Quantity decides which processes are economically available before the drawing does. A four-step framework — volume, geometry, material, lead time — with a 10,000-unit cost comparison for injection molding, MIM, CNC and 3D printing.
You have a finished part design and a purchase order number. Now comes the question every hardware team faces: which manufacturing process should we use?
The answer depends less on the drawing than on the number in the order. Quantity determines which processes are even economically available — and in this guide we show you how to choose a manufacturing process by quantity in four steps, from 1–100 units to 10,000+ units.
The short answer: 1–100 units → 3D printing or CNC machining. 100–1,000 units → CNC machining. 1,000–10,000 units → bridge-tooled injection molding or metal injection molding (MIM). 10,000+ units → production steel-tooled injection molding or MIM. Complexity, material and lead time then narrow the choice further.
Why Quantity Is the First Question in Manufacturing
Every manufacturing process carries a different mix of tooling cost and unit cost. A hardened steel production mold costing tens of thousands of dollars is a rounding error across one million parts — and a deal-breaker at 500 units. 3D printing needs no tooling at all but carries a high per-part cost. CNC machining sits between the two: production-grade materials, no mold investment, and unit costs that stay flat no matter how many you order.
That is why "which process is best" is the wrong question. The right question is "how many do I need?" Once quantity is fixed, the number of economically viable processes usually shrinks to two or three.
The Four-Step Selection Framework
We use the same framework internally whenever a customer sends a drawing without a volume forecast. Answer these four questions in order and the process largely chooses itself:
- Quantity. Which volume band are you in — 1–100, 100–1,000, 1,000–10,000, or 10,000+?
- Complexity. Can a cutting tool reach every feature of the part?
- Material. Which alloy or resin does the design require?
- Lead time. When do you physically need the parts?
Step 1: Match Volume to the Process
| Volume band | Preferred processes | What changes at this volume | Typical lead time |
|---|---|---|---|
| 1–100 | 3D printing, CNC machining | No tooling — setup cost dominates | 3–5 days / 1–2 weeks |
| 100–1,000 | CNC machining (+ 3D printing) | Production-grade materials without mold investment | 1–2 weeks |
| 1,000–10,000 | Bridge-tooled injection molding or MIM | Bridge mold cost amortizes; unit cost falls sharply | 3–4 weeks |
| 10,000+ | Production steel-tooled injection molding or MIM | Higher mold investment, lowest unit cost | 8–10 weeks |
Read the bands as starting points, not verdicts. At exactly 10,000 units, a low-cost bridge mold can still beat a hardened steel mold on total cost — the tooling difference outweighs the per-part saving. A production steel mold starts paying for itself when annual demand clears roughly 50,000 units, the design is frozen, and the market is validated.
Step 2: Let Geometry Narrow the Field (CNC vs MIM)
Volume picks the process family; geometry picks the process. If your part is a simple block with drilled holes, CNC machining handles it quickly and cheaply — no tooling, production-grade materials, and a one-to-two-week lead time.
The calculus changes when geometry is complex: undercuts, internal channels, thin walls. An end mill cannot reach an internal channel. A three-piece assembly introduces tolerance buildup at every joint. MIM and injection molding form these features in a single shot.
- Metal parts: MIM handles 0.1–100 g parts with walls down to 0.2 mm, holding ±0.02 mm — think surgical jaws, lock cylinders and LiDAR mirrors.
- Plastic parts: injection molding reproduces the same complex geometry in ABS, PC, PEEK or medical-grade resins.
- Simple parts: if CNC can machine every feature in one setup, it usually wins on cost and speed.
Rule of thumb: if the drawing contains a feature no cutting tool can reach, the decision has already moved to molding — and the material decides which one.
Step 3: Match the Process to the Material
Material and process are locked together. You cannot sinter PEEK, and you do not injection-mold 17-4PH stainless steel. The material specification narrows your process list before you ever call a supplier.
- Stainless and specialty alloys (316L, 17-4PH, Ti-6Al-4V, Kovar): small, complex metal parts point to MIM, which sinters to 95–98% density — enough for medical and automotive requirements.
- Engineering and medical plastics (ABS, PC, PEEK): precision injection molding, with ±0.02 mm dimensional control as standard and ±0.01 mm inspection.
