ВЗАЄМОДІЯ ГРАФІТУ З МАТЕРІАЛОМ РІЗАЛЬНОГО ІНСТРУМЕНТУ НА ОСНОВІ PCBN ПРИ ОБРОБЦІ ЧАВУНУ

The article presents a comprehensive analysis of the problem of machining high-strength cast iron with vermicular graphite (CGI) using cutting tools made of polycrystalline cubic boron nitride (PCBN).The relevance of the study is determined by the importance of CGI in the automotive industry for improving engine performance and reducing harmful emissions. However, its widespread use is hampered by low machinability, which is significantly inferior to gray cast iron. Based on the analysis of scientific documents, the main reasons for the low stability of PCBN tools have been systematized. The unique microstructure of PCBN is recognized as the key problem: vermicular graphite combined with low sulfur content. This leads to intense thermomechanical stresses and prevents the formation of a protective sulfide layer (MnS), which effectively reduces wear when machining gray cast iron. As a result, thermochemical and diffusion wear become the dominant wear mechanisms, accompanied by the penetration of iron into the tool structure and the destruction of boron nitride grains. The article discusses possible ways to solve the problem, in particular, development of new PCBN grades with improved binding materials. Application of innovative processing methods, such as modulation-assisted machining (MAM). It is shown that MAM converts continuous cutting into intermittent cutting, which reduces thermal loads and significantly increases tool life. In addition, the review highlights that cutting speed and thermal management strategies play a crucial role in controlling the intensity of diffusion wear. Optimizing these parameters can partially compensate for the lack of a lubricating sulfide layer and improve the overall machining performance of CGI. Moreover, recent studies indicate that controlled cooling techniques can further stabilize the cutting zone, thereby reducing tool degradation and enhancing dimensional accuracy during CGI machining.