Pressure Advance and Input Shaper

Theoretical Background

Viscoelasticity and Fluid Dynamics (Pressure Advance)

When 3D printing, filament behaves as both an elastic solid and a viscous fluid (a viscoelastic material) under the high temperatures and pressures inside the hotend. As the extruder motor pushes the solid filament into the melt zone, it acts like a piston compressing a liquid through a narrow orifice (the nozzle).

Because of the elasticity of the filament (especially over long distances in Bowden setups) and the viscous resistance (shear stress) of the molten polymer inside the nozzle, there is a distinct time delay between the extruder motor input and the actual flow of plastic out of the nozzle. This is governed by the relation of volumetric flow rate:

Impact on Print Quality & Time

• Print Quality: Properly calibrated Pressure Advance yields sharp 90-degree corners, consistent line widths, and eliminates blobs at start/stop points. Input Shaper removes ringing and ghosting, allowing for smooth vertical walls even at acceleration rates exceeding $5000{\text{ mm/s}}^2$.
• Print Time: Input Shaper reduces print times by 30% to 50% because it allows the printer to run at much higher speeds and accelerations without sacrificing surface quality. Pressure Advance does not directly reduce print time, but it enables high-speed extrusion transitions that would otherwise fail or look poor.

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Configuration in PrusaSlicer

Pressure Advance Setup

PrusaSlicer handles Pressure Advance (PA) in a filament-specific manner because PA depends heavily on the viscosity, temperature, and elasticity of the material.