Investigation of nonisothermal fusion bonding for extrusion additive manufacturing of large structural parts

Abstract

Fusion bonding is understood to be the decisive mechanism for the interlayer strength in extrusion additive manufacturing. This study links the characteristic temperatures of semicrystalline thermoplastics, namely, PA6 with 40% carbon fibers, to the bond formation in respect to real-world processing conditions. Based on theoretical investigations, a process window is proposed for bonding to occur without polymer degradation. This range from the glass transition to the initial degradation temperature was determined through differential scanning calorimetry and thermogravimetric analysis. A second process window for optimal bonding is proposed from the extrapolated onset crystallization temperature, (Formula presented.), to the melt temperature, (Formula presented.). The validation of these process windows was conducted by bending tests according to DIN EN 178. (Formula presented.) was confirmed as the upper limit, with the part's geometric integrity compromised at higher temperatures. (Formula presented.) had to be refuted as lower limit as no discrete reduction in bond strength was determined in alignment with (Formula presented.). Authors suggest the lower limit is defined by the lowest substrate temperature to lead to interface temperatures above the onset of melt temperature. By utilizing thermal analyses, less time and resources are required to detemine a suitable process window for extrusion additive manufacturing.