You send a die-casting drawing to a few Vietnamese suppliers, compare the unit prices, and place the order with the one that looks right. For a while nothing goes wrong. Then, a year or two into production, dimensions start drifting to the edge of tolerance, a pressure-tight housing begins leaking on your assembly line, and the deburring you assumed was included turns out not to be.
None of this is really about the quality of the factory. It comes from three things nobody wrote down at the start: how long the die is expected to last and who pays when it does not, how internal porosity is specified and checked, and which operations after casting are included in the price. This article is for buyers of high-pressure aluminium die castings who want those three settled before price negotiation starts.
💬 Want to know whether your part is a realistic die-casting job in Vietnam before you spend time on a full enquiry? Send us the drawing.
The three gaps a die-casting quotation does not show
A die-casting quotation usually assumes a new die, visual inspection only and no machining — and every one of those assumptions surfaces later if it was never written down.
| Gap 1 — die life | Gap 2 — internal defects | Gap 3 — secondary operations | |
|---|---|---|---|
| Visible in the quotation? | No | No | Barely |
| When it surfaces | Well into production | At your assembly line or in the field | At the first delivery |
| What it costs | A replacement die | Sorting, recalls, line stoppages | The unit price itself |
| How to close it | Guaranteed shots and an end-of-life criterion | Defect limits by zone on the drawing | An included / excluded table per operation |
| When to decide | Before the first quotation | When the drawing is issued | When the enquiry goes out |
A good factory does not remove these gaps by itself. If they are not agreed, the same arguments happen with the best supplier as with the worst.
Gap 1: die life — how many shots, guaranteed by whom?
The quoted price assumes a healthy die; as shots accumulate the die wears, and dimensions and surface finish move with it.
The two classic forms of wear are heat checking — a network of fine cracks on the die surface caused by repeated thermal cycling, which transfers to the casting as a rough, veined surface — and soldering, where the aluminium bonds to the die steel. Four points belong in writing:
- Guaranteed shot count, as a number in the quotation or the die agreement.
- End-of-life criterion, phrased so anyone reaches the same verdict: dimensions out of tolerance after correction, heat checking beyond an agreed area on a cosmetic face, and so on.
- Who pays for the replacement die — the buyer in full, shared, or already amortised in the unit price.
- Maintenance records — cleaning, repair and shot-counter history. Without them, a die-life discussion becomes one opinion against another.
Achievable die life depends heavily on alloy, geometry, wall thickness, cycle and die steel, so another supplier’s figure tells you little. What matters is that a figure and a criterion exist on paper. Ownership, marking and release of the die are covered in tooling and mould ownership in Vietnam.
Gap 2: internal defects — how do you specify what you cannot see?
Misruns show on the surface; porosity does not, and on pressure-tight, threaded or thin-walled features it has to be specified on the drawing or it will be found by your customer.
A misrun is metal that froze before filling the cavity, and it is visible. Porosity is the general term for internal voids: shrinkage porosity from solidification and gas porosity from entrapped air or gas. It appears neither in the quotation nor on the surface, yet it decides pressure tightness and the strength of threaded bosses. Machining often exposes it, which is why porosity frequently shows up only after a casting has been drilled or faced.
| Method | What it reveals | Destructive? | Usable on every part? | Typical use |
|---|---|---|---|---|
| Visual inspection | Surface defects only | No | Yes | 100% cosmetic sorting |
| Sectioning | Actual porosity at a cut face | Yes | No | Process set-up and periodic audits |
| Radiography (X-ray) | Presence and rough position of internal voids | No | Depends on part and equipment | Assurance on critical zones |
| Industrial CT | Position and shape of voids in three dimensions | No | Usually sampling | Failure analysis, initial qualification |
| Leak or pressure test | Leakage under service-like conditions | Normally no | Yes | Release test for pressure-tight parts |
Put four things on the drawing and specification:
- Porosity limits by zone. A blanket limit protects nothing where it matters and wastes yield where it does not. Write it as “no pore larger than X within Y mm of this machined face”, or reference a radiographic standard such as ASTM E505 for the zones that need it.
- Sectioning frequency. At lot start, after any process change, and periodically — and who judges the result.
- Leak or pressure test conditions. Test pressure, hold time and the acceptable leak rate.
- Whether radiography is in-house or outsourced. If outsourced, lead time and responsibility change.
However tight a visual AQL is set, it catches no internal porosity at all. Sampling plans for what can be seen are covered in pre-shipment inspection and AQL.
