Short answer: for one-offs, prototypes, and small runs, 3D printing is usually faster and cheaper, because there's no mould to pay for. Injection moulding wins once you need thousands of identical parts, because each part then costs very little.
How they work
Injection moulding forces melted plastic into a steel or aluminum mould under high pressure. Once the mould exists, a machine can make a part every few seconds to a minute. But the mould has to be designed and machined first, and that's where most of the cost and waiting is.
3D printing builds each part layer by layer straight from a 3D file. There's no mould and no setup beyond preparing the file, so the first part costs about the same as the hundredth.
Side by side
| 3D printing | Injection moulding | |
|---|---|---|
| Upfront cost | None: no mould | A mould, typically from a few thousand dollars for a simple aluminum mould to tens of thousands for a steel production mould |
| Cost per part | Higher, and about the same for every part | Very low once the mould is paid for |
| Time to first part | Hours to a few days | Usually several weeks while the mould is made |
| Changing the design | Edit the file and print again | Change or remake the mould, which costs time and money |
| Best quantity | One to a few hundred (sometimes more) | Thousands and up |
| Shapes | Almost anything, including hollow and interlocking parts | Must release from the mould: draft angles, even walls, no trapped shapes |
| Surface finish | Layer lines on most methods; can be sanded, smoothed, or painted | Smooth and consistent straight from the mould |
| Materials | Many plastics, resins, nylons, and metals | The widest choice of production plastics |
Why 3D printing wins for small runs
- No mould to pay for. With injection moulding, the mould cost is spread across every part. Spread over 50 parts, a $5,000 mould adds $100 to each one. A 3D printed part carries no such cost.
- Parts in days, not weeks. You can hold a printed part within a day or two, instead of waiting weeks for a mould to be cut.
- Change your design for free. Found a problem after the first batch? Change the file and print the next batch. With a mould, changes can mean recutting steel.
- Shapes a mould can't make. Hollow parts, internal channels, lattices, and parts that print already assembled are all possible.
- Make only what you need. Print in small batches as orders come in, instead of paying for thousands of parts up front and storing them.
- Every part can be different. Personalised names, custom fits, and one-off variations cost nothing extra.
When injection moulding is the better choice
- You need thousands of identical parts, so the mould cost is shared across many of them.
- The part needs a smooth, uniform finish straight off the machine, or a specific production plastic.
- The design is final and won't change.
- You need the lowest possible cost per part for a product you'll make for years.
Finding the break-even point
A simple way to compare for your own part:
- Get a 3D printing quote for your part (the price per part).
- Get an injection moulding quote: the mould cost, plus the price per part.
- The break-even quantity is roughly the mould cost ÷ (3D printing price per part − moulding price per part).
For example, if printing costs $8 a part, moulding costs $0.50 a part, and the mould costs $6,000, the break-even point is about 6,000 ÷ 7.50 = 800 parts. Below that, 3D printing is cheaper. Above it, moulding pays off. Every part is different: small, simple parts favour moulding sooner, while large or complex parts can favour printing into the thousands.
The in-between options
- Print first, mould later. Many products start life 3D printed. Selling printed parts tests the design and the demand before you commit to a mould.
- Casting from a 3D printed master. For runs of roughly 10 to a few hundred parts, a shop can 3D print a master part, make a silicone mould from it, and cast parts in urethane resin. It costs far less than a machined mould and gives a smooth, moulded finish. Look for shops offering mould making and casting.
- Industrial powder printing. SLS and MJF printers make strong nylon parts in batches, and are often used for production runs in the hundreds or low thousands.
Find a shop near you
Ready to price your project? Find 3D printing shops near you, or ask a local shop to quote both a printed run and a cast run so you can compare.