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Titanium alloy has long been known in the industry as a "difficult-to-machine material." Its machining difficulty stems from a unique combination of physical, chemical, and mechanical properties. The specific reasons are as follows:

1. Poor Thermal Conductivity

Titanium alloy's thermal conductivity is only about 1/7 that of steel and 1/16 that of aluminum. This means the heat generated during cutting cannot be effectively dissipated through the workpiece or chips—up to 80% of the heat concentrates on the cutting edge, causing rapid tool wear, thermal cracking, and even premature failure.

2. High Strength Retained at Elevated Temperatures

Most metals soften when heated, but titanium alloy maintains its strength at high temperatures. This property is an advantage for aerospace applications but a nightmare for machining—the cutting edge endures extreme stress without the benefit of thermal softening, making it prone to chipping and deformation.

3. High Chemical Reactivity — It "Sticks" to Tools

Titanium alloy is highly chemically reactive, especially at elevated temperatures. It readily reacts with tool materials such as cemented carbide and cobalt, forming built-up edge (BUE) and causing diffusion wear. This adhesion leads to smearing, deteriorated surface quality, and accelerated tool failure.

4. Low Elastic Modulus

Titanium alloy's elastic modulus is only about half that of steel. This means it deflects noticeably under cutting forces and springs back after the tool passes. This "springback" causes chatter, vibration, and rubbing, resulting in poor surface quality, low dimensional accuracy, and increased tool wear. Achieving tight tolerances is particularly difficult.

5. Work Hardening

Titanium alloy has an extremely strong work-hardening tendency. During cutting, the surface layer becomes harder than the underlying material, accelerating tool wear and making subsequent cutting even more difficult. This is especially pronounced in operations such as drilling and tapping.

6. Narrow Chip Formation

Titanium alloy produces thin, serrated chips that concentrate stress on the cutting edge. Unlike the long, curled chips of steel that carry heat away, titanium alloy chips are difficult to evacuate, leading to chip recutting and further exacerbating tool wear.