What is the main advantage of plastic injection molding over additive manufacturing?

The short answer

One number carries the whole argument

Every other difference between the two processes is downstream of a single fact: injection molding produces a part in seconds and additive manufacturing produces one in hours. Molding pushes molten resin into a steel cavity at 60 to 150 MPa and the part is solid within 15 to 60 seconds. A printer deposits or fuses material layer by layer, so the same part takes 30 minutes to 12 hours, and that time is what the customer pays for. A moulding cell runs 500 to 5,000 parts an hour once the tool is qualified; a print farm scales only by buying more printers.

That is why the per-part price of a moulded component falls year on year as the tool amortises, while the per-part price of a printed component stays almost flat whether you order 50 or 5,000. The two cost curves are shaped differently, and the crossover between them is the only decision that really matters.

Where the money actually goes

It helps to separate the four cost lines, because three of them behave in opposite directions.

• Tooling. A prototype aluminium tool can start near USD 1,500 to 4,000 for a simple single-cavity part. Production tooling in hardened steel with multiple cavities, hot runners and optimised cooling runs USD 8,000 to 40,000, and multi-shot or over-moulded tools reach USD 60,000 to 150,000. Lead time is 2 to 4 weeks for aluminium and 4 to 8 weeks for hardened steel.
• Material. This is where the gap is widest and least discussed. Moulding compound is bought as pellets by the tonne. Filament, resin and powder for additive processes cost roughly 8 to 15 times more per kilogram for comparable engineering polymers, and support material is additional waste.
• Cycle time. At 15 to 60 seconds per shot, one machine produces tens of thousands of parts a week. A printer needs days of continuous running for the same quantity, and someone has to load, unload and post-process each batch.
• Secondary operations. A well-designed moulding usually needs none. A printed part almost always needs support removal, and often sanding, filling, priming or dyeing before it looks like a product.

Material cost is where the gap is widest

Buyers comparing quotations often attribute the price difference to tooling alone, and they are wrong by a wide margin. Tooling is a one-time figure that is divided by the annual volume. Material is a recurring figure that is paid on every single part. When the feedstock costs 8 to 15 times as much per kilogram and a meaningful share of it becomes support structure or failed builds, the material line alone can exceed the entire moulded part price. That is why the crossover arrives earlier than most first-time buyers expect on parts with real mass in them, and later than expected on thin, low-mass parts where the print uses very little material.

Where the gap shows up in real numbers

How to calculate your own break-even

The arithmetic is simple enough to do before requesting a quotation, and it is worth doing because the answer changes the conversation.

1. Get the printed part price. Ask for a quote at the real quantity, not a sample price. Add support removal and any finishing you would actually need.
2. Estimate the moulded part price. A supplier can quote a per-part price for the volume band you expect, with tooling shown separately.
3. Subtract, then divide. Break-even quantity equals tooling cost divided by the difference between the two unit prices. An USD 8,000 tool against a USD 4.00 printed part and a USD 0.50 moulded part gives 8,000 divided by 3.50, or about 2,300 pieces.
4. Check the tooling against the program. If the expected lifetime volume is below the break-even, the tool never pays for itself. If it is three or four times the break-even, the tooling decision is already made.

Two adjustments are worth making to the raw result. First, add shipping, packaging and inventory carry to the printed side, because printed parts are usually ordered in small batches and shipped as such. Second, treat the break-even as a range rather than a point, because it moves with part mass, cavity count and the finishing requirement.

Where additive manufacturing still wins, and should

• Anything before the design is frozen. A printed prototype that exposes a design error costs a fraction of a mould that has to be modified or replaced. During development the cheapest process is the one that lets you change your mind.
• Volumes under a few hundred. Spare parts programs, clinical trials, custom fixtures and trade-show units rarely justify a tool, and a print holds no inventory.
• Geometry a mould cannot open. Internal channels, lattices and organic load paths with no parting line are the clear case where a printer is not a compromise but the only route.
• Bridge production. While a tool is being cut, printed parts can supply early builds and testing so that a launch is not delayed by tooling lead time.

Getting a costed comparison rather than a rule of thumb

A useful quotation shows the break-even instead of asserting a volume. Send the part or the STEP file with the annual volume and expected program life, the resin family or the performance requirement, the cosmetic surfaces, and any tolerance that matters to assembly. We mould engineering resins and can set the print alternatives beside the moulded price at two or three volumes so that the tooling decision is visible on the page. See plastic injection molding for the process and its design rules, FDM 3D printing and SLS 3D printing for the additive routes we quote alongside it.