Many enterprises find it difficult to process titanium metal. On the one hand, it is because of the high hardness of titanium, and on the other hand, it is also because titanium processing is a new process and lacks a model for reference. When workers are used to processing metals with lower requirements such as cast iron, titanium, which is harder than stainless steel, naturally becomes a member of the list of difficult to process materials. In fact, compared with most materials, metallic titanium is also a material that can be directly processed. As long as the workpiece is stable, the clamping is firm, and the processing parameters are correctly selected, the matter is not as complicated as expected. However, there are still some problems that must be paid attention to in the processing of workpieces with complex shapes, which may contain many fine or deep cavities, thin walls, inclined surfaces and thin brackets.
Vibration and heat must be considered
It is better to equip ISO 50 spindle with short tool overhang for processing metal titanium. However, the current situation is that most machine tools are equipped with IS0 40 spindle. If the strength of the machine tool is too high, it is impossible to maintain the sharpness of the tool for a long time. In addition, how to clamp the parts with complex structure is also a thorny problem. However, the biggest challenge actually comes from vibration and heat.
Sometimes the cutting process in titanium metal processing must be used for full groove milling, side cutting or contour milling, which will cause vibration and form poor cutting conditions. Vibration can cause the blade to break, damage the blade and produce many unpredictable results. Therefore, when setting the machine tool, attention must be paid to the principle of improving stability to reduce the occurrence of vibration. One improvement measure is to adopt multi-stage clamping to make the parts closer to the main shaft to help counteract the vibration.
A large amount of heat will be generated during the processing of titanium metal, resulting in an increase in temperature. Unfortunately, the high temperature will affect the cutting performance of the tool, but it will not affect the hardness of the workpiece. Titanium metal can still maintain extremely high hardness and strength at high temperature, and even work hardening may occur, which makes processing more difficult and is not conducive to some subsequent cutting processes. Therefore, selecting the best indexable blade grade and groove shape is the key to the success of machining. According to past experience, fine grain uncoated blade grades are very suitable for titanium metal processing; Today, the blade grade with PVD titanium coating has greater advantages in improving cutting performance.
Accuracy, conditions and correct cutting parameters
The runout accuracy of the tool in the axial and radial directions requires special attention. For example, if the insert is not properly installed in the milling cutter, the surrounding cutting edge can be easily damaged. In addition, the manufacturing tolerance of the tool is wrong, the tool wear, the spindle wear and the defects of the tool shank will also greatly reduce the service life of the tool. In all cases of poor processing performance, the proportion caused by the above factors accounted for 80%.
Compared with the positive rake groove tool that most people like, the tool with a slightly negative rake groove can remove material at a higher feed rate, and the feed rate per tooth can reach 0.5 mm. However, this requires that the machine tool is very solid and the clamping is extremely stable. In addition to insert milling, the main deflection angle of 90 ° should be avoided as far as possible, which can improve the cutting stability, especially in the case of shallow cutting depth. In deep cavity milling, it is an ideal way to use a tool with variable length through the tool shank. Its processing effect is better than using a long tool with a single length in the whole process.
When milling titanium metal, it is required to accurately calculate the feed rate of each tooth of the tool, so that it is not less than the minimum feed rate - usually 0.1mm. In addition, it is also possible to reduce the spindle speed to achieve the initial feed rate, which is also conducive to improving the tool life. If the minimum feed per tooth is used and the spindle speed is too fast, the impact on the tool life can be as high as 95%. Once the stable working condition is established, the spindle speed and feed rate can be increased accordingly to obtain the best performance.
