When cutting metal, the tool cuts into the workpiece, and the tool angle is an important parameter used to determine the geometry of the part the tool cuts.
1. The composition of the cutting part of the turning tool
Three sides, two blades and one point
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The cutting part of the turning tool is composed of the rake face, the main flank face, the auxiliary flank face, the main cutting edge, the auxiliary cutting edge and the tool tip.
1) Rake face The surface on the tool where chips flow.
2) The main flank The surface on the tool that is opposite to and interacts with the machined surface on the workpiece is called the main flank.
3) Sub-flank The surface on the tool that is opposite to and interacts with the machined surface on the workpiece is called the sub-flank.
4) Main cutting edge The intersection line between the rake face and the main flank face of the tool is called the main cutting edge.
5) Minor cutting edge The intersection line between the rake face and the minor flank of the tool is called the minor cutting edge.
6) Tool nose The intersection of the main cutting edge and the minor cutting edge is called the tool nose. The tip of the tool is actually a short curve or straight line, called rounding tip and chamfering tip.
Second, the auxiliary plane for measuring the cutting angle of the turning tool
In order to determine and measure the geometric angle of the turning tool, it is necessary to select three auxiliary planes as references, which are the cutting plane, the base plane and the orthogonal plane.
1) Cutting plane - the plane cut at a selected point of the main cutting edge and perpendicular to the bottom plane of the tool holder.
2) Base surface - the plane passing through a selected point of the main cutting edge and parallel to the bottom surface of the tool holder.
3) Orthogonal plane - a plane perpendicular to the cutting plane and perpendicular to the base plane.
It can be seen that these three coordinate planes are perpendicular to each other, forming a space Cartesian coordinate system.
3. The main geometric angle and selection of the turning tool
1) The principle of rake angle (γ0) selection
The size of the rake angle mainly solves the contradiction between the firmness and sharpness of the cutter head. Therefore, the rake angle should be selected first according to the hardness of the processed material. If the hardness of the processed material is high, the rake angle should be taken as a small value, otherwise, a large value should be taken. Secondly, the size of the rake angle should be considered according to the nature of the processing. The rake angle should be taken as a small value during rough machining, and the rake angle should be taken as a large value during finishing machining. The rake angle is generally selected between -5° and 25°.
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Usually, the rake angle (γ0) is not pre-made when making the turning tool, but the rake angle is obtained by sharpening the chip flute on the turning tool. Chip flute is also called chip breaker. Its function is to break chips without winding; control the flow direction of chips to maintain the accuracy of the machined surface; reduce cutting resistance and prolong tool life.
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2) The principle of the selection of relief angle (α0)
Consider processing properties first. In finishing machining, take a large value for the back angle, and in rough machining, take a small value for the back angle. Secondly, consider the hardness of the processing material. The hardness of the processing material is high, and the main back angle should be small to enhance the robustness of the cutter head; otherwise, the back angle should be small. The relief angle cannot be zero or negative, and is generally selected between 6° and 12°.
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3) The selection principle of the main deflection angle (Kr)
Firstly, consider the rigidity of the turning process system composed of lathes, fixtures and tools. If the system has good rigidity, the leading angle should be small, which is conducive to improving the service life of turning tools, improving heat dissipation conditions and surface roughness. Secondly, the geometric shape of the processed workpiece should be considered. When processing steps, the main declination angle should be 90°, and for workpieces cut in the middle, the main declination angle should generally be 60°. The main deflection angle is generally 30°～90°, and the most commonly used ones are 45°, 75°, and 90°.
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4) Selection principle of secondary deflection angle (Kr’)
First of all, consider that the turning tool, workpiece and fixture have sufficient rigidity to reduce the secondary deflection angle; otherwise, a large value should be taken; secondly, considering the nature of processing, the secondary deflection angle can be 10° to 15° for finishing machining, and 10° to 15° for rough machining. , the secondary deflection angle is about 5°.
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5) Selection principle of blade inclination angle (λS)
It mainly depends on the processing nature. During rough machining, the workpiece has a large impact on the turning tool, and λS≤ 0° is taken. During finishing machining, the impact force of the workpiece on the turning tool is small, and λS≥ 0°; usually λS=0°. The blade inclination angle is generally selected from -10° to 5°.
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