A sheet-metal or stamped part usually reaches a Vietnamese supplier the same way: a drawing that has worked for years with a local shop, sent out for a comparison quotation. By the time the first quotation comes back, much of the outcome has already been decided — by what the drawing did not say.
With a long-standing supplier, a great deal goes unwritten. The general tolerance is understood, burrs are removed “as usual”, a mill certificate arrives without being asked for. None of that transfers to a new supplier. This article covers the four things specific to sheet metal and stamping that a buyer should decide before the enquiry goes out: material and blanking, bending and piercing, who does the finishing, and which extra records to ask for. General tolerances and material grade notation are shared with machined parts and covered in CNC machining in Vietnam.
💬 Not sure whether to ask for fabrication or stamping prices? Send us the drawing and the volumes and we will help you frame the enquiry.
Fabrication or stamping: which are you actually buying?
Fabrication without dedicated dies and stamping with dies are different purchases with different start-up costs, and the enquiry should ask for the one that matches how long the design will stay unchanged.
| Point | Sheet-metal fabrication | Press stamping |
|---|---|---|
| Dedicated tooling | Usually none; laser or turret punching and press-brake bending | A die per part, often progressive for higher volumes |
| Start-up cost | Low; set-up and programming | Die cost comes first |
| Best suited to | Prototypes, low volumes, many variants, changing designs | Stable designs repeated over long runs |
| Design changes | Absorbed by reprogramming | Need die modification |
| What to ask in the quotation | Processing and set-up cost, nesting assumptions | Die cost breakdown, die ownership, expected die life |
The decision depends less on the size of the first order than on how many years the shape will stay as it is. A design that is still moving can start as fabrication and move to stamping once it settles. Die ownership, maintenance and release belong in the contract; see tooling and mould ownership in Vietnam.
1. Material and blanking: thickness tolerance and grain direction
What moves a sheet-metal part is less the grade name than the actual thickness of the coil going in and the direction the blank is cut from the sheet.
Thickness. A nominal thickness comes with a permitted tolerance in the product standard, and the coil actually used will sit somewhere within it. When thickness varies, the bend allowance varies, and the outside dimensions after bending move with it. State the nominal thickness, the band you accept, and whether the shop must measure and record the thickness of each coil it uses.
Grain direction. Rolled sheet has a direction. A bend line running parallel to the rolling direction is more prone to cracking on the outside of the bend, particularly with higher-strength steel and some aluminium tempers. On parts with many or tight bends, specify the blank orientation on the drawing or at least write “no cracking at bends”. Without that, the shop will nest the blanks in the way that saves the most material.
Forming grade. If the part is drawn rather than only bent, the grade suffix matters. Cold-rolled low-carbon steel comes in commercial, drawing and deep-drawing qualities — DC01, DC03 and DC04 under EN 10130, or SPCC, SPCD and SPCE under JIS G 3141. Vietnamese stockists commonly describe sheet by its JIS name, so “SPCC” may be what is offered by default. Writing only the commercial grade on a deep-drawn shape leaves room for splits during forming.
2. Bending and piercing: flat pattern and burr side
A bent part’s dimensions come from the bend angle and springback, from how the flat pattern was calculated, and from the stack-up of holes across bends; a pierced part also needs the side the burr is allowed on.
Who produces the flat pattern. If you send only the finished-shape drawing, the shop develops the flat pattern using its own bend allowances. The same finished part can produce different flat patterns at different shops. Decide before quotation whether you supply the flat pattern, or the shop develops it and you verify it at first article. Specify the inside bend radius too; otherwise the shop uses the tooling it has.
Bend angle and springback. Material springs back after bending by an amount that depends on thickness, grade and method. Without an angle tolerance a bend will be “about square”. Where squareness matters to function, give the tolerance together with the reference face and how it will be measured.
Holes across bends. Holes are normally pierced flat and bent afterwards, so each bend adds to the error between holes on different flanges. That is a property of the process, not a defect. Show on the drawing which face and edge holes are measured from, and set realistic tolerances for features across a bend.
Burr side. A punched edge has rollover on the punch side, a sheared band, a fractured band, and a burr on the far side. The burr side is fixed by the punching direction, so name it: “burr on face B”. A requirement that mating faces or handled faces be burr-free only exists if it is on the drawing.
For appearance — scratches, dents, discolouration — agree physical limit samples rather than words. Welded assemblies need weld symbols with size, position and extent, and a tolerance for distortion after welding, with the measurement method.
💬 We can review a sheet-metal drawing against what Vietnamese shops will ask, then run the quotation round on the same basis for every candidate — see sourcing from Vietnam.
3. Finishing: who does it, and who answers for it
Plating, painting, powder coating and heat treatment are often done by a different workshop from the one that formed the part, and that handover is where lead time and responsibility split.
