Titanium alloy has the following cutting characteristics:
(1) Small deformation coefficient: This is a significant feature of titanium alloy cutting processing. The deformation coefficient is less than or close to 1. The sliding friction distance of chips on the rake face is greatly increased, accelerating tool wear.
(2) High cutting temperature: Since the thermal conductivity of titanium alloy is very small (equivalent to only 1/5 to 1/7 of No. 45 steel), the contact length between the chip and the rake face is extremely short, and the heat generated during cutting is not easily transmitted. Out, concentrated in the cutting area and a smaller range near the cutting edge, the cutting temperature is very high. Under the same cutting conditions, the cutting temperature can be more than twice as high as when cutting 45 steel.
(3) The cutting force per unit area is large: the main cutting force is about 20% smaller than when cutting steel. Since the contact length between the chip and the rake face is extremely short, the cutting force per unit contact area is greatly increased, which can easily cause chipping. At the same time, due to the small elastic modulus of titanium alloy, it is prone to bending deformation under the action of radial force during processing, causing vibration, increasing tool wear and affecting the accuracy of parts. Therefore, the process system is required to have good rigidity.
(4) The cold hardening phenomenon is serious: Due to the high chemical activity of titanium, at high cutting temperatures, it can easily absorb oxygen and nitrogen in the air to form a hard and brittle outer skin; at the same time, plastic deformation during the cutting process will also cause surface hardening. . The cold hardening phenomenon will not only reduce the fatigue strength of parts, but also aggravate tool wear, which is a very important feature when cutting titanium alloys.
(5) Tools are easy to wear
: After the blank is processed by stamping, forging, hot rolling and other methods, a hard and brittle uneven skin is formed, which can easily cause chipping, making the removal of the hard skin the most difficult process in titanium alloy processing. In addition, due to the strong chemical affinity of titanium alloys to tool materials, tools are prone to adhesive wear under conditions of high cutting temperatures and large cutting forces per unit area. When turning titanium alloy, sometimes the wear of the rake face is even more serious than that of the flank face; when the feed rate f<0.1 mm/r, the wear mainly occurs on the flank face; when f>0.2 mm/r, the wear of the front face is even more serious than that of the flank face. The tool surface will wear; when using carbide tools for finishing and semi-finishing turning, it is more appropriate for the wear of the flank surface to be VBmax <0.4 mm.
