Cast housings and covers in aluminium and zinc

We cast housings, covers and enclosures to the customer’s drawing, in zinc or aluminium, and machine the sealing faces, contact faces and threaded holes here in Råde. A zinc loudspeaker housing is one of our product examples.

What characterises a housing

A housing is a shell with functions hung on the inside. The shell must be thin and even. The functions, such as screw bosses, ribs, cable entries, locating pins and gasket grooves, must be anchored in the shell without creating local accumulations of metal.

That conflict decides whether the housing turns out well. Where a screw boss meets a wall, the section suddenly doubles in thickness. That is where the metal solidifies last, and that is where you get shrinkage porosity. The fix is to core out the boss from the back and tie it into the wall with a rib instead of blending it into a lump.

When casting fits

• Thin walls and integrated features in one operation. An injection moulded plastic housing can do this too, but gives no EMC shielding, no heat conduction and no fire resistance.
• Dimensional stability. Two halves that meet along a sealing face must hold the same dimensions in every single part. The tool delivers that.
• Metal conducts heat out. Electronics that generate heat can shed it through the housing instead of needing a fan.
• Metal shields. A continuous metal housing acts as a Faraday cage against electromagnetic interference. A plastic housing has to be metallised to achieve the same.
• Mass can be a function. In audio equipment, weight damps unwanted vibration. Then zinc is the right choice, not a compromise.

When casting does not fit

• The housing is a straight prismatic box in small numbers. Press-braked sheet and a couple of welds is cheaper.
• The housing is long with a constant cross section. An extruded profile with end caps is cheaper and lighter.
• There are no EMC, thermal, fire or stiffness requirements and weight must come down. Plastic is right.
• The housing must be transparent or electrically insulating. Metal does not solve that.

Zinc or aluminium for a housing

Zinc gives finer detail, thinner walls, better dimensional accuracy and a surface that is often finished straight from the tool. The tool also lasts longer, because zinc melts at around 380–390 °C, while aluminium is cast at 680–700 °C. When you own the tool, that is a direct commercial argument.

Aluminium gives lower weight and better thermal conductivity. If the housing is load-bearing, or sits in something that has to be lifted, aluminium is usually right. Specific thermal conductivity and tensile figures are provided on request for the alloy in question. There is more on the choice in zinc or aluminium.

Sealing, IP rating and EMC are settled for your part

A cast housing can be made tight, shielding and heat-conducting, but none of it happens by itself. If the enclosure needs an IP rating, has to be pressure tight or must pass an EMC test, the requirement belongs in the enquiry, together with how it is to be verified. We then assess what can be achieved and documented for that particular part, before the tool is designed. We do not promise tightness or approvals in general terms.

From drawing to finished housing

We review the drawing before the tool is ordered: wall thickness, parting line, sealing faces and screw bosses. We procure the tool, and you own it. Casting, machining and blasting happen here. Powder coating, and anodising of aluminium housings, are done by sub-suppliers we order and follow up. Remember that coating insulates: if the housing has to shield, the contact faces must be masked or machined clean, and that has to be on the drawing. More on this under surface finishing.

What customers usually ask

What do I need to send for a price? The drawing, quantities per order and per year, and the housing’s requirements for sealing, shielding, heat and surface. Request a quote.

When is zinc the right material? Read zinc die casting: when zinc is right.