The finish is functional
Where the enclosure is the earth reference, or where panels have to be bonded to each other for EMC, the contact surfaces must be conductive. That means masking before coating, or choosing a finish that is conductive by nature — zinc-coated steel left bare, or a masked contact area on a coated panel.
The trap is the bolted joint. Two coated panels bolted together look bonded and are not. Where a joint carries bonding current, both faces need a masked land and the fixing is often a plated screw rather than a coated one. This is a drawing note, not a shop-floor decision.
Clearance, creepage and mechanical design together
| Requirement | Sheet metal consequence |
|---|---|
| Creepage distance across a surface | Ribs, slots or barriers formed into the metal rather than added as parts |
| Clearance through air | Internal spacing set by the tallest component plus the required gap |
| Bonding between panels | Masked lands, plated fixings, conductive gaskets where panels are removable |
| Heat sink mounting | Flatness and thickness under the sink; screw torque on a formed face |
| Airflow over hot components | Vent placement and ducting, agreed with the thermal design |
| EMI containment | Gasket grooves, finger stock lands, aperture sizing on the seam |
Heat sinks and flatness
A heat sink transfers heat only as well as it touches. Where the enclosure surface is the mounting face, its flatness matters: a bowed panel means a partial contact area and a hot device. The flatness requirement should be stated with a value and a measurement method, and it is normally met by forming a stiffening feature into the panel rather than by increasing thickness.
Thickness matters in a second way at the fixing. Screw torque on a formed face works the material, so bosses, inserts or additional layers are specified where a device is repeatedly tightened — a rework risk that shows up in service rather than on the line.
- Nominate every bonding and contact surface for masking, and say whether the tolerance applies before or after coating.
- Keep a conductive finish option open: bare zinc-coated steel is common for the inside of a bonded panel.
- Specify heat-sink face flatness with a value and a method; "flat" means nothing.
- Consider where a technician’s hand goes during service, and form or deburr accordingly.