Supplier non-conformance: how incoming material is checked

A coil of 1.2 mm CRCA arrives with a mill certificate that matches the purchase order in every field. The first draw splits at the radius on four blanks out of ten. The micrometer says 1.14 mm at the centre of the sheet and 1.16 mm at the edge. The certificate is accurate, the coil is compliant, and the die was set for 1.2 mm of material.

Incoming material inspection exists to catch that gap before the blanks are cut. It is three comparisons, made in a fixed order: the certificate against the tag, the tag against the material, and the material against the process it was bought for. The first two are paperwork and discipline. The third is engineering.

The plant, quality and sustainability hub collects the other controls that sit around this one, from calibration to shift handover.

How incoming material inspection catches a non-conformance

It catches one by refusing to accept a document as a description of the sheet in front of it, and by measuring the property that the next operation depends on.

The certificate describes a heat. A heat can be 200 tonnes and become forty coils, and the coil on the floor is one of them. The tag on the coil carries the heat number, the grade, the size and the coil number; if the tag and the certificate agree, the chain is intact as far as the mill is concerned. If the tag is missing, handwritten or refers to a heat that the certificate does not cover, the material is unidentified and no measurement fixes that.

The third comparison is the one a buyer should care about most, because it is where a compliant coil becomes a non-conforming part. A 1.2 mm sheet at the bottom of the permitted thickness band is 5% thin. On a formed part, each 90° bend moves by about 0.04 mm because the bend allowance depends on thickness, so a part with four bends accumulates roughly 0.16 mm before anyone touches the press. On a drawn part the effect is worse: the blank that the tool was designed for is now feeding a draw ratio and a blank-holding force that no longer match.

What the certificate has to carry

A certificate is usable when it names the standard it was tested against, the grade designation, the heat or cast number, the ordered dimensions, the chemical composition, the mechanical results (yield, tensile and elongation) and, for coated material, the coating mass. The mill's name, the date and an authorised signature complete it.

Two failures recur. A photocopy with the heat number illegible is not a certificate, because the one field that links the document to the coil cannot be read. A certificate that reports typical values rather than the results for that heat is a specification sheet, and it tells you what the mill can do rather than what it delivered. Ask for the heat-specific document, and compare the chemistry to the grade the drawing calls for rather than to the trade name on the order.

The checks worth making, and how often

The table is the working goods-in set for sheet and coil. It is built around what changes the next operation, not around what is easy to measure.

Two rows deserve emphasis because they are commonly skipped. Camber looks like a nesting issue and is really a material flatness issue; a coil with 6 mm of camber over 2.5 m loses more at the laser than the price difference between suppliers. White rust is the failure mode of storing galvanised sheets wet: zinc hydroxide forms between stacked sheets and the coating is gone before the part is cut.

The three checks that catch most of the real problems

Thickness, grade and coating mass account for most of the material non-conformances that reach a press shop, and each has a signature that shows up downstream.

Thickness. The measurement is trivial and the interpretation is not. A 1.2 mm sheet at 1.14 mm sits inside a mill tolerance in most width classes, so a rejection on that basis will not survive a supplier argument. What the measurement gives you is a process decision: the die was set for 1.2 mm, the draw is splitting, and the material is at the low limit. The options are to adjust the process for the actual thickness, to specify a tighter band and pay for it, or to change the blank. Deciding that at goods-in, with the number on the record, is a different conversation from discovering it in the tool room three days later.

The bend arithmetic is worth keeping in mind because it applies to every formed part: on a 90° bend with a 1.2 mm inside radius and a K-factor of 0.44, the bend allowance at 1.2 mm is 2.71 mm. At 1.14 mm it is 2.67 mm. That is 0.04 mm per bend, and it lands directly on the flange height.

Grade. CRCA is not one material. The drawing may call for a drawing quality that will stretch at a radius, and a commercial quality coil of the same thickness will split there. Both are cold reduced, both are 1.2 mm, and both pass a dimensional check. The only controls are the certificate, the tag, and a rule that a substitution is never made at the press because the rack is empty. The material certificate guide sets out which fields to compare.

Coating mass. For galvanised sheet, the coating mass is the corrosion life. The conversion is simple and worth doing in front of the supplier: zinc at 7,140 kg/m³, so 275 g/m² spread across two faces is 137.5 g/m² per face, which is 19.3 µm per face. A lot that weighs 20% light has lost 20% of its zinc and roughly a fifth of its time to red rust. ISO 1461 covers hot-dip coating acceptance for fabricated articles, and the same logic applies to the coil.

