How does exceeding the glass transition temperature (Tg) affect the dimensional stability of a 3D printed part?

Exceeding the glass transition temperature (Tg) of a 3D printed part significantly reduces its dimensional stability. The glass transition temperature is the temperature range at which an amorphous solid, or the amorphous regions within a semi-crystalline polymer, transitions from a rigid, glassy state to a more rubbery, viscous state. Above the Tg, the material becomes much softer and more susceptible to deformation under load or even its own weight. This can lead to warping, sagging, or other dimensional changes, compromising the part's accuracy and functionality. The extent of the deformation depends on how far above the Tg the temperature rises and the magnitude of any applied stress. For example, a PLA part exposed to temperatures above 60°C (its approximate Tg) will soften and deform easily, while an ABS part (Tg around 105°C) will remain more rigid at the same temperature. Therefore, maintaining temperatures below the Tg is crucial for preserving the dimensional integrity of 3D printed parts.