The specific strength of titanium alloy products is very high in metal structural materials. Its strength is comparable to that of steel, but its weight is only 57% of steel. The thermal conductivity of titanium alloy is small and the specific heat is small, so the local temperature rises fast and the cutting temperature is very high when processing titanium alloy. Under the same conditions, the cutting temperature of titanium alloy is more than twice as high as that of 45 steel, and the heat generated during processing is difficult to be released through the workpiece. Therefore, the temperature of the tool is very high, the sharp wear of the tool tip, and the service life is reduced.
The low elastic modulus of titanium alloy makes the machined surface easy to produce rebound, especially the processing of thin-walled parts rebound is more serious, easy to cause strong friction between the surface and the machined surface, so as to wear the tool and break the edge.
Titanium alloy has strong chemical activity, and it is easy to interact with oxygen, hydrogen and nitrogen at high temperature, which increases its strength and decreases its plasticity. The oxygen-rich layer formed in the heating and forging process makes machining difficult.
Ultrasonic vibration cutting is a kind of pulse cutting in microcosmic sense. In one vibration cycle, the effective cutting time of the tool is very short, more than 80% of the time the tool is completely separated from the workpiece and chip. The tool and the workpiece, chip intermittent contact, which makes the tool by the friction is small, the heat generated greatly reduced, the cutting force significantly decreased, to avoid the ordinary cutting "let the knife" phenomenon, and do not produce chip nodules. With this vibration cutting, precision machining can be carried out on ordinary machine tools. Roundness, cylindricity, flatness, parallelism, straightness and other shape and position tolerances are mainly determined by the precision of machine tool spindle and guide rail, which can reach close to zero error, making it possible to replace grinding with turning, drilling instead of hinge, and milling instead of grinding. Compared with high speed hard cutting, it does not require higher machine rigidity and does not destroy the microstructure of the workpiece surface. In the finishing process of curved contour parts, we can use CNC lathes, machining centers and so on to carry out copying processing, which can save the expensive purchase cost of CNC grinder.
