The decision is made, the budget is approved, and a date is set. What you actually have on your desk is the drawings you sent to the Chinese supplier, a bill of materials, and a file of past quality problems. Most writing on “China plus one” is about the decision — why Vietnam, how costs compare. Very little is about the week after, when someone has to start moving real parts.
This article is about that work: transferring existing production parts, one by one, from a Chinese supplier to a Vietnamese one. The uncomfortable truth first. The core of the job is not finding a cheaper factory. It is pulling out, in writing, everything the old supplier has quietly absorbed over years of production. Skip that, hand over the drawings alone, and you receive parts that match the drawing and still do not work on your line.
💬 Moving a family of parts and want a second opinion on where to start? Send us the list and we will help you put it in a sensible order.
Which parts move first, and which move last?
A transfer happens part number by part number, so move first the parts whose failure would not stop your production, and leave the most constrained parts until the route is proven.
| Criterion | Easier to move first | Better left until later |
|---|---|---|
| Process | Few operations, one workshop | Several operations or several suppliers |
| Material | Common grade, several sources | Special grade or a named brand with one route |
| Tolerances | General tolerances suffice | Tight geometric tolerances or fits |
| Inspection | Standard instruments decide pass or fail | Special gauges, non-destructive testing or test rigs |
| Approval constraints | You can approve the change yourself | Customer approval, certification or regulatory filing |
| Volume and stock | Stable demand, easy to stock ahead | Volatile, bulky or with a shelf life |
This table is not a list of what can and cannot move; it is a way of ordering the discussion inside your company. The bottom two rows are the ones most often missed. A part under customer approval or certification may need re-approval the moment the manufacturing site changes, on a timetable that has nothing to do with whether the new factory can make it. Do not let engineering set the order alone.
Why the same drawing does not produce the same part
A drawing is only part of the specification; the rest lives inside the old supplier as habit, and a new factory fills the same gaps with its own habits.
The longer a supplier relationship runs, the more unwritten decisions the supplier carries for you: which stockist the material comes from, how far burrs are removed, how many scratches are tolerated, which dimensions are measured on how many parts. These were settled in the early months, in calls and emails, and have sat there ever since.
The difficulty is that those decisions are in the part but not on the drawing. A new factory, acting in good faith, fills them in with its own standard. When you reject the result, it can rightly say the part conforms to the drawing. “We have the drawing, so why can’t they make the same part?” almost always turns out to mean “we never wrote down what ‘the same’ is”.
The specification inventory
The central task of a transfer is to write down what the old supplier was doing without being asked, in a form the new supplier can work to.
| Item to capture | On the drawing? | Where to find it |
|---|---|---|
| Material standard and actual brand or mill | Standard yes; actual source no | Material certificates, old supplier’s purchasing records |
| Surface treatment and thickness | Type yes; thickness and measuring points often vague | Finisher’s specification, past inspection reports |
| Heat treatment and hardness test location | Hardness yes; location often missing | Work instructions, hardness test records |
| Welding as actually done | Symbol yes; leg size and sequence no | The part itself, the old supplier’s welding instruction |
| How tolerances are actually checked | Tolerances yes; sampling no | Incoming inspection records, report formats |
| Cosmetic limits — scratches, burrs, colour | Rarely | Limit samples, past rejected parts |
| Where the limit samples are | No | Old supplier, your inspection area, your customer |
| Packing | Often not | The packed part, the old supplier’s packing instruction |
| Inspection report items and format | No | Past delivery documents |
| Past defects and containment actions | No | Your corrective action records and complaint log |
The items whose source is “the old supplier” are the ones to collect before the relationship changes. Once the old supplier knows the work is leaving, cooperation may become slower. Limit samples deserve particular attention: they show the boundary between pass and fail as physical parts, which no paragraph can do. Find out where they are, how many exist and who approved them.
Which documents to ask the new supplier for, and when, is set out in quality documents to request from a Vietnamese parts supplier; how to settle tolerances and measurement is in CNC machining in Vietnam.
💬 We can turn the inventory into a specification package a Vietnamese factory can work to, in Vietnamese, and run the supplier search on that basis — see sourcing from Vietnam.
Material: an equivalent grade is not the same grade
Chinese GB, Japanese JIS, American ASTM and European EN standards are separate systems; a line in a cross-reference table does not make two grades identical.
