Key takeaways
- The profile sets the wall, the groove and the internal mounting plane before any secondary machining starts.
- Sealing depends on a continuous gasket groove, a flat mating face and the right compression, not on gasket thickness alone.
- Anodising insulates. A grounded enclosure needs masked contact points or a conductive finish on the mating faces.
- Send the profile drawing, the end plate design, the IP target and the earthing path with the RFQ.
What the extrusion decides before machining
An extruded aluminium enclosure begins as a constant cross-section. The die sets the outside shape, the wall thickness, the internal ribs, the gasket groove and any T-slot or mounting channel. Everything that changes along the length, such as end plates, cable entries, windows and threads, is added later by machining.
That split matters for cost. Features that run the full length are almost free once the die exists, because the press produces them with the profile. Features that stop part way along the body need a milling operation, a fixture and inspection. A design that puts a mounting boss on the inside face of a side wall looks simple on a 3D model and is expensive on the shop floor.
The profile also sets the tolerance base. Extruded sections are governed by the profile standard and by the die wear over the run. A machined face can be held closer, but the as-extruded wall and groove carry the general tolerance of the profile.
The features that matter in a profile
Most electrical enclosures use a small set of profile features. Reading a section drawing in terms of these features makes the sealing and grounding questions easier to see.
Infographic
Features of an extruded enclosure profile
What each zone of the section is doing
Outer wall
Carries impact and sets the external size. Wall thickness drives weight and stiffness.
Gasket groove
A continuous channel that locates the seal and limits compression.
Mating face
The flat land that the end plate clamps against. Flatness decides the seal.
Internal rib
A mounting plane for a PCB or a DIN rail. It must stay parallel to the base.
T-slot
A captive channel for fixings, earth studs or external brackets.
Corner radius
The outer corner as extruded. A sharp corner is a die wear point.
Sealing: groove, gasket and compression
An enclosure reaches a protection rating through the whole assembly, not through the profile alone. Water enters at the end plate joint, at cable entries, at a display window and at any fastener that passes through the wall. The gasket groove controls only the first of these.
A moulded or cut gasket sits in the groove and is compressed when the end plate is fastened. Too little compression and the seal leaks under a jet or a pressure change. Too much and the gasket takes a set, the end plate bows and the screws lose preload. The groove depth, the gasket section and the screw spacing need to be designed together.
Corners are where seals fail. A cut gasket with mitred corners leaves a joint. A moulded gasket with a continuous corner seals better but needs a groove that follows the same path. If the groove is interrupted by a rib or a boss, the seal is interrupted too.
A gasket groove is a tolerance stack, not a channel
Groove depth, gasket thickness, end plate flatness and screw torque all add up. Put the compression range on the drawing so the supplier can check it, rather than specifying only the gasket part number.
Grounding and bonding across a coated body
An aluminium enclosure is often the earth path for the equipment inside. That path has to survive the finish. Anodising is an oxide layer and it insulates. Powder coating insulates. A chromate conversion coating is thin enough to leave some contact, but it is not a substitute for a designed bond.
There are three practical routes. Mask the contact areas before anodising or coating so bare aluminium is exposed at the earth stud and the end plate joint. Fit a dedicated earth stud with a star washer that bites through the finish. Or use a conductive gasket or a braid that bridges the coated faces.
Whichever route is chosen, the drawing should show the bond points. A note that says the enclosure must be earthed is not enough, because the supplier cannot see where the current is meant to flow. Mark the masked areas, state the finish on the mating faces and ask for a continuity check in the inspection plan.
