Structural Design and Milling Performance of Diamond Micro Ball-end Mills for Machining Tungsten Carbide Microstructures

Owing to its extremely high hardness, outstanding wear resistance, excellent thermal stability, and superior chemical inertness, tungsten carbide (WC) has been widely recognized as one of the most important hard and brittle materials for advanced precision manufacturing applications. In particular, tungsten carbide microstructured components have attracted increasing attention in fields such as micro-optical systems, biomedical devices, microfluidic chips, and precision molding technologies due to their excellent mechanical properties and dimensional stability. As the demand for high-precision micro-manufacturing continues to increase, tungsten carbide has become a critical functional material for manufacturing precision microstructured molds. However, the intrinsic characteristics of tungsten carbide, including its ultrahigh hardness, low fracture toughness, and strong resistance to mechanical deformation, present significant challenges for microscale machining. Conventional micro-cutting processes often lead to severe tool wear, unstable cutting forces, edge chipping, surface cracking, and other machining defects, which greatly restrict the fabrication efficiency and quality of tungsten carbide microstructures. To address these challenges and achieve high-quality machining of tungsten carbide microstructured surfaces, three types of polycrystalline diamond (PCD) micro ball-end mills with different structures are designed and fabricated in this study. Considering the excellent hardness, wear resistance, and chemical stability of PCD materials, PCD micro-milling tools are regarded as promising candidates for machining hard and brittle materials. However, the performance of PCD micro ball-end mills is strongly affected by their geometric structures, especially the interaction between the cutting edge and the workpiece. Therefore, optimizing the tool geometry is essential for reducing cutting stress concentration, improving machining stability, and enhancing tool service life. Based on the geometric intersection principle of planes, cylinders and spheres, three polycrystalline diamond micro ball-end mill structures (flat rake face, cylindrical-spherical rake face and double-cylindrical rake face) are designed to optimize the contact stress between the cutting edge and the workpiece. Through micro-milling simulations and experiments of tungsten carbide, the influences of tool geometry on the tungsten carbide microstructures surface roughness, micro-milling force and tool wear are investigated, and the structural parameters of micro-milling tools applicable to tungsten carbide microstructure machining are determined. The finite element simulation results of micro-milling indicate that the hydrostatic stress of cylindrical-spherical polycrystalline diamond micro ball-end mills generated during the milling process is the lowest, while an intermediate hydrostatic stress is observed for flat rake-face polycrystalline diamond micro ball-end mills. The tungsten carbide micro-milling experiments show that uniform and consistent machined surface morphologies are obtained using the three types of self-designed polycrystalline diamond micro ball-end mills, with no obvious defects such as tearing and pits being detected. Consequently, superior surface quality is achieved in comparison with commercial polycrystalline diamond micro ball-end mills. The best milling surface quality and relatively low micro-milling forces are obtained by double-cylindrical polycrystalline diamond micro ball-end mills. The smallest tool wear is observed on the cylindrical-spherical PCD micro ball-end mill. The performance of the three self-designed polycrystalline diamond micro ball-end mills is superior to that of commercial micro-milling tools. Among them, the double-cylindrical polycrystalline diamond micro-milling tool exhibits the best milling quality. The cylindrical-spherical PCD micro-milling tool demonstrates the best wear resistance. This work offers a feasible technical reference for the structural design of PCD micro mills applied to precision machining of hard brittle microstructures.