Geometrical Angle and selection principle of turning tool

In order to determine the sharpness of turning tool edge and its position in space, a coordinate system must be established, which is composed of three reference planes. The following external turning tool as an example, introduces the geometric Angle of turning tool.

Base plane: the plane passing the selected point of the main cutting edge. This plane contains the main cutting edge when the main cutting edge is horizontal and is parallel to the bottom surface of the tool mounting, that is, the horizontal plane. This plane is mainly used as the reference plane to measure the position of the front cutting face in space.

Cutting plane: the plane which is tangent to the main cutting edge and perpendicular to the base plane through the selected point of the main cutting edge. This plane is mainly used as a datum to measure the space position of the main rear cutter face.

Main section: the plane passing the selected point of the main cutting edge and perpendicular to both the base plane and the main cutting plane.

(1) Rake Angle γ0 rake surface and base surface Angle, measured in the main section. The size of the rake Angle affects the sharpness and strength of the cutting edge. Increasing the rake Angle can make the edge sharp, reduce the cutting force and cutting temperature, but too large rake Angle will reduce the edge strength and easily cause edge damage. The value ranges from -8° to +15°.

The general principle of front Angle selection is: the size of the front Angle and the cutting tool cutting part of the material, processed materials, working conditions are related. When the cutting tool cutting part of the material is brittle and low strength, the front Angle should be small. When the workpiece material strength and hardness are low, a larger front Angle can be selected. In heavy cutting and impact conditions, the rake Angle can only be small and sometimes even negative. Generally, under the condition of ensuring the cutting edge strength of the tool, large rake Angle should be selected as far as possible. Such as hard alloy turning tool processing steel material rake Angle value can be 5°-15°.

(2) Main rear Angle α0 The Angle between the main rear cutter face and the cutting plane is measured in the main section. Its function is to reduce the friction between the cutter surface and the workpiece. It also affects the strength and sharpness of the cutting edge as well as the front Angle.

The selection principle is similar to the front Angle, which is generally 0 to 8°.

(3) Main Angle κ R The Angle between the main cutting edge and the feed direction, measured in the base plane. Its effect is reflected in affecting the cutting edge working length, resistance, tip strength and heat dissipation conditions. The smaller the main deflection Angle, the greater the tool resistance, the longer the cutting edge working length, the better the heat dissipation conditions.

The selection principle is: workpiece coarse rigidity good, desirable small value; In order to reduce radial cutting resistance and avoid workpiece bending, a larger value should be selected. Usually between 15° and 90°.

(4) Accessory Angle κ 'r The Angle between the cutting edge and the opposite direction of the feed is measured in the base plane. Its function is to affect the roughness of the machined surface, reducing the offset Angle can make the machined surface smooth.

The selection principle is: when finishing, in order to improve the quality of the processed surface, a smaller value should be selected, generally 5 to 10°.

(5) edge inclination λs The Angle between the main cutting edge and the base plane, measured in the main cutting plane. The main effect is to affect the chip flow direction and the strength of the tip. When the main cutting edge is parallel to the bottom of the shank, λs =0, chips flow out in the direction perpendicular to the main cutting edge. When the tool tip is the lowest point of the cutting edge, λ S is negative and the chip flows to the machined surface. When the tip is the highest point of the main cutting edge, λ S is positive and chips flow to the surface to be machined.

Generally, the edge Angle λ S is -5° to +10°. When finishing, in order to avoid chips scratching the machined surface, it should be positive or zero. When roughing or cutting hard materials, negative value is desirable to improve the strength of the cutter head.