Revision control for sheet metal: how a change reaches the floor

Four hundred brackets were cut last week to revision B. This week the customer emailed a DXF called bracket_final_v2.dxf with one hole moved 1.5 mm and no drawing attached. Revision control for sheet metal did not fail at the drawing; it failed at the filename. The file was opened, nested and cut. The brackets are dimensionally correct to the file and wrong to the drawing, the bin now holds two revisions, and the only record of which is which is the date on a nesting report.

A revision reaches the shop floor through a chain of records, and it only arrives when every record in the chain agrees. The drawing is one of them. The flat pattern, the cutting program, the bend program, the router, the inspection plan and the packing label are the others, and a change that updates the drawing but not the nesting file has not been controlled at all.

This guide sets out what a revision has to move, how to write effectivity so a bin can be sorted, how to name files so the machine picks the right one, and when a change should stop being a revision and become a new part number. The design-side context sits in the design and CAD hub.

Which artefacts does a bend change invalidate?

A change to a bend line invalidates four artefacts at once: the flat pattern, the cutting or nesting program, the bend program and the checking fixture. A change to a single hole position in a flat area usually invalidates one, the cutting program, and the drawing. That difference is the whole cost model of revision control, and it is why a change is classified before it is scheduled.

The flat pattern is derived from the bend allowance, which depends on the radius, the angle, the material and the K-factor. Move a bend line by 1 mm and the blank length changes by about 1 mm at each bend, the blank outline moves, the nest changes and the cut length changes. On a progressive die the same change moves the station position, which means plugging and re-cutting the die block while the pilots stay where they are.

The checking fixture is the artefact most often forgotten. A fixture built for revision A locates the part from datums that revision B may have moved. It will still accept a good part and reject a good part in equal measure, and the rejections look like a process problem for a week.

The same logic applies to material. A thickness change from 1.5 mm to 2.0 mm changes the bend allowance, the blank size, the tonnage, the weld settings and the coating rack positions. It is a new part in everything but the drawing number.

What has to be re-issued, by change type

Revision letters, effectivity and file names

The revision letter is a label, and the effectivity is the instruction. A change without effectivity is a note that says something is different without saying which parts are different, which is exactly the situation a mixed bin creates.

Revise by letter, skipping I, O, Q, S, X and Z so a letter cannot be read as a digit in a handwritten note. Record the revision in the drawing block with the zone, a description short enough to read at arm's length, the date and the approver. Then write the effectivity in one of three forms: from serial number 1042, from the delivery dated 12 March, or from the first part made after the change. The third is the weakest, because it depends on somebody remembering, so it should only be used for a one-off.

On the file side, the convention is PARTNO_REV with no other text: GM-4210-C.dxf, GM-4210-C.step, GM-4210-C.pdf issued together. A revision that arrives as three files with three different names is a revision that will be partly applied. The file that decides the part is the DXF, so the DXF revision is the one that must match the drawing, and the check at goods-in is that the flat pattern in the DXF matches the flat pattern in the model.

Naming conventions are also how a transferred part arrives. When a part moves from another supplier, the tooling and the file set arrive with whatever names the previous owner used, and the first job is a cross-check of the drawing, the flat pattern and the tool, which is covered in transfer tooling from an existing supplier.

Revision control for sheet metal on the shop floor

The chain has six links, and each one is a record that can be audited.

Change request and review. The customer raises a change; the supplier's engineering team classifies it as drawing-only, process-affecting or tooling-affecting. The classification sets what has to be re-issued and who has to sign. ISO 9001:2015 clause 8.5.6 requires changes to production to be reviewed and controlled to the extent needed to keep conformity, and the review record is the evidence that the classification happened.

Document control. The new revision is registered, the old one is marked superseded and moved to a read-only location, and the distribution list is updated. ISO 10007 sets out this discipline as configuration management — identification, status accounting, change control and audit — and the useful part for a fabricator is status accounting: at any moment, which revision is current for which part number.

Item master and router. The ERP item carries the revision, and the router that travels with the job carries it too. The router is the document the operator actually reads, so a revision that is current in the ERP but stale on the router is stale.

