AI-Generated Sheet Metal Drawings: The Seven Predictable Failures
AI drawing tools produce geometry that looks right and specifications that are not. The output is usually dimensionally inconsistent, missing a tolerance standard, and occasionally physically impossible to form. This page lists what actually goes wrong, because recognising it saves a week of email.
Fulei Metal reviews every drawing before quoting, whoever or whatever produced it. If your drawing was AI-generated, send it anyway — the review is the same, and it is free.
Failure 1: Dimensions that contradict each other
The most common and most expensive. A view says one thing, the bill of materials says another, and neither is marked as the requirement.
What it looks like: a view shows one quantity and the BOM lists another. A stated overall length conflicts with the length the views imply. A total weight on the title block disagrees with the material volume of the parts listed. All of it is on the same drawing, and nothing marks which number is the requirement.
Why it happens: AI tools generate each view and each table independently. Nothing checks that they agree.
What we do: stop and ask. We do not pick the number that suits us, because if we guess wrong the parts are scrap and the argument is unwinnable.
Failure 2: No tolerance standard
Every dimension carries a bare number and no reference to ISO 2768, ISO 2768-c, or a per-feature table.
Why it matters: without a standard, we do not know what we are being held to. Holding tight tolerances on every feature costs more and slows the job down; assuming loose ones risks rejection at your incoming inspection. Neither default is safe for either side, so we do not pick one silently.
The fix: one line — “general tolerance ISO 2768-m unless noted” — resolves most of it.
What the numbers actually are
Two figures, so you can sanity-check your own drawing before sending it:
| Feature | What we normally work to | What really decides it |
|---|---|---|
| Laser-cut outline and hole positions | ±0.1 mm | Material grade, sheet thickness, overall part size and nesting |
| Bent dimensions with no separate callout | The general tolerance named on your drawing. ISO 2768-m gives ±0.2 mm on 6–30 mm, ±0.3 mm on 30–120 mm, ±0.5 mm on 120–400 mm | Material, thickness, bend length, V-die opening, and how much that particular alloy springs back |
Those are working figures, not a blanket promise stamped on every drawing. A bent flange does not hold the same deviation as a laser-cut edge, and the same flange in 304 and in 5052 does not behave alike — so anything tighter than ±0.1 mm is confirmed feature by feature during drawing review. If it cannot be held on that material and thickness, we say it then rather than quote it and hope.
Which brings the point back to where it started: if a dimension genuinely governs how the part assembles, mark it. If it does not, leave it to the general tolerance in the title block, and the part gets cheaper for everyone involved.
Failure 3: Bend geometry that cannot be formed
| What the drawing says | Why it fails |
|---|---|
| Inside radius below what the material and thickness will take | The outer fibre cracks at the bend. We flag any radius the material cannot hold rather than attempting it |
| Flange that collides with the tooling | The bend cannot be made because the punch or die has nowhere to go |
| A bend too close to a hole | The hole distorts during forming |
| Hem or flange folded back on itself with no relief | Material has to go somewhere; without a relief notch it buckles |
None of these is visible in a rendered image. All of them are visible the moment you try to make the part.
Failure 4: Material grades that do not exist
A grade named without a standard behind it, so nobody knows what is being certified to. Two grades treated interchangeably when they differ in corrosion behaviour or in price. A temper called out that the forming route will destroy, or one that carries no meaning for the part as drawn. All three are common, and none of them survive contact with a purchase order.
The fix: name the grade and, where acceptance depends on it, the standard — “304 to EN 10088-2” rather than “stainless”.
Failure 5: No BOM and no assembly relationship
Individual plates with no indication of what joins to what. We cannot tell whether we are looking at one part or six, and whether fasteners are in our scope.
The fix: a parts list, even a rough one, plus an assembly sketch showing which faces mate.
Failure 6: Photographs passed off as drawings
A PDF containing a photograph of a part with a few dimensions typed on top. It happens more often than you would expect, including on genuine RFQs from real companies.
Why it fails: a photograph carries no geometry. Perspective distortion alone makes it unusable for anything but identifying the part.
What we do: tell you it is a photograph, and offer the reverse-engineering route — measured from a sample, with the dimensions you cannot measure from outside flagged for your input.
Failure 7: Scale and proportion errors
A feature pattern that does not fit inside the plate it is drawn on, or a length that does not agree with the dimensions stacked beside it. These are dangerous because they are silent — nothing on the drawing flags a problem, and they are only caught when somebody checks the arithmetic against the view.
The fix: dimension from datums, not by chaining. Chained dimensions accumulate error and hide this class of mistake.
What to do with an AI-generated drawing
| Situation | Action |
|---|---|
| It is geometrically plausible and internally consistent | Send it. Add a tolerance standard line and the material specification, and it is quotable |
| It has contradictions | Send it anyway. We list the contradictions, you resolve them — usually in one reply |
| It has impossible bends | Send it. We propose the corrected geometry before quoting, not after the order |
| It is a photograph | Send it with a sample part if you have one. Reverse engineering is a route, not a refusal |
The worst outcome is not sending a bad drawing. It is sending a bad drawing, getting a quotation against it, and discovering the contradiction at the sample stage.
What we will not do
Beyond those four, everything else is quotable. The drawing package checklist covers what belongs in the file in the first place, and the DFM review covers what happens to it once it arrives.
- Guess between contradictory dimensions. If two numbers disagree, we stop and ask
- Assume a tolerance standard. We propose one and wait for your approval
- Quote a photograph. We will tell you it is a photograph and what we would need instead
- Design the part for you. If the part needs designing rather than correcting, we say so and you need an engineering partner
Frequently asked questions
Is an AI-generated drawing always unusable?
No. Some are fine, particularly simple bent parts where the geometry is unambiguous and the material is specified. The problem is not the tool, it is the missing cross-checks — a tolerance standard, a consistent BOM, and bend geometry that has been checked against the material.
Can you just fix it?
For corrections, usually yes, and we propose them before quoting. For a part that needs designing rather than correcting, no — that is engineering work and we are a fabricator.
Will you tell me if my drawing is bad?
Yes, in the first reply, as a question list alongside the quotation. We would rather have that conversation before the order than after the parts arrive.
Does a bad drawing affect the price?
Not directly. It affects the time. A drawing that needs three rounds of clarification takes three rounds of engineering time, and that shows up in the lead time rather than the unit price.
How fast can you review a drawing?
The review happens with the quotation. Simple laser-cut and bent parts are quoted within 24 hours on working days (GMT+8); complex assemblies get a confirmed date after review rather than a guessed one.
Send the drawing, whatever produced it
If there is nothing to send yet — a sample part and no file — the reverse engineering route is a separate path. If you are comparing suppliers on an enclosure rather than a single part, start from the enclosure selection page instead.
Send the drawing with quantity, material, thickness, finish, tolerance and destination port. If it was AI-generated, say so — it changes nothing about how we review it, and it saves the embarrassment of discovering it at the sample stage.