## 2 Manufacturing Processes of Musical Instruments Made of Composites and Alternative Materials
### Composites in Musical Instrument Manufacturing
The manufacture of specimens with different lay-up procedures was described and a completed acoustic guitar with a soundboard made from carbon fiber-reinforced polyurethane foam was presented. The lay-up procedure and lamination stack were described as a symmetric lay-up of [0/90/Uf]s, where the 0 direction corresponds to the grain and the 90 is the cross direction. [PERSON] et al. [33] manufactured a Turkish folk violin, Kemane, using glass fiber and carbon fiber composites with polyester resin, as an alternative to the traditional gourd manufacturing. Ib\(\acute{\text{a}}\)[PERSON] et al. [16] produced a drum shell using a carbon fiber-reinforced epoxy composite laminate. The shell, crafted with an autoclave method, involved the laying of three or more collinear plies. The autoclave process was crucial for eliminating voids generated during the curing process. The drum shell was manufactured using a GFRE mold with an epoxy-based coating finish. [PERSON] et al. [29] produced the composite shell for an Indian drum using a sandwich structure. The drum shell consisted of a carbon fiber/epoxy face sheet and a balsa core to which the drumhead was attached. The shell structure was crafted through a combination of wet lay-up and vacuum molding techniques. Figure 3 demonstrates the detailed lay-up procedure and the sequence of manufacturing of the percussion instrument. Figure 1: Development of a violin top plate. (**a**) Marked profile of the top plate on prepreg fabric with protective films, (**b**) cut preform of the prepreg, (**c**) treated female mold, (**d**) placement of the fabrics, (**e**) release film on top of the fibers to help the separation of the cured part from the breather and the vacuum bag, (**f**) vacuum bagging. Reprinted from [3] with permission from Spinger Nature. Copyright 2015 Springer Nature. Figure 3: (**a**) Two-part mold; (**b**) prefabricated balsa core; (**c**) placement of carbon fiber; (**d**) vacuum bagging; (**e**) demolded part; (**f**) assembly of drumhead; (**g**) finished drum. Reprinted from [29] with permission from Elsevier. Copyright 2015 Elsevier. Figure 2: Manufacturing of a Greek bouzouki. (**a**) Lamination process: 1. Mold 2. Final composite lamination 3. Peel ply, expendable detachable fabric that helps to separate the cured composite from the other expendables 4. Green flow, net that helps the air to escape and the resin to infuse the lamination 5. Sealing tape 6. Vacuum bag. (**b**) VARTM process: 1. Resin, 2. Vessel that contains resin 3. Suction tube 4. Complete lamination with expendable materials 5. Sealing tape 6. Overflow resin tube 7. Excess resin 8. Resin trap 9. Sealing tap 10. Vacuum generator tube. [PERSON] et al. [23] described the manufacturing process of a carbon fiber bouzouki based on a 3D scan of a wooden bouzouki. They developed a 3D CAD surface model of the musical instrument using the point cloud generated by the 3D scan. The molds for each carbon fiber part were then manufactured by CNC machines based on the G-codes produced by CAM programs. These molds played a crucial role in creating the carbon fiber bouzouki parts, from which the final musical instrument was assembled. The carbon fiber parts underwent proper machining and surface finishing to ensure a precise fit and ease of proper assembly through gluing. The fabrication of carbon fiber fabric parts employed a vacuum-assisted resin transfer (infusion) process, involving specific temperature control and duration. The chosen raw fabrics included (a) 200 g/m\({}^{2}\) Twill, that reinforces the composite in two directions, and (b) 300 g/m\({}^{2}\) UD--providing strength in only one direction to the composite. Three corresponding top plates with slightly varying characteristics were manufactured, resulting in the assembly of three carbon fiber instruments (C01, C02, and C03). The manufacturing of the three top plates involved the use of Twill and UD carbon fiber layers in varying sequences and fiber directions.