Cutting angle of tool and its function
A tool’s cutting angles are a core component of tool geometry, directly impacting the smoothness of the cutting process, machining quality, tool life, and production efficiency. These angles include rake angle, relief angle, lead angle, secondary angle, and rake angle. Each angle has a specific definition and function, requiring appropriate adjustment under varying machining conditions. Understanding and mastering the role of tool cutting angles is crucial for proper tool selection and use, as well as for optimizing cutting processes.
The rake angle is the angle between the front face of the tool and the base surface. Its main function is to affect the sharpness of the cutting edge and the amount of cutting force. A larger rake angle can make the tool edge sharper, reduce cutting deformation, reduce cutting force and cutting power, and at the same time facilitate the formation and discharge of chips, making it particularly suitable for processing plastic materials. However, an excessively large rake angle will weaken the blade strength, reduce the tool’s heat dissipation capacity, and easily cause tool chipping. Therefore, when processing hard and brittle materials or performing rough processing, the rake angle should be appropriately reduced. For example, when processing plastic materials such as aluminum alloys, the rake angle can be selected from 15° to 25°; when processing brittle materials such as cast iron, the rake angle is usually 5° to 15°.
The back angle is the angle between the back face of the tool and the cutting plane. Its main function is to reduce the friction between the back face and the workpiece processing surface. At the same time, it affects the sharpness of the tool together with the rake angle. A larger back angle can effectively reduce friction, reduce tool wear, improve the surface quality of the machined surface, and is suitable for fine machining. However, if the back angle is too large, the tool wedge angle will decrease and the blade strength will be reduced. Therefore, a smaller back angle should be used for rough machining. Generally speaking, the back angle of high-speed steel tools is slightly larger than that of carbide tools. When processing plastic materials, the back angle is larger than when processing brittle materials. For example, the back angle can be 8°~12° for fine machining and 5°~8° for rough machining.
The lead angle is the angle between the projection of the main cutting edge on the base surface and the feed direction. It significantly affects the distribution of cutting forces, tool life, and workpiece shape accuracy. A smaller lead angle increases radial cutting forces and decreases axial cutting forces, which helps improve tool life but can easily cause workpiece deformation and vibration. An increased lead angle decreases radial cutting forces, making it suitable for machining workpieces with poor rigidity, such as slender shafts, but can reduce tool tip strength. Common lead angles include 45°, 60°, 75°, and 90°. Smaller lead angles are suitable for machining workpieces with good rigidity, while larger lead angles are recommended for workpieces with poor rigidity.
The secondary rake angle is the angle between the projection of the secondary cutting edge on the base surface and the opposite direction of the feed. Its main function is to reduce the friction between the secondary flank and the machined surface of the workpiece, prevent the tool from scratching the machined surface, and affect the surface roughness. A smaller secondary rake angle can enhance the finishing effect of the tool and reduce the surface roughness value, but it will increase friction and vibration; a larger secondary rake angle has the opposite effect. Usually the secondary rake angle is 5°~15°, with a smaller value for fine machining and a larger value for rough machining. The rake angle is the angle between the main cutting edge and the base surface. It can control the direction of chip discharge and affect the strength of the tool tip. A positive rake angle causes the chips to be discharged upward to avoid scratching the machined surface, while a negative rake angle enhances the strength of the tool tip and is suitable for machining occasions with greater impact.
