Key takeaways
- Keep bead depth at 1–3t: 3.6 mm on 1.2 mm CRCA, with a 2t end radius, or the bead tears at the run-out.
- A 3 mm bead raises a 1.2 mm strip from 14.4 mm⁴ to about 50 mm⁴ of second moment of area, so the same load deflects about 29% as far.
- Beads stiffen across their run, not along it. Two beads in the load direction do less than one bead across it.
- Bead forming adds 2–3% developed length; a 3 mm bead on a 12 mm width needs about 2.5 mm more blank.
- An M6 thread in 1.2 mm sheet needs 6 mm of engagement, which means a 4.8 mm emboss with a 20° draft, not a tapped flat.
Embosses and beads are how a flat panel gets stiff without gaining weight. A flat 1.2 mm panel is a spring. Put 100 N on the middle of a 600 mm span and it moves visibly, and the paint on the reverse face shows a star crack a month later. The obvious fix is a thicker gauge, which adds weight to every panel on the machine and cost to every square metre. The cheaper fix is a bead: a narrow rib formed into the same blank, using material that is already there.
The arithmetic is worth doing before the tool is cut. A stiffening bead 3 mm deep and 12 mm wide raises a 100 mm wide strip of 1.2 mm CRCA from about 14.4 mm⁴ to about 50 mm⁴ of second moment of area. Deflection goes with the inverse of that, so the same load moves the panel about 29% as far, and the weight changes by the 2.5 mm of developed length the bead consumes.
What follows is where a bead earns its place, the depth and width limits that keep it from tearing, the emboss rules for threads and locators, and the note that has to be on the drawing so the tool is cut to the right depth.
Why embosses and beads are stiffer than a thicker panel
Bending stiffness of a plate goes with the cube of thickness, so a bead that lifts material away from the neutral axis does the same job as adding gauge, but only where the bead runs.
Take a 100 mm wide strip of 1.2 mm CRCA. Its second moment of area about the mid-plane is 100 × 1.2³ ÷ 12, or 14.4 mm⁴. Form a bead 3 mm deep and 12 mm wide down the middle, with 45° walls, and the section becomes a shallow channel: two inclined webs about 4.2 mm long and a 6 mm flat at the bottom. The webs sit 1.5 mm off the mid-plane and contribute most of the gain. The total comes out near 50 mm⁴, which is 3.5 times the flat strip.
That is the same gain as going from 1.2 mm to about 1.8 mm sheet, and it costs 2.5 mm of developed length instead of 50% more steel.
The catch is direction. The gain applies to bending across the bead. Along the bead the section is still 1.2 mm thick and the stiffness is barely changed. A panel with two beads running left to right is stiff against a load pushing it in and out, and still floppy against a load pushing it sideways. Rib layouts that ignore that end up with a panel that is stiff in the wrong plane.
Emboss and bead limits
| Parameter | Typical value | Ganesh limit or note |
|---|---|---|
| Bead depth, single stage | 1–3t | 3.6 mm maximum on 1.2 mm CRCA |
| Bead width | 6–12t | 8 mm minimum at 1.2 mm; narrow beads shear |
| Bead end radius | at least 2t | 3 mm at 1.5 mm; square ends crack |
| Bead corner radius | at least 1t | Round the tool; sharp corners split |
| Bead spacing | at least 3t | 4 mm between bead edges at 1.2 mm |
| Bead to bend distance | 2t plus bend radius | 3.4 mm at 1.2 mm with a 1 mm radius |
| Bead draft angle | 10–20° | 15° releases cleanly; vertical walls thin |
| Added developed length | 2–3% | 2.5 mm on a 3 mm bead at 12 mm width |
| Emboss height for a thread | one thread diameter | M6 needs 6 mm; 4.8 mm emboss in 1.2 mm |
| Emboss draft | 15–30° | 20° typical on a 4.8 mm emboss |
| Emboss corner radius | at least 0.5t | 0.6 mm at 1.2 mm |
| Emboss wall thickness | 60–80% of sheet | Below 60% the wall splits at the base |
The depth limit is a forming limit, not a stiffness limit. A 6 mm bead on 1.2 mm sheet would be stiffer still, but the material at the run-out cannot stretch that far in one stage, and the tear starts at the end radius on the first or second hit.
