In machining aluminum alloy that contains a large amount of silicon, highly wear-resistant cutting tools such as diamond coated ones are needed because silicon particles in the matrix of aluminum quickly wear the tools. However, diamond coatings on cutting edges actually debond off easily.
Diamond-coated drills for cutting high silicon aluminum alloy have successfully been developed. In order to overcome the weak adhesion of diamond coatings on cutting tools, discussion was focused on the possible reduction of mechanical stress in the coating at cutting edges and improvement of the strength of diamond coating. To reduce the stress at the cutting edge, we optimized the drill shape for cutting high silicon aluminum alloy. Application of multi-layered diamond coating was also examined for the possible enhancement of toughness of coatings. The important aspects are summarized as follows.
The mechanical load applied to the coating at cutting edge during drilling operation decreases with larger rake angle. However, at the same time, the cutting load may tend to concentrate at the tip of cutting edge with larger rake angle, which leads to severe local stress concentration in the coating. In between these two factors in conflict with each other, we were able to find that the rake angle of 208 showed the best performance for cutting high silicon aluminum alloy.
The coating toughness was measured for the two cases of single and multilayered coatings. Multilayered coating had twice as large toughness as that of conventional single-layered coating. The drill coated with multi-layered coating showed better performance than that with single-layered coating in cutting high silicon aluminum alloy.
Standing on the successful improvement of cutting performance achieved in this study, it should be concluded that the durability of diamond-coated drills were able to be improved from the view point of mechanical strength of coatings rather than wear resistance at least for the case of cutting high silicon aluminum alloy.
From the reference: Development of high performance diamond-coated drills for cutting high silicon aluminum alloy,authors are H. Hanyua,*, S. Kamiyab, H. Odagia, Y. Murakamia, M. Sakab