3D printing vs injection molding usually gets answered with a number. Someone says the crossover is a few hundred parts, or a few thousand, and everyone writes it down. That number is almost always wrong, because the crossover is not a property of the two processes, it is a property of your specific part.
What is stable is the shape of the two cost curves and the list of things that move where they intersect. Get those right and you can work out your own crossover in about ten minutes, which is more useful than any figure we could print here.
The Two Cost Curves
Injection moulding front loads its cost into a mould and then makes parts very cheaply. Additive manufacturing has no tooling cost at all and makes every part for roughly the same price as the one before it. That is the entire economic difference, and everything else follows from it.
Draw it and moulding is a steep initial step followed by a nearly flat line, while printing is a straight line from the origin with a shallower slope than moulding has at low quantity. They cross once. Below the crossing, printing is cheaper because you never paid for a mould. Above it, moulding is cheaper because the mould has been paid off and the marginal part is very cheap.
| Factor | Laser sintered 3D printing | Injection moulding |
|---|---|---|
| Up front tooling | None | A mould that must be designed, cut and proved before the first good part |
| Cost per part | Roughly flat, set by the build volume the part occupies | Falls steeply with quantity as the mould cost spreads |
| Lead time to first part | Days | Weeks to months, dominated by the mould |
| Cost of a design change | The cost of reprinting | A mould modification, and sometimes a new mould |
| Geometry | Internal channels, lattices and consolidated assemblies are effectively free | Must draft, must eject, must fill, and undercuts need side actions |
| Minimum sensible quantity | One | However many it takes to justify the mould |
| Cost driver to watch | Part volume and build packing | Mould complexity, cavity count and cycle time |
Why the Crossover Is Not a Fixed Number
The intersection moves because both curves move, and they move independently for every part.
On the moulding side the step height varies enormously. A simple single cavity mould in aluminium for a small part is a different order of investment from a multi cavity hardened steel tool with side actions and hot runners. Part size, undercuts, cavity count, tolerance and expected tool life all change it, and any of them can move the crossover by a factor of several.
On the printing side the slope varies with how the part packs a build. Sintering charges by the build volume a part occupies, so a compact part that nests densely is far cheaper per unit than a sprawling one of the same mass. Two parts weighing the same can print at very different prices.
And the quantity itself is rarely a single number. Annual volume, total programme volume and order size are three different figures, and using the wrong one is the most common mistake in this calculation. A mould amortised over five years of production is a different proposition from one amortised over a single order.
Work Out Your Own Crossover
The calculation is simple arithmetic once you have four numbers, and any moulder and any printing supplier can give you them for your actual part.
Take the total mould cost including design, manufacture and sampling. Take the moulded price per part at the quantity you would actually order. Take the printed price per part. Then the crossover quantity is the mould cost divided by the difference between the printed price and the moulded price. Below that quantity printing costs less in total, above it moulding does.
Two adjustments make the answer honest. Add the cost of the design changes you expect, because a mould modification is a real cost that printing does not have, and early production usually finds something. And decide the time horizon, because a crossover computed on lifetime volume can look very different from one computed on the next twelve months, and the money is spent now either way.
Lead Time Is Often the Real Decision
Cost gets the attention and lead time frequently makes the call. Printed parts arrive in days because there is nothing to build first. Moulded parts arrive after the mould does, and the mould takes weeks at best.
That gap has a value that never appears in the part price. A line held up waiting for tooling, a product launch that slips a quarter, a recall fix that cannot wait: in all of those the printed part can be more expensive per unit and still be the cheaper decision by a wide margin.
It also creates a middle path that is often the right answer. Print the first production quantities while the mould is being built, so the product ships on schedule and the design has a chance to be corrected before it is cut into steel. That is bridge production, and it is one of the applications our 3D printing services for the molding industry exist to support, alongside printed casting moulds and over-moulded parts.
Design Freedom Changes What You Are Comparing
The cost comparison quietly assumes both processes make the same part, and often they cannot. Moulding imposes draft angles, uniform walls, ejection access and no undercuts without side actions. Sintering imposes almost none of that, because there is no mould to open and the surrounding powder supports the part, and the design rules that do apply are standardised in ISO/ASTM 52911-2, the design standard for laser-based powder bed fusion of polymers.
That lets a printed design consolidate what would otherwise be several moulded components plus fasteners and assembly labour. When that happens the honest comparison is not printed part against moulded part, it is printed part against moulded parts plus hardware plus assembly time plus the inventory of all those line items. Crossovers calculated on a single component frequently miss this and favour moulding wrongly.
It also runs the other way. If the part is a simple moulded shape with no consolidation opportunity, high volume and loose tolerances, moulding will win decisively and no amount of design freedom changes that. Our design guidelines for SLS set out what the printed side can actually hold.
A Practical Way to Choose
Print when the quantity is low, the design is not frozen, the lead time matters more than the unit price, the geometry consolidates an assembly, or the part is a tool, fixture or spare rather than a product.
Mould when the quantity is high and committed, the design is stable, the geometry is mouldable without heroics, and the unit price genuinely dominates the total cost of the programme.
Do both when the schedule and the volume disagree, which is more common than either camp admits. Bridge production is not a compromise, it is the correct answer to a real timing problem.
We are Anubis 3D Industrial Solutions. We design and manufacture end-of-arm tooling and produce parts by selective laser sintering in polyamide at our facility in Mississauga, Ontario. We do not injection mould, so when the answer is a mould we will say so, and when it is bridge production or printed tooling for the moulding process itself, that is work we do, including the end-of-arm tooling that unloads the moulding machine.
Printing and Moulding Questions
At what quantity does injection molding become cheaper than 3D printing?
There is no universal number, because the mould cost varies by orders of magnitude between a simple aluminium tool and a multi cavity hardened steel one. Divide the total mould cost by the per part saving moulding gives you over printing, and that is your crossover quantity for that specific part.
Why is 3D printing cost per part flat?
Because there is no tooling to amortise. Sintering charges essentially by the build volume a part occupies, so the hundredth part costs about what the first one did. Moulding is the opposite: a large fixed cost up front and a very low marginal cost afterwards.
Can 3D printing replace injection molding?
For low and medium volumes, parts with changing designs, consolidated assemblies and anything needed quickly, yes. For high volume stable products with simple mouldable geometry, no, and moulding will remain substantially cheaper per part.
What is bridge production?
Printing production parts while the injection mould is being built, so the product can ship on schedule and the design can still be corrected before it is cut into steel. It is the usual answer when the volume argues for moulding but the timing does not allow it.
Want the Crossover Run on Your Part?
Send us the part, the quantity and when you need it, and our team will give you a printed price to put against your moulding quote, and tell you honestly which side of the crossover you are on.
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