Where the stiffness actually comes from
Depth beats width
Doubling the bead depth roughly quadruples the second moment of area, because the webs move twice as far from the neutral axis. Doubling the width adds a little more flat at the bottom and very little stiffness. When a panel needs more resistance, deepen the bead before widening it, up to the 3t limit. Past that limit the answer is a second bead or a change of gauge, not a deeper one.
Ends and terminations
A bead has to fade out, not stop. A bead that ends in a square shoulder concentrates the forming strain at the corner and leaves a stress raiser in service. Run the end out over 2–3 times the bead width with a radius of at least 2t, or run the bead into a flange or a bend so the end is supported by a fold.
The same applies where two beads cross. A cross-junction is a spot where the material is stretched from four directions and the tool has to relieve one of the runs. Offset the crossing by 10 mm, or stop one bead short of the other and let the flange carry the load.
Beads and flatness
A bead is also a flatness control. A 1.2 mm panel 600 mm × 900 mm with no beads deflects about 16 mm at 100 N in the centre, and the paint on the concave side cracks at the point where the panel takes a set. Two beads across the short direction and one along the long direction cut that deflection by roughly 3×, and the panel stops oil-canning when it is lifted by one corner.
The bead pattern matters more than the bead count. Beads spaced at 100–150 mm across a large panel divide it into smaller stiff fields, and the panel behaves like a set of small plates rather than one large one. Three beads at 300 mm do less than six at 150 mm for the same formed length.
Embosses for threads, locators and weld nuts
An emboss is a local raised form. It does three jobs: it gives a thread enough engagement, it provides a locating boss or a datum, and it stiffens a local area around a fastener.
Thread engagement is the one that fails in service. A tapped 1.2 mm flat gives 1.2 mm of engagement, which is about one fifth of what an M6 bolt needs. The rule is one diameter of engagement in steel, so 6 mm for M6. In 1.2 mm sheet that means a 4.8 mm emboss on the far side, with a 20° draft and a wall thickness of about 0.9 mm. The thread is then rolled or tapped through the emboss and the bolt sees a real length of material.
The emboss has a direction. Put it on the side away from the mating face so the bolt head seats on flat sheet, and keep the emboss clear of any gasket line. An emboss under a gasket is a leak path, for the same reason a clinch button is.
Locator embosses are shallower. A 1 mm deep dimple with a 3 mm radius locates a bracket or a bracket's slot and is formed in the same tool as the beads. Give it a 3 mm flat at the bottom so the locator has a face to sit on, and position it from the same datum as the holes it registers against.
Weld nuts and clinch nuts need a flat annulus around the hole. A 1.2 mm panel with a bead running within 5 mm of a weld nut distorts the seating face when the nut is welded, and the nut then sits at an angle. Keep beads 10 mm clear of any welded fastener.
Worked example: a 600 mm door panel
A 1.2 mm CRCA door, 600 mm wide and 900 mm tall, hinged on one long edge. Without stiffening it deflects about 16 mm at 100 N applied at the centre, which is roughly the force of a hand leaning on it. The paint cracks on the inside face at the point of maximum curvature, and the door does not sit flat against its gasket.
Add two horizontal beads 3 mm deep and 12 mm wide, one at 300 mm from the top and one at 300 mm from the bottom, run out at both ends over 25 mm. Across the bead the section stiffness rises 3.5×, and the panel's deflection at the same 100 N falls to about 5 mm. The developed length grows by 2.5 mm per bead, so the blank grows 5 mm in the vertical direction and the blank size changes from 900 mm to 905 mm. The mass grows by about 28 g.
Add a third bead down the middle, vertical, and the panel stops oil-canning when it is carried flat. Three beads, 7.5 mm of extra developed length, and no change of gauge. That is the whole trade.
What Ganesh runs
Bead and emboss tools are built in our tool room as part of the press tool for the part, and run on the 20–300 T mechanical press line, with 250 T of punching capacity when the panel is wide enough to need it. A bead that runs the full width of a 1,200 mm panel needs a tool with that bed, and the press selection is made on the forming force, not on the punching force.
