# Design of Fiber-Composite/Metal-Hybrid Structures Made by Multi-Stage Coreless Filament Winding
## 1 Introduction
(a) Digital representation of the CFW object during the design phase; (b) Robotic manufacturing of the fiber composite by hybrid CFW; (c) Eigenfrequency testing of the load-bearing fiber-composite structure; (d) Final component after assembly. Unlike CFW, additive manufacturing (AM), in the form of 3D printing, has evolved in the last decades, from being used in prototyping and research to industrial manufacturing. One reason for this is the presence of the complete digital process chain from design to machine control in AM. A variety of AM processes, for thermoplastic, short-/long-fiber-reinforced plastics, and metals enables the user to create complex shapes that are not possible or not economical with conventional manufacturing technologies, such as lathing, milling, and drilling. Similar to CFW, in AM, specific parameters become relevant, such as layer-interphases, supports and infills, wall thicknesses, warping, sagging, build plate adhesion, overhangs, and multi-material phenomenon. AM also decouples the component design from the manufacturing tool, which allows each component to be individual. Although CFW is restricted to having similar component topologies within the same fabrication setup, it outperforms AM in build volume and speed [19]. In this study, laser powder bed fusion (LPBF) was utilized to manufacture the anchor elements for the CFW structure. In LPBF, a moveable laser beam selectively melts metal powder layer-by-layer together under an inert atmosphere [38]. Conventional manufacturing technologies remain a valid option for manifold applications, especially when AM or CFW do not match the needed design language, are too slow in manufacturing, exhibit too high material costs, or lack other features. A combination of AM with the subsequent use of conventional technologies is possible but not advisable in CFW due to the fiber-composite character of the structures. This study presents methods to synergistically combine CFW, AM, and conventional manufacturing methods, and to exploit the specific characteristics of each process and material system. Within an application-based case study, this design approach was showcased, together with a custom-coded CFW design and data management tool that accompanied all project phases. The selected case study object offered a direct comparison with the state of the art in mechanical engineering. The digital tool aims to improve the CFW design workflow by utilizing graph-theoretical representations to streamline manufacturing by providing a digitally verified winding plan and to facilitate object management through database capabilities. A holistic digital representation can increase the process efficiency and manageability, resulting in overall cost savings. The implementation of multi-stage winding [39] into CFW aims to reduce the deformation of the fiber net caused by fiber-fiber interactions, which simplifies digitally representing the object. Manufacturing characteristics of the used LPBF processes were investigated with relevance to the design approach and fiber-composite material. In particular, the dimensional accuracy of the winding anchors must be ensured for the multi-material interplay.