CRCA stamping for OEM brackets and panels

CRCA stamping is judged in the field, not in the press. The bracket that fails is rarely the one that cracked in the press. It is the one that passed the press, passed the gauge, took a 70 µm powder coat, and then rusted from a sheared edge inside a chassis rail eighteen months later. CRCA has no corrosion protection of its own, so the grade, the blank, the bend and the coating sequence are one specification, not four.

This page is for the engineer who has to specify a cold rolled bracket or panel and defend the choice. It covers the IS 513 grades and what each one buys, the tonnage a 2 mm bracket needs, the difference between a 92% and a 95% blank nest, the stretcher strains that appear on a painted panel, and the drawing notes that keep the part from failing after it leaves the press shop.

Which CRCA grade should a bracket or panel use?

Match the grade to the strain, not to the habit. A bracket with one or two bends runs on D grade. A panel drawn at a draw ratio above about 1.8, where the draw ratio is blank diameter ÷ cup diameter, needs DD grade. Commercial O grade is for flat parts and shallow flanges where ductility is not doing any work.

The column that matters is elongation, and behind it the plastic strain ratio r measured to ASTM E517. Drawing-quality grades run r of 1.6–2.0, which means the sheet resists thinning while the flange feeds in. A DC01 bracket bent in a V-die does not care; a 90 mm deep housing drawn from DC01 will thin at the punch nose and split where a DC04 blank of the same shape would run.

Grade also sets the price direction. Every step from O to EDD costs more per kilogram and buys a narrower window of forming. A part that converts a D-grade split into a stable process by adding one bend station to the tool is usually cheaper over the programme than a part that moves the whole volume to DD grade. Price the two routes against each other before the die is cut.

What blanking load does a 2 mm CRCA bracket put on the press?

Blanking force is perimeter times thickness times shear strength. For CRCA at 400 MPa tensile, shear sits near 300 MPa. An 800 mm blank perimeter in 2 mm sheet needs 800 × 2 × 300 = 480,000 N, or 480 kN.

That is 49 tonne-force of pure cutting. Add 20–30% for stripping, friction and press losses and the job asks for about 600 kN, or 61 tf. A 63 T press is the floor at that number and gives nothing away; an 80 T press gives real margin over the 61 tf the job needs. A 100 T press is chosen only if the same tool also pierces a heavy hole pattern or coins a boss.

The piercing side adds up faster than most bracket drawings suggest. A bracket with twelve 8.5 mm holes has a cut length of 12 × π × 8.5 = 320 mm. At 2 mm and 300 MPa that is 192 kN, which is 40% of the blanking load for a feature nobody priced. Add the two and the press sees 672 kN before allowance. The general tonnage method explains how to compare that peak against the press curve rather than against the rated tonnage.

Thickness variation goes straight into the load. The mill tolerance on cold rolled strip at 2 mm is of the order of ±0.10 mm at commercial widths, and a 0.10 mm step is 5% of the thickness, so the shear load moves 5% between coils. That is tolerable on a blank and less so on a draw, where the same tool closes to a different gap and the flange height moves with it. Specify the thickness tolerance class, not just the nominal.

How much does blank nesting change the material bill?

It changes the scrap, not the steel per part, and most suppliers blur the two. On a 1,000 × 2,000 mm sheet in 2 mm CRCA, a 240 × 160 mm bracket nests four across and twelve down with a 4 mm web between blanks and a 4 mm edge margin: 48 parts from 1,843,200 mm² of the 2,000,000 mm² sheet, or 92% utilisation.

Widen the blank to 245 × 162 mm and the same four-across, twelve-down grid still fits, because the extra 1,290 mm² comes out of the gutters: 48 parts from 1,905,120 mm², or 95%. The part is 3.4% larger in area and the sheet yield is 3.1 points better, with a 4 mm web still between every pair.

That gain is real, and it is not free steel. Both layouts take 48 blanks from one sheet, so the material per part is 2,000,000 ÷ 48 = 41,667 mm², or 0.65 kg at 7.85 g/cm³, either way. The 240 × 160 blank weighs 0.60 kg and leaves 0.05 kg as offcut; the 245 × 162 blank weighs 0.62 kg and leaves 0.03 kg. The nest moved 0.02 kg per part out of the offcut bin and into the part, which is worth doing when the extra area is a feature the assembly needs, and worth nothing when it is not.

On 10,000 brackets a month that is 200 kg less offcut. What changes the material bill is the number of blanks per sheet, and the lever for that is blank shape, web width and sheet width together, not the utilisation percentage on its own. The weight calculator gives the per-part mass from the developed blank so the comparison can be run before the tool is designed.

Three nesting levers buy blanks per sheet, in order of return: rotate the blank, interlock the profiles and change the blank shape.

• Rotate the blank to put the long side along the coil direction. Grain direction and yield are usually compatible on a bracket and in conflict on a visible panel, so check before rotating a cosmetic part.
• Interlock the profiles, so the narrow end of one blank sits against the wide end of the next. That is what turns a 4 mm gutter into a 2–3 mm one and, on the right part, adds a row.
• Change the blank shape with a corner relief or a notch that is scrap anyway, if it lets two parts share an edge.

Why do stretcher strains appear on a painted panel?

Because the strip strain-aged before it was pressed. Cold rolled steel is skin-passed at the mill to suppress the yield point, but carbon and nitrogen diffuse back to the dislocations over time, more quickly in a warm store. When the material is then formed at 1–3% strain, it yields unevenly and produces Lüders bands: visible bands of coarse, orange-peel-like strain across the low-strain areas of the panel.

