Guard panel: design, materials and manufacturing

A guard panel is judged twice: once in the safety review, where the opening and the distance to the hazard are checked against ISO 13857, and once in the field, where the coating either holds at the cut edge or lifts within a season. Neither check cares how the panel looks on the machine, and both are decided by lines most drawings leave blank.

The part looks trivial, which is why it gets under-specified. It is a piece of 1.2–2 mm sheet, folded once or twice, with a hole pattern or a perforation, bolted to a frame. Then the guard arrives 40 mm from a rotating fan with 10 mm slots and fails the review, or it arrives with 70 µm of powder on the face and 30 µm on the edge and rusts from the perimeter inwards.

This guide sets out the opening rule, the stiffness rule and the coating rule, then the cut-form-weld-coat route that produces the panel.

What does a guard panel have to stop?

Three different things, and they are not solved by the same thickness. A guard can stop a hand reaching a hazard, contain debris or fluid thrown by a moving part, or simply close off a hot or dirty zone so nobody leans on it.

Reach is a geometry problem, not a strength problem. A 1.5 mm panel with a 4 mm slot will stop a finger regardless of how it is mounted, provided the panel is close enough to the hazard. A 3 mm panel with 25 mm slots will let a hand through and no amount of thickness fixes that.

Debris and impact are a strength and stiffness problem. A stone thrown from a tyre, a broken belt end or a dropped spanner loads the panel in a way that a flat 1.2 mm sheet handles badly. That is where a 3 mm panel, a rib or a closer bolt pitch earns its cost.

A guard panel is not an overhead guard. A roof structure that protects the operator from falling objects is designed and tested to ISO 6055, and the overhead guard design guide covers that separate set of limits. A side panel or a mast cover has no such test behind it, which is why the opening rule and the mounting detail carry the whole justification.

Appearance and washdown are a finish problem. On a tractor side panel or a forklift mast guard, the panel is also part of the machine's face and has to survive a pressure washer without the coating lifting at the edge.

Openings: the number that gets checked

ISO 13857:2019 sets safety distances that prevent hazard zones being reached through openings in protective structures. The distances depend on the opening size, so the panel's hole pattern and its standoff from the hazard have to be chosen together.

The numbers that decide most industrial guards: an 8 mm opening needs at least 80 mm between the opening and the hazard, a 20 mm opening needs 120 mm, and an opening in the 20–30 mm band needs 850 mm. The jump at 30 mm is the one that catches people out. A guard with 25 mm square mesh mounted 150 mm from a drive fails the table, because 25 mm sits inside that last band; moving the same mesh out to 900 mm makes it compliant. That is why large-opening guards end up as remote barriers, while close-mounted covers are built from small perforation.

Small perforation is also the only way to get a close-mounted guard that still ventilates. A 5 mm round hole in 1.5 mm sheet falls in the smallest opening band, where the required separation is measured in millimetres, so the panel can sit at a working distance of 40–60 mm and still keep the hazard out of reach.

Perforation has a second number that matters for ventilation: open area. Round holes on a square pitch give 30.7% open area at 5 mm holes on an 8 mm pitch, because the fraction is 0.785 × (5/8)². The same holes on a 60° staggered pitch give 35.4%, using 0.907 × (5/8)². If a canopy needs more airflow, changing the pitch pattern is usually cheaper than punching larger holes that break the distance rule.

Guard panel specification and the limits we hold

Stiffening a panel that wants to drum

A flat 1.5 mm panel is a drum. At 800 mm × 600 mm it weighs 5.7 kg at 11.8 kg/m², and it will flex visibly under a hand and rattle at a frequency the operator hears before anything wears out. The fix is geometry, not thickness.

Three options, in order of cost:

• A return flange around the perimeter, 15–20 mm deep, which turns the panel into a shallow tray and multiplies its stiffness at almost no material cost. This is the default for a bolted guard.
• A swaged rib or a joggled bead across the middle of a span over 600 mm, formed in the same press stroke as the flange where the tooling allows.
• A thicker panel, which adds weight, cost and coating area and is the least efficient of the three.

Fastener spacing follows the stiffness. A 1.5 mm panel on four fixings at the corners will lift at the middle under vibration; on six or eight fixings it stays put. Where the guard is bolted to a tube frame, the bolt pitch should follow the frame nodes rather than being spread evenly around the perimeter.

Attaching a panel that must not rattle

A guard panel is a large thin plate on a vibrating machine, so the fasteners do the work that stiffness does not. Three details decide whether it stays quiet.

Use a bolt with a captive or flanged head and a thread-locking element, not a plain set screw. Vibration on a tractor or a forklift will back out an unsecured M6 faster than most people expect, and a missing guard bolt is an inspection finding on its own.

Put a resilient washer under the head, not between the panel and the frame. A washer between panel and frame creates a gap that collects water and grit, loosens the joint and starts a corrosion cell. Under the head it absorbs the vibration without opening the joint.

Keep the bolt pitch under about 250 mm on a panel over 600 mm long. Four corner bolts on an 800 mm panel leave the middle free to drum, and the rattle is what the operator reports long before anything cracks.

Material and finish choices

CRCA at 1.2–2.0 mm is the default for a painted guard. It is flat, it takes pretreatment well, and it forms cleanly at the radii a guard needs. Hot-rolled 3 mm mild steel is the choice where the panel takes impact, and it comes with mill scale that has to be blasted before coating.

