This study proposes a simultaneous optimization of component design and machining-process planning for complex and low-stiffness components manufactured by Powder Bed Fusion (PBF). While PBF is well-suited for intricate, lightweight structures, such workpieces often require challenging post-machining to remove support structures and meet geometric, surface-quality requirements. Their complexity hinders fixturing and machining strategies, and low stiffness leads to excessive displacement at cutting points during machining, causing poor surface quality. Previous studies have focused on either design (Design for Additive Manufacturing), introducing geometric changes to improve stiffness and handling[1], or machining process optimization, developing toolpath planning to reduce displacement under cutting forces[2]. However, addressing these aspects separately may not ensure successful post-machining for all geometries. In particular, though printable via PBF, topology-optimized components often require design modification for stable post-machining. Ideally, the component should be designed or modified considering subsequent machining operations. Therefore, this study simultaneously optimizes component design and post-machining processes, targeting scenarios where slight modifications of predefined component design can facilitate post-machining. The proposed method, summarized in the figure, minimizes design modifications while determining key machining conditions such as fixture arrangement, tool orientations, and feed directions. The matrix stiffness method formulates the optimization problem, ensuring the component secured by the fixture has sufficient stiffness against cutting forces. A case study confirms that the proposed approach reduces necessary design modifications and/or enhances machining efficiency compared to individual optimizations. This contributes to simplifying and automating PBF process chains for components with demanding post-machining needs.