Additive manufacturing of non-planar layers using isothermal surface slicing

Additive manufacturing creates physical objects from digital models by superimposing layers of material. However, conventional layer-based 3D printing has limitations, including poor surface roughness, feeble strength due to layer seams, and material waste for supporting structures. In conventional layer-based 3D printing processes, each slicing layer is regarded “iso-height surface” consisting of only points with the same z-coordinate component. This indicates that every layer is a parallel, flat plane to the build platform. However, the stair-stepping effect, which occurs when the layers are visible on the surface of the printed object, can result in a poor surface quality. One solution to this problem is to increase the resolution in the Z-direction, which can substantially reduce the stair-stepping effect but significantly increases printing time. In addition, printing frequently necessitates supporting structures to facilitate overhanging structures.

In a new study published in the peer-reviewed Journal of Manufacturing Processes, PhD candidate Yujie Shan, Yiyang Shui, Junyu Hua and led by Professor Huachao Mao from Purdue University proposed a novel approach to generate non-planar layers using isothermal surfaces. This method involved creating isothermal surfaces from a simulated temperature field with predetermined boundary conditions, which were then used to divide the 3D model into curved layers. Each selected curved layer was divided into infill line scans by modeling a different heat transfer method on it. In contrast to conventional planar-layer-based printing, the suggested heat-guided algorithm sought to enhance surface quality and mechanical performance while decreasing material waste and printing time. By using isothermal surfaces instead of iso-height surfaces, this approach could reduce material waste and printing time while accommodating overhanging structures without requiring additional supporting structures. Because planar-layer-based printing could produce weak spots or gaps between layers, non-planar slicing enhanced mechanical performance as well.

The research team validated the process, for that purpose, two printing devices were customized with 3-axis and multi-axis motions, respectively. Both a commercially available planar slicer and the suggested curved-layer-based slicing method were used to model and slice two samples with well-defined curved surfaces. The top curved layer’s surface roughness was then measured and compared. The findings demonstrated that, in comparison to conventional planar-layer-based printing, the suggested method for additive manufacture of non-planar layers employing isothermal surface slicing can greatly enhance surface quality. In particular, the suggested method reduced the surface roughness of the top curved layer by up to 80%. To assess the advantages of mechanical qualities, a shell-like construction was chosen and produced using both the suggested slicing approach and conventional layer-based manufacturing procedure. Tensile tests were then carried out using the created grips. In comparison to the identical structure printed using conventional layer-based manufacturing procedures, the results demonstrated that the shell-like structure produced using the suggested approach had superior strength and endurance. More specifically, the shell-like structure created via isothermal surface slicing had fewer weak spots or seams between layers.

The authors discussed the limitations of the proposed approach including collisions due to curved layers and incompatibility with complex objects. Additional study is required for collision detection algorithms, as well as the development of novel approaches to the generation of non-planar layers. The development of compatible materials and the improvement of the slicing algorithm are both tasks that will be addressed in further work.

In conclusion, Professor Huachao Mao and his research team demonstrated that the new strategy has the potential to improve additive manufacturing processes by lowering the amount of material waste, speeding up the printing process, improving surface quality, and increasing mechanical performance. The offered solution was able to eliminate stair-stepping effects and accept overhanging buildings without the need for extra supporting structures since it generated non-planar layers by using isothermal surfaces rather than iso-height surfaces.