💬 Porosity specifications are where many die-casting enquiries stall. We can help turn your functional requirement into a drawing note a Vietnamese caster can quote against — see sourcing from Vietnam.
Gap 3: secondary operations — who does what, and where?
The unit price depends on how many operations it includes, and some of those operations may be done by another company, which blurs both responsibility and lead time.
The most effective tool is a single table that every supplier fills in the same way:
| Operation | Included / excluded | In-house / outsourced | Subcontractor disclosed? |
|---|---|---|---|
| Trimming and deburring | |||
| Gate and overflow removal | |||
| Shot blasting | |||
| Machining (tapping, spot facing, sealing faces) | |||
| Surface treatment (anodising, paint, powder coat) | |||
| Assembly and press-fitting | |||
| Final inspection and packing |
Where an operation is outsourced, settle three things: who decides whether a defect came from the casting or the machining, and who pays; how much time the transfer between workshops adds; and whether the drawing and inspection criteria actually reach the subcontractor. Drawing practice for the machined features is in CNC machining in Vietnam.
What to add to a die-casting enquiry
Die-casting quotations stop being comparable when each supplier quotes on different assumptions, so give the process-specific data up front.
- Projected area and expected locking force. Locking force is derived from the projected area of the casting, runners, overflows and biscuit multiplied by the casting pressure. With that figure a supplier can tell at once whether its machines can take the part.
- Maximum and minimum wall thickness. Thick sections invite shrinkage porosity; thin sections invite misruns.
- Draft angles. If unspecified, each supplier assumes its own.
- Alloy and standard. ADC12 is defined in JIS H 5302. The alloys usually quoted as equivalents — A383.0 in ASTM B85, the EN AC-46000 family in EN 1706, and YL113 in the Chinese GB standard — do not have identical composition ranges. Many Vietnamese casters quote ADC12 by default, so if your drawing names another alloy, agree the composition range itself and require a chemical analysis report.
- As-cast and machined tolerances separately. For as-cast dimensions, a general casting tolerance grade such as the DCTG grades of ISO 8062-3 gives both sides the same yardstick.
- Annual volume, lot size and the secondary-operations table above.
What to look at in a die-casting plant
A die-casting floor looks much the same everywhere; what separates plants is whether process conditions are recorded and controlled.
The general visit checklist is in what to check on a first visit to a Vietnamese factory. Specific to die casting:
- Melting and holding furnace temperature records — and whether they look written at the time or filled in afterwards.
- Degassing — whether the melt is degassed and how; this drives gas porosity.
- Shot parameters by machine — injection speed, casting pressure, cycle — with a history of changes.
- Die maintenance log — shot counts and repair history. Gap 1 can only be managed if this exists.
- Composition and dimensional checks — whether the plant has its own spectrometer and coordinate measuring machine, or sends samples out.
For automotive parts, IATF 16949:2016 certification will come up; it builds automotive-specific requirements on ISO 9001:2015 and replaced ISO/TS 16949. Whether a given plant holds it can only be established plant by plant, and checked with the certification body.
Ask for the right document names too. “Mill certificate” describes a steel mill’s certificate; for a die casting, ask for a chemical composition report for the melt and an inspection report for dimensions and appearance. The full document set is in quality documents to request from a Vietnamese parts supplier.
💬 Sunsho Trade does not own a foundry, so we are not selling any particular plant. For each project we find, vet and manage the die caster that fits the part. Tell us about yours.
Frequently asked questions
1. Who normally pays for a replacement die?
There is no “normally”, which is why it must be agreed at the first quotation. If it is not, the argument at end of life starts with whether the die has actually reached end of life, and production stops while it is settled.
2. Can visual inspection find internal porosity?
No. It finds only what reaches the surface. Where internal soundness matters, specify which method — sectioning, radiography, CT or leak testing — applies to which zone and how often.
3. One quotation is far below the others. What should I check?
First the scope of secondary operations, then the scope of inspection, then the alloy composition range. Having every supplier fill in the same operations table usually explains the gap immediately.
4. If I write ADC12, will every factory use the same alloy?
Not necessarily. Equivalent alloys in other standards do not share identical composition ranges. Agree the composition range itself, and make a chemical analysis report a condition of delivery.
5. Should I avoid casters who outsource machining or finishing?
No. Outsourcing is common and not a weakness in itself. What matters is that it is disclosed, responsibility at each handover is defined, and your drawing and acceptance criteria reach the subcontractor.
Sources: JIS H 5302; ASTM B85; EN 1706; ISO 8062-3; ASTM E505; IATF 16949:2016. Checked on 17 October 2026.