Abstract
The polycrystalline cubic boron nitride (PCBN) milling tool can be used in the mold industry to replace cemented carbide tools to improve machining efficiency and quality. It is necessary to study the tool wear and failure mechanism to increase machining efficiency and extend tool life. Cr12MoV is used to analyze the failure form of PCBN tools in the interrupted cutting of hardened steels at low and high speed conditions in milling experiments. Experimental results show that the failure forms of PCBN tools include chipping and flank wear at low speed, and the failure modes at high speed are flank wear, the surface spalling of the rake face, and the fatigue failure on the flank face. The failure mechanism of different failure forms is analyzed by observing the surface morphology of the tool and using the theory of fracture mechanics. The results show that a high cutting speed should be selected to avoid the early damage of low speed and achieve better application of PCBN tools. At high cutting speed, tool failure is mainly caused by mechanical wear, diffusion wear, and oxidation wear. Moreover, a fatigue crack will occur at the cutting edge on the chamfered tool under thermal–mechanical coupling because of the intergranular fracture of the CBN grain and binder. A large area of accumulated fatigue damage may appear due to the influence of alternating mechanical stress and thermal stress. Finally, the control method to avoid tool failure is presented.
Highlights
With the development of automobile technology, the automobile mold is in great demand in automobile production, especially for medium and large-sized covering parts of high-grade cars [1].The tool steel Cr12MoV is a commonly used material for the automobile mold of cover parts
The results show that a high cutting speed should be selected to avoid the early damage of low speed and achieve better application of polycrystalline cubic boron nitride (PCBN)
At present, cemented carbide tools are usually used for most of the molds, and tool failure in the processing is severe because the cutting tool often suffers from the large cutting force, high temperature, and intermittent shock on milling process resulting in rapid tool wear and low production efficiency [6,7]
Summary
With the development of automobile technology, the automobile mold is in great demand in automobile production, especially for medium and large-sized covering parts of high-grade cars [1]. The life of cemented carbide tools can be higher than that of PCBN tools when the cutting speed is less than 400 m/min in ball-end milling. Wojciechowskl et al [24,25] conducted a series of experiments in milling of hardened steel using PCBN tools, their results indicated that tool life of cemented carbide tools can be higher than that obtained using PCBN tools in a specific range of cutting speed. A similar conclusion was obtained with the intermittent hard turning of bearing steel [29]; the cutting performance of the tool with a lower content of CBN was better than that of the tool with a high content of PCBN in terms of tool wear and surface integrity. Avoiding unreasonable failures at low and high cutting speed to provide the theoretical basis for the application of the PCBN tool in the machining of automobile covering parts
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