Characteristics and Application of Commonly Used Thread Machining Tools
Thread turning tools are key tools for lathe thread machining, and their performance directly affects the thread’s precision, surface quality, and machining efficiency. Commonly used thread turning tools can be divided into high-speed steel thread turning tools, carbide thread turning tools, and ceramic thread turning tools, based on the tool material. Different types of turning tools exhibit significant differences in hardness, wear resistance, and toughness, making them suitable for different machining scenarios. In actual production, thread turning tools must be selected based on the thread type (e.g., triangular, trapezoidal, rectangular), workpiece material (e.g., steel, cast iron, nonferrous metals), and machining requirements (e.g., roughing, finishing) to ensure machining quality and economy.
High-speed steel (HSS) thread turning tools are relatively early adopters of thread machining. Their key features include excellent toughness, ease of sharpening, and the ability to produce a sharp cutting edge, making them suitable for machining threads and non-ferrous metal workpieces requiring high precision. However, HSS thread turning tools have relatively low red hardness and low cutting speeds (generally no more than 30 m/min), resulting in relatively low processing efficiency. They are primarily suitable for single-piece, small-batch production or low-speed precision thread turning. For example, when machining threads in highly ductile non-ferrous metals such as brass and aluminum alloys, HSS tools effectively prevent chip sticking and ensure a smooth thread surface finish. Furthermore, HSS thread turning tools offer low sharpening costs and can be ground to various tool nose angles (e.g., 60° for standard threads and 30° for trapezoidal threads), providing increased flexibility and widespread use in repair shops and small-batch production.
Carbide thread turning tools, thanks to their high hardness (HRC70 and above) and excellent red hardness, have become a staple tool for high-speed thread cutting. Compared to high-speed steel tools, carbide thread turning tools can achieve cutting speeds 3-10 times higher (up to 80-200 m/min when machining steel), significantly improving processing efficiency and making them suitable for high-volume production. Carbide thread turning tools are categorized by insert material into tungsten-cobalt (YG), tungsten-titanium-cobalt (YT), and general-purpose (YW) types. YG is suitable for machining brittle materials such as cast iron and non-ferrous metals, YT is suited for machining plastic materials such as steel, and YW is adaptable to a wide range of materials. However, carbide has poor toughness and impact resistance, making it difficult to sharpen. Therefore, caution should be exercised when rough machining or machining threads with intermittent surfaces to avoid chipping. To improve the impact resistance of carbide thread turning tools, coatings (such as TiN coatings) can be used, which not only enhance wear resistance but also reduce friction and lower cutting temperatures.
Ceramic thread turning tools are high-performance tools with exceptional hardness (HRC90 and above) and wear resistance. They can produce threads at higher cutting speeds (200-500 m/min), making them suitable for threading difficult-to-machine materials such as high-strength steel and hardened steel. Ceramic turning tools offer excellent chemical stability and resist adhesion to metals, effectively reducing built-up edge and ensuring high thread surface quality. However, their toughness is extremely poor, and their impact resistance is far inferior to that of high-speed steel and cemented carbide. Therefore, they are suitable only for continuous cutting and finishing, requiring high machine tool rigidity and workpiece clamping accuracy. In practice, ceramic thread turning tools are typically used for high-precision, high-strength threads in large quantities, such as precision threads in automotive transmissions. They can significantly improve production efficiency and processing quality, but initial investment costs are high and require a rigid, high-precision lathe.
The geometric parameters of a thread turning tool significantly impact thread machining quality and require precise design based on the thread type and material being machined. The tool tip angle must be consistent with the thread profile angle. For example, the tool tip angle for a standard triangular thread is 60°, while for a trapezoidal thread it is 30°. Otherwise, thread profile errors will occur. The selection of rake and clearance angles must balance cutting force and edge strength. When machining plastic materials, a rake angle of 5°-15° is recommended to minimize cutting deformation; when machining brittle materials, a rake angle of 0°-5° is recommended to enhance the cutting edge. The clearance angle is generally 6°-10° to minimize friction between the flank and the thread flank. Furthermore, the radial rake angle of a thread turning tool affects the actual profile angle. If the radial rake angle is not 0°, the tool tip angle must be adjusted to compensate to ensure the thread profile angle meets the requirements. For example, if the radial rake angle is 10°, a 60° thread profile angle needs to be corrected to approximately 57° to offset the rake angle’s effect on the profile. When installing a thread turning tool, ensure that the tool tip is at the same height as the workpiece axis and that the tool centerline is perpendicular to the workpiece axis. Otherwise, the two sides of the thread will become asymmetrical, affecting the thread fit accuracy.
