How much does injection molding cost?

Injection molding has two separate costs, and understanding both is the key to deciding when to use it:

1. The mold (tooling): a one-time, up-front cost.
2. The part price: what each part costs once the mold exists.

New to molding? Start with What is injection molding?

1. The mold: what drives the price

• Part size: bigger parts need bigger, heavier molds.
• Complexity: each undercut (a feature that stops the part coming straight out) needs a moving mechanism in the mold (a slide or lifter), and each one adds cost.
• Number of cavities: a mold that makes 4 parts per shot (a "1×4") costs more than one that makes 1, but each part is cheaper.
• Steel type: harder steel lasts longer and costs more. Aluminum is cheapest. (See Aluminum vs steel molds.)
• Surface finish: high polish (for glossy or clear parts) or texture adds cost.
• Hot runner vs cold runner: a hot runner system wastes less plastic but makes the mold more expensive.

Rough feel (not a quote): a small, simple single-cavity steel mold is often a few thousand US dollars; a larger enclosure mold with several slides can be over ten thousand; multi-cavity and hot-runner molds more again. Always get several quotes.

2. The part price: what drives it

• Material: how much plastic, and what type. Engineering plastics cost more than ABS or PP.
• Cycle time: how many seconds each shot takes. Thick parts cool slowly, so they take longer and cost more.
• Machine size: big parts need big, more expensive machines.
• Labour and secondary steps: assembly, painting, printing, packing.

For small parts at volume, the part price is often cents to a few dollars.

When does molding become cheaper?

Here's a simple way to compare. Suppose (made-up numbers, just to show the method):

• Mold: $5,000, then parts at $0.50 each
• Urethane casting: no mold, but $15 per part

For 100 parts: molding = $5,000 + $50 = $5,050; casting = $1,500. Casting wins. For 1,000 parts: molding = $5,000 + $500 = $5,500; casting = $15,000. Molding wins.

The break-even point is where the lines cross; here, around 350 parts. Do this sum with your real quotes.

Hidden costs first-timers miss

• Mold modifications after the first trial (T1). Budget for at least one round.
• Samples and shipping of samples.
• Texture and colour matching.
• Second molds if you later need more capacity or a different colour setup.
• Design changes after the mold is made. These are the most expensive of all.

How to lower the cost

• Simplify the design to remove undercuts.
• Start with fewer cavities (1 or 2).
• Use aluminum or softer steel for a first run of a few thousand.
• Combine small parts into one family mold (several different parts in one tool). It's cheaper up front, though harder to perfect.
• Get a DFM review before quoting, so the design is right the first time.

Next steps

• How to get an injection mold made in China
• Design rules for injection-molded parts
• Get quotes from mold makers