When cutting titanium alloy, the turning angle α0 of the turning tool is the most sensitive of all the tool parameters, because the metal elastic recovery under the cutting layer is large and the processing hardness is large. Generally, large rear angle can make the edge easy to cut into the metal layer and reduce the wear of the flank, but if the rear angle is too small (less than 15 degrees), metal adhesion will occur. If the rear angle is too large, the tool will be weakened and the blade will be fragmented easily. Therefore, most cutting tools for cutting titanium alloys use a 15° relief angle. From the perspective of tool durability, α0 is less than or greater than 15°, which will reduce the durability of the turning tool. In addition, the turning edge with α0 of 15° is sharper and can reduce the cutting temperature.
Since the titanium alloy forms a hard and brittle compound with oxygen, hydrogen, nitrogen, etc. in the air during the cutting process, causing tool wear (mainly on the rake face of the turning tool), a small value front angle should be used; In addition, the plasticity of the titanium alloy is low, and the contact area between the chip and the rake face is small, and a small value of the rake angle should also be used for this purpose. By doing so, the contact area between chip and rake face can be increased, so that cutting heat and cutting pressure can not be too concentrated near the edge. It is not only conducive to heat dissipation, but also strengthens the cutting edge and avoids cutting edge collapse due to the concentration of cutting force. Therefore, when a (α+β) titanium alloy is processed with a cemented carbide tool. Take the rake angle γ0=5° and grind the chamfer f (width 0.05~0.1mm), γf=0°?10°, the tool tip is ground into r=0.5mm small arc, and the blade inclination angle λ=+3 °.
However, the research work shows that the tool has the best durability when the front angle of the turning tool is in the range of 28° to 30°. Increasing the radius of tool tip arc can also reduce tool collapse.
General geometry of turning titanium alloy external turning tools: Chamfering = 0.3 to 0.7 mm, γf = 0°, γ0 = 8° to 10°, α0 = 15°, r = 0.5 mm, λ = 0°, κr = 45°, κ'r = 15°.
Handling of difficult titanium parts
Effect of cutting amount on cutting temperature
When the titanium alloy TA2 is turned by the YG8 insert, the relationship between the change in the cutting parameters and the change in the cutting temperature is known. The cutting temperature t during the machining increases sharply as the cutting speed v increases, and increasing the cutting amount f also increases the cutting temperature t, but the influence thereof is smaller than the effect of increasing the speed. The change in depth of cut has little effect on the cutting speed.
The high cutting speed during machining causes the cutting tool to wear sharply. Further, the titanium alloy has the ability to absorb oxygen and hydrogen from the surrounding atmosphere, resulting in so-called "alphalation of the structure" and strengthening the machined surface.
The cutting temperature is usually maintained at around 800 °C when the cutting speed and the amount of cutting are selected. That is, when the amount of the cutter f is f.11 to 0.35 mm/r, the cutting speed v=40 to 60 m/min is taken.
Effect of cutting amount on surface roughness
Titanium alloys are sensitive to stress concentration and can seriously reduce their fatigue strength when scratches or dents occur, so the processing requirements of surface quality of titanium alloy parts are very high.
Cutting tool amount has a great influence on surface quality. From the processing of titanium alloy TC6 (speed v = 40m / min, cutting depth ap = 1mm, after the flank wear h ≤ 0.1mm), the relationship between the cutting tool amount and the surface roughness of the machined surface can be known. In order to obtain a surface roughness Ra1.6μm, the amount of pass f = 0.16mm / r must be selected; If the amount of pass f = 0.25 mm / r, 0.35 mm / r and 0.45 mm / r, respectively, is used, the corresponding machined surface roughness obtained is Ra 3.2 μm, Ra 6.3 μm and Ra 12.5 μm.