Cemented carbide indexable turning tools come in various structural types, such as lever type, insert bolt type, wedge type, pressure type, eccentric type, pull pad type, and pressure hole type. Among these, some use positioning pins for clamping, but due to the susceptibility of positioning pins to deformation, this can affect the reliability of the clamping (e.g., wedge-type tools). Others offer more reliable clamping but have complex structures and poor manufacturing processes (e.g., lever and plug types). The key-guided tension-adjustable turning tool combines the advantages of stable clamping, easy blade indexing and replacement, and a simple, manufacturable design. Its structure is illustrated in Figure 1.
Figure 1: Key-guided tension-type turning tool
1. Knife pad
2. Blade
3. Key pin
4. Blade body
5. Spring washer
6. Nut
This clamping system has several notable features:
1. It uses a threaded bevel lever mechanism, providing strong and reliable clamping force.
2. The key pin ensures smooth alignment between the knife pad and the blade body under load, reducing cutting vibration and improving tool rigidity and stability.
3. Blade indexing and replacement are straightforward—just adjust the tail nut.
4. The overall tool head is compact, making it suitable for a wide range of machining applications.
When designing SNU U160602FR inserts with key-guided tightenable indexable turning tools, the main cutting edge angle (kr) can be set at 45°, 60°, 75°, or 90° (typically 75°). The rake angle (gog) is usually between -8° and -15°, while the clearance angle (lsg) ranges from 0° to 10° (commonly 0°). The nose radius (erg) is typically between 80° and 90° (usually 90°), and the side cutting edge angle (krg) ranges from 45° to 90°. The fit of the keyway on the sipe plane and the knife pad is H9/h9, while the key pin and its corresponding slot on the blade body require D10/h9 (or F7/h6). The key pin’s cylindrical surface and the blade hole should have a fit of C11/h11 (or B12/h12), and the dynamic fit between the cylinder and the outer diameter of the tail screw must be B12/h12. By adjusting the tail nut, the blade can be quickly clamped or released for rapid indexing and replacement. A spring washer is added between the nut and the cutter body to prevent looseness caused by cutting vibrations.
The tool head body is made from 45 steel, which must be forged to improve material toughness. The heat treatment hardness should be maintained at 38–42 HRC. If too hard, the tool may crack under load; if too soft, it may deform under chip pressure. The sipes on the tool head are milled, and the keyway position must be perpendicular to the two right-angled surfaces. These surfaces are processed simultaneously to ensure verticality and parallelism. The key pins, which bear the cutting load, are made from 40Cr steel (tempered) or 45 steel (hardened to 35–38 HRC). Their hardness must be carefully controlled to ensure strength and wear resistance while maintaining good toughness. The key pin’s surface finish should be Ra 1.6–3.2 μm, and the contact area between the key pin’s cylindrical surface and the blade hole should cover at least 1/2 to 2/3 of the blade thickness. To achieve this, the root of the key pin’s cylinder is ground 0.2–0.4 mm on a tool grinder. The knife pad is made from 40Cr steel (tempered) or 45 steel (normalized), with parallelism of both ends within 0.01–0.03 mm and a surface roughness of Ra 6.3–3.2 μm.
In application, when roughing, the maximum depth of cut (ap) should be determined first, followed by a larger feed rate (f) based on blade strength and machine capacity, and finally an appropriate cutting speed (v) that matches the machine's power. For deep cuts, if the chipbreaker groove is too narrow, chipping may occur. In finishing, a large rake angle insert with a chipbreaker is recommended to reduce cutting forces and improve surface quality. High cutting speeds are preferred, with reduced ap and f, but the cutting layer thickness should not be less than 0.05 mm to avoid surface hardening. Table 1 provides reference cutting parameters for different materials.
When working with low-carbon steels, stainless steels, and other ductile materials, it is best to use single-sided, positive quadrant inserts with effective chip breakers. Proper clamping of the insert is essential, ensuring full contact between the insert bottom and the knife pad, as well as the two sides of the blade with the right-angled bases of the sipe. When blade wear reaches VB = 0.3 mm, it should be indexed or replaced promptly. This tool is also suitable for hardened steel and gray cast iron, and can be adapted for triangular thread turning, boring, and milling tools through changes in tool tip geometry.
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