Note: This article is based on the presentation “Smart Toolpath Design for Large-Scale Additive Manufacturing” delivered by Nikoleta Sidiropoulou, Lead R&D Engineer at the High-Performance Polymeric Additive Manufacturing Event, held on 11–12 September 2024 by the University of Exeter.
Large-scale additive manufacturing (AM) faces unique challenges in achieving precision, adaptability, and consistent quality, especially when scaling up for industrial applications. Toolpath design—the programming that controls the path and extrusion of the print head—is key to overcoming these obstacles. Traditional toolpaths work well for smaller objects but often fall short when applied to the larger scales and more complex geometries needed in industrial applications. This article introduces “smart toolpath” design, an advanced approach that adapts toolpathing to improve large-format printing quality, precision, and adaptability.
In traditional AM, toolpaths are designed as sequences of points that guide an extruder’s path. Nowadays, a smart toolpath incorporates not only geometrical features of the bead in each point, but also process parameters such as heat zone temperatures and laser power. These data points allow for dynamic adaptation, tailored to the unique requirements of each print section.
The bead dimensions in large-scale AM can range from 1.5 to 4 mm in layer height and 2 to 20 mm in bead width. This variability, along with material behaviour during printing, introduces specific challenges, especially in maintaining fidelity to complex design features. Smart toolpath design addresses these issues, and examples of its application are provided below.
Challenge 1: Capturing geometrical features with very low printing resolution.
A common issue in large-scale AM is preserving fine details, as larger bead dimensions can make it difficult to maintain accuracy in intricate designs, especially with complex angles. This issue is even more pronounced in areas where the print surface becomes parallel to the build plane, making it harder to control material spread and maintain precision.
Smart toolpaths allow for fine control over parameters like tool orientation, bead height, and bead width at each point along the path. This capability enables smoother transitions between layers and minimises material waste. In Aibuild software, multiple slicing modes improve accuracy by adapting each layer to follow the shape of the model. These modes are organised into two main types: 2D slicing modes and 3D slicing modes.
To address such challenges, Aibuild software contains multiple slicing modes, which allow layers or points to follow specific orientations or adapt/morph to fit a model’s topology. This method effectively enhances accuracy, especially when printing parts that would otherwise require substantial post-processing due to introduced support structure like in traditional slicing methods. The multiple slicing modes inside Aibuild software can be organised in two categories based on the topology of the layer produced: the 2-dimensional slicing modes and the 3-dimension slicing modes.
The 2D slicing modes align each layer with a unique plane, enabling different orientations between layers. This flexibility is achieved through guide planes or central paths, allowing layers to adapt to the model shape and reducing the need for support structures. This results in better precision for complex shapes.
The 3D slicing modes create layers in three-dimensional space, with individual points along each layer adapting in rotation and height as needed. Layers are defined based on guide surfaces or a topology analysis of the model, producing layers that align precisely with the shape of the part. This method allows more accuracy for intricate shapes.
Aibuild software through the above slicing strategies demonstrates the benefits of smart toolpathing in applications like prosthetics and complex moulds. For example, printing curved moulds traditionally requires extensive support material, complicating post-processing. Smart toolpaths, however, enable efficient printing on curved surfaces without needing additional supports, reducing material use and post-processing time.
Challenge 2: Porosity in the build.
Porosity can be a persistent issue in large-scale AM, particularly when multiple walls are printed to achieve a specified thickness for structural or post-processing purposes. In materials like polymers, printing adjacent walls can trap air pockets between layers due to the natural rounded edges of the beads. This effect is magnified when beads are larger, as they are in large-scale AM.
In smaller-scale AM, this issue is often mitigated by overlapping the beads slightly. However, in large-scale AM, this technique can lead to significant over-extrusion, resulting in extruder crashes, or fibre accumulation when using composite materials.
A more effective solution is the use of a polyline vertical offset, whereby walls are shifted by half a layer height in the vertical direction. This approach not only mitigates the risk of over-extrusion but also ensures a higher overlap that minimises air pockets, especially in materials that are less elastic and thus more prone to porosity issues.
Similar porosity challenges arise in infill areas and in the interface zones between walls and infill. For example, in a zigzag infill pattern, gaps may form between infill and wall sections, while in concentric infill, sharp corners may fail to fill correctly, causing potential weak points.
For zigzag infill, smart toolpathing enables dynamic adjustment of extrusion rates and printing speeds in areas close to walls, effectively closing potential air pockets.
In concentric infill configurations, another approach is taken: low-extrusion areas in sharp corners are either reinforced with an additional bead or replaced with a wider single bead to increase stability. In this way, the smart toolpath adapts not only the shape but also the extrusion parameters to prevent porosity in these critical areas.
These adaptations help eliminate air entrapment, which can improve the part’s structural and thermal stability. By minimising internal gaps, smart toolpaths open new possibilities for industrial applications, such as sand casting moulds for autoclave processes, where consistent density and strength are crucial.
Challenge 3: Lack of accuracy due to material limitations
Corners and high-curvature areas present challenges in AM, particularly for large-scale processes where extrusion behaviour varies by material. In thermoplastic extrusion, for example, outer corners often suffer from under-extrusion (leading to curling), while overhangs may experience sagging due to the material’s properties. In concrete printing, sharp corners may experience inner-corner over-extrusion, while in metal printing, high-curvature areas can overheat, impacting quality.
Smart toolpaths automatically adapt parameters like printing speed and extrusion rate at high-curvature points, compensating for these material-specific behaviours. By fine-tuning these variables in real-time, the toolpath can mitigate issues such as curling and sagging, improving dimensional stability and allowing AM to achieve complex geometries without sacrificing quality.
Challenge 4: Capture geometrical features due to material limitations
Thermal stability is essential for high-quality prints, particularly when dealing with polymers and metals. In polymer AM, excessively hot layers may cause beads to sag, while cold layers may weaken interlayer adhesion, leading to structural issues.
In metal Wire Arc Additive Manufacturing (WAAM), thermal consistency between layers impacts bead size and porosity, affecting overall part quality.
By linking smart toolpath design to real-time monitoring data—such as temperature and bead dimensions—the system can dynamically adapt point-specific parameters to ensure optimal adhesion between layers. This closed-loop feedback prevents defects like warping, sagging, and cracking, ensuring that each layer adheres effectively to the previous layer. The result is a smoother, more consistent build that maintains its structural integrity throughout the print.
The advent of smart toolpathing represents a transformative advancement in large-scale additive manufacturing, addressing challenges related to geometry, material behaviour, and thermal stability. By integrating material properties, hardware capabilities, and application-specific needs into the toolpath design, smart toolpaths enhance print quality, reduce material waste, and improve the reliability of first-run prints. Looking forward, expanding the adaptive capabilities of smart toolpaths—particularly by incorporating real-time feedback from in-situ sensors—will allow for even greater precision and adaptability in AM.
Smart toolpaths are more than just programming for extruders; they represent a significant leap forward, enabling “first-time-right” prints and expanding the possibilities of additive manufacturing technologies.
Acknowledgement
Special thanks to the University of Exeter for organising the High-Performance Polymeric Additive Manufacturing event. We are excited to share future developments as we continue to refine and expand the capabilities of large-scale AM.
