## 4 Comparative Evaluation of Magnetic Gear Core Materials
### Technical Specifications and Numerical Comparisons
#### 4.2.2 Manufacturability Assessment of Core Materials  
In this section, the manufacturability of selected core materials is systematically evaluated with respect to material properties, applicable production techniques, and expected production volumes. The analysis focuses on three widely used magnetic core materials: M400 50A electrical steel, Somaloy 700 HR 5P soft magnetic composite, and Vacodur 50A cobalt steel. Each material is assessed across four primary manufacturing methods: conventional machining, wire electrical discharge machining (EDM), investment casting, and powder metallurgy. Furthermore, both low-volume prototyping and mass production scenarios are considered, given their significant impact on process feasibility and economic viability. The evaluation aims to identify the most practical manufacturing routes for each material by taking into account factors such as process compatibility, tooling requirements, production cost, and scalability.  
M400-50A electrical steel, with moderate hardness (\(\sim\)200 HV) and excellent ductility, offers acceptable machinability using standard HSS or carbide tools. Although its silicon content slightly increases tool wear, it is widely used in both prototyping and industrial manufacturing environments with minimal process complications [80]. The machinability index for M400-series steels typically ranges between 50 and 65 when normalized against free-machining steels [81]. This makes it highly suitable for low-volume prototyping, as parts can be rapidly machined with minimal investment. For mass production, however, conventional machining becomes less attractive due to longer cycle times compared to press-based or cast alternatives, although CNC-based automation can partially compensate.  
Vacodur 50A, a Fe-Co alloy with exceptional magnetic saturation (\(\sim\)2.35 T), is considerably more difficult to machine. Its high hardness (\(\sim\)350 HV) and abrasive behavior cause accelerated tool wear, necessitating CBN or PCD tooling under low cutting speeds (20-30 m/min). These constraints significantly increase the cost and duration of part fabrication [82]. While technically feasible for low-volume prototypes, Vacodur's poor machinability renders it unsuitable for conventional high-speed machining in mass production unless supported by specialized tooling, optimized parameters, and possibly grinding-based finishing processes.  
Somaloy 700 HR 5P, as a bonded soft magnetic composite, is inherently not suitable for conventional machining. Its brittle microstructure, composed of insulated iron particles and organic binders, tends to fracture or delaminate under cutting loads [83]. Although specially formulated machinable SMC grades (e.g., Hoganas SPM) exist for limited prototyping, these do not fully replicate the magnetic performance of pressed components. Therefore, machining is discouraged for both prototyping and mass production, especially when material integrity is critical.  
Wire EDM is an effective method for producing precise geometries in hard-to-machine metals, particularly in prototyping stages. Vacodur 50A and M400-50A are both compatible with this technique and allow high-precision contouring without inducing mechanical stress. Due to these characteristics, EDM represents a suitable manufacturing method for low-volume, high-precision applications where sharp features and tight tolerances are required. However, EDM is inherently slow and energy-intensive, making it unsuitable for mass production. Furthermore, localized thermal effects during processing may alter the magnetic surface properties, requiring post-process annealing to restore magnetic permeability [84].  
In contrast, Somaloy 700 HR 5P is unsuitable for EDM. The process degrades the surface insulation layer and induces localized carbonization of the binder, leading to severedeterioration in magnetic and mechanical integrity [85]. As a result, EDM must be strictly avoided for both the prototyping and production of SMC parts.