Bottom Lift Speed and Distance

Mechanics of the Peel Cycle and Release Film Deformation

In Vat Photopolymerization (SLA, DLP, MSLA), printing is a cyclic process: exposing a layer, lifting the build plate to separate the cured layer from the release film, letting new resin flow in, and lowering the plate back down. The separation phase is the most mechanically demanding part of the print cycle, particularly for the Bottom Layers.

1.1 Release Film Elastic Deflection

The bottom of the resin vat is lined with a thin, flexible release film, typically made of Fluorinated Ethylene Propylene (FEP), Perfluoroalkoxy (PFA / nFEP), or a specialized Multi-layer film (ACF).

When a layer is cured, it bonds to the build plate (or previous layer) on top and rests against the release film on the bottom. To peel the layer off the film, the Z-axis lifts the build plate. Because the film is flexible, it does not separate instantly. Instead, it deforms and stretches upward like an elastic membrane.

Z-axis lifts:
       [ Build Plate ]
             | |
      [ Cured Layer ]
          \       /
           \     /    <-- Stretched Release Film (Deflection \delta)
____________\___/____________ [ Vat Bottom ]

The separation occurs as a peeling front that travels from the outer edges of the cured geometry inward toward the center. Complete release is only achieved when the film snaps back to its flat state.

1.2 The Hydrodynamic Suction Force (Stefan's Law)

As the cured layer lifts away from the vat floor, a narrow gap is created. Liquid resin must flow into this gap to fill the void. Because the gap is extremely narrow (equal to the layer height, e.g., $50\mu \text{m}$) and resin is viscous, this flow creates a strong suction force (vacuum effect).