3D printing & additive manufacturing
Polymers dominate 3D printing — most printed parts are plastic. Building a part layer by layer needs no mould, which makes it unbeatable for prototypes, custom shapes and low volumes. Here is how it actually works, what to print in, and the one property fact that catches people out.
On the numbers: bulk-polymer values below link to their cited database entries. The print-specific figures — nozzle temperatures, layer-adhesion knock-downs — are typical engineering ranges, because a printed part's real properties depend heavily on the machine, the settings and the build orientation. That dependence is the whole point, not a footnote.
Almost all polymer printing is one of three ideas: melt a filament, cure a liquid, or fuse a powder.
FDM / FFF
A thermoplastic filament is melted in a hot nozzle and laid down road by road, layer by layer, onto the growing part.
- Cheapest hardware and material
- Widest material range, from PLA to PEEK
- Large build volumes are affordable
- Visible layer lines; rougher surface
- Strongly anisotropic — weak between layers
- Overhangs need support structures
Typical: Prototypes, jigs and fixtures, low-volume functional parts
SLA / DLP / MSLA
A liquid photopolymer resin is cured by UV light one thin layer at a time — a laser (SLA), a projector (DLP) or an LCD mask (MSLA).
- Finest detail and smoothest surface
- Nearly isotropic — layers chemically bond
- Excellent for small, intricate parts
- Often brittle; many resins keep curing and embrittle in UV
- Uncured resin is messy and an irritant — needs wash + post-cure
- Smaller build volumes; thermoset, so no remelting
Typical: Dental and jewellery masters, miniatures, fine detail
SLS / MJF
A bed of polymer powder is fused selectively — a laser (SLS) or a fusing agent plus infrared (MJF) — then a fresh layer is spread on top.
- No support needed — the powder bed holds the part
- Strong, functional parts; the most isotropic of the three
- Nests many parts in one build
- Grainy, matte surface finish
- Higher machine and material cost
- Material choice is narrow — PA12 dominates
Typical: End-use functional parts, complex assemblies, low-volume production
The common printing polymers, from the easiest to the most demanding. Where we hold cited bulk-property data, the row links to it.
| Material | Process | Print temp | What it's like | Cited data |
|---|---|---|---|---|
| PLA | FDM | 190–220 °C | Easiest to print, stiff but brittle, biodegradable — but softens near 60 °C, so not for hot or load-bearing use. | PLA data → |
| PETG | FDM | 230–250 °C | The tough all-rounder: good chemical and moisture resistance, less brittle than PLA, easy enough to print. | PETG data → |
| ABS | FDM | 230–250 °C | Tough and heat-resistant, but warps badly without an enclosure and gives off styrene fumes. | ABS data → |
| ASA | FDM | 240–260 °C | ABS with UV and weather resistance — the go-to for outdoor parts. | — |
| Nylon (PA) | FDM · SLS | 250–280 °C | Tough, wear- and chemical-resistant — but hygroscopic, so it must be dried before printing. | Nylon (PA) data → |
| TPU | FDM | 220–240 °C | A flexible elastomer: rubbery, abrasion-resistant, prints slowly. | TPU data → |
| PC | FDM | 260–310 °C | Strong, impact- and heat-resistant; needs an enclosure and drying. | PC data → |
| PEEK / PEKK | FDM | 360–400 °C | The high-performance ceiling: strength, heat and chemical resistance — needs a 400 °C hotend and a heated chamber. | PEEK / PEKK data → |
| PEI (Ultem) | FDM | 350–380 °C | Flame-retardant, high-temperature engineering thermoplastic used in aerospace interiors. | PEI (Ultem) data → |
| Photopolymer resin | SLA/DLP | UV-cured | A thermoset — grades run from stiff-and-brittle 'standard' to tough, flexible, castable, high-temp and biocompatible. | — |
| PA12 powder | SLS/MJF | Laser-sintered | The workhorse of powder printing: strong, near-isotropic functional parts, often glass- or carbon-filled. | — |
A printed part is not the bulk polymer
An FDM part is really a little layered composite: strong along the printed roads, weaker across the layers. The bond between layers is formed by partial re-melting and never fully heals, so the build (Z) direction carries voids and weaker welds than the solid polymer around them.
Interlayer (Z) strength is typically only 30–70% of the in-plane strength — and can be lower with poor settings.
So orientation is a load-bearing design decision: lay the part down so the tension and bending run along the layers, never across them. SLA is more isotropic because layers cross-link chemically (but the resin is often brittle); SLS is the most isotropic of the three. This is exactly the gap between a datasheet number and the number a real part can hold.
This is the printing version of a bigger lesson — the gap between a handbook value and what a real part holds. See design allowables and the Make flow's final step.
See it for yourself — rotate this printed block, then pull it along the layers and across them:
Orientation first
Choose how the part lies on the plate before anything else — it sets the strength direction, the surface quality and where supports are needed. These three often pull against each other.
Walls carry the load, not infill
The solid perimeters (walls) do most of the structural work. Infill percentage is a stiffness-vs-weight-vs-time trade, and its effect on strength is far from linear — more than ~40% rarely pays off.
Design for the process
Add fillets at corners to cut stress risers, avoid long unsupported overhangs (roughly past 45°), and keep walls a sensible multiple of the nozzle width so slicing is clean.
Know when not to print
Printing wins for prototypes, low volume, and complex or custom geometry that no mould can make. It loses to injection moulding on high volume (cost per part), and it is the wrong call when you need fully isotropic, watertight, bulk-property performance.
Part of the Make map — the first domain grown into its own page. New to all this? Start with the guided learning path, or browse the cited materials database.