Question

When printing with semi-crystalline polymers like PEEK, why must the build chamber be maintained above the material&#x27;s glass transition temperature throughout the entire process?

Accepted Answer

Semi-crystalline polymers like PEEK consist of two regions: amorphous zones, where polymer chains are randomly arranged, and crystalline zones, where chains are neatly ordered. The glass transition temperature is the specific temperature point where the amorphous regions of the polymer transition from a hard, glassy state to a soft, rubbery state. Maintaining the build chamber above this temperature ensures that the material remains in this rubbery state during the printing process. This is critical because cooling below the glass transition temperature too quickly induces internal stresses caused by the polymer chains attempting to reorganize. These stresses lead to warping and delamination, where the layers of the print peel apart or distort as the material shrinks unevenly. Furthermore, keeping the chamber hot allows for sufficient molecular mobility, which enables the polymer chains to migrate across the interface between the new layer being deposited and the previous layer. This process, known as polymer chain diffusion, creates a strong bond between layers. If the temperature drops below the glass transition temperature, the material becomes too rigid for these chains to move and entangle, resulting in poor layer adhesion and a fragile, brittle finished part. By keeping the entire part at an elevated temperature, the material undergoes a controlled cooling process, allowing the semi-crystalline structure to form uniformly and minimizing residual stress throughout the part.

Home → All Courses → Engineering and Technology Courses → Additive Manufacturing (3D Printing) Engineering → Flashcard

When printing with semi-crystalline polymers like PEEK, why must the build chamber be maintained above the material's glass transition temperature throughout the entire process?