Meeting Defense Standard: Specifying Reliable Diecast Enclosures For Military Applications

PROTECT YOUR BATTLEFIELD ELECTRONICS

When you design electronics for frontline military use, a diecast aluminum enclosure is not just a box – it is a structural, thermal, electromagnetic and environmental shield between your circuitry and an aggressive world that is determined to break it.

Whether your device sits inside an M1A2 tank, an Arleigh Burke-class destroyer or is held by an infantryman struggling through horizontal rain, the enclosure plays a key role in your electronics’ survivability, operational availability and overall lifecycle cost.

What follows in this blog post is:

• a view of what “good” looks like for diecast aluminum enclosures in defence applications
• the standards that really matter
• the features that separate dependable kit from something that ends up abandoned in the stores.

COMBATING VIBRATION

It’s tempting to imagine that an electronic device mounted in a vehicle will somehow lead a charmed and protected life. Not so – heavy tracked vehicles impart broadband vibration with significant energy below 200 Hz and nasty higher-frequency content from track slap and engine harmonics.

Wheeled vehicles are no gentler – just different – with excitation dominated by tyre and driveline inputs and punctuated by shock from potholes and kerb strikes. The enclosure must translate those inputs into stresses that your PCB, solder joints and connectors can live with.

For UK programmes you will be qualifying against environmental regimes aligned to US Department of Defense MIL-STD-810H shock and vibration tests, and often to demanding DEF STAN 00-35 requirements.

And if your electronics are shipborne, expect additional requirements from MIL-STD-167-1A for vibration and MIL-DTL-901E for medium- and high-impact shock. These tests are designed around the reality of machinery spaces and underwater explosions. A box that looks over-engineered in the CAD model often looks just right on a destroyer after its first shock test.

SPECIFY THE RIGHT INGRESS PROTECTION

After ruggedness, the second non-negotiable for defense electronics is environmental sealing. Devices must routinely contend with suspended dust, diesel mist and salt fog. Enclosures are washed down with fire hoses and are often left to bake or freeze in harsh weather.

IP 67 ingress protection is a sensible baseline for most land-vehicle enclosures, and IP 68 is increasingly required for environments where deeper-than-one-metre immersion is likely. IP 69K is recommended for enclosures that will undergo regular high-pressure spray cleaning.

But achieving and maintaining those IP ratings is more subtle than simply specifying a gasket. The diecast interface must present a flat, continuous sealing area with a controlled surface finish and sufficient width for the chosen gasket. The lid must be strong enough to ensure that adequate compression is maintained after thermal cycling.

ROLEC’s premium aluDOOR enclosures (shown above) – which feature tough integrated hinges – are rated to IP 66, IP 67, IP 68 and IP 69K. This advanced enclosure was honoured at the German Innovation Awards.

PRESERVING RFI/EMI SHIELDING IN HARSH CONDITIONS

Effective RFI/EMI shielding is essential on the modern hi-tech battlefield. Consider a separate, parallel path for environmental sealing so you are not relying on a single material to do two different jobs for years on end. The real test is how well the mechanical design supports compliance with MIL-STD-461G and the broader electromagnetic environmental effects expectations of MIL-STD-464C.

Electrolytic couples are the enemy: stainless steel fasteners going into aluminum need isolation or proper finishes and lubricants. Conductive gaskets should be compatible with the alloy and finish to avoid galvanic corrosion, particularly in naval service. ROLEC’s conFORM and conTROL enclosures both feature built-in RFI/EMI shielding – with no need for a separate (and usually fragile) shielded gasket. Both these housings are rated to IP 66, IP 67 and NEMA 4 .

conFORM has a flat smooth top (shown above).

conTROL has a deep recessed top for protecting controls (shown above).

IN THE HEAT (AND COLD) OF BATTLE

Thermal management is the third key consideration. Aluminum has excellent thermal conductivity but this helps only if you provide a low-resistance path from the heat sources into the walls or base and onwards to ambient.

In a tank turret with sun loading and minimal convection, you must assume that the outside skin may be hotter than the inside. Consider using an internal thermal spreader or an integral baseplate. Use compliant thermal gap fillers to bridge from components to the lid or base, and machine heat-spreading lands in the casting.

You may be tempted to consider external cooling fins but beware. They can clog during off-road use. And on shipboard electronics in machinery spaces, fins can create drip points under overhead leaks. Also, consider the effect of paint. Naval coatings – or a Chemical Agent Resistant Coating (CARC) on military vehicles – can add thermal resistance. Plan for that in your heat path analysis.

SPECIFYING THE RIGHT ALLOYS

Material and finish choices differentiate enclosures that survive just five years from those that last two decades. In the diecasting world, LM24/A380 is the workhorse alloy for strength and castability. LM6/A413 offers improved corrosion resistance and is often the choice for naval applications or anything exposed to the aggressive de-icing salts used on airfields and railheads.

If you need mechanical properties across a wide temperature range – such as for a deck-mounted antenna tuner that will winter north of the Arctic Circle – consider a heat-treatable alloy and a post-cast T6 process but be mindful of dimensional stability and porosity.

