Oct 27, 2026Sourcing Guides
Sheet Metal Enclosure FAI: A Sign-Off Checklist for the First Build
A first article can look right on the bench and still come from the wrong revision, the wrong route or the wrong fixture. The checks that decide whether a run should be released.
A first article arrives as a folder. There are photos of a finished enclosure, a drawing with ticks in the margin, and a sheet that says approved. On the bench the part looks right. Then the production run starts, and within a few weeks the door begins to catch, a weld pulls a panel out of square, and the coating wears thin at a cut edge.
The first article was fine. The process behind it was not.
That distinction matters. Signing off a first article says little about the next unit. It is a decision about whether the line that made that unit can repeat it. In our reading, first article inspection (FAI) is a release decision, and it rests on three things: a named drawing revision, a unit built on the production route, and a record that shows what was measured.
Our work is sourcing custom sheet metal enclosures in China. The founder's family owns a metal shop that does hardware and sheet metal work, and this is how we would vet the release of a first production run.
Lock the Drawing Revision Before Any Measurement
Every measurement depends on a document that may already be out of date. So the drawing comes first, before anyone talks about a number.
A first article is measured against something. We want four identifiers on the table before a dimension is discussed: the purchase order line, the drawing revision, the model version if the factory builds from a 3D file, and the revision printed on the FAI record. If those four do not agree, the measurement has no reference. Stop there.
Start with the mundane causes. Purchasing sends a revised drawing after the order is placed. The factory quotes from the PDF in its inbox rather than the one attached to the PO. A 2D drawing and a 3D model disagree about a hole or a bend relief. None of that is sabotage. All of it produces a first article that passes against a document nobody is building to.
Decide which document governs when the model and the drawing conflict, and write that rule into the order. Otherwise each side measures against the file that flatters it.
Ask for the change list as well. A revision letter with no visible change is a question, not proof of control. On a sheet metal drawing, watch material, finish, insert positions, hole pattern and bend lines.
Version first. Measurement second.
Build the First Article on the Same Line
A first article is evidence only if it comes off the route that will make the order. Some do not. The sample shop builds one enclosure by hand, the production line builds the rest, and the buyer approves the sample shop.
The shortcuts are easy to spot once you know where to look. A part cut on a turret punch instead of the laser that will run production. A bend made without the fixture, or on a brake the factory does not plan to use. A weld laid by the sample technician rather than the welder on the cell. A finish sprayed from a can because the coating line was busy. Hardware fitted at a bench instead of at the station where production fits it. Each shortcut removes the error the first article exists to catch.
We ask for the route card, sometimes called a traveler. It should name the machine, the program, the fixture and the operator at each step, with initials or a signature. Then we ask where this unit came from. Was it the first piece off the run, or one pulled aside and finished separately?
If coating is subcontracted, ask whether the coater that finished the first article is the coater that will run the order. A finish approved from a different line is a finish nobody has seen.
A hand-built sample proves hands.
The Flat Pattern Is Not the Finished Enclosure
A flat pattern check is cheap and early. It tells you the cut outline, the hole pattern and the notch positions. It does not tell you the enclosure is right. Between the flat and the finished box, the metal moves.
Bending moves it first. A single angle can measure correctly while the stack of bends is wrong, because each bend carries a little error into the next. Check the cumulative dimension across the sequence, and check it once the part is released from the brake. A part measured while it is still clamped can read true and spring back the moment it is free.
Welding moves it again. Heat pulls a panel. A door that was flat before welding can arrive at coating with a twist that only shows up as a door gap. Look at squareness and diagonals after welding, before the finish goes on.
Coating hides the move. We measure the bare part before coating and agree how the coating is counted in the final dimension. Then we look at the places a flat face cannot test: an exposed cut edge, a weld bead, the inside of a corner, the threads of an insert, a masking line on a mating face. Coating inside a thread is a rework ticket. Masking is part of the drawing, not a workshop preference.
Assembly is where the earlier errors meet. Fit the door, the latch, the hinge and the gasket before anyone signs.
Measure after the step that moves the metal. A flat pattern signed off in the cutting room has not met a brake yet.
