In Situ, Real-Time Temperature Mapping and Thermal FE Simulations of Large-Format 3D Printed PETG/CF Vertical Wall

Current research on additive manufacturing often overlooks the precise thermal dynamics during large-scale printing. While prior studies have explored residual stresses and warping in 3D printed parts, they typically rely on simplified assumptions about thermal behavior. Established knowledge shows that repeated deposition of hot material onto cooler layers introduces residual stresses. However, no prior work had resolved how convection coefficients vary with height during printing. This gap motivated the current investigation into thermal history modeling. The study addresses a need for more accurate finite element simulations of thermal processes in large-format additive manufacturing. Thermal contact conductance and convection coefficients are key variables in such models. Existing models often assume constant convection, which may not reflect real-world conditions. The absence of real-time temperature data from vertical structures in prior studies further highlights the need for this work. By integrating thermocouples and FE simulations, the research aims to improve thermal predictions.

The primary aim of this study was to enhance the accuracy of finite element models used to predict thermal history in large-format additive manufacturing. The specific problem addressed is the variability of convection coefficients during vertical wall printing. The motivation stems from the limitations of existing models that assume constant convection. The research sought to determine how thermal contact conductance and convection coefficients change with height in printed structures. By placing thermocouples at various heights, the study aimed to capture real-time temperature data. This data was then used to refine FE models and improve thermal predictions. The goal was to generalize findings to other vertical structures printed using the BAAM system. The work also aimed to derive a correlation equation for broader application.

The study employed a Big Area Additive Manufacturing (BAAM) system to print a vertical wall using PETG with carbon fiber reinforcement. Thermocouples were embedded at different heights to monitor temperature in real time. The material used was a thermoplastic composite consisting of poly(ethylene terephthalate) glycol with short carbon fiber. The printing process involved incremental deposition of hot material onto cooler layers. A finite element (FE) model was developed to simulate thermal behavior during printing. The model included thermal contact conductance between the printed part and the bed. Convection coefficients were calculated and found to vary linearly with wall height. The model was validated by comparing simulated temperatures with thermocouple measurements. The study also tested the impact of constant versus variable convection coefficients on stress predictions.

The FE model revealed a thermal contact conductance of 10 W/m²K between the printed part and the bed. Convection coefficients were found to increase linearly from 3 to 15 W/m²K through the wall height. The model with a variable convection coefficient provided more accurate temperature predictions than the constant coefficient model. The constant coefficient model under-predicted temperatures at the beginning of the printing process. This discrepancy led to higher stress values in the constant coefficient model. The variable coefficient model showed better alignment with thermocouple data. A correlation equation was derived to generalize findings to other vertical structures. The study demonstrated that convection coefficients are not uniform and must be height-dependent for accurate simulations.

The authors propose that variable convection coefficients improve the accuracy of thermal simulations in additive manufacturing. The findings suggest that constant convection assumptions may lead to under-predicted temperatures and overestimated stresses. The derived correlation equation allows generalization of results to other vertical structures. The study demonstrates the importance of real-time temperature data in refining FE models. The authors suggest that thermal contact conductance is a critical parameter in modeling. The results indicate that FE models must account for height-dependent convection coefficients. The work provides insights into material characterization and thermocouple placement. The authors conclude that accurate thermal modeling is essential for predicting residual stresses in large-format additive manufacturing.