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In the micro-end-milling of surfaces, thin walls, and micro channels, etc, both peripheral and end cutting edges of micro end mills are engaged in cutting. However, the microcutting fundamentals for end cutting edges have not been well studied, even though those for peripheral cutting edges have been studied widely. Key micromilling variable analyses show that the order of significance is the axial depth of cut (ap), feed per tooth (fz), and radial depth of cut (ae). It means that the microcutting mechanisms of the end cutting edge need to be studied and compared with that of the peripheral cutting edge in order to understand micro-end-milling mechanisms more thoroughly. Simulations using the finite element method (FEM) show that the minimum undeformed chip thickness (MUCT) is different for peripheral and end cutting edges, even though the cutting edge radius remains unchanged. The results of those simulations have been experimentally validated. It shows that the MUCT of the end cutting edge is larger than that of the peripheral cutting edge. That means the MUCT is not only the size of a certain proportion of the cutting edge radius, as mentioned in previous studies, but also has a close relationship with the location of the cutting edge. Therefore, ap could be several times larger than fz according to the relationship between MUCT and the micromilling parameters. It creates a solid basis for the selection and quantization of micro-end-milling parameters in the fabrication of complicated geometries as thin walls and micro channels.

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The cutting performance of cutting tools in high-speed machining (HSM) is an important factor restricting the machined surface integrity of the workpiece. The HSM of AISI 4340 is carried out by using coated tools with TiN/TiCN/TiAlN multi-coating, TiAlN + TiN coating, TiCN + NbC coating, and AlTiN coating, respectively. The cutting performance evaluation of the coated tools is revealed by the chip morphology, cutting force, cutting temperature, and tool wear. The results show that the serration and shear slip of the chips become more clear with the cutting speed. The lower cutting force and cutting temperature are achieved by the TiN/TiCN/TiAlN multi-coated tool. The flank wear was the dominant wear form in the milling process of AISI 4340. The dominant wear mechanisms of the coated tools include the crater wear, coating chipping, adhesion, abrasion, and diffusion. In general, a TiN/TiCN/TiAlN multi-coated tool is the most suitable tool for high-speed milling of AISI 4340, due to the lower cutting force, the lower cutting temperature, and the high resistance of the element diffusion.

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