Programs. The nesting file and the bend program are re-issued against the new revision, and the old program is retired rather than left in the machine's local folder. A press brake that still holds the previous bend program will run it the next time the operator selects by part number without checking the revision.

First piece. The first part after the change is inspected on every critical characteristic, not just the changed one, because a flat-pattern change moves dimensions the change note never mentioned. The results are recorded against the new revision and kept with the job.

Stock and concession. Parts made to the previous revision are quarantined, labelled with their revision and dispositioned: rework, scrap, or use-as-is under a written concession with the customer's signature. A bin that contains both revisions without labels is a defect waiting for a shipment.

The cost of catching the change late follows a familiar shape. A design-stage change costs an edit; a change after tooling costs a die modification, a trial and a first article; a change after 400 parts are made costs the parts as well. The 1:10:100 rule of thumb that circulates in manufacturing engineering is a rough statement of that curve, and it is a reason to run the review early rather than a number to quote in a report.

The change that never reaches the drawing

Not every change is a customer revision, and the ones that are not are the easiest to leave uncontrolled. A fixture re-clamped because the last batch drifted, a nesting strategy changed to improve yield, a weld sequence altered to pull less distortion: each is a process change, and each has to be recorded against the part even though the drawing revision does not move.

The record can be short. What changed, why, which parts it applies to from which date, who approved it, and what evidence shows the part is still conforming. That is the same configuration discipline applied one level down, and it is what stops a good fix from being reversed by the next shift because nobody knew it had been made.

The test is simple: if an inspector asked why this batch was made differently from the last one, would there be a document to show them? If the answer is a conversation, the change is not controlled. This is also where a supplier audit looks first, because process changes hidden behind an unchanged revision are the ones that move a part without anyone approving the move.

What Ganesh runs for a revision

The revision arrives against the item, not against an email thread. Engineering registers it, the tool room checks whether the change touches a press tool, a welding fixture or a checking fixture built in-house, and the program is re-issued before the job is released. Checking fixtures are built and maintained in the same tool room, so a fixture change is scheduled with the tool change rather than discovered at inspection.

Cutting runs on the 12 kW fibre laser with its 40 ft × 16 ft bed and on the 6 kW and 3 kW support machines, forming on the 200 T, 5-axis brake with the 4,450 mm bed, welding on three CLOOS robotic MIG cells or at the 30+ manual stations. A revision that reaches the nest is logged with the part number and revision so the cutting record and the drawing agree. PPAP and first article inspection are available, and the FAI report names the revision it was measured against.

For customers including Mahindra, Mahindra Powerol and Indian Railways, revisions on running parts are handled as a scheduled change rather than a surprise: the effectivity is agreed, the old revision runs out on a stated quantity, and the first part off the new revision is inspected and reported before the next release. The full route from drawing to dispatch is described in build to print sheet metal manufacturing, and tooling that belongs to the customer is covered in customer-owned tooling storage and maintenance.

What the revision has to say

• The revision letter, the zone of the change, a description of the change and the date.
• The effectivity: serial number, date or quantity, stated as one of the three.
• Which files are re-issued, listed by name, with the revision embedded in each.
• Whether the part is interchangeable with the previous revision, and if not, the new part number.
• Whether the checking fixture is affected, and the fixture revision that goes with it.
• The inspection requirement for the first part, including the characteristics to be re-measured.
• The disposition of stock made to the previous revision.
• The person who approved the change, with a name and a date.

The drawing set that carries these fields is the one described in the STEP files for bend review guide and the DXF and RFQ checklist. Send a change through the quote form with the effectivity stated and it can be scheduled into the existing release rather than run as an emergency.

When a revision is the wrong instrument

Two cases. The first is a part that is no longer interchangeable: the mounting pattern moved, the interface changed, the part will not fit where the old one fitted. That is a new part number, and issuing it as revision F invites both revisions into the same stores bin and onto the same machine. The second is a change that exists only to correct a drawing error that never reached production. That still gets a revision, because the record has to be straight, but it should not trigger a first article and a tooling review.

Everything else belongs in the chain: classified, effectivity written, files renamed, fixture checked, first part measured. A revision that is only in the drawing is not a revision; it is a note in a file that nobody on the floor has read.