Milling Machinability of TiC Particle and TiB Whisker Hybrid Reinforced Titanium Matrix Composites

The milling machinabilities of titanium matrix composites were comprehensively evaluated to provide a theoretical basis for cutting parameter determination. Polycrystalline diamond (PCD) tools with different grain sizes and geometries, and carbide tools with and without coatings were used in the experiments. Milling forces, milling temperatures, tool lifetimes, tool wear, and machined surface integrities were investigated. The PCD tool required a primary cutting force 15% smaller than that of the carbide tool, while the uncoated carbide tool required a primary cutting force 10% higher than that of the TiAlN-coated tool. A cutting force of 300 N per millimeter of the cutting edge (300 N/mm) was measured. This caused excessive tool chipping. The cutting temperature of the PCD tool was 20%-30% lower than that of the carbide tool, while that of the TiAlN-coated tool was 12% lower than that of the uncoated carbide tool. The cutting temperatures produced when using water-based cooling and minimal quantity lubrication (MQL) were reduced by 100℃ and 200℃, compared with those recorded with dry cutting, respectively. In general, the PCD tool lifetimes were 2-3 times longer than the carbide tool lifetimes. The roughness Ra of the machined surface was less than 0.6 μm, and the depth of the machined surface hardened layer was in the range of 0.15-0.25 mm for all of the PCD tools before a flank wear land of 0.2 mm was reached. The PCD tool with a 0.8 mm tool nose radius, 0° rake angle, 10° flank angle, and grain size of (30+2) μm exhibited the best cutting performance. For this specific tool, a lifetime of 16 min can be expected.