Chinese national standards come in mandatory (GB) and recommended (GB/T) forms. Vietnam has its own national standards system, TCVN, under the Ministry of Science and Technology, though Vietnamese shops very often work in JIS or ASTM designations in practice. Composition ranges and test methods can differ between systems, so rather than relying on a cross-reference, compare the actual values on the material certificates from the old supplier with the values the new supplier proposes, and approve the grade in writing.
Recovering assets and approving the new supplier
Confirm ownership of moulds, fixtures and gauges before you announce the move, then bring the new supplier up through trial, first-article inspection, renewed limit samples and production approval.
Your moulds, fixtures, gauges and limit samples may be yours by contract, but they are physically in China. If storage charges or an unpaid invoice are raised after you announce the move, recovery can stall. Check the contract terms and the physical location of every item before the conversation. The clauses that make recovery possible are in tooling and mould ownership in Vietnam.
At the new supplier, the sequence is trial, first-article inspection, renewed limit samples and production approval. Do not import sector frameworks where they do not belong: AS9102 is an aerospace first-article standard and PPAP comes from automotive practice. For a general industrial part, “measure every characteristic on the first lot and attach the report” is enough. Expect to re-agree the limit samples from the first lot: a different process can produce scratches and colour differently. The sample chain is covered in sample approval stages.
Parallel production and the cut-over lot
The old supplier’s last lots and the new supplier’s first lots always overlap, and how thick you make that overlap decides whether the transfer is safe.
Decide four things: until when you keep ordering from the old supplier, from which lot the new supplier becomes the approved source, how much buffer stock you hold in between, and whether the cut-over is defined by production lot or by shipment date. The fourth matters later. When a defect appears, you must be able to say at once which factory made the part.
There is no honest general figure for how long the overlap should be; it depends on how simple the part is, whether certification is involved, and how easily it can be stocked. Build the calendar for your own part: last production at the old supplier, sea transit, the new supplier’s approval, one allowance for a failed first lot, and the Lunar New Year shutdown if it falls inside the window. See planning production around Tết and planning production lead time in Vietnam.
If the materials still come from China
Moving the final process to Vietnam does not remove supply risk if the materials and components still come from China, and it may not give the goods Vietnamese origin.
Supporting industries in Vietnam are deeper for some products than for others, and many Vietnamese factories import part of their materials, including from China. That is a matter of how each supply chain has developed, not of capability. Ask the new supplier, in Vietnamese, where each material and bought-in component will come from, and record the answer.
Origin is the second consequence. Final processing in Vietnam does not by itself make goods Vietnamese for preferential tariffs: each agreement’s product-specific rules decide whether a change in tariff classification, a regional value content or a specific process is required. How the rules and the enforcement work on both sides is covered in origin and transshipment risk in Vietnam sourcing, and which proof of origin each destination accepts in proof of origin by destination.
💬 For each part, we find, vet and manage the Vietnamese supplier that fits, and confirm in Vietnamese where its materials come from. Tell us what you are moving.
Frequently asked questions
1. The old supplier will not release our moulds. What now?
Gather the ownership clause and the evidence of payment first. Even where ownership is clear, release can stall over storage charges or open invoices. Price the alternative — a new tool in Vietnam, and how long it takes — so you know how much room you have in the negotiation.
2. We have the drawings. Why can’t the new supplier make the same part?
Because the drawing is not the whole specification. The actual material source, coating thickness, cosmetic limits and sampling habits usually sit with the old supplier as practice. Most of the work in a transfer is writing those down.
3. How long should parallel production run?
There is no general figure. Build the calendar for your part from the old supplier’s last lot, transit time, the new supplier’s approval and an allowance for one failed lot, and add the Lunar New Year shutdown where relevant.
4. Can a Vietnamese supplier provide material certificates?
Many can, but the content has to be specified: composition or mechanical properties, how the certificate links to the lot, and which certificate type under EN 10204 you require.
5. Will processing in Vietnam reduce our import duty?
Possibly, if the goods meet the origin rules of an agreement your destination applies. The fact of processing alone does not decide it; the product-specific rule for the tariff code and the origin of the materials do. Check before you build the cost case on it.
Sources: EN 10204; AS9102; national standards systems GB/GB/T (China) and TCVN (Vietnam). Checked on 17 October 2026.