Validating Closed-loop Quality Control in Melt Extrusion Printing

Additive manufacturing (AM) is revolutionizing both research and production, creating new opportunities for innovation. Melt extrusion remains the most used AM process for part fabrication. However, it is challenging due to complex interactions between thermal, mechanical, and environmental factors, often leading to inconsistent part quality and reliability. These challenges are particularly evident in low-cost desktop melt extrusion systems (priced under $5000), which frequently suffer from unpredictable material properties, unreliable print processes, and significant waste in terms of time and materials. As a result, inexperienced users encounter print failure rates as high as 20%.

In our ongoing investigation into in-situ closed-loop error correction for melt extrusion, we present the findings of our pilot study quantifying the effects of closed-loop control on part quality. Our in-situ filament diameter measurement enables live adjustment of volumetric flow rate, improving the accuracy of feedstock deposited in each part. This enhances layer adhesion and improves the mechanical properties of printed parts by preventing variations in volumetric flow that lead to over- and under-extrusion. To validate the performance of our closed-loop control system, the filament was precisely deformed and then printed as pressure testing tubes. The induced deformation reduces the diameter, causing localized road variation within the tubes which reduces road bonding. Different filament deformation size and strain combinations were tested to induce a range of defects in printed parts. These tubes were then pressurized, and pressure decay rate was analyzed to obtain an accurate measure of the bonding quality in printed parts. We will present our methods and results, including correlation between diameter variation and part quality, effects of closed loop correction on pressure decay rate and variance in decay rate, and overall assessment of our method as a surrogate for part quality.