The record: what an NCR has to contain

A non-conformance report that says "material thin" is a complaint. Eight fields make it a record that a supplier can act on and a buyer can audit.

1. Part number, drawing revision and the material specification.
2. Heat or coil number, quantity and location, so containment has a boundary.
3. The requirement, quoted from the standard or the purchase order, with its tolerance.
4. The measurement, with the instrument and the number of points.
5. The method, so the supplier can repeat it and argue with the result rather than the conclusion.
6. The disposition: return, concession, rework or scrap, with who approved it.
7. Containment: what was stopped, what was already issued, and what is in transit.
8. The corrective action reference and the date it is due.

The disposition is where discipline is tested. A concession is legitimate when the deviation does not affect fit, function or finish, and it has to be approved by the customer's quality function when the customer owns the requirement. Releasing a thin coil to the press without a concession turns a documented deviation into an undocumented part.

Frequency follows the risk. Containment within 24 hours, a root cause and corrective action within two weeks for a safety-related or repeat issue. The supplier score should record the response date, not only the defect, because a supplier who answers late is the supplier whose defect returns.

Containment needs a countable boundary

"The coil is on hold" is not a boundary until the quantity is known. A 5,000 kg coil of 1.25 m wide, 1.2 mm CRCA contains 424 m of strip at 7,850 kg/m³, which is about 169 blanks at 2.5 m each. That number is the quantity to search for finished parts, packed parts and parts already at the customer, and it is the number the NCR should carry instead of a weight.

The same calculation tells a buyer whether a containment is plausible. A supplier who reports "about a tonne affected" when the coil held 5 tonnes has either found a smaller source or has not traced the material.

What Ganesh runs

Ganesh has manufactured since 1992 and operates five units across Mumbai (Vasai) and Nagpur with more than 200 people. Parts are produced from 0.8 mm to 40 mm on mechanical presses from 20 T to 300 T, a 250 T punching line, a 12 kW fibre laser with a 40 ft x 16 ft bed, a 200 T five-axis brake with a 4,450 mm bed forming to 10 mm, and three CLOOS robotic MIG cells alongside more than 30 manual stations.

That range is why incoming checks are set by process rather than by a single specification. A 0.8 mm CRCA panel for an enclosure and a 6 mm bracket for a frame do not need the same thickness check, and a galvanised canopy panel needs a coating check that a cold rolled bracket does not. Material is cut, formed, welded, pretreated in seven tanks and coated in an 18 ft x 14 ft powder booth inside the same system, so a material decision at goods-in is visible at the coating line weeks later.

The works hold ISO 9001:2015 and ISO 14001:2015 certification, and first article inspection and PPAP are available where a programme requires them. Mill certificates are available with the lot, and the stamping capability describes the press range that the material is bought for.

What to put on the purchase order

The drawing rarely carries the material controls that decide whether a coil is accepted. Put them in the enquiry and the order.

• The grade by standard, not by trade name, with the drawing quality if the part is drawn.
• The thickness with an explicit band, and whether a mill tolerance at the low limit is acceptable.
• The coating designation for galvanised material, in g/m² or µm per face.
• The certificate type and the fields you want on it, including the heat number.
• Whether a test certificate from a third party is required, and for which properties.
• The storage and packaging requirement for galvanised sheet, because white rust starts in the warehouse.
• The concession rule: who may approve a deviation, and whether the customer must approve it.

The quotation request takes the material callout with the drawing. Naming the grade and the thickness band at enquiry is what lets the route and the tooling be set for the material that will actually arrive.

When incoming inspection is the wrong control

Inspection at goods-in can stop a bad lot. It cannot make a variable mill consistent, and a shop that inspects harder every month is usually compensating for a supply decision it has not made.

Three boundaries are worth stating. First, sampling has limits: one sheet per bundle will not find a defect that affects one sheet in fifty, and no practical goods-in check will. If the failure rate matters, the control belongs in the process, in the die protection, or in a supplier change. Second, a certificate audit does not test the steel; if the mechanical properties decide the part, specify the test and pay for it. Third, incoming inspection does not cover storage. A coil that was correct on arrival and sat under a leaking roof for two months is a non-conformance created in-house, and the stamping defect guide lists the surface and forming failures that follow.

Send the drawing with the material callout, the thickness band and the finish, and the engineering team will confirm the mill route, the goods-in checks and the certificate pack before quoting.