Basic angles and functions of turning tools
The basic angles of turning tools are the rake angle (γo), clearance angle (a0), main angle (Kr), secondary deflection angle (κr’) and cutting edge inclination angle (λs). To determine the angle of the turning tool, three coordinate planes are set: the cutting plane, the base plane and the main section. In turning, if we ignore the influence of the installation of the turning tool and the cutting movement, the cutting plane can be regarded as the vertical plane; the base plane is the horizontal plane; when the main cutting edge is horizontal, the section is perpendicular to the main cutting edge. edge is the main section.
The rake angle γo is measured in the main section and is the angle between the rake surface and the base surface. Its function is to make the blade sharp and facilitate cutting. However, the rake angle should not be too large, otherwise the strength of the blade will be weakened and it will easily wear out or even break. When processing plastics, the rake angle can be larger. For example, if a carbide turning tool is used to cut steel parts, it is recommended that γo=10~20. When processing brittle materials, the rake angle γo of the turning tool should be larger than that in roughing to facilitate sharpening the blade. The roughness of the workpiece is small.
The clearance angle a0 is measured in the main section and is the angle between the main flank surface and the cutting plane. Its function is to reduce the friction between the flank surface of the main body and the workpiece during turning. The generally used value is a0=6~12°, with a small value in rough turning and a large value in finish turning.
The main deviation angle Kr is measured in the base plane and is the angle between the projection of the main cutting edge on the base plane and the feed direction. Its function is:
1) The length of the main cutting edge involved in cutting can be changed, which affects the tool life.
2) Affects the magnitude of the radial cutting force.
A small leading angle can increase the length of the main cutting edge involved in cutting, which improves heat dissipation, which helps to extend the service life of the tool. However, when processing a thin shaft, the rigidity of the workpiece is insufficient. A small main deflection angle will increase the radial force of the tool on the workpiece, which is prone to bending and vibration. Therefore, the main deflection angle should be selected larger. Commonly used leading angles for turning tools include 45°, 60°, 75°, 90°, etc., among which 45° is the most common.
The secondary deflection angle κr’ is measured on the base surface and is the angle between the projection of the secondary cutting edge on the base surface and the opposite feed direction. Its main function is to reduce the friction between the secondary cutting edge and the machined surface so as to improve the roughness of the machined surface.
Under the condition of the same cutting depth ap, feed f and main deflection angle Kr, decreasing the secondary deflection angle κr’ can reduce the residual area after turning, thereby reducing the surface roughness. Generally, κr’=5~15° is selected. .
The edge inclination angle λs is measured in the cutting plane and is the angle between the main cutting edge and the base surface. Its main function is to control the direction of chip flow. The main cutting edge is parallel to the base surface, λs = 0. The tool tip is at the lowest point of the main cutting edge, λs is a negative value, the strength of the tool tip increases, and the chips flow down to the workpiece surface. It is used for roughing, with the tool tip at the main cutting edge. At the highest point, As is a positive value, the strength of the tool tip is weakened, and the chips flow down to the workpiece surface for finishing. The angle of inclination of the rotary blade λs is usually selected within the range of -5-+5°.
