Cutting principle of threaded blade
2024.09.20
The cutting principle of thread inserts involves the fundamental principles and techniques of thread machining. Below, I will explain in detail how thread inserts work.
Cutting Principle
Thread inserts are used to form threads on workpieces, and their working principle is based on metal cutting technology. During the machining process, the workpiece rotates while the thread insert moves along the axis of the workpiece, removing material to form the desired thread shape. The ideal thread tool varies depending on factors such as the type of thread, the material, and the size of the workpiece1.
Thread Turning
In thread turning, for each revolution of the workpiece, the turning tool moves along the axis of the workpiece by one pitch. The movement of the cutting edge forms the thread surface of the workpiece4. For thread turning, the sharpening requirements for the thread turning tool include an apex angle equal to the tooth profile angle α in the axial section of the thread. The rake angle γ0 is usually set to 0°, but in rough turning operations, a tool with a positive rake angle (γ0 = 5° to 15°) may be used to improve cutting conditions. In addition, the installation requirements for the thread turning tool include positioning the cutting edge level with the center of rotation of the workpiece and ensuring the bisector of the cutting edge angle is perpendicular to the axis of the workpiece9.
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Thread Milling
Thread milling is another method of thread machining, achieved through the three-axis联动 (three-axis linkage) of a CNC system. The thread milling cutter performs helical milling under the drive of the spindle, moving one pitch (lead) along the Z-axis direction of the tool for each helical milling pass2. Compared to traditional thread turning, thread milling offers greater advantages in terms of machining accuracy and efficiency, and is not limited by the structure or direction of the thread6.
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Cutting Methods
There are several different types of tool paths in thread cutting, including radial feeding, improved lateral feeding, and alternating feeding5. Different tool paths affect chip formation, tool wear, and surface quality. For example, radial feeding is the most common traditional method, where the feeding direction of the insert is perpendicular to the spindle axis of the workpiece, with both sides of the insert participating in the cutting simultaneously. This method is suitable for machining threads with small pitches, but for coarse-pitched threads, there is a risk of vibration and poor chip control5.
Tool Selection
Choosing the right thread insert requires consideration of several factors, including the material being machined, the type of thread, and the size of the thread. For instance, carbide thread inserts are suitable for machining hard materials1. For larger diameter threads (e.g., D > 25 mm), indexable thread milling cutters may be a better choice, especially when machining aluminum alloys8.
Precautions
When using thread inserts, some precautions need to be observed, such as selecting the correct lead angle of the insert, which can be adjusted by changing the insert seat to adapt to different machining conditions10. Moreover, the highest axial cutting force occurs during entry and exit of the thread, so it is necessary to carefully choose the cutting parameters to prevent loosening or damage to the insert11.
Proper use of thread inserts can not only improve machining efficiency but also ensure that the final product quality meets the requirements.
Note: The term "three-axis linkage," which refers to the coordinated movement of three axes in a CNC machine to perform complex operations such as thread milling.
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