Thermo-optical-rheological interactions in variothermal powder bed fusion of carbon fiber modified PEEK

Non-linear fractal exposure strategies enable the cold, support-free laser powder bed fusion (PBF) of semicrystalline thermoplastics by transiently decoupling crystallization-induced shrinkage from the macroscopic geometry at powder bed temperatures significantly below the crystallization onset. This paper addresses the interaction between optical characteristics, quasi-simultaneous exposure conditions, and rheological melt properties in the processing of carbon fiber (CF) modified polyetheretherketone (PEEK) at a powder bed temperature of 50 °C. Extended instantaneous dwell times under identical accumulated energy densities are interlinked with pronounced charring, implying that degradation is governed by the intensity-time product, corresponding to the area energy density per exposure pass, rather than the isolated focal intensity. Increased exposure velocities under correspondingly reduced cycle times allow for mesoscopic coalescence while limiting transient thermal peaks. Complementarily, increased CF fractions constrain the inter-layer fusion through elevated melt stiffness, corroborating the coupled significance of optical properties, exposure-induced temperature fields, and melt rheology in cold PBF.