The Enclosure Fits the Mating Part, Not the Drawing Alone
Treat the enclosure as an assembly. The dimensions that decide fit are interfaces. The drawing shows the box. The fit shows whether the box works.
Start with the door. Close it against the gasket, if the design has one, and look at the gap around the perimeter. It should be even. If the gap closes at one corner and opens at another, the frame is twisted, the hinge is out of line, or the gasket is not seated. Then work the latch. It should pull the door in without force and release without a tool. Open and close the door several times, then let it hang open.
Look at the seal face before the gasket goes on. Trace the contact line with a finger. Check for a step at a weld, a gap at a corner, a spot weld proud of the surface. A gasket can only seal what it touches.
Inserts and threads come next. An insert should sit flush, hold its thread and show no coating inside. Spin a screw in by hand. If it binds, the insert was masked badly or set at an angle. Thread type matters as well. A mating part cut for one thread and an enclosure tapped for another is a mismatch you find at assembly, not at inspection.
Then we bring in the mating part. Ask for its drawing, and better, the part itself. A mounting plate, a chassis, a wall bracket, a cable gland: whatever the enclosure has to accept, fit it. Openings should line up, fasteners should engage, and clearances should survive a coat of paint.
A drawing does not close a door.
A Record a Buyer Can Read Without Calling the Factory
An FAI record has one test. Can someone who was not in the room decide, from the document alone, whether the part was built to the drawing? If the answer is no, the record is a souvenir.
The fields are not exotic. Purchase order and line. Drawing revision. Unit tag or serial. Date and work cell. Material lot or certificate reference. Each process step with the machine and program used. The measured value, the point it was taken at, and the instrument. The inspector's name. Anything found out of spec, what was decided, and who approved it. Photos with a scale and the measurement point marked.
Values carry the argument. A tick says someone looked. A value says where the part sits inside the limit and how much room the next run has to drift. A record with no measured values cannot support a release decision, however many signatures it carries.
A first article that found nothing at all is worth a second look. A first build can turn up something: a hole slightly off, a bend that needed a shim, a thread with coating in it. What matters is that the finding is written down, dispositioned and closed. A clean sheet with no measurements behind it is not a clean part.
Signatures belong to the people who did the work. A sales manager's approval is commercial. The inspector's name is evidence.
We read the record in the order of the drawing. It should arrive as one file, not a folder of loose photos and a chat thread.
A tick is not a value.
What FAI Leaves to the Sealed Unit and the Shipping Gate
Approving a first article does not approve a shipment, and it does not replace the checks that come later.
The first thing FAI leaves behind is a physical reference: after the first article is approved, two units are signed and sealed, one stays at the factory and the other is held by us, so the line has something to compare against that is not a PDF.
The second is the inspection before shipment, where we compare production units against the approved first article and that sealed reference, item by item. On our orders the deposit is 30% and the remaining 70% is paid after inspection, so the gate carries commercial weight.
The third is supervision at loading, which watches the container being filled rather than the parts being made.
What FAI does not do is approve the carton, the pallet or the packing sequence. Those belong to the pre-shipment stage. It also does not replace in-process checks during the run, or the batch records that show which unit was built when. Treating one approved first article as a license for the whole order can turn a good start into a late claim.
When an enclosure ships in a consolidation with other product categories, we check the mix against our five-category limit before we book the container.
FAI releases a process, not a shipment. Supplier vetting and supervision at loading sit outside FAI. Both are covered at (/b2b-sourcing) under sourcing.
Lay the Drawing Set and the FAI Record Side by Side
Two documents decide the release. One is the drawing set. The other is the FAI record. Put them side by side and the gaps show themselves: a revision that differs from the order, a dimension with no value behind it, a mating part nobody fitted.
Lay the drawing set and the FAI record side by side (/contact-us). Add the mating part drawings for anything the enclosure has to accept, and the purchase order line the first article was built against. We read the packet for version control, route, measurement and fit, and send back a first article review checklist and a pre-production hold point list.
The contract for this work sits with Dore Technology Co., Ltd. We work with B2B buyers who spend at least USD 10,000 annually.
The packet does not need to be tidy. A record with a problem marked on it beats a clean folder with no values.
Two documents decide the release.