The blank is cut on the 12 kW fibre laser with the 40 ft × 16 ft bed, which matters when the bead changes the developed length: the blank has to be cut to the developed size, not to the flat size on the drawing. First article is checked on a checking fixture for bead position, panel flatness and the emboss height, and a formed panel that has been measured is the only way to confirm the tool hit the depth the drawing asked for.
The press tooling route covers how the bead is built into the tool, and the springback guide covers the related problem of a formed panel that springs out of flat after the tool opens.
What to put on the drawing
- Bead position from a datum, with the run direction and where each bead starts and ends.
- Bead depth and width, with a tolerance of ±0.3 mm on depth.
- End radius and taper, or a note that the run-out is 2t minimum.
- Clearance from bends and from fastener seating faces, stated as a minimum.
- Panel flatness after forming, with the measurement method and the support condition.
- Emboss height and thread where an emboss carries a fastener, with the engagement length.
- Which side the bead is formed on, because a bead on the visible face shows as a highlight under paint.
The deep drawing design rules cover the deeper forms where a bead becomes a drawn feature, and the enclosure bending guide covers the corner geometry that a bead has to stay clear of.
When a bead is the wrong answer
A bead is wrong on a sealing face, on a hygienic surface, and on a panel that has to be flat for another reason. Each of those is a case where the stiffness has to come from somewhere else.
A gasketed door or a flange that seals against a rubber profile cannot carry a bead across the sealing line. The bead leaves a gap under the gasket and the panel leaks at the crossing point. Move the bead inside the gasket line, or use a separate stiffener spot-welded to the inside face.
A hygienic or food-contact surface cannot have a bead because the fold traps material and cannot be cleaned. The alternative is a thicker gauge, a rolled edge or an external stiffener, and the decision is driven by cleanability rather than by stiffness.
A panel that is a datum or a mounting face cannot carry a bead either, because the formed surface is no longer flat within the tolerance the datum needs. In that case a swage around the perimeter, a hemmed edge or a separate frame does the stiffening without touching the face.
Very thin sheet is the last limit. Below about 0.8 mm, a 3t bead is only 2.4 mm deep and the gain is small, while the risk of the bead edge showing through paint rises. At that gauge the answer is usually a change of material or a change of panel size, not a bead.
Send the panel size, the material and the load it sees through the RFQ route. The stamping capability page sets out the press range behind the tool, the custom parts range covers the panel family, and the design and CAD hub collects the rest of the forming rules.
Frequently asked questions
How deep can a stiffening bead be in sheet metal?
Three times the material thickness in a single press stage, so 3.6 mm on 1.2 mm CRCA. Deeper beads need a draw stage or a thinner panel, and a square-ended deep bead will tear at the run-out before the depth is reached.
How much stiffness does a bead add?
A single 3 mm deep, 12 mm wide bead raises a 100 mm wide strip of 1.2 mm CRCA from 14.4 mm⁴ to about 50 mm⁴ across the bead. The gain is about 3.5×, so the same load deflects roughly 29% as far.
Do beads add weight?
Almost none. The bead is formed from the existing blank, so the only addition is developed length: 2–3% on a typical bead, or about 2.5 mm of extra strip on a 3 mm bead. The mass stays within a few grams.
Why do embossed threads pull out?
Because the emboss is too shallow for the thread. An M6 needs 6 mm of engagement, which is a 4.8 mm emboss in 1.2 mm sheet. A tapped flat gives 1.2 mm of engagement and fails at a fraction of the bolt's proof load.
Can a bead run across a bend line?
No. A bead crossing a bend changes the developed length locally, and the bend pulls into the bead and distorts both. Keep the bead at least 2t plus the bend radius away from the bend line.
Sources and further reading
- IS 513 — Cold reduced carbon steel sheets and strips: mechanical properties including elongation for forming grades · reviewed 3 Nov 2026
- ISO 2768-1 — General tolerances for linear and angular dimensions without individual tolerance indications · reviewed 3 Nov 2026
- ISO 6892-1 — Metallic materials: tensile testing at room temperature, including the elongation measurement used to set forming limits · reviewed 3 Nov 2026
Have a panel that oil-cans in service?
Send the panel size, the material and the load it sees. We will check whether a bead, a swage or a thicker gauge is the cheaper way to stop the deflection.
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