Influence of Hot-Air Jet (HAJ) Additional Heat Source on the Deposited Polymer in FFF Printing

The paper presents part of the results of larger research aimed at evaluating the possibility of improving the characteristics of the FFF printed product by using hybrid heating sources.The results presented aim at the influence of the cooling rate on the characteristics of parts manufactured by 3D FFF printing from Polylactic acid (PLA), with a focus on the structural, thermal and mechanical properties, when the additional heat source is represented by a hot air jet.Microscopic analysis showed that rapid cooling generates a more irregular texture, poor interlayer adhesion and a rougher surface, while slow cooling ensures a uniform texture, improved interlayer adhesion and fewer defects.From a thermal point of view, the glass transition temperature ( ) was slightly higher for the slowly cooled samples, due to the relaxation of internal stresses.The crystallization temperature ( ) increased progressively with the reduction of the cooling rate, indicating a higher initial crystallinity, and the energy associated with the crystallization reaction decreased.The melting temperature ( ) showed minimal variations, but the melting enthalpy was higher for the slowly cooled samples, reflecting better organized crystals.Mechanical properties revealed that the rapidly cooled parts have higher stiffness at low temperatures, due to internal stresses, but brittle behaviour.The slowly cooled parts showed higher stiffness at high temperatures and ductile behaviour, with progressive deformations before fracture, due to the relaxation of internal stresses and the formation of partial crystals.The results emphasize the importance of controlling the cooling rate in the FFF process to optimize the interlayer adhesion, mechanical properties and thermal stability of the printed parts, allowing to adapt their performance to specific application requirements.