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How to cutting Titanium

Titanium alloy is an ideal material for aircraft and engine because of its high strength, good mechanical properties and corrosion resistance. However, its poor machinability has restricted its application to a large extent for a long time. With the development of processing technology, in recent years, titanium alloys have been widely used in the manufacture of compressor section, hood, exhaust device and other parts of aircraft engine, as well as the manufacture of structural frame parts such as beam diaphragm of aircraft. Titanium alloy parts of a new aeroengine in our company account for about 11% of the total number of parts. This paper is a summary of the experience accumulated during the trial-manufacture of the new machine in understanding the cutting characteristics of titanium alloy materials and the specific characteristics shown under different processing methods and the technological measures to be taken.
 
Characteristic and machinability of Titanium:
1.Titanium alloys have the following advantages over general alloy steels:
Higher specific strength: Titanium alloy density is only 4.5g/cm3, much smaller than iron, and its strength is similar to that of common carbon steel.  
 
2.Good mechanical properties: Titanium alloy melting point is 1660 C, higher than iron, has a higher thermal strength, can work below 550 C, at the same time at low temperature usually shows better toughness.
 
3.Good corrosion resistance: Titanium alloy is easy to form dense oxide film on the surface below 550 C, so it is not easy to be further oxidized. It has high corrosion resistance to atmosphere, sea water, steam and some acid, alkali and salt media.
 
4.On the other hand, the machinability of titanium alloy is poor. The main reasons are: poor thermal conductivity, resulting in high cutting temperature and reduced tool durability.
 
When the temperature is above 600 C, hard oxide layer is formed on the surface, which has a strong wear effect on the tool. Chinese style
Low plasticity and high hardness make the shear angle increase, the contact length between chips and rake face is very small, the stress on rake face is very large, and the rake edge is easy to be damaged.
 
These characteristics in the cutting process of titanium alloy make it very difficult to process, resulting in low processing efficiency and high tool consumption.
 
According to the properties of titanium alloys and the characteristics of cutting process, the following aspects should be considered in processing:
1.As far as possible, cemented carbide tools, such as tungsten cobalt cemented carbide and titanium alloy, have low chemical affinity, good thermal conductivity and high strength. Ultra-fine Grain Cemented Carbide with impact resistance can be selected for intermittent cutting at low speed. High-speed steel with good high temperature performance can be used for forming and complex cutting tools.
 
2.A smaller front angle and a larger rear angle are used to increase the contact length between chips and rake face and reduce the friction between workpiece and rake face. The arc transition edge is used to improve the strength of the tool tip and avoid sharp corner burning and edge collapse.
 
3.Keep the blade sharp to ensure smooth debris discharge and avoid sticky debris avalanche.
Cutting speed should be low in order to avoid excessive cutting temperature; moderate feed, too large burnable knife, too small because of the cutting edge working in the hardening layer and wear too fast; cutting depth can be large, so that the tool tip works below the hardening layer, which is conducive to improving tool durability.