proper thread every time
- Rivet nuts where the panel is too thin for a PEM
- Captive panel screws where the fastener stays with the panel and cannot be dropped inside the machine
3. Gasketing that reseats correctly
The gasket has to be located so it cannot creep out of position when the panel is refitted, and it has to be compressed evenly. Our default is a continuous EPDM or silicone gasket in a retained groove or bonded to one face, with multi-point latches on doors so the compression is even around the full perimeter rather than tight at the handle side and loose at the hinge side.
So which should you choose?
Choose welded if the enclosure is sealed for life, never needs internal access, and the priority is maximum stiffness or maximum sealing at minimum piece-part count.
Choose bolted if anyone will ever need to service what is inside it, if you may change the internal layout, if shipping volume matters, or if you sell into a market where end-of-life material separation is becoming a requirement.
Consider the hybrid if you want both: a seam-welded shell for the sealed, structural part, with bolted service panels and a bolted door on the faces that need access. For many machines this is the right answer, and it is often what we end up recommending.
Converting an existing welded design
If you have a welded enclosure and want it modularised, the process is usually:
- You send the STEP model and the assembly drawing, plus any weight distribution data for the internals.
- We identify which faces actually need to come off for service, and which can stay welded.
- We redesign those faces as folded, gasketed, bolted panels with captive fasteners.
- We build a first article and, where sealing matters, test it — for acoustic enclosures that means a sound reading, for outdoor units a water ingress check.
- Only after the first article passes do we talk about production quantities.
The important part is step 2. Modularising everything is usually unnecessary and adds cost. Modularising only what needs to come off is where the value is.
Have a welded enclosure you want modularised?
Send the STEP file and tell us what has to be reachable for service. We will tell you which faces to convert, what it does to cost, and what it does to sealing — before you commit to tooling.
Ningbo Fulei Metal Products Co., Ltd. — laser cutting, bending, welding, PEM / rivet nut installation and assembly in-house; powder coating on audited partner lines that we specify and inspect. Welding capability · DFM review.