- Large parts or exotic alloys: machining or casting — processes with no practical size ceiling.
Do not reverse the order. Choosing the cheapest process and then bending the material around it is how you end up with a part that cannot pass the test it was designed for.
Step 4: Let Lead Time Compress the Options
When the date on the calendar is fixed, lead time filters the list again:
- 3–5 days: 3D printing — for iteration and urgent validation.
- 1–2 weeks: CNC machining.
- 3–4 weeks: bridge-tooled injection molding or MIM.
- 8–10 weeks: production steel tooling.
A clinical trial that needs 500 cleanroom-grade housings in 15 days cannot wait for a steel mold. That is when rapid-prototype injection molding — 50–1,000 units in 10–18 days — becomes the practical answer. Deadline pressure does not lower your quality bar; it simply eliminates the processes that cannot make the date.
What the Cost Comparison Looks Like at 10,000 Units
To see the framework in action, here is the full cost picture for an automotive sensor housing at 10,000 units. Figures are indicative and quoted per project.
| Metric | Production steel mold | Bridge mold (P20) | 3D printing | CNC machining |
|---|---|---|---|---|
| Tooling cost | Approx. $65,000 | Approx. $8,500 | $0 | $0 |
| Unit cost | Approx. $0.80 | Approx. $2.50 | Approx. $15.00 | Approx. $8.00 |
| Total cost (10,000 pcs) | Approx. $73,000 | Approx. $33,500 | Approx. $150,000 | Approx. $80,000 |
| Lead time | 8–10 weeks | 3–4 weeks | 3–5 days | 1–2 weeks |
Read the total column, not the unit column. The production mold's low unit cost looks unbeatable — until you add the tooling. At 10,000 units the bridge mold's total cost is roughly half that of the production mold. The honest comparison is always mold cost plus unit cost times quantity. For a deeper look at where the crossover sits, see our guide to bridge production economics and bridge mold versus production mold.
Frequently Asked Questions
What is the best manufacturing process for 100 units?
3D printing or CNC machining. Both need no tooling, so setup cost dominates. Choose 3D printing for 3–5 day iteration, or CNC machining when you need production-grade materials and tighter tolerances at a 1–2 week lead time.
What is the best manufacturing process for 1,000 units?
CNC machining is still viable, but bridge-tooled injection molding or MIM starts to pay off: a low-cost bridge mold amortizes across the batch and pulls unit cost down sharply against a machined part.
When should I use MIM instead of CNC?
Use MIM when the part is a small metal component (0.1–100 g) with complex geometry — undercuts, internal channels, walls down to 0.2 mm — and volume runs from a few hundred pieces upward. CNC remains the better choice for simple, larger parts in very small batches.
How much does an injection mold cost?
A bridge mold in pre-hardened P20 steel typically costs a fraction of a production mold and supports roughly 500–10,000 parts. A hardened steel production mold is a substantially larger investment, designed for hundreds of thousands to millions of cycles. Exact pricing depends on cavitation, part size and lead time.
What is bridge tooling?
Bridge tooling is a transitional, pre-hardened steel mold that fills the gap between prototyping and mass production. It delivers production-grade parts at 3–4 week lead times and unit costs far below machining or 3D printing at 10,000 pieces — without committing to a production mold.
How many units before injection molding is cost-effective?
From roughly 1,000 units with bridge tooling. Production steel tooling becomes cost-effective when annual demand clears about 50,000 units, the design is frozen, and market demand is validated.
Conclusion: The Right Process for Your Quantity
There is no universally "best" manufacturing process — only the best process for your quantity. Start with the number, let geometry and material close the field, and let the deadline make the final call. Get that order right and you stop overpaying for parts you do not need yet, and stop underbuilding parts you will need soon.
Not sure where your part lands? Send us your drawing and your volume forecast — we will map it through the four steps and show you the total cost at your quantity. Haoding Precision provides contract manufacturing for MIM, precision injection molding, CNC machining and 3D printing, with ISO-aligned quality control and ±0.01 mm inspection.
Send your drawing for a volume-based process review
Related reading: MIM vs CNC vs 3D printing for medical and automotive parts and precision plastic injection molding explained.