Performance and manufacturability co-driven process planning for topology-optimized structures fabricated by continuous fiber-reinforced polymer additive manufacturing

Abstract

The advancement of continuous fiber-reinforced polymer additive manufacturing (CFRP-AM) enables the fabrication of intricate geometries. While topology-optimized structures are known for their lightweight and superior properties, these complex forms introduce significant challenges in fiber toolpath design due to irregular geometric variations, particularly where fibers converge and diverge. Moreover, this complexity has been compounded by a separation between structural design and its direct application to manufacturing, leading to inefficiencies in the production process. To address this issue, a strut-joint (S-J) feature fiber toolpath planning method is developed that considers both performance and manufacturability. This method employs a divide-and-conquer strategy by separately optimizing the fiber paths in strut and joint regions to improve overall structural integrity. For topology-optimized structures with intricate geometries, a curl-based feature recognition method has been proposed. This method calculates the curl of the fiber orientation field and leverages the principle where angular variations result in increased curl values to categorize topology-optimized structures into two fundamental features: strut and joint. Subsequently, in strut regions, continuous fiber paths are generated using a field projection method, with the projection period determined by the minimal printable spacing. In joint areas, two specialized sub-optimization problems are introduced—connection and shape design. The connection problem uses integer linear programming to optimize the matching of fiber paths from different struts, while the shape design ensures extensive fiber coverage with no overlap, improving print quality and mechanical performance. This S-J feature approach maximizes fiber alignment with optimized material orientations in strut regions and minimizes performance degradation in joint areas, ensuring the structural integrity and effectiveness of the design. By directly translating the structural design results into continuous toolpaths for manufacturing, this approach bridges the gap between design and manufacturability. Mechanical tests revealed that the Messerschmitt-Bolkow-Blohm (MBB) model fabricated with S-J toolpaths exhibited increases in stiffness of 21.5 % and 25.2 %, in strength of 29 % and 25.8 %, and in fiber infill ratio of 43.1 % and 6.7 %, respectively, when compared to the equally-spaced method (EQS) and Offset methods. Numerical simulation and digital image correlation (DIC) further validated the method, demonstrating a more uniform strain distribution and reduced stress concentrations, leading to enhanced strength. This research advances toolpath planning for topology-optimized structures, highlighting future innovations to improve performance and manufacturability of CFRP structures.