Titanium alloy has high strength and high hardness, so it requires large power of processing equipment, mold and tool should have high strength and hardness. During machining, the contact area between the chip and the front cutter surface is small, and the stress of the cutter tip is large. Compared with 45 steel, although the cutting force of titanium alloy is only 2/3 -- 3/4, but the chip and the front tool surface contact area is smaller (only 1/2 -- 2/3 of 45 steel), so the stress of the cutting edge is greater, the tip or cutting edge is easy to wear; Titanium alloys have high friction coefficient and low thermal conductivity (only 1/4 and 1/16 of iron and aluminum, respectively). Tool and chip contact length is short, cutting heat accumulation in a small area near the cutting edge is not easy to distribute, these factors make the cutting temperature of titanium alloy is very high, resulting in faster tool wear and affect the processing quality. Because the elastic modulus of titanium alloy is low, the workpiece spring back during cutting is large, which is easy to cause the aggravation of tool face wear and workpiece deformation. Titanium alloy at high temperature chemical activity is very high, easy to react with hydrogen, oxygen and other gas impurities in the air, hardening layer, and further aggravate the wear of the tool; In titanium alloy cutting, the workpiece material is easy to bond with the tool surface, and the cutting temperature is very high, so the tool is easy to produce diffusion wear and bonding wear.
Titanium and titanium alloy have many excellent properties, mainly reflected in the following aspects:
1. High intensity. Titanium alloy has a very high strength, its tensile strength is 686-1176MPa, and the density is only about 60% of steel, so the specific strength is very high.
2. High hardness. The hardness HRC of titanium alloy (annealed) is 32 -- 38.
3. Low elastic modulus. The elastic modulus of titanium alloy (annealed) is 1.078×10-1.176×10MPa, about half that of steel and stainless steel.
4. Excellent high and low temperature performance. At high temperature, titanium alloy can still maintain good mechanical properties, its heat resistance is much higher than aluminum alloy, and the operating temperature range is wide, the current new heat-resistant titanium alloy operating temperature can reach 550 -- 600℃; At low temperature, the strength of titanium alloy increases compared with that at normal temperature, and has good toughness. Low temperature titanium alloy can maintain good toughness at -253℃.
