Titanium alloy, with its unique advantages, occupies an important position in aviation, aerospace, medical and other fields, and has also risen in the 3C consumer electronics field in the past two years, being applied to the body and structural parts of a number of hot-selling high-end smartphones. Titanium alloy has the performance advantages of light weight, high strength and good texture, which helps to improve the appearance design of smartphones and significantly reduce the weight of the body, and is expected to become a trend of material innovation in consumer electronics. However, titanium alloys are difficult to process, which has always been a problem for engineers and technicians.
Titanium Alloy Processing Difficulties
1. Temperature concentration: the thermal conductivity of most titanium alloys is extremely low, only 1/7 of steel, 1/16 of aluminum and 1/25 of copper, so the heat generated during the cutting process is not easy to emit, but concentrated in the cutting area. The temperature of the tool tip can rise to 1000°C, leading to rapid tool wear, cracking, and chip accumulation, shortening tool life. The high cutting temperature also destroys the surface integrity of the titanium alloy part, reduces the geometric accuracy of the part, and triggers the work-hardening phenomenon, which severely reduces its fatigue strength.
2. Elastic deformation: the modulus of elasticity of titanium alloy is relatively low, for example, the modulus of elasticity of TC4 is only 110Gpa, which is much lower than the 210Gpa of 45 steel and common stainless steel about 200Gpa. When processing titanium alloy, it is easy to produce elastic deformation, especially in the processing of thin-walled or ring-shaped parts more obvious. Thin-walled parts in the processing of local deformation beyond the elastic range, resulting in plastic deformation, cutting point material strength and hardness increased significantly.
3. Strong affinity: titanium alloy affinity is good, in the turning and drilling process is easy to form long and continuous chips, these chips will wrap around the tool and hinder its function. When the cutting depth is too large, it is easy to cause sticking, burning or breaking of the tool.
4. Vibration: The elasticity of titanium alloys becomes the main cause of vibration during the cutting process. The vibration generated by processing titanium alloy is 10 times that of steel. As the cutting heat is concentrated in the cutting part, it produces jagged chips, which leads to fluctuations in cutting power.
Countermeasures for difficult machining of titanium alloys
1. Cooling: Use coolant to reduce high cutting temperatures. Usually, non-soluble oil coolant is suitable for low-speed heavy-duty cutting, and soluble cutting coolant is suitable for high-speed cutting. In addition, low-temperature cutting methods can be used, such as the use of liquid nitrogen (-180 ℃) or liquid CO2 (-76 ℃) as a cutting fluid, which can effectively reduce the temperature of the cutting zone, improve the quality of the machined surface, and prolong the life of the tool.
2. Choose the right tool: the selection of appropriate cutting tools can significantly improve processing efficiency. Keeping the cutting edge sharp can reduce the cutting force. Grinding technology with polished flutes and high positive angle indexable inserts can help reduce cutting pressure. If necessary, use coated tools to minimize alloy stickiness and break up long chips.
3. Constant feed or increased feed rate: Maintaining a constant feed is critical to minimizing work hardening. If equipment performance allows, try increasing the feed rate to reduce the amount of time the tool spends in the machining area, thus reducing the chance of heat buildup and work hardening.
4. Reduce cutting speed: Use 1/3 or less of the steel cutting speed for titanium machining to control heat release.
5. Change tools according to the process: For high-volume titanium machining, carbide tools are preferred; for low-volume machining, high-speed carbide tools are more appropriate.
6. Use highly rigid machine tools: Highly rigid machine tools are critical to the successful machining of titanium alloys. The ideal titanium milling machine must be rigid, with a spindle that can operate at low speeds and high torque to absorb vibration and reduce chatter during cutting.
7. Regular Cleaning: Regular cleaning of machining equipment and tools prevents debris deposits that can affect machining results.
Through the above countermeasures, the challenges of titanium alloy machining in 3C consumer electronics can be effectively dealt with, promoting the application of titanium alloy in more high-end smartphones and consumer electronics.
