An Interlaced Toolpath Method for Void Reduction in Material Extrusion Additive Manufacturing
Creators: name: Sun, Xiaochen
Publisher: name: RMIT University
Year: 2025
Subjects: classificationCode: 400707
subject: Manufacturing robotics

description: Additive Manufacturing (AM) has transformed industries by enabling the layer-by-layer fabrication of complex geometries. Among the various AM techniques, Material Extrusion (MEX), also known as Fused Filament Fabrication (FFF), is widely recognised for its versatility and accessibility. Despite advancements in FDM, existing void reduction strategies face significant limitations. Pre-deposition approaches often require costly hardware modifications, in-situ methods are rarely optimised for complex geometries, and post-processing adds time and expense. These challenges highlight the need for scalable, hardware-independent techniques that reduce inter-track voids during deposition without compromising process efficiency. Furthermore, there is limited research on the application of such methods across diverse material systems, including thermoplastics, composites, and concrete. 
This thesis addresses these challenges by developing the "interlaced printing method," an innovative in-situ toolpath strategy that reduces inter-track voids without requiring hardware modifications or significant increases in print time. The method is systematically applied to various material systems, optimising process parameters to balance porosity reduction and dimensional accuracy.
This research aims to reduce inter-track voids in MEX prints without requiring additional hardware modifications or significant increases in print time. Initially, the method was applied to PLA filaments, demonstrating significant reductions in porosity (from 10% to 1.15%) and a 19% improvement in mechanical strength. Subsequent chapters explore the influence of process parameters, such as extrusion rate and temperature, on void formation, revealing how these factors can be optimised to enhance the quality of MEX prints further.
The key contributions of this thesis include demonstrating significant porosity reduction and mechanical property improvements in PLA through the interlaced method, identifying material-specific limitations in PETG-CF and concrete, and providing a framework for optimising additive manufacturing processes.
Key findings reveal that while the method is effective in some materials, its impact varies significantly based on material properties, such as flexibility and thermal behaviour. Mechanical testing, including three-point bending tests and μCT porosity analysis, is used to quantify the improvements achieved with the interlaced method. The results suggest that in rigid thermoplastic materials like PLA, the interlaced method effectively reduces porosity and enhances mechanical properties. For composite materials like PETG-CF, the method reduces porosity without improving mechanical performance. 
The thesis concludes with recommendations for future research, including refining the interlaced method to better accommodate composite and other FFF-compatible materials. It also proposes the need to explore advanced process control strategies, such as real-time temperature adjustments and machine learning algorithms, to optimise the interlaced printing method further in both small-scale and large-scale material extrusion-based additive manufacturing systems.