Choosing a finish
The finish has to match the environment and the earthing plan. The table below compares the common routes for an aluminium enclosure. Thickness figures are typical ranges and the final call belongs on the drawing with a standard.
| Finish | Where it suits | What to watch |
|---|---|---|
| Mill finish | Internal frames and parts that are painted later | Handling marks and white corrosion in damp storage |
| Anodising, Type II | Indoor and outdoor housings that need wear resistance and colour | Insulating layer, colour variation between batches, masking for earth points |
| Hard anodising, Type III | High wear faces and abrasive environments | Thicker, darker and more insulating, so bond points must be masked |
| Powder coating | Outdoor equipment and customer-facing surfaces | Build up on threads and mating faces, chipping at edges |
| Chromate conversion | Parts that need corrosion protection and some electrical contact | Thin coating, limited colour range, process control of the bath |
Typical coating thickness ranges are indicative. Specify the standard, the thickness and any masked areas on the drawing.
Machining after extrusion
Secondary operations turn a length of profile into an enclosure. The body is cut to length, the ends are faced, the end plate holes are drilled and tapped and the cable entries are cut. If the profile is thin walled, the clamping force during milling can distort it, so a support fixture or a low-pressure clamping method is needed.
Threads in aluminium are weak in thin walls. A tapped hole in a 1.5 mm wall will strip before the screw reaches torque. Use a boss, a rivet nut, a thread insert or a thicker section at the fixing point. For repeated assembly, a thread insert is usually worth the extra operation.
Cut edges of an anodised body expose bare metal. That is fine for appearance on an internal face, but it is a corrosion point on an external one. If the cut face is visible, plan a touch-up or a masked finish that covers it.
Tolerances and inspection
The drawing should separate the profile tolerance from the machined tolerance. The as-extruded section follows the profile standard. The machined end, the hole pattern and the gasket groove depth can be held closer, but each tighter call adds a setup and a check.
For a sealed enclosure, the critical calls are the flatness of the mating face, the depth of the gasket groove, the position of the end plate holes and the squareness of the cut end. A first article should record these, plus the finish thickness on a sample and a continuity result at the earth points.
A leak test is the functional check. The method depends on the target rating: a water jet, an immersion test or a pressure decay test. Agree the method, the sample size and the acceptance limit before production, because a leak test with no stated method cannot be repeated.
What to send for a useful quote
An enclosure quote needs the profile section, the length, the end plate design and the environment. Without the section, a supplier can only guess at the die and the wall.
- Profile section drawing with the gasket groove and internal features
- Length, cut tolerance and end finish
- End plate drawing and fixing method
- Target protection rating and the test method
- Earthing points and any masked areas
- Finish, colour and thickness
- Annual volume and the number of lengths per order
Frequently asked questions
Can an extruded enclosure be watertight?
Yes, if the end plate joint, the cable entries and any window are sealed as one system. The gasket groove, the flatness of the mating face, the screw spacing and the compression range all have to be designed together, and the result should be proved with an agreed leak test.
Does anodising affect earthing?
Yes. An anodised layer is an insulator, so an earth path through an anodised face is not reliable. Mask the bond points before anodising, fit an earth stud with a star washer, or use a conductive gasket or braid to bridge the coated faces.
What wall thickness should an extruded housing use?
It depends on the size, the load and the thread requirements. A thin wall saves weight and cost but distorts during machining and strips at tapped holes. Thicken the section at fixings and mounting points rather than increasing the whole wall.
How is an extruded enclosure different from a die cast one?
An extrusion has a constant section, so it suits long, simple bodies with machined ends. A die casting can carry bosses, ribs and complex end geometry in one part. Extrusion tooling is usually cheaper, while a casting can remove secondary operations at higher volumes.
Sources and further reading
- ISO 2768-1:1989, General tolerances, linear and angular dimensions
- IEC 60529:1989, Degrees of protection provided by enclosures
- EN 755-9, Aluminium and aluminium alloys, extruded profiles, tolerances
Qumek Engineering Desk
Engineering team
The engineering team behind Qumek drawings, DFM notes, tolerances and inspection standards. Every guide is reviewed against the drawings and processes used on live programmes.
Have an enclosure section that needs a review?
Send the profile, the end plate and the target rating. The engineering desk will reply with notes on the groove, the earth path and the finish.
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