CourseWiki/Materials and Manufacturing Processes/Plastics

FDM 3D Printing

Read an FDM part as deposited roads and layers, then choose orientation, walls, infill and supports for its job.

A slicer turns a solid model into deposited layers

Material extrusion is the standard family in which material is selectively dispensed through a nozzle. This page covers thermoplastic filament printing, often called fused filament fabrication (FFF). Fused deposition modeling (FDM) is a registered trademark of Stratasys for an implementation of this mechanism. The machine feeds filament into a heated nozzle and lays down narrow roads of softened material that bond as the part builds. Relative motion between the nozzle and build plate advances the layers; the nozzle itself does not have to move upward on every printer.

A slicer converts the model into tool paths, including walls, internal fill and any temporary supports. Preview those paths before printing. An enclosed shape on a CAD screen does not tell you how its underside will be supported.

Schematic FDM cross-section: filament enters the heated nozzle above deposited layers; outer walls enclose sparse infill; removable supports stand beneath an overhang on the build plate. — A section through a partly printed part. Walls, infill and supports are different tool paths. The large lines are illustrative, not a scale drawing.

Compare material extrusion with the other standard routes in Additive Manufacturing Process Families.

Where additive manufacturing fits the five course categories

This course uses purpose to choose a primary category. Additive shape-building is Forming because creating the shape is the intended result; bonding between deposited roads is a secondary fabricating effect rather than joining previously separate parts. Other technical taxonomies organize these processes differently. The standard AM family name here is material extrusion. Subsequent support removal is Separating; annealing is Conditioning; sanding or painting is Finishing.

Layer height, walls and infill do different jobs

Layer height is the vertical increment between layers. A smaller height makes steps on sloping surfaces finer and usually adds print time. It does not make all small horizontal features printable: nozzle size, road width and motion accuracy also matter.

Walls or perimeters trace the boundary. Top and bottom layers close the part. Infill is the pattern inside those boundaries. More infill generally adds material and time, but strength also depends on walls, orientation, bonding and load direction. A 20% infill setting does not mean the entire part uses 20% of its solid volume, because the walls and skins remain.

Simple layer-count example: for a 24 mm height with every layer 0.20 mm thick, 24 ÷ 0.20 = 120 layers. Real slicers may use a different first-layer height or variable layers. Halving layer height roughly doubles the layer count, not necessarily the total print time.

Orient for the load as well as for fewer supports; Checklist

Orient for the load as well as for fewer supports

FDM parts are anisotropic: properties depend on direction. A load that pulls layers apart can expose a weaker bond than a load carried along continuous deposited roads. Avoid placing the main tensile load across layer interfaces when an orientation can carry it along the layers. This is a design starting point, not a strength rating.

An overhang extends beyond the layer below. A short bridge spans between supported ends. A long unsupported underside may need temporary support material. Support contacts can leave marks, so keep them away from critical visible or mating surfaces where possible. There is no universal overhang angle that works for all materials and settings.

For a rectangular test bar pulled along its length, laying its length in the build plane usually gives a better starting orientation than standing it upright and pulling across stacked layers. A bracket may have several important load directions; choose a compromise or change the design, then test it.

Mark the main load direction and critical fit surfaces on the model.
Compare orientations for layer direction, build-plate contact and unsupported undersides.
Preview walls, infill and supports one layer at a time.
Check that support can actually be removed from each enclosed space.

Choose filament for service conditions and printer capability

Filament	Useful starting point	Check before choosing
PLA	Stiff models and easy-to-print prototypes	Heat exposure and impact requirements; a neat print is not automatically suitable for a warm enclosure.
PETG	Tougher functional parts with useful layer bonding	Stringing, moisture and support-removal behavior for the grade.
ABS / ASA	Applications needing greater heat resistance than ordinary PLA; ASA is often chosen for outdoor exposure	Warping control, equipment capability and processing requirements.
TPU	Flexible parts	Hardness grade and whether the feed system can handle flexible filament.
Nylon (polyamide)	Tough engineering parts	Moisture control, dimensional change and the required printing conditions.

PVA is used as a water-soluble support material in compatible multi-material systems; it is not a universal companion for every filament. Use the exact filament manufacturer's settings and the printer's limits. Consult Equipment Operating Procedure and Chemicals and Safety Data Sheets for process controls.

Material guidance is grade-specific

Filament names describe families, not identical recipes. Pigments, fillers and blends change behavior. Prusa's material guide separates common filament families and their printing requirements. It does not establish what any particular shop printer can process.

Estimate mass from deposited volume, not infill alone; Practice

Estimate mass from deposited volume, not infill alone

Mass = deposited volume × density. If a simplified model has 8 cm³ of solid walls and skins plus a 32 cm³ interior at 25% infill, its estimated deposited volume is 8 + (32 × 0.25) = 16 cm³. At an assumed density of 1.24 g/cm³, that is 19.84 g. Supports, brims and purge material add more.

This estimate treats infill percentage as a volume fraction of the interior. A slicer estimates the actual paths more closely. Time also includes travel, acceleration, heating and cooling constraints; volume alone does not give an exact printing duration.

Post-processing choices are in Conditioning and Finishing Plastics. Practice estimating filament mass

Appears in

DET 130 DET Plastics Processing