Research On Cutting Performance Of Coated Tools Under Dry Drilling Al-Si Alloy

The aluminum-silicon (Al-Si) alloy is broad applied in many field, such as aviation, spaceflight, shipbuilding and automobile, because of its small-proportion, high-intensity, eroding resistance, wear resistance, good thermal conductivity and reproducible. But in cutting process, the tools were worn serious and harder to acquire lower roughness or higher precision, so it's difficult to machining material.The machinability of Al-Si alloy was analyzed, especially in drilling under dry cutting condition. Which indicates that the tools materials used for drilling Al-Si alloy not only have high hardness, exceptional wear resistance, high thermal stability, low frictional coefficient and good thermal conductivity, but high intensity and toughness, etc. It is hardly possible to a tool material to satisfy these properties desired. Coatings technique offered the solution about this problem. So it was noticed by many countries, and rapidly developed and used in manufacturing.In this paper, DLCU GLC, DLC+Si,GLC+Cr and GLC+MoS₂ was deposited onto high speed steel (HSS) twist drills with PVD technique. The drilling tests to Al-Si alloy was carried out under dry cutting. The cutting performances and mechanics characteristics were analyzed. Results show the cutting performance of DLC,DLC+Si, GLC,GLC+Cr and GLC+MoS₂ coated HSS twist drills is remarkably improved. The average drill life of these coated drills are respectively 2.28, 5.25, 6.75, 6.5 and 6.5 times higher than those of the uncoated drills, and The cutting performance of GLC and its composite coated drills is better than those of the DLC and its composite coated drills.It is found in test that the coated drills have an outstanding figure feature of the flank wear, namely flank wear is smaller in the major cutting edges middle part and biggest in the outer corner regions, and that the running-in stage has not evident difference to coated and uncoated drills, but normal friction and wear stage is prolonged to the coated drills. The average cutting forces (F_z and M_z) of coated drills are smaller than those of uncoated drills, but they have not evident differences in coated drills. Additional, the holes surface quality is better, and the holes dimension disperse is lesser to coated drills.