1. Physical phenomena of titanium processing
The cutting force of titanium alloy processing is only slightly higher than that of the same hardness steel, but the physical phenomenon of processing titanium alloy is much more complicated than that of processing steel, which makes the processing of titanium alloy face great difficulties.
Most titanium alloys have very low thermal conductivity, only 1/7 of steel and 1/16 of aluminum. Therefore, the heat generated during the cutting of the titanium alloy is not quickly transferred to the workpiece or carried away by the chips, but accumulates in the cutting area, and the temperature generated can be as high as 1 000 ° C or more, causing the cutting edge of the tool to rapidly wear, crack and The formation of built-up edges, the rapid emergence of worn edges, and the production of more heat in the cutting area, further shortening the life of the tool.
The high temperatures generated during the cutting process also destroy the surface integrity of the titanium alloy parts, resulting in a decrease in the geometric accuracy of the parts and a work hardening phenomenon that severely reduces the fatigue strength.
The elasticity of titanium alloys may be beneficial to the performance of the part, but the elastic deformation of the workpiece during the cutting process is an important cause of vibration. The cutting pressure causes the "elastic" workpiece to leave the tool and bounce, thereby causing the friction between the tool and the workpiece to be greater than the cutting action. The friction process also generates heat, which increases the problem of poor thermal conductivity of the titanium alloy.
This problem is exacerbated when machining thin-walled or toroidally deformable parts, and it is not an easy task to machine titanium alloy thin-walled parts to the desired dimensional accuracy. Because the local deformation of the thin wall has exceeded the elastic range and plastically deformed as the workpiece material is pushed away by the cutter, the material strength and hardness of the cutting point are significantly increased. At this time, the machining becomes too high according to the originally determined cutting speed, which further causes the tool to wear sharply.
"Hot" is the "culprit" of difficult machining of titanium alloy!