Evaluation of in process heating for extrusion printing of tall thin-walled structures

Abstract

Compared to other additive manufacturing processes, extrusion printing offers a cost-effective solution in prototyping thin-walled structures across diverse applications. However, transitioning these prototypes into fully functional parts remains difficult due to weak interlayer bonding and the presence of voids. Post-processing methods such as annealing can mitigate these issues but often compromise geometric accuracy, which is critical in fields such as automotive and aerospace. Recently, in situ heating with a simple heater block has demonstrated improvements in mechanical strength by enhancing layer-to-layer adhesion. In this work, the attributes of the heating method, such as the heater block alignment and temperature, along with other process parameters, such as print speed and material conditioning, are evaluated in detail for their effect on flexural strength and geometric accuracy. A detailed design of experiments (DOE) study is conducted using a novel design of heater block to evaluate the statistical effects of these key parameters at different levels on mechanical and geometric accuracy of a unique double bead, tall thin-walled structure printed out of polylactic acid (PLA) filament. Statistical analysis indicates that studied parameters (individually or in interaction(s)) significantly affect bending strength while the average deformation in height, width, and length is less than ± 2 mm. Furthermore, highest average model-predicted bending strength of 51.10 MPa, representing 25.0% increase compared to standard specimens (41 MPa) printed without heater block, is achieved through a combination of the aligned heater block at 245 °C using dried filament printed at a speed of 1200 mm/min. The increase in strength can be attributed to improved layer-to-layer bonding, change of shape of voids from sharp edge to circular, and more effective neck growth between rasters, all while maintaining geometric accuracy. Overall, this research work contributes towards the use of the in situ heating method for printing tall thin-walled structures that meet practical strength requirements.