The bands are not a die mark, and no amount of polishing will remove them. A powder coat at 60–80 µm follows the surface, so the band shows through the finish after cure and the panel is rejected at final inspection. First-in first-out with a dated mill certificate, and IF grade (DC06) for a visible low-strain panel, are the two controls that work:

• First in, first out, with a mill certificate that carries the rolling date. Steel more than about six months old in a warm shop should be tested before it goes to a cosmetic part.
• IF grade (DC06) for panels where the strain is low and the surface is visible. Interstitial-free steel does not strain-age, and it is the standard answer for a Class A panel.

A third option is a small pre-strain pass, which is what skin-passing does at the mill. Running a cosmetic blank through a leveller before forming restores the effect, at a cost in handling and in the flat pattern.

How should a CRCA bracket be protected from rust?

The faces are the easy part. A seven-tank pretreatment removes oil and oxide, converts the surface to a phosphate layer that the powder can bond to, and rinses before the dry-off oven. Powder at 60–80 µm dry film over that system is the standard for an indoor industrial bracket, and the dry film thickness and cross-hatch adhesion results belong on the inspection record.

The edges are the hard part. A sheared edge has a cut face with no coating and a burr that the powder can bridge but cannot seal. On a bracket that sees condensation, rust starts at the edge and creeps under the film, and the failure is a blister rather than a red patch. Deburring before coating, choosing a corrosion-resistant base material for a wet zone, and specifying the salt spray test are the three ways to slow it:

• Deburr before coating, so the film can wrap the edge instead of bridging a sharp corner. A 0.2 mm radius at the edge is enough.
• Choose the right base material for the exposure. Where the edge is in a wet zone, a galvanised or pre-coated sheet, or a stainless grade, is a material decision rather than a coating decision.
• Specify the test, not the promise. ISO 9227 neutral salt spray defines the test method and the hours belong on the drawing; without a number, two suppliers can both claim salt spray testing and mean different things.

The degreasing guide for mild steel parts covers what the pretreatment stage has to remove before any of this works. The stamping tolerance guide covers the dimensional side of the same bracket.

What weld and assembly notes belong on the drawing?

CRCA welds easily because there is no zinc coating to contaminate the arc or the spot. That is an advantage over galvanised sheet and the reason most OEM brackets are CRCA with a coating applied after welding. It does not remove the need for a weld schedule.

• Spot welds: 2 mm CRCA typically wants 10–13 kA and 10–14 cycles on a 50 Hz machine with water-cooled electrodes, set by a schedule trial on the actual stack. Weld spacing below 25 mm on thin sheet shunts current and produces a cold weld.
• MIG welds: a short-circuit transfer on 0.8 mm wire suits 1.5–3 mm CRCA. Clean the mill oil off the joint first; oil in the arc produces porosity that shows up as a leak test failure.
• Weld nuts and studs: place them before coating and mask the contact face, or specify a weld after coating with the coating removed locally.
• Distortion: a bracket with two parallel flanges welded at the ends will pull. Sequence the welds from the centre outward and check the flange spacing in a fixture.

How is CRCA stamping run at Ganesh Multitech?

CRCA is the mainstay of the press shop: mechanical presses from 20 T to 300 T, 250 T punching, single-stage and progressive tools designed and built in the in-house tool room, with checking fixtures built alongside the tool. Formed tolerance is ±0.5 mm typical with tighter features by agreement, the custom-part range is 0.8–40 mm, and first article inspection or PPAP documentation is available where the programme requires it.

Coating runs through seven-tank pretreatment, a 16 ft × 16 ft shot blast chamber and an 18 ft × 14 ft electrostatic powder booth, with a wet paint booth and curing oven where the specification calls for paint. Dry film thickness and cross-hatch adhesion are measured and recorded.

The business has pressed and fabricated since 1992, with ISO 9001:2015 and ISO 14001:2015 certification and five units in Mumbai (Vasai) and Nagpur. Customers include Mahindra, Mahindra Powerol, Godrej & Boyce, TKE, Eros Elevators, Minda, Gunnebo and Indian Railways, and the sheet metal supply to Mahindra's Farm Division has been recognised with an Annual Commodity Award.

When CRCA is the wrong material

CRCA is the wrong choice for a part that spends its life wet. A bracket under a genset canopy in a coastal installation, or a panel that collects condensate, will rust from the edge whatever the coating, and a galvanised or stainless blank removes the argument. It is also the wrong choice for a structural member that carries load at 350 MPa or more; that is HSLA or hot rolled territory, and the thickness is set by strength rather than by formability.

It is the wrong choice for a part with a machined pad, a ground bore or a bearing seat. Pressed CRCA holds a formed profile, not a machined tolerance, and a bracket that needs a true face needs a second operation on a different machine.

We do not galvanise in-house, we do not run presses above 300 T, and we do not carry out heat treatment after forming. Where the drawing needs any of those, the route changes and the quotation should say so rather than absorb it.

What to put on the drawing

• Grade and standard reference, for example IS 513 D, not the word CRCA alone.
• Thickness with the tolerance class, and the coil width if the nest depends on it.
• Bend radii, flange lengths and the hole-to-bend distance for any hole near a bend.
• The critical features that locate the bracket in the assembly, with their tolerances.
• Surface finish: pretreatment system, powder or paint, colour, and the dry film thickness range.
• Edge condition: deburred or not, burr side, and the burr height limit.
• Salt spray test method and duration if the part is exposed.
• The general tolerance class from ISO 2768-1, plus any tighter geometric callout.
• Annual volume, release pattern and the expected life of the part, so the tool decision can be priced.

Send the drawing, the grade and the volume to request a quote. The stamping and press tools hub carries the design rules for blank size, springback and tooling that sit behind every CRCA bracket.