Finite element prediction of distortion during the fused filament fabrication process of PLA

Purpose – Parts printed using fused filament fabrication (FFF) contain a complex residual stress distribution leading to part distortion during and after manufacture. Determining this distortion is often achieved through time consuming trial-and-error approaches. This paper aims to predict distortion for Poly(lactic acid) (PLA) “bridge” parts using the finite element method. Design/methodology/approach – Based on a comprehensive review of existing prediction models, Abaqus software is used to simulate the FFF process for PLA. Initial models accurately predict distortion found in literature with lower computational cost. However, when results are compared with prints completed using a PRUSA I3 MK3S+, the total distortion was found to be approximately 0.06 mm, while the model predicts distortion of 3.88 mm. Findings – Further literature analysis indicates the magnitude of strain rate sensitivity of PLA below the glass transition temperature. The model material data is refined to include a two-layer viscoplasticity approach which results in an improved predicted distortion of 0.118 mm. However, when results are compared with a detailed computed tomography (CT) scan of a printed part, some geometric discrepancies remain. These occur due to limited materials data and the models’ inability to model some complexity, including the inclusion of voids. Practical implications – This work highlights the importance of correctly choosing model variables to ensure accurate predictions and the importance of careful sample removal from the build plate to prevent the introduction of distortion. Originality/value – This manuscript demonstrates that viscoplastic properties can be included in a model to predict residual stress in FFF artifacts, thereby indicating that the approach can be extended to complex geometries and a range of materials.