Process selection
Injection molding vs 3D printing
One forms a part by injecting molten plastic into a machined tool, the other builds the same geometry one thin layer at a time from a 3D model with no tool at all. The real question is not which process is more advanced, it is where your volume, material and tolerance needs cross the line that makes a tool worth paying for, and that line moves further for printing than most buyers expect.
Injection molding fills a machined cavity in seconds and repeats it, unchanged, for the life of the tool. 3D printing builds the same geometry one thin layer at a time with no tool at all, trading the tooling cost and the cycle-time speed of molding for a build time that scales with the part's height, not with how many are ordered.
What injection molding is
Molten thermoplastic is injected under pressure into a machined steel or aluminum tool. The tool closes, the shot fills and cools, the tool opens, the part ejects. Every part after the first comes out of the same cavity, which is what makes molding a repeat-production process rather than a one-off one.
- The tool is a one-time cost, paid before part one exists. A production tool runs 4 to 8 weeks to design, cut and sample here, by tool class and complexity, and that cost is the same whether the run is 500 parts or 500,000.
- A repeat order is fast because nothing has to be built again. Off existing tooling, a reorder runs about 3 working days, material and cycle time only.
- Tolerance is set by the tool, then repeats exactly. ±0.05 mm on critical, CMM-verified features and ±0.1 mm typical, to DIN 16742, and part 100,000 holds the same number as part one.
- Material choice is a production resin, not a printable stand-in for one. ABS, PC, PC-ABS, PP, PA6, PA66, glass-filled PA, POM, PBT, PMMA, TPE and TPU run in-house, across a 25 to 3,000 ton press range with an 8 kg shot capacity in-house and to 15 kg through partner presses.
What 3D printing is
An additive process builds the same geometry one thin layer at a time, straight from a 3D model, with no tool, no fixturing, and nothing to sample before the first part exists. That removes the cost item that dominates molding, at the price of a part that is built up rather than formed in one shot, which shows up in both its strength and its dimensional behaviour.
- No tool means no wait before part one. Turnaround here runs 2 to 7 working days on FDM and SLA, 5 to 10 on the SLS and MJF powder processes, and 2 to 4 weeks on DMLS metal, depending on which process the part needs rather than a tool that has to be cut first.
- Layer construction makes the part anisotropic. It is weaker across layers than along them, and its accuracy is not one fixed number: it varies with process, material, part size and orientation in the build, and deviation generally scales with dimension rather than holding to a single tolerance across the whole part.
- Material and process are chosen together, not separately. PLA, ABS, ASA, PETG, PC, nylon (PA11, PA12), glass-filled PA and TPU on the polymer processes, plus AlSi10Mg aluminum, 316L stainless and Ti-6Al-4V on DMLS metal; a material is only available if the process that prints it is available.
- "3D printing accuracy" is not one answer. Layer resolution runs 0.1 to 0.3 mm on FDM, 25 to 100 microns on SLA, 80 to 120 microns on SLS and MJF, and 20 to 60 microns on DMLS, five genuinely different processes under one name.
Injection molding against 3D printing
| Injection molding | 3D printing | |
|---|---|---|
| Upfront cost | Tool: 4 to 8 weeks, paid once | None; no tool, no fixturing |
| Lead time, first part | 4 to 8 weeks (new tool) | 2 to 7 working days FDM/SLA; 5 to 10 SLS/MJF; 2 to 4 weeks DMLS |
| Lead time, repeat order | 3 working days off existing tooling | Same as the first order; no tool to reuse |
| Tightest achievable accuracy | ±0.05 mm critical, CMM-verified, repeats every part | Varies by process and scales with dimension, not a fixed tolerance across the part |
| Material family | Thermoplastic and elastomer resins | Polymer or metal depending on process; material and process chosen together |
| Part strength | Isotropic, the same in every direction | Anisotropic, weaker across layers than along them |
| Cost driver | Tool amortization, then material and seconds of cycle time | Machine time and material per part, at every volume |
Which one, for which part
- A single prototype, or a design still changing, print it. There is no tool to pay for and no risk of paying to cut steel around a shape that changes again next week.
- A few hundred parts and up, in a thermoplastic or elastomer, with the geometry fixed, mold it. Per-part cost drops hard once the tool is paid off, and printing's per-part cost does not fall with volume the way molding's does.
- A metal part needing real alloy properties at low volume, DMLS is the only one of the two that prints metal at all, though at 2 to 4 weeks and a materially higher cost per part than polymer printing.
- A part that must carry identical strength in every direction, mold it. Layer construction gives a printed part a genuine weak axis that a molded part does not have.
Where the crossover sits
The tool is the whole reason molding costs more up front and less per part later, so the crossover volume is wherever the tool cost, divided across the run, drops below the price of printing the same part one at a time. That number moves more for printing than it does for machining, because 3D printing itself spans a far wider cost range than machining does: an FDM prototype in PLA and a DMLS titanium part share almost nothing in per-part cost, so there is no single crossover volume that applies to "3D printing" as one category. Send the part, the material, and the expected volume, and the quote states which of the two, or which specific printing process, actually wins at that number, rather than assuming one answer covers every printed part.
Our status
Trumould runs both in-house: 25 to 3,000 ton presses for molding, and FDM, SLA, SLS, MJF and DMLS printing on the same quoting desk, so a part can move from a printed prototype to a molded production run without changing supplier or losing the design history in between.
More
Related guides
Injection molding capabilities
Tooling options, materials, tolerances, finishes, and lead times.
3D printing capabilities
Processes, materials by process, achievable tolerances, and design rules.
Injection molding vs CNC machining
Tooling cost, lead time, and tolerance, and where the crossover volume actually sits.
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