AN-064 Build guides · cluster
Injection Molding Cost: Parts, Tooling, and the Volume Curve
Injection molding cost is a one-time mold plus a per-part price. How each is built up, a worked example, and where molding beats 3D printing on volume.
by the HardwareMap editors4 min read
Contents
Injection molding cost has two parts: a one-time mold, and a price per part that is mostly machine time and resin. Molds start around $1,500est for a simple aluminum tool. Parts cost cents to dollars. The volume decides which number dominates. This note, part of how to start a hardware company, builds both numbers for a real part.
What injection molding cost is made of
Per-part cost, fully loaded, is:
part cost = resin + machine time + secondary work + molder margin + (mold cost / lifetime volume)
- Resin. Xometry lists commodity resins at $0.90 per pound for polypropylene, $1.30 for ABS and $2.30 for polycarbonateest (Xometry). Add the runner and startup scrap.
- Machine time. The press hourly rate divided by parts per hour. Xometry puts cycle time at roughly 60 percent of final part cost, and cooling at about 80 percent of the cycle. Thick walls cool slowly, so wall thickness is a cost decision.
- Secondary work. Degating, inspection, inserts, pad printing, packing.
- Margin. The molder's overhead and profit.
- Tooling amortization. The mold, spread over every part it will make. At low volume this is the whole story. See injection molding tooling cost for what sets the mold price.
The press itself is not your cost unless you buy one. Formlabs puts industrial injection molding machines at $50,000 to $200,000 or moreest (Formlabs). Startups rent press time through a molder.
Worked example: an enclosure half
The part is the top half of the sensor enclosure from our bill of materials example: ABS, 25 g, walls 2 mm, no undercuts, light texture. Assumptions are stated so you can swap in your own quotes.
The resin is 10 to 17 percent of the piece price. Machine time is most of the rest. The second cavity halves machine time per part, which is why high-volume tools have more cavities.
The injection molding cost volume curve
Add the mold, divided by volume, to the piece price:
Three readings. First, below 1,000 units the mold is almost the entire cost, so every dollar off the tool matters more than every cent off the part. Second, on paper the steel tool only wins past about 47,000 parts. Third, that crossover arrives sooner in practice: Protolabs gives about 10,000 parts as a rule of thumb for aluminum tooling, though often much higher depending on material and geometry (Protolabs). If your aluminum tool needs replacing, add a second mold to that column.
Formlabs publishes a similar curve for a small enclosure, from $4 per part at 100 units with a printed mold to $1.70 at 100,000est (Formlabs). The shape is the same in every version of this table: steep, then flat.
Where molding beats printing
Below a few hundred units, 3D printing has no tooling line at all. A printed enclosure half might cost $5 to $15est depending on process and finish, which beats the 500-unit aluminum number above. The design for additive manufacturing note covers designing for that route. The usual path:
- Prototype and EVT: printed parts. No tooling.
- DVT and pilot: aluminum or bridge tooling, a few thousand parts.
- Production: steel, multi-cavity, once orders support the forecast.
Formlabs, in the index, sells resin printers that also make low-run printed molds for benchtop presses, a middle option for runs of tens to hundreds.
What drives injection molding cost up
Most of the cost is set in CAD, before any quote. Protolabs' design guidance is the cheapest review you will get (design guidelines):
- Wall thickness. Protolabs lists ABS at 0.045 to 0.140 in. Thicker walls cool slower and sink. Keep walls uniform; ribs and bosses at 40 to 60 percent of the adjacent wall (Protolabs on uniform walls).
- Draft. About 1 degree per inch of depth as a rule of thumb, more for textured faces.
- Undercuts. Each one needs a side action or a hand-loaded insert. Both add mold cost, and inserts add cycle time.
- Tolerances and cosmetics. Tight tolerances and high-gloss finishes mean more tool work and more rejects.
The design for manufacturing checklist covers the rest, and hardware unit economics shows where the molded part lands in your margin.
How to read a molding quote
Quotes arrive as two numbers, and the comparison breaks if the terms behind them differ. Before comparing molders, check each quote states:
- Mold class or rated life in shots, so an aluminum tool is not compared with a steel one as if equal.
- Cavities, and whether the piece price assumes all of them run.
- Resin grade and color, by manufacturer and grade, not just "ABS".
- Sample rounds: how many T1 sample iterations and tool tweaks are included before you pay for changes.
- Mold ownership and transfer: whether you own the tool and can move it to another molder.
- Minimum run quantity and setup charge, which raise the effective piece price on small orders.
Continue with Plastic Injection Molding Cost Calculator: The Formula and a Worked Example.
Frequently asked questions
How much does plastic injection molding cost?
Two numbers: the mold and the part. Published starting points for molds run from about $1,500 for a simple aluminum tool to $100,000 or more for a complex multi-cavity steel tool. Small parts then cost cents to a few dollars each, mostly driven by machine time and resin. Divide the mold by your volume and add it to the part price for the real number.
At what volume is injection molding cheaper than 3D printing?
It depends on part size and the mold, but for small enclosure parts the crossover usually falls in the hundreds to low thousands of units. Below that, printing avoids the tooling bill entirely. Run the arithmetic for your own part: printed price per unit against mold cost divided by volume plus the molded piece price. The table on this page shows the method.
What makes a molded part expensive?
Thick walls, which lengthen cooling and so the cycle. Undercuts that need side actions in the mold. Tight tolerances and cosmetic surface finishes. Large parts that need a bigger press. Engineering resins like PEEK instead of commodity ABS or polypropylene. Most of these are design choices, which is why design for manufacturing review before tooling saves more money than negotiating the quote.
How can I get low cost injection molding for a startup?
Start with an aluminum or bridge tool sized for your first few thousand parts, not a production steel tool. Combine small parts into a family mold where cosmetics allow. Design out undercuts. Keep walls uniform. For runs of a few hundred, consider 3D printed molds on an in-house press. Then move to steel only when the volume forecast is backed by orders.
HardwareMap catalogues the startups that took their parts from printer to press. Building one? Submit it and get a part number.
Building one?
Submit it to the index and get a part number. Every entry is reviewed by hand.