Three rules cover most parts:
- Solid, prismatic, tight-tolerance geometry in low or medium volume → CNC machining.
- Flat or folded sheet parts, prototypes and low-to-mid volume → sheet metal fabrication.
- Thin parts with a frozen design and high, repeat volume → metal stamping with a die.
Everything below explains where those rules bend. We are a sourcing and freight team in Shenzhen, not a machine shop, so we have no process to sell you. What we do see is the quote stack: buyers comparing a machining quote against a stamping quote without noticing that one of them contains a tooling investment and the other does not.
Start with geometry, not price
CNC machining is subtractive — you start with a solid billet and cut away everything that is not the part. That makes it the right route for deep pockets, precision bores, bearing fits, threads and complex 3D surfaces, and the wrong route for a wide, thin shell that would waste most of a billet.
Sheet metal fabrication cuts a flat blank (laser, waterjet or turret punch), then forms it on a press brake, adds hardware, welds and finishes. It suits brackets, panels, covers, chassis, trays and enclosures, and it needs no dedicated tool, so design changes are cheap.
Metal stamping presses sheet or coil between a punch and a die. Once the tool is built, a press produces parts at a rate none of the other two can match, with repeatability that comes from the die rather than the operator. The trade-off is a significant upfront tooling commitment and a design that is expensive to change.
If the part needs to be formed into a 3D shape from sheet, ask whether a bending operation or a forming die does it. If it needs a deep pocket machined into a solid block, sheet routes are not in the conversation. Geometry narrows the field before cost enters it.
The decision table
| Decision factor | CNC machining | Sheet metal fabrication | Metal stamping |
|---|---|---|---|
| Starting material | Solid billet or bar | Flat sheet or plate | Sheet or coil stock |
| Best geometry | Solid blocks, deep pockets, precision bores, complex 3D | Folded shells, panels, brackets, enclosures, welded assemblies | Thin, flat or formed parts with a stable design |
| Where precision comes from | Machine, setup and inspection plan | Cutting accuracy, bend deduction, fixturing | Die precision and press condition |
| Upfront tooling (NRE) | None for standard work; fixtures for complex parts | Very low; standard press brake tooling | High — a dedicated die must be designed and built |
| Unit cost as volume rises | Falls slowly; machine time dominates | Falls modestly; material utilisation and nesting matter | Falls sharply once tooling is amortised |
| Cost of a design change | Low — update the program | Low — update the flat pattern | High — may require reworking or rebuilding the die |
| Design freeze needed? | No | No | Yes |
| Typical parts | Housings, optical mounts, heatsinks, shafts, manifolds | Cabinet doors, brackets, trays, chassis, guards | Clips, shields, terminals, washers, automotive brackets |
Two columns cause the most arguments. “Precision” is not a single scale — a CNC shop can hold a very tight feature, while a well-built die holds repeatability across a hundred thousand parts. Ask what the supplier can hold on your specific feature, in your material, and how it will be measured. And “no tooling” is not the same as “no setup”: programming, workholding and first article inspection are real costs on a five-piece order.
Find your volume break-even with tiered quotes
There is no universal quantity where stamping becomes cheaper. It depends on your part’s geometry, the number of stations in the die and the machining cycle time. But you can make the supplier calculate it for you.
Ask every shortlisted factory for prices at 1, 10, 100, 1,000 and 10,000 pieces in the same RFQ, with tooling and NRE listed separately. Then compare:
Machining route = unit price × quantity (+ fixtures, if any)
Stamping route = die / tooling NRE + (unit price × quantity) + secondary operations + die maintenance
The crossing point is your break-even. Above it, the die pays for itself. Below it, you are buying an asset you cannot use.
We are not publishing price ranges here, and you should be suspicious of any that are not attached to your drawing. Tool steel grade, cavity count, station count, tried-out die life and annual volume all move the number. A generic figure from a blog is not a quote. Ask for a line-item tooling breakdown instead — a reputable toolroom will show die design, material, machining and EDM hours, heat treatment, tryout and inspection as separate lines.
Also ask about die life in terms of strokes, and what happens at the end of it. A cheap die that needs replacing halfway through your programme is not cheap.
The die types you will be quoted
- Single-stage (simple) die — one operation per stroke, manual handling between operations. Lowest tooling cost, suited to simple parts and lower volumes.
- Compound die — several cutting operations in one stroke at one station, e.g. blanking the outline and piercing the holes together. Good positional accuracy for flat parts.
- Progressive die — the strip feeds automatically through multiple stations; each stroke performs a different operation and a finished part exits at the last station. Highest tooling cost, lowest piece cost at volume.