When finishing is outsourced, parts leave the press shop and come back. If nobody planned that round trip, delivery slips; if a defect appears, the press shop and the finisher can each point to the other — was the substrate wrong, or the coating? Before ordering, establish:
- which workshop performs each step, and whether you can approve or nominate the finisher;
- who inspects parts when they return from finishing, and against what;
- who pays for rework and recoating, and how much time it adds.
When you specify a finish, write the type (zinc electroplating with a named passivation, powder coat, anodising), the thickness requirement, the colour reference or physical colour sample, and — the line most often missed — which areas must not be finished: threaded holes, earthing points, mating faces. The “do not coat here” instruction is one of the most frequent causes of rejected lots. What to check on a first visit to a Vietnamese factory covers how to ask which steps leave the building.
4. The extra records to ask a press shop for
On top of the usual material certificate and inspection report, sheet-metal and stamped parts justify four extra records that make later problems traceable.
The general set of quality documents, their English names and how to read EN 10204 certificate types are in quality documents to request from a Vietnamese parts supplier. Specific to sheet and stamping:
- Coil-to-lot traceability. Sheet arrives in coils, and a coil change mid-run can put two materials into one delivery lot. Agree how each material certificate is linked to each part lot.
- Measured thickness. The thickness actually measured on the material used, not the nominal value. When bent dimensions are off, this one line often explains why.
- Coating thickness records. Measured by whoever applied the finish. Specify where and how many points are measured, or you will receive readings from the easiest flat face.
- Flat pattern confirmation at first article. Record which flat pattern was cut, in a file and on a retained part, so a later change in the flat pattern can be detected.
Sampling plans for the delivered lots are covered in pre-shipment inspection and AQL.
The enquiry checklist
Attach this information to the drawing; whatever cannot go on the drawing goes in a short specification sheet.
| Information | What to write | What happens if it is missing |
|---|---|---|
| Material | Grade, standard number, required properties, substitution rule | Material to another standard is used |
| Thickness | Nominal thickness, accepted tolerance, blank orientation | Bent dimensions drift; bends crack |
| General tolerance | Standard and class in the title block | The shop’s own practice applies |
| Bends | Inside radius, angle tolerance, whether you supply the flat pattern | Developed and formed to the shop’s standard |
| Burrs | Burr side, maximum burr height, deburring required or not | Burrs on mating or handled faces |
| Welds | Weld symbols, size, full or partial, finish and distortion limit | Disputes on both appearance and dimensions |
| Finish | Type, thickness, colour reference, masking of untreated areas | Areas you needed bare are coated |
| Appearance | Scratch and dent limits, physical limit samples | Different eyes, different verdicts |
| Quantities | Annual volume, order lot size, split deliveries allowed or not | Quoted terms and real orders do not match |
| Packing and rust prevention | Corrosion protection method, inner and outer packing, stacking limit | Rust and dents after a sea voyage |
The last line deserves more attention than it usually gets. Sheet-metal parts are bulky, and conditions inside a container change with temperature and humidity on the way. Decide between rust-preventive oil, volatile corrosion inhibitor paper and desiccants, whether parts are separated so they cannot rub, and how high pallets may be stacked.
Unit prices, die costs, lead times and defect rates depend on the part, the thickness, the forming difficulty, the volume and each shop’s equipment. There is no market rate worth quoting. The only real comparison is quotations on identical terms from several shops.
💬 If you want the candidate shops checked on the floor — including which finishing steps go out — tell us about the part.
Frequently asked questions
1. If I write a thickness on the drawing, will the sheet be exactly that thick?
No. Sheet is supplied within a thickness tolerance and real coils vary inside it. Because that changes the bend allowance, state the band you accept and ask for the actual thickness to be measured and recorded.
2. Should I supply the flat pattern?
Either works, but decide in advance. Shops use different bend allowances, so a finished-shape drawing alone lets each shop develop its own flat. If you do not supply it, require the flat pattern to be confirmed at first article.
3. What extra documents should I ask a press shop for?
Coil-to-lot traceability, measured sheet thickness, coating thickness records and confirmation of the flat pattern at first article, on top of the usual material certificate and inspection report.
4. Can I place small sheet-metal orders in Vietnam?
That depends on the shop’s equipment and focus. Fabrication without dies suits smaller quantities, but freight and documentation costs do not shrink with quantity, so compare the landed total rather than the unit price.
5. How do I specify colour and coating so there is no dispute?
Give the finish type, the thickness requirement, a colour number or physical sample, and the masking instruction for areas that stay bare. Agree a physical limit sample for appearance.
Sources: EN 10130 and JIS G 3141 (cold-rolled low-carbon steel forming qualities); EN 10204; ISO 2859-1. Checked on 17 October 2026.