3D printing vs injection molding
Which is cheaper comes down to one number: how many you need. Why printing wins small runs and molding wins big ones, how to find the crossover for your own part, the bridge processes in between, and what to change before you switch.
The short answer
3D printing has no tooling: the hundredth part costs about the same as the first. Molding needs a mold up front, then each part costs a fraction of a printed one. So printing wins at low quantities and molding wins at high ones.
Where they cross depends on the part. For small and medium plastic parts it's often somewhere between a few hundred and a few thousand units. Big, thick or complex parts move it, and the calculator below finds it for a part of your size.
Find the crossover for your part
Drag the quantity slider, or click across the chart. Each line is one process's cost per part, and the markers show where the cheapest option changes.
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Why the lines cross
Every process's cost per part has two pieces: a share of the one-time setup, and the cost of making each part.
- Printing has almost no setup, but each part takes machine time and material, so its line is nearly flat.
- Molding starts with the cost of the mold, spread over every part you make. At 100 parts that share is huge; at 10,000 it's small, and a molded part takes seconds to make.
Plot both against quantity and the molding line falls until it passes under printing. That point is the crossover.
The middle ground: bridge processes
Between a desktop printer and a steel mold, there are options that make sense for a few dozen to a few thousand parts:
- Industrial printing (SLA, SLS, MJF). No tooling, better surfaces and strength than desktop printing, and a higher cost per part.
- Urethane casting. Parts cast in silicone molds made from a master. Each silicone mold makes roughly twenty parts, with surfaces close to molded.
- CNC machining. Strong, accurate parts from solid plastic or metal, with a small setup cost and a high cost per part.
- Aluminum molds. Real injection molding with a cheaper, shorter-lived tool, often a sensible first production run.
A common path is print, then bridge, then mold, moving up as orders prove demand. Pilotrun shows that path for each of your parts, with the quantity where each step starts to pay off.
What changes when a printed part becomes a molded part
A design that prints well doesn't always mold well. Check these before asking for mold quotes:
- Draft. Walls along the direction the mold opens need a slight taper (often 1–2°) so the part releases. On tall parts that taper changes dimensions, so check anything that has to fit.
- Even walls. Thick sections cool slowly and sink. Core them out or use ribs, which can change how the part looks.
- Undercuts. Clips, side holes and overhangs need side actions or lifters, which add tool cost.
- Solid, not infill. A molded part is solid, so it's heavier and stiffer than a print at low infill. Snap fits and hinges tuned on prints may behave differently.
- Texture. Print textures don't carry over; a mold texture has to be specified.
Pilotrun's Part lab checks walls, draft and undercuts on your 3D file and lists what to fix before tooling.
Before you switch: a checklist
- Know your real volume: first order and the next twelve months.
- Freeze the design. Changing a mold costs far more than changing a print.
- Fix draft, wall thickness and undercuts, or accept their cost.
- Get quotes for an aluminum tool and a steel tool, at two or three quantities.
- Compare the total cost of the run, tooling included, not just the price per part.
If molding only wins well above your volume, keep printing and spend the difference on the product. What a mold costs, and why quotes vary.