With regard to finishes, hexavalent chromate conversion is rightly disappearing. Specify trivalent chromate conversion – as per MIL-DTL-5541 Type II, Class 3 or an equivalent RoHS-compliant process – to provide a conductive, low-resistance bond surface under paint and at RFI/EMI interfaces.

Hard anodizing to MIL-A-8625 Type III is excellent for wear and corrosion but is less conductive. When you need both wear protection and RFI/EMI shielding you can mask bond lines or over-plate with a thin electroless nickel on contact lands.

Topcoats must suit the application: CARC systems for land vehicles, approved naval paint systems for shipboard use, and UV-stable powder coats for handhelds that spend their life outdoors. Do not rely on paint as an shielding path, and do not expect any coating to rescue a poor casting finish – the best shielding seams are bare, clean metal under the gasket.

SURVIVAL IN AN UNCOMPROMIZING WORLD

Remember that units may need to be swapped in appalling weather. It pays to specify enclosures with ‘lid closed’ installation – enabling housings to be installed or removed without disturbing the ingress protection seal.

On naval platforms, specify hinges or retaining straps on all lids to prevent critical parts from vanishing into bilge spaces. Part numbers, torque limits and seal replacement intervals should be cast, engraved or laser-etched on to the enclosure so the information survives manuals going missing in the heat of operations.

Cable management should be part of enclosure design, not an afterthought. A good diecast housing should feature cable entries at angles that prevent tight bend radii. It should provide integral saddles or clamps that isolate connector shells from cable strain, and it should route power and signal to minimize coupling.

On a vehicle radio rack, your unit may be side-by-side with high-power amplifiers. So site your power inlet well away from your sensitive RF front end and consider a dual-chamber housing (shown above) such as aluTWIN (IP 66, IP 67) that offers the protection of an internal wall.

Plan for braided shield termination at or immediately outside the connector backshell and specify an earthing stud that bonds to the vehicle ground scheme in accordance with the platform bonding plan. On many military vehicles, the bonding and earthing regime is controlled and audited; creating a point for an earthing strap is quicker and more cost-effective in CAD than it is in the field with a drill.

RUGGED HANDHELD ENCLOSURES FOR SERVICE PERSONNEL

For handheld equipment, the priorities shift in proportion rather than in kind. A handheld controller or test instrument carried by a soldier may need to survive drops, constant handling with wet and gloved hands, and unexpected torsional loads (such as being used as an impromptu pry bar).

Diecast aluminum is still a superb choice for handheld housings but ergonomics and impact management are crucial. Specify an enclosure with rounded corners and walls that are thick enough for thread engagement and shock energy distribution but scalloped in non-critical areas to keep mass down.

For sealing, IP 67 is again a sensible target but remember that handhelds endure repeated battery swaps, connector insertions and lens cleanings. And remember, EMC expectations do not relax merely because a unit is handheld – you still want conductive paths across seam lines, and you should specify conductive coatings or conversion layers under the topcoat.

Where displays are present, look for an enclosure with a generous recess – a proud glass edge chips on first contact with an equipment rack. Drop and functional shock testing to MIL-STD-810H Method 516 remains the yardstick; test the unit with gloved users and on rough surfaces, not just on rubber mats in a laboratory.

Connector and user interface choices matter more in handhelds than anywhere else. Choose tactile controls that are operable with cold-weather gloves and sit within diecast guards; recess the charging and data ports and consider magnetic pogo pin solutions behind sealed doors if the use case permits.

Weight distribution is a function of casting and internal architecture. Support PCBs and displays with the centre of mass near the grip, not the nose, so a user can hold the device steady while travelling at speed over uneven ground.

Finally, build your device for the life you expect…and think about the one you don’t. Some army vehicles, navy warships and auxiliaries may stay in service far longer than was initially planned. Your device’s enclosure may be opened and resealed more times than you intend; spare gaskets will be fitted in a sandstorm; fasteners will be driven by impact wrenches. Label things clearly. Provide generous QR codes as shortcuts to the technical manual, and put the earthing point where a technician under pressure (or incoming fire) can reach it.

ROLEC ENCLOSURES FOR DEFENCE ELECTRONICS

As an experienced enclosures specialist with a long history of innovation, ROLEC can supply customized housings to the highest military standards.

Options include highly weather-resistant powder coatings (F9) with WIWeB approvals and camouflage coatings for military applications. The premium polyester powder 5936 is available in standard colors RAL 6031-F9 bronze green, RAL 1039-F9 sand beige, RAL 8027-F9 leather brown and RAL 9021-F9 tar black.

These colors offer excellent camouflage in the visible and near-infrared spectral range. Available as both powder coatings and wet paint, they meet all military requirements – including the defence equipment standard (VG 95211).

ROLEC can supply enclosures customized to your exact requirements. Services include CNC machining, engraving, laser processing, powder coating, painting, digital printing, screen printing, RFI/EMI shielding, transparent windows for displays, and assembly of accessories.

GET EXPERT TECHNICAL ADVICE

Contact our expert team for specialist advice on specifying enclosures for military applications – and don’t forget download the 3D model or request a sample.