Layer by Layer
FDM builds objects by tracing cross-sectional contours with a bead of molten thermoplastic, stacking hundreds or thousands of layers to form a three-dimensional part. The process is deceptively simple — heat plastic, push it through a nozzle, move the nozzle precisely — but the physics of polymer melt flow, crystallization kinetics, thermal bonding, and residual stress make it a rich engineering challenge. This simulator exposes the key parameters that determine print quality.
Extrusion Dynamics
The volumetric flow rate Q = h × w × v must match the melt capacity of the hot end. A standard 0.4 mm nozzle at 210°C can deliver roughly 10-15 mm³/s of PLA before the heater cannot maintain temperature. Exceeding this limit causes under-extrusion — gaps, weak bonds, and dimensional errors. The simulator calculates flow rate in real time as you adjust layer height, width, and speed.
Interlayer Bonding
The Achilles heel of FDM is z-axis strength. When a new bead is deposited on a cooled previous layer, thermal energy from the fresh extrusion must re-melt a thin interface zone for molecular chains to diffuse across and create a bond. Higher nozzle temperatures, slower speeds, and thinner layers all increase the thermal energy available at the interface, improving bond strength. The simulation visualizes this bonding quality as you adjust parameters.
Surface Quality Trade-offs
Surface roughness in FDM is primarily determined by layer height: each layer creates a stair-step artifact with roughness approximately Ra ≈ h/4. A 0.1 mm layer yields Ra ≈ 25 μm (smooth by FDM standards but rough compared to injection molding). Reducing layer height improves finish but doubles or triples print time. Post-processing — sanding, vapor smoothing, or coating — can achieve injection-mold-quality surfaces when needed.