Since the thread turning tool belongs to the forming turning tool, in order to ensure the accuracy of the thread, the thread turning tool must be properly sharpened and clamped.
1.Sharpening of thread turning tools
Sharpening thread turning tools can also be divided into rough grinding, fine grinding and sharpening with a grinding stone. The sharpening steps of the pipe thread lathe are generally: first grind the front side parallel to the bottom surface of the cutter body, sharpen the radial rake angle and chip groove when necessary, and then sharpen the left rear and right rear respectively, in order to ensure the half angle of the tooth shape. At the same time, according to the direction and size of the helix angle, sharpen the rear corners on both sides, and sharpen the arc of the tool tip after detecting the corner of the tool. Finally, use a grindstone to grind all parts of the cutting edge.
The sharpening requirements for thread turning tools are:
1) 5 is allowed for the thread rough turning tool. – IO. The radial rake angle of the finishing tool should generally be equal to oo.
2) At radial rake angle 7,=O. When , the tool nose angle of the turning tool must be equal to the tooth profile angle of the thread, that is, q=d. When the radial rake angle is 7,) 04, it should be sharpened according to the calculated corrected tool nose angle.
3) – Under normal circumstances, the edges on both sides of the thread turning tool should be in a straight state, only when the normal cutting or radial rake angle is used, , > 0. , When turning a thread with high precision, the straight cutting edge is corrected to a convex curve.
4) The static relief angle of the two sides of the turning tool of the pipe thread lathe should be offset with the direction and size of the thread lift angle, so that the relief angle in the feeding direction increases by one thread lift angle, and the relief angle in the opposite direction decreases by one thread angle of rise.
5) The bisector of the inner thread turning tool of the pipe thread lathe should be perpendicular to the shank, and the cutting edge should also be ground with a double relief angle. The width from the tool tip to the rear side of the tool shank should be smaller than the small diameter of the thread to facilitate tool retraction.
6) When sharpening the thread turning tool on the pipe thread lathe, the force should be light and steady. Sharpening high-speed steel turning tools should be immersed in water for cooling in time to prevent overheating of the tool tip;
2.Typical thread turning tool
(1) Triangular thread turning tools can generally be divided into rough turning tools, fine turning tools, and high-speed steel and carbide turning tools.
1) High speed steel triangular external thread turning tool. The pipe thread lathe has sharp cutting edges, good toughness, and can withstand larger impacts and obtain lower surface roughness values. But it has poor heat resistance, so it is often used for low-speed cutting or thread finishing.
For smooth cutting, y = 15 should be selected when rough turning the thread of plastic material. The radial rake angle should not be too large to prevent the phenomenon of “knife sticking”.
When turning the thread of brittle material or fine turning plastic material, 7r=o should be selected. the radial rake angle. The angle between the two edges should be equal to the profile angle.
2) Carbide triangular thread turning tool. It has the characteristics of high hardness, good Td grinding and high temperature resistance. However, the impact resistance is poor. When turning a thread with a larger pitch or a higher material hardness, a width of 0.2 to 0.4 mm.y is often ground on the two main cutting edges. ． is -5. The negative chamfer c is due to the extrusion phenomenon when cutting the thread at high speed, which makes the actual tooth angle swell. Therefore, when sharpening the sharp corner of the knife, the tooth angle of the knife is reduced by about 0.50.
The cross-sectional area of the shank should be increased as much as possible for the internal thread turning tool to ensure the space for retracting the tool, and the length of the stalk should be as short as possible. At the same time, the cutting edge should be clean and sharp to make up for the lack of rigidity and strength of the arbor.
(2) Trapezoidal thread turning tools When turning trapezoidal threads, due to the large radial cutting force, rough turning tools and fine turning tools are generally used for roughing and finishing respectively. The tool material is also selected according to the processing properties. High-speed steel or hard Made of alloy.
The head width w of the rough turning tool should generally be equal to – or slightly smaller than the width of the groove bottom of the thread.
Typical trapezoidal thread finishing tool. In order to ensure the profile accuracy of the trapezoidal thread on the pipe thread lathe, the radial rake angle of the cutting edge is n: . . , parallel to the base plane P, and the 7J sharp angle of the two cutting edges is strictly equal to the profile angle. In order to improve the surface quality of the tooth profile and make the cutting smooth, the two cutting edges of the turning tool are ground with different rake angle chip grooves according to the direction and size of the thread rise angle.
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