- Transfer die — the part is moved between stations by a transfer system rather than staying on the carrier strip. Used for larger or deeper-drawn parts.
One terminology note that saves real arguments. In English-language purchasing, the tool is a die or stamping tooling; “mould / mold” belongs to injection moulding and die casting. A punching die is only the hole-making station, not the whole tool. If a quotation says “punching mold”, ask which die architecture is actually being priced before you compare it with anything else.
Put tooling ownership in the purchase order
This is the clause buyers forget and then regret. For any die, mould, fixture, welding jig or custom gauge, state in writing:
- Who owns the tool, and from which payment milestone.
- Where it is stored, its identification number, and photos after acceptance.
- Expected life in strokes, and who pays for maintenance and replacement.
- Whether the supplier may use it for another customer.
- That payments are tied to design approval, first trial and sample acceptance — not 100% up front.
- That any change to a cavity, insert or cutting program after approval requires a new sample review.
Without that clause, a supplier can hold your tooling hostage during a commercial disagreement, and moving production to a second source means paying for the tool twice.
Tolerances and finishes: where the money quietly goes
Over-specifying tolerances is the most expensive habit in mechanical design, and it is entirely avoidable. Tighten the features that matter functionally — bearing bores, mating faces, pin locations — and leave everything else to a stated general tolerance such as ISO 2768-m. Asking for a tight band on twelve dimensions when two need it adds slower passes, extra inspection and scrap risk across the whole part.
The same applies to finishes. Write Ra values where surface roughness matters, specify an edge break where handling safety or assembly does, and name the coating process, thickness range, colour reference and masking requirements rather than “black finish”. Plating and anodising change dimensions, so decide whether threads are masked or chased after coating before production starts.
These details belong in the RFQ pack, because every supplier should be quoting the same interpretation of your drawing. Our sourcing checklist has the full file list.
When the honest answer is more than one process
Most products are not one process. A single assembly might have a machined manifold, laser-cut and folded brackets, stamped clips and a powder-coated enclosure. Very few factories do all of it well in-house, which means several suppliers, several production schedules and several quality standards to reconcile.
That is usually where a project slips — not in machining, but in the hand-offs. We coordinate the factories, inspect each part against its own approved sample, and consolidate everything in our Shenzhen warehouse into one shipment with one customs entry. The buyer gets one inspection report, one invoice and one tracking link instead of five.
Five questions before you choose
- Is the design frozen, or will it change after the first batch?
- Is the part a solid block or a thin formed shell?
- Which features genuinely need a tight tolerance, and how will they be measured?
- What is the realistic annual volume, not the launch-order quantity?
- Has every supplier quoted the same drawing revision, finish and quantity tiers?
Answer those five and the process choice usually makes itself. The quote comparison is the last step, not the first.
Frequently asked questions
Is metal stamping cheaper than CNC machining?
At high, repeat volume, yes — the die cost is amortised over many parts and the cycle time is far shorter. At low volume, no: the upfront tooling has too few parts to spread across. Ask for tiered quotes at 1, 10, 100, 1,000 and 10,000 pieces with tooling itemised separately, and find the crossing point for your own part.
When should I use sheet metal fabrication instead of CNC machining?
When the part is wide, thin, folded or shell-like, with flanges, vents, tabs or welded panels. Machining the same geometry from a billet wastes material and machine time. If the part is thick, prismatic, has deep pockets or needs precision bores, machining is still the better route.
What is the difference between a progressive die and a compound die?
A compound die performs several cutting operations in one stroke at a single station, which gives good positional accuracy on flat parts. A progressive die feeds a strip through multiple stations, each doing a different operation, and produces a finished part at the last station. Progressive dies cost more to build but suit high-volume automated production.
Who owns the stamping die after I pay for it?
Only if the purchase order says so. State ownership, storage location, identification, expected life, maintenance responsibility, whether the tool can be used for other customers, and that payment is tied to design approval and sample acceptance. Without the clause, moving production to another supplier usually means paying for the tool again.
Can one factory handle CNC, sheet metal and stamping for the same product?
Some can, but many subcontract the secondary processes. Ask which operations are in-house and who is accountable when a subcontracted finish fails. For mixed-process products it is often more reliable to source each process to a specialist and consolidate the finished parts into one inspected shipment.
Not sure which route your part belongs on? Send the drawing, a photo or even a rough sketch, plus your target quantity and destination. We will have vetted factories quote it both ways where it makes sense, and tell you honestly which process fits. Send your part and we will come back within 24 hours.