Volume matters when comparing 3D printing and injection molding, but it is only one input. Geometry, material, design maturity, tooling and supplier terms can change the answer. A useful comparison starts with quotes for the same requirements.
The earlier version of this guide included illustrative prices and broad quantity thresholds. Those figures have been removed because they are not current project quotes or a reliable rule for every part.
Separate fixed and per-unit costs
For each supplier proposal, identify costs that occur once and costs that repeat with each unit or order. Tooling, setup, samples, finishing and inspection may be listed differently between suppliers.
A simple comparison can use:
Total cost = fixed costs + (quantity × per-unit cost).
If the per-unit costs stay constant, the mathematical crossover between two options is the difference in fixed costs divided by the per-unit saving. If there is no per-unit saving, that simplified model has no payback quantity.
Use actual quoted inputs. Price breaks, minimum orders and changes to the manufacturing approach can make the relationship different from that simple formula.
Include what the unit price leaves out
- Design work: does the part need changes for the proposed process?
- Samples and revisions: how are sample approval, tooling changes and repeat samples priced?
- Finishing and assembly: are secondary operations included?
- Inspection: which requirements will be checked, and what records are supplied?
- Order terms: what is the minimum quantity, payment schedule and treatment of rejected parts?
- Logistics: include packaging, freight and any applicable import costs in the comparison.
Ask both suppliers to quote the same design revision and requirements. A cheaper part with a different material or finish may not be a comparable offer.
Account for design changes and inventory
A design that is still changing carries a different commitment from a stable repeat order. Ask what a revision would mean for files, tooling, samples and stock already made.
Likewise, compare the quantity you need with the quantity you must buy. Inventory can tie up cash and become obsolete after a revision. Demand assumptions should be visible rather than hidden in the cost-per-part calculation.
Compare the schedule and geometry too
The relevant date is when acceptable parts are available for their intended use, including design work, samples and review. Ask suppliers to explain dependencies rather than relying on a generic lead-time range.
A process change may also require different geometry, split components or additional assembly. Review those changes before treating two fabrication methods as interchangeable.
Prepare the design for a fair quote
9OneFour can help with manufacturing preparation, CAD revisions and supplier handoff. General production printing and injection molding are not advertised as in-house services. The small-batch handoff page explains the current scope.