When cutting metal, the tool cuts into the workpiece, and the tool angle is an important parameter used to determine the geometry of the cutting part of the tool.
1. The composition of the cutting part of the turning cnc mill tool
The cutting part of the turning tool is composed of a rake face, a main flank face, a secondary flank face, a main cutting edge, a secondary cutting edge and a tool tip.
▲ Three sides, two blades and one point
1) Rake face The surface on the tool through which the chips flow.
2) Main flank The surface on the tool that is opposite and interacts with the machined surface on the workpiece is called the main flank.
3) Secondary flank The surface on the tool that is opposite and interacts with the machined surface on the workpiece is called the secondary flank.
4) Main cutting edge The intersection line between the rake face of the tool and the main flank is called the main cutting edge.
5) Minor cutting edge The intersection line between the rake face of the tool and the counter flank is called the minor cutting edge.
6) Tool nose The intersection of the main cutting edge and the secondary cutting edge is called the tool nose. The tool tip is actually a small curve or straight line, called the rounding tool tip and the chamfering tool tip.
2. Auxiliary plane for measuring the cutting angle of the turning tool
In order to determine and measure the geometric angle of the turning tool, three auxiliary planes need to be selected as the datum. The three auxiliary planes are the cutting plane, the base plane and the orthogonal plane.
1) Cutting plane-a plane cut at a selected point of the main cutting edge and perpendicular to the bottom plane of the toolholder.
2) Base surface-a plane that passes through a selected point of the main cutting edge and is parallel to the bottom surface of the toolholder.
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 spatial rectangular coordinate system.
Three, the main geometric angle and selection of turning milling machining tools
3.1 Principles for the selection of rake angle (γ0)
The size of the front angle mainly solves the contradiction between the firmness and sharpness of the cutter head. Therefore, the rake angle must first be selected according to the hardness of the processed material. The hardness of the processed material is high, the rake angle is small, and vice versa. Secondly, the size of the rake angle should be considered according to the processing nature. The rake angle should be small when roughing, and the rake angle should be large when finishing. The rake angle is generally selected between -5° and 25°.
Usually, the rake angle (γ0) is not pre-made when making the turning tool, but the rake angle is obtained by sharpening the chip flutes on the turning tool. The chip flute is also called chip breaker. Its function is great to break the chips without entanglement; control the outflow direction of the chips and maintain the accuracy of the machined surface; reduce the cutting resistance and extend the tool life.
3.2 Principles for the selection of relief angle (α0)
First consider the processing properties. When finishing machining, the clearance angle is larger, and when rough machining, the clearance angle is smaller. Secondly, consider the hardness of the processed material. The hardness of the processed material is high, and the main relief angle should be a small value to enhance the robustness of the cutter head; on the contrary, the relief angle should be a small value. The clearance angle cannot be zero or negative, and is generally selected between 6° and 12°.
3.3 The selection principle of entering angle (Kr)
First consider the rigidity of the turning process system composed of lathes, fixtures and tools. If the system has good rigidity, the entering angle should be a small value, which will help increase the tool life, improve heat dissipation conditions and surface roughness. Secondly, consider the geometry of the workpiece. When processing steps, the entering angle should be 90°. For workpieces cut in the middle, the entering angle should generally be 60°. The entering angle is generally between 30° and 90°, and the most commonly used are 45°, 75°, and 90°.
3.4 The selection principle of the secondary declination angle (Kr′)
First, consider that the turning tool, workpiece, and clamp have sufficient rigidity to reduce the secondary deflection angle; otherwise, take a larger value; secondly, consider the nature of the processing. When finishing, the secondary deflection angle can be 10°～15°. For rough machining , The secondary declination angle can be about 5°.
3.5 Selection principle of blade inclination (λS)
Mainly depends on the processing nature. During rough machining, the workpiece has a large impact on the turning tool, which is set to λS ≤ 0°. During finishing, the workpiece has a small impact on the turning tool, which is set to λS ≥ 0°; usually, λS=0°. The blade inclination angle is generally selected between -10°～5°.
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