Fused Deposition Modeling (FDM)

Fused Deposition Modeling (FDM) builds thermoplastic parts by extruding molten filament layer-by-layer, delivering low-cost prototypes with visible layer lines and anisotropic strength.

Overview

Fused Deposition Modeling (FDM), also called FFF, is a plastic 3D printing process that melts and extrudes filament through a nozzle to form parts layer-by-layer. It’s widely available, quick to iterate, and supports a broad set of thermoplastics from basic PLA/ABS to engineering grades like PETG, Nylon, and polycarbonate.

Choose FDM for prototypes, jigs/fixtures, and low-volume functional parts where cost and turnaround beat surface finish and tight tolerances. It handles large envelopes well and can create internal features with supports, but fine details, watertightness, and cosmetic surfaces are limited by layer lines and nozzle size.

Tradeoffs: strength is directional (weaker across layers), dimensional accuracy varies with machine tuning and geometry, and supports add time and cleanup. Expect post-processing (sanding, vapor smoothing, inserts) when fit, appearance, or threads matter.

Common Materials

  • PLA
  • ABS
  • PETG
  • Nylon
  • Polycarbonate
  • TPU

Tolerances

±0.010–0.020 in (±0.25–0.5 mm) typical; tighter on small features with tuning

Applications

  • Assembly fit-check prototypes
  • Jigs, fixtures, and drill guides
  • Custom brackets and housings for pilot builds
  • Ergonomic grips and handles
  • Ducting and cable management prototypes
  • Low-volume end-use replacement parts

When to Choose Fused Deposition Modeling (FDM)

Pick FDM for fast, low-cost iterations and functional prototypes where moderate accuracy and visible layer lines are acceptable. It fits low volumes (one-offs to small batches) and parts that benefit from common thermoplastics, simple finishing, or large build sizes. Plan around directional strength and support removal on complex overhangs.

vs Stereolithography (SLA)

Choose FDM when you need tougher, more heat-resistant thermoplastics (ABS-like is common, but true engineering filaments are the draw) and lower cost for larger parts. FDM is usually better for jigs/fixtures and rugged prototypes where surface finish isn’t the priority. Expect rougher surfaces and less crisp small features than SLA.

vs Selective Laser Sintering (SLS)

Choose FDM when you want lower part cost for simple geometries, faster quoting, and easy material selection without powder handling. FDM is a good fit for larger parts with straightforward support strategies and for shop-floor fixtures. SLS wins on complex, support-free geometry and more uniform mechanical properties, but costs more for one-offs.

vs Multi Jet Fusion (MJF)

Choose FDM for prototypes and low-volume parts where you don’t need the production-like consistency and isotropic strength typical of MJF. FDM often beats MJF on large, simple parts and quick single-unit turns. If your part needs repeatable dimensions across a batch, fine features, or better surface uniformity, MJF is usually the step up.

vs Digital Light Processing (DLP)

Choose FDM when you need true thermoplastic behavior (impact resistance, temperature capability) and don’t want to manage resin handling, wash, and cure steps. FDM is often cheaper for larger components and fixtures. DLP is better for small, high-detail parts and smooth surfaces.

vs PolyJet

Choose FDM when you need durable thermoplastics at a fraction of the cost and can accept visible layers and fewer material options in a single build. FDM suits functional prototypes and fixtures; PolyJet suits presentation models, fine detail, and multi-material/overmold-like prototypes. PolyJet parts can be more sensitive to heat and long-term mechanical loading.

Design Considerations

  • Orient the part so primary loads run along the filament paths and not across layer lines
  • Avoid long flat spans; add ribs or slight curvature to reduce warping and improve bed adhesion
  • Use 45° chamfers instead of supports where possible; keep overhangs to ~45° or less
  • Design holes undersize and plan to drill/ream to final diameter for accurate fits
  • Use heat-set inserts or captive nuts for threads; printed threads wear and vary with orientation
  • Call out critical datums and fit features explicitly and allow machining stock if tight tolerances are required