FDM 3D Printing
Also: FDM, fused deposition modeling, FFF, fused filament fabrication, material extrusion, filament 3D printing, Ultem 3D printing, PEEK 3D printing
FDM 3D printing extrudes thermoplastic filament layer by layer: the cheapest, largest prints, from PLA prototypes to Ultem 9085 and PEEK parts.
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Fused deposition modeling (FDM), also called fused filament fabrication (FFF) or material extrusion, feeds thermoplastic filament through a heated nozzle and lays it down in beads, or roads, that trace each layer. The outline is printed as solid perimeters and the interior as a sparse or solid infill. Overhangs are held up by support material, which on industrial machines is often soluble and dissolves away in a bath.
FDM is the cheapest way to print plastic and offers the largest build volumes. Desktop machines print PLA, PETG and ABS for form checks; industrial machines with heated chambers print ABS, ASA, polycarbonate, nylon and the high-temperature polymers Ultem 9085, Ultem 1010 and PEEK from lot-controlled material. That makes it the standard process for jigs, fixtures, check gauges, drill guides and end-of-arm tooling, and for flame-retardant Ultem 9085 aircraft interior parts.
The weaknesses are built into the process. Layers bond less well than the plastic within a road, so strength in the build direction (Z) is often 50-80% of the in-plane strength and parts fail along layer lines. Layer lines show on every surface, features smaller than about 1 mm (0.040") print poorly, and small voids between roads make parts porous to gas and liquid unless they are sealed. Orient the part so the main load runs along the layers, and machine or sand the surfaces that matter.
At a glance
| Typical tolerances | Industrial FDM: standard ±0.25 mm (±0.010"); with care ±0.13 mm (±0.005") or 0.15% of the dimension, whichever is greater, on well-supported features. Desktop machines hold about ±0.3-0.5 mm (±0.012-0.020"). Holes print undersize and are drilled or reamed to size; large flat parts shrink and warp, especially in ABS, nylon and the high-temperature polymers. |
|---|---|
| Size limits | Desktop machines build about 250 x 210 x 210 mm (10 x 8 x 8"); industrial machines 355-610 mm (14-24") on a side, with the largest common machine at 914 x 610 x 914 mm (36 x 24 x 36"). Large-format pellet-fed extruders at a few shops print molds and tooling several meters long. Walls should be at least two roads wide, about 1-1.5 mm (0.040-0.060"). |
| Surface finish | Layer lines at the layer height, 0.13-0.33 mm (0.005-0.013") on industrial machines, give roughly 10-25 µm Ra (400-1,000 µin) on side walls, with stair-stepping on shallow curves; support interfaces are rougher. Sanding, filling and painting, or vapor smoothing ABS and ASA, brings cosmetic faces to about 1-2 µm Ra (40-80 µin); machined faces reach 1.6 µm Ra (63 µin). |
| Lead time | Prototypes in 1-3 business days in PLA or ABS; 3-7 business days for Ultem, PEEK or nylon on industrial machines; fixture and tooling batches in 1-2 weeks. |
Typical of U.S. job shops; confirm with the shop for your part.
Materials
PLA and PETG for quick, inexpensive form models; ABS, and ASA where UV stability matters, for general prototypes and fixtures; polycarbonate and PC-ABS for stiffness and heat resistance; nylon (usually PA6 or PA12, often carbon- or glass-filled) for tough, wear-resistant fixtures; TPU for flexible parts. High-temperature machines print Ultem 9085 (a flame-retardant PEI blend used for aircraft interior parts under FAR 25.853), Ultem 1010, PEEK and PEKK. The nylon link points to machined nylon 6/6 for comparison; printed nylons are different grades with lower, direction-dependent properties. Metal FDM, using bound metal filament that is debound and sintered, exists but is a niche.
What drives the cost
- Print time: deposited volume, layer height, infill density and number of perimeters
- Material: Ultem and PEEK filament cost several times ABS and need high-temperature machines with higher hourly rates
- Support material volume and removal, soluble or breakaway
- Part size and height: large parts tie up a machine for days
- Finishing: sanding, painting, vapor smoothing, inserts and machining
- Material traceability and certification for aerospace Ultem 9085 parts
- Quantity: FDM deposits one road at a time, so the price per part falls little with volume
When to use it
- Jigs, fixtures, check gauges, drill guides, soft jaws and end-of-arm tooling
- Large, inexpensive prototypes and form-fit models
- Low-volume housings and brackets in ABS, ASA, polycarbonate or nylon
- Flame-retardant aircraft interior parts and ducting in Ultem 9085 with traceable material
- High-temperature or chemically resistant parts in PEEK or Ultem where machining the shape from stock would waste expensive material
When not to
- Fine detail, small text or smooth cosmetic surfaces as-printed: SLA does these better
- Parts loaded across the layers, such as bosses pulled in the build direction
- Watertight or pressure-bearing parts, unless the part is sealed and tested
- Tolerances tighter than ±0.13 mm (±0.005") without post-machining
- Quantities above a few hundred: SLS, MJF or molding cost less per part
Design tips
- Orient the part, or tell the shop the load direction, so the main load runs along the layers rather than pulling them apart.
- Make walls a multiple of the road width, at least 1-1.5 mm (0.040-0.060"), and specify infill and perimeter count when strength matters.
- Use heat-set brass inserts for threads that will be assembled more than a few times; printed threads wear quickly.
- Keep overhangs at 45° or steeper from horizontal, and use chamfers instead of flat overhanging ledges to cut support material.
- Model holes slightly oversize, or leave them undersize and drill or ream to final size.
- Add fillets where walls meet the base and avoid large flat bottoms, which warp and lift off the bed.
- For aerospace Ultem 9085, state the certification and traceability requirements on the RFQ.
Frequently asked questions
- Is FDM strong enough for functional parts?
- Often, if the load runs along the layers. In-plane, FDM parts reach a good fraction of molded strength in the same polymer; across layers they are often only 50-80% as strong and fail by delaminating. Fixtures, brackets and housings in ABS, polycarbonate, nylon and Ultem work well; impact and high-cycle fatigue across the layers do not.
- What is the strongest FDM material?
- For strength and stiffness, carbon-fiber-filled nylon and PEEK; for heat and flame resistance, Ultem 9085, Ultem 1010 and PEEK. Polycarbonate is the strongest of the common engineering filaments. Continuous-fiber printers, an FDM variant that lays carbon or glass fiber into nylon, reach much higher in-plane stiffness, but only in-plane.
- Are FDM parts watertight?
- Not reliably. Small voids between roads and layers let gas and liquid seep through, especially at thin walls. More perimeters, thicker walls and tuned settings help; for sealing, parts are coated, epoxy-impregnated or vapor smoothed (ABS, ASA) and pressure tested.
- What is Ultem 9085 used for?
- It is a flame-retardant PEI blend printed on industrial FDM machines for aircraft interior parts, ducts, brackets and enclosures, because it meets FAR 25.853 flammability requirements and is available with lot traceability. It is also used for high-temperature fixtures. Its Z-direction strength is well below its in-plane strength, so orientation matters.
