Machinability and General Principles of Titanium Alloy
Titanium alloy according to the metal structure is divided into a phase, Silicon b phase, a + b phase, respectively, TA, TB, TC said its grades and types. General casting, forging using TA series, bar with TC series.
Titanium alloy relative to the general alloy steel has the following advantages:
Higher than the high: titanium alloy density of only 4.5g / cm3, Silicon much smaller than the iron, and its strength and ordinary carbon steel similar.
Good mechanical properties: titanium melting point of 1660 ℃, Silicon higher than the iron, with high thermal strength, can work below 550 ℃, while at low temperatures usually show better toughness.
Good corrosion resistance: 550 ℃ below the surface of titanium alloy is easy to form a dense oxide film, it is not easy to be further oxidation of the atmosphere, sea water, steam and some acid, Silicon alkali, salt media have a high resistance to corrosion.
On the other hand, the titanium alloy has poor machinability. Silicon The main reasons are:
Poor thermal conductivity, resulting in a high cutting temperature, reducing tool durability.
600 ℃ above the temperature, the surface of the formation of oxidized hard layer, the knife has a strong wear effect.
Low plasticity, high hardness, Silicon so that the shear angle increases, chip and the rake face contact length is very small, the rake face stress, blade prone to damage.
Low modulus of elasticity, elastic deformation, Silicon close to the flank surface of the workpiece surface rebound, so the surface has been processed with the flank contact area, wear serious.
Titanium alloy cutting process of these characteristics make its processing becomes very difficult, resulting in low processing efficiency, tool consumption.
The general principle of cutting
According to the nature of titanium and cutting process characteristics, processing should consider the following aspects:
As far as possible the use of carbide cutting tools, Silicon such as tungsten cobalt carbide and titanium alloy chemical affinity small, good thermal conductivity, strength is also higher. Low-speed intermittent cutting can be used when the impact of ultra-fine grain carbide, forming and complex tools can be used high-temperature performance of high-speed steel.
Using a smaller rake angle and a larger rear angle to increase the contact length of the chip and the rake face, reducing the friction between the workpiece and the flank, Silicon the tip of the use of circular transition edge to improve the strength, to avoid sharp corners And chipping.
To keep the blade sharp, to ensure that the chip is smooth, to avoid crumbs chipping.
Cutting speed should be low, so as not to cut the temperature is too high; moderate feed, too easy to burn knife, too small because the blade in the work hardening layer work and wear too fast; cutting depth can be larger, so that the tip in the hardened layer The following work, Silicon is conducive to improving tool durability.
Always cool the coolant when processing.
Cutting titanium alloy when the knife resistance to large, Silicon so the process system to ensure that there is sufficient rigidity. As the titanium alloy is easy to deform, so the cutting clamping force can not be large, especially in some finishing process, if necessary, Silicon can use a certain auxiliary support.
Above is the general principle of titanium alloy processing to be considered, Silicon in fact, with different processing methods and under different conditions there are different contradictions and solutions to solve the problem of focus.