How Sheet Metal Fabrication Companies Work: 5 Checks Before You Send a PO

• 1
  Five things to check first
• 2
  What to compare across sheet metal suppliers
• 3
  How sheet metal fabrication companies work in practice
• 4
  Material and thickness decide which supplier can help
• 5
  Tolerance, inspection and what the numbers actually mean
• 6
  Lead time, minimum order quantity and quoting habits
• 7
  Estimating cost and avoiding the usual mistakes
• 8
  How to vet a sheet metal supplier in six steps

A sheet metal shop turns a flat blank into a formed part through a fixed sequence: programming, cutting, forming, joining, finishing and inspection. Most quotes only describe the cutting step, because that is the easy part to price. The steps that decide whether your part fits are forming and joining, and those are the ones you should ask about.

Laser cutting holds a kerf of roughly 0.1–0.3 mm depending on material thickness and beam mode. That is not where the risk sits. Risk sits in bend deduction. If the shop uses a generic K-factor instead of one measured on your material and tooling, a part with six bends can drift 0.3–0.8 mm out of position before it ever reaches assembly.

Joining changes the geometry again. Spot welding pulls thin panels; full welds on 3 mm stainless move 0.5 mm or more along a 600 mm edge unless the shop sequences the passes and uses fixtures. Ask how they control heat input, and whether flatness is measured or eyeballed.

Finally, look at what happens after forming. Deburring, anodizing, powder coating and laser marking all add tolerance stack and lead time. A shop that runs all of them under one roof can hold one set of inspection records. A shop that brokers them out cannot.

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  Cutting sets the blank, forming sets the partMost dimensional complaints trace back to bend deduction and springback, not the laser.
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  Ask for a first-article reportA dimensional report on the first piece tells you more than a brochure.
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  Watch the finishing handoffEvery external process adds a day and a chance for damage.

Mild steel and aluminium are the common ground. Almost every fabricator cuts and bends 1.0–3.0 mm 5052 or 6061 aluminium and 1.0–2.0 mm cold-rolled steel without discussion. Once you go thinner than 0.8 mm, handling damage and oil canning become the dominant defect, and you want a shop that has vacuum tables and soft tooling.

Above 6 mm, the process mix changes. Fiber lasers still cut, but edge quality drops on thick mild steel and you may need a secondary machining pass on mating faces. Stainless 304 and 316 work-harden, so bend radii should stay at or above one material thickness to avoid cracking, and 17-4PH needs a tighter rule.

Tight-tolerance work often mixes processes. A bent aluminium chassis with machined internal bosses, threaded inserts or a milled connector face is normal. A supplier with both sheet metal and CNC capacity under one quality system can hold the interface between the two instead of blaming the other shop.

Material grade matters for finishing. 6061 anodizes to a clean clear or black; 5052 takes color more evenly on large panels. If the finish is cosmetic, pick the alloy for the finish, not just for the strength.

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  Thin stock under 0.8 mmExpect oil canning; ask about handling and support tooling.
• 2
  Stainless bendsKeep the inside radius at one thickness or more on 304 and 316.
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  Mixed partsMachined bosses plus bent shell is one part, so keep it with one supplier.
• 4
  Cosmetic panelsChoose the alloy by how it finishes, not only by yield strength.

A general tolerance block on a drawing is not a process capability. When a shop states ±0.005 mm, that figure applies to machined features on a CNC, not to a 1,200 mm bent panel. Formed sheet metal lives in a different range: ±0.1 mm on hole-to-hole position is realistic, and ±0.5° per bend angle is a fair target.

This gap causes most of the arguments. An engineer writes a tight general tolerance, the fabricator quotes it, and the first article fails on a bend. Better practice is to tolerance only what functions. Mark the mounting holes, the mating faces and the connector cutout. Leave the rest at a shop-standard block.

Inspection depth is the second question. 100% inspection before shipment is achievable on small and mid-volume runs, and raw material checks plus in-process monitoring catch problems before finishing. Ask for the report format before you place the order, not after a defect appears.

For regulated products, the quality system is the real product. ISO 9001:2015 is the baseline. IATF 16949:2016 applies to automotive work, ISO 13485:2016 to medical devices, and ISO 27001:2022 to how your files are stored. Match the certificate to your audit, not to the marketing page.

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  Tolerance only what functionsA tight general block raises cost and does not improve the assembly.
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  Separate machined and formed tolerances±0.005 mm on a milled face, ±0.1 mm on hole position after bending.
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  Name the report before the POFirst-article, dimensional and material reports should be agreed up front.

Quoting is a capability test. A supplier that returns a price in 12 hours with a DFM note has read your files. A supplier that returns a number in five days without comment has priced a drawing, not a part. The DFM note is where you learn that a 0.5 mm bend radius will crack, or that two bends could be replaced by one tab.

Minimum order quantity shapes the relationship. A shop with no minimum order quantity will run one prototype and the same part at 10,000 pieces, which keeps the fixture and the inspection plan continuous. A shop with a 500-piece floor is telling you it is set up for volume and will treat your prototype as an interruption.

Lead time should be broken into stages: quote, programming and material, cutting, forming, finishing, inspection. Parts that ship in 3–5 days are normal for simple brackets and panels. Anything with welding, anodizing or assembly needs more, and a supplier who promises otherwise is either fast or optimistic. Ask which.

One more habit worth checking: how they handle changes. A revision that arrives after cutting but before forming is cheap. After anodizing it is a new order. Suppliers who flag this early save you money.

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  A quote without DFM feedbackTreat it as a price, not engineering support.
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  No minimum order quantityKeeps prototype and production on the same process and fixture.
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  Stage-by-stage lead timeAsk for the breakdown, then decide where the risk sits.

Cost in sheet metal is driven by four items: material area, cut length, number of bends and finishing steps. A part with 20 holes and 12 bends costs more than its material suggests. If you need to cut cost, reduce bends and consolidate holes before you shop for a cheaper rate.

The most common mistake is designing a part that needs a press brake but has no clearance for the punch. A 30 mm flange on a 3 mm panel is hard to form without a special tool. Give the flange at least four times the material thickness where you can, and check the bend line against the tool envelope.

The second mistake is asking for a cosmetic finish on a welded assembly. Weld beads and anodizing do not hide each other. Either specify a brushed or powder-coated finish that tolerates the joint, or plan a post-weld machining step.

The third is splitting a part across two suppliers to save a few percent. The bent shell comes from one shop and the machined insert from another, then nobody owns the interface tolerance. Keep the interfaces with one quality system whenever the tolerance is tighter than ±0.2 mm.

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  Cost sits in bends and finishingMaterial area is often the smallest line item.
• 2
  Check tool clearanceShort flanges need special tooling; flag them before quoting.
• 3
  Do not split interfacesOne supplier should own any tolerance tighter than ±0.2 mm.