Stainless 304 is used where the guard sees washdown, food or chemical exposure. It removes the coating step and its cost, but it also removes the colour match, and a bare stainless guard next to a painted chassis looks like a repair. Aluminium at 2 mm saves roughly two thirds of the weight against steel, and it brings a galvanic problem at every steel fastener that has to be designed out with isolating washers.

The finish is where most guard panels are lost. Seven-tank pretreatment followed by powder at 60–80 µm is the baseline, and it is enough for a machine that works indoors or in dry weather. For a tractor working in the field, or a forklift working in a wet yard, 80–120 µm is a better specification, and the edge treatment matters more than the extra 30 µm.

Powder pulls back from a sharp corner. On a laser-cut edge the film typically lands at 30–40 µm against 70 µm on the face, which is where the rust line starts. Deburring to a 0.5 mm radius, blasting the edge so the profile gives the powder something to grip, and keeping the phosphate coating uniform along the edge is what makes the difference. The laser-cut edge coating guide covers that mechanism in detail.

The route from coil to coated panel

Guard panels run as flat blanks first. On the 12 kW fibre laser with the 40 ft × 16 ft bed, a 2,400 mm side panel and its full perforation pattern are cut in one pass, which keeps the hole pitch consistent along the whole length. Thin CRCA at 1.2 mm cuts fast and cool, so the edge stays clean and the deburr is light.

Forming follows on the 200 T, 5-axis brake with the 4,450 mm bed. A 2,400 mm guard with a return flange on all four sides needs two set-ups at most, and the stored programme per part number means a repeat release bends to the same angle. Springback on 1.5 mm CRCA at a 1.5 mm radius is small, around half a degree, so flange angles hold without a correction pass.

Welding is where panels distort. Guard panels are usually stitched rather than seamed: 25 mm of weld at 50 mm pitch on a short return, or 25 mm on 100 mm along a long one, holds the panel without pulling a wave into the face. Where the guard needs a bracket or a hinge plate, the bracket is welded before the panel is coated, in a fixture that holds the panel flat. A 1.5 mm panel welded freehand will bow 1–2 mm over a 1,000 mm edge, and a bowed guard shows a gap at the frame. The fixture and sequence rules for a welded guard are the same as for any frame, and the forklift overhead guard fabrication guide works through them on a heavier section.

Then blast, seven-tank pretreatment, powder in the 18 ft × 14 ft booth and oven cure, all in the same flow. Because the coat follows the weld on the same site, a bracket that needs rework does not have to be stripped and recoated somewhere else.

Three causes of rework on guard panels

Welding after coating. A hinge or a bracket added after the powder stage means a bare weld, a touched-in patch and a colour mismatch. Put every welded item on the drawing before the first lot.

Threads and inserts coated. Weld nuts and clinch nuts fill with powder, and a coated M6 nut is a tap and a rework ticket. Mask them, or specify a post-coat tap and a touch-in.

Flatness measured before coating. A panel checked flat before the oven can come out with a 1 mm bow after cure, because the powder shrinks as it cross-links. Check flatness on the coated part, on a surface table, with the panel supported at its mounting points rather than at its corners.

Inspection that proves the guard will fit

The inspection plan for a guard panel is short. Measure the hole pattern against the drawing, check the opening size and the pitch with a pin gauge or callipers, and check the standoff distance to the mating part in the assembly, not on the bench.

For the finish, measure DFT on the face and on the edge of a sample from each lot, and run a cross-hatch adhesion test to ISO 2409. Class 0 or 1 is what pretreated CRCA should give; a class 3 result means the pretreatment, not the powder, is at fault. Where the guard is welded, a visual weld inspection to ISO 5817 level C catches the undercut and the crater that would start a crack at a bracket.

Then fit it. The most useful check on a guard is to bolt it to the frame it belongs to, with the fasteners at the torque the drawing specifies, and look at the gap. That check catches the accumulated error that no single dimension shows.

What to put on the guard drawing

1. Panel material, thickness and grade, with the finish system.
2. Opening size and pattern, plus the standoff distance to the hazard that the opening is chosen against.
3. Mounting holes, with one round hole and one slot, and the slot length tied to the fit tolerance.
4. Return flange depth and rib positions, where the span needs stiffening.
5. Weld symbols to ISO 2553, stitch length and pitch, with the quality level.
6. Edge treatment: deburr radius, and whether the edge is blasted before coating.
7. Masking schedule for threads, inserts and any earth point.

The forklift parts range covers guards, brackets and chassis panels, and the tractor, forklift and material handling hub carries the related guides. The coating flow behind the panel is described on the paint shop capability page.

When a fabricated guard is the wrong answer

A fabricated steel guard is the right route for a fixed barrier, a side panel, a mast guard or a wheel arch. It is the wrong route for a guard that has to be certified as a safety component with a defined performance level, which needs a risk assessment and often a tested design; we build to drawing and do not certify guards.

It is also the wrong route for a wire mesh guard bought as a catalogue item, for a moulded plastic guard on a high-volume machine, and for any panel where the customer's specification calls for a cast or a forged bracket that a fabrication cannot match in shape. Those are worth saying early, because a guard panel is cheap to make and expensive to re-engineer after a failed review.

Send the drawing with the opening rule and the standoff distance on it through the RFQ route, and the quotation comes back with the material, the stiffening and the coating system named.