A comparative study on the 3D printing process of semi-crystalline and amorphous polymers using simulation

Abstract

Polymers have been widely used in the field of fused deposition modelling (FDM). The part integrity of the final printed part is affected by parameters such as processing conditions and the material properties of the polymer. Build-up of residual stresses are the main cause of shrinkage and warpage (i.e., part distortion) in the FDM parts. Among the thermoplastic polymers, semi-crystalline polymers are more prone to part distortion due to crystallisation. Therefore, it is important to understand and predict part distortion in FDM of polymers to achieve good quality prints with desirable mechanical properties. Several studies have investigated the resulting part distortion in FDM parts through empirical, analytical, and numerical approaches. In most cases, the simulation results are not quantitatively validated, mainly because the temperature dependent properties of the polymers and the crystallinity of semi-crystalline polymers are often overlooked. In this study, the thermal-mechanical properties of the polymer of study such as specific heat capacity, thermal conductivity and density and the crystallisation kinetics are invoked as a function of temperature. Furthermore, an amorphous polymer was also simulated with consideration of its respective material properties. Both the semicrystalline and the amorphous polymer models were simulated under various layer thickness (0.1 and 0.5mm), in order to investigate the effect of layer thickness on the induced thermal stress and resulting warpage. Based on the simulation results, for 0.1mm layer thickness, the amorphous polymer model exhibited a warpage drop of 77%. And for 0.5mm, the warpage noted was found to decrease by 63%, on comparison with the warpage noted from semi-crystalline polymer model. These warpage values from the simulated models were then measured against the 3D scan results of the printed samples for quantitative validation. An excellent agreement was observed between the experimental and the simulated samples.