Concurrent optimization of structural topology and toolpath for additive manufacturing of continuous fiber-reinforced polymer composites

The advancement of continuous fiber-reinforced polymer additive manufacturing (CFRP-AM) enables the fabrication of lightweight structures with intricate geometries and superior properties. However, existing design methods treat structural optimization and toolpath design as distinct stages, typically implementing toolpath design as a post-processing step following structural optimization. This sequential workflow hampers the full exploitation of CFRP-AM's potential, hindering optimal structural integrity and manufacturability. In this paper, an integrated structure and toolpath optimization (ISTO) method is proposed for improving the final product's structural performance and manufacturability simultaneously. In ISTO, two different strategies are employed to address different aspects of the design space: bi-material topology optimization for the structural layout and scalar field projection for continuous fiber toolpaths. Correspondingly, elemental pseudo densities and scalar field gradients serve as design variables for structural topology and toolpath parameterization, respectively, in a compliance minimization problem. This facilitates analytical sensitivities for seamless integration with gradient-based optimization algorithms. Additionally, incorporating volume fraction constraints of both the solid structure and the fiber percentage relative to the solid guarantees the attainment of predetermined weight reduction targets and ensures calculation accuracy. Thus, the proposed ISTO establishes a comprehensive framework for concurrent CFRP-AM optimization, incorporating design-to-manufacturing information to optimize structural topology and continuous CFRP-AM toolpaths concurrently. Finally, the effectiveness of the proposed method is validated by typical numerical examples. Comparisons with existing optimization methods show that the proposed ISTO can remarkably boost structural stiffness while ensuring manufacturability and moreover it effectively tackles design challenges of smooth toolpath planning including different initial cutouts.