The cutting angle is the core of tool geometry, encompassing rake angle, clearance angle, primary rake angle, secondary rake angle, and inclination angle. These angles directly influence cutting forces, cutting temperatures, tool wear, and surface quality during the cutting process. The rake angle, defined as the angle between the tool’s rake face and the base plane, primarily functions to minimize cutting deformation and friction. A larger rake angle results in a sharper tool and reduced cutting forces, but also reduces tool strength. For example, when machining plastic materials, a larger rake angle (15°–25°) effectively reduces friction between the chip and the rake face, inhibiting built-up edge. When machining brittle materials, a smaller rake angle (5°–15°) is recommended to enhance tool edge strength and prevent chipping. The clearance angle, defined as the angle between the tool’s flank face and the cutting plane, reduces friction between the flank face and the machined surface of the workpiece. A larger clearance angle reduces friction, but the tool’s wedge angle decreases, impacting tool strength. Typically, the clearance angle ranges from 6° to 12°, with larger values used for finishing and smaller values for roughing.
The lead angle is the angle between the projection of the main cutting edge on the base plane and the feed direction. Its primary function is to change the distribution of cutting forces and the heat dissipation of the tool. A smaller lead angle increases radial cutting forces, decreases axial cutting forces, increases tool heat dissipation, and extends tool life, but also increases workpiece deformation. An increased lead angle decreases radial cutting forces and increases axial cutting forces, making it suitable for machining slender shafts or thin-walled parts to avoid workpiece bending and deformation. Common lead angles include 45°, 60°, 75°, and 90°. Smaller lead angles are preferred for machining rigid workpieces, while larger ones are preferred for machining less rigid workpieces. The secondary angle is the angle between the projection of the secondary cutting edge on the base plane and the direction opposite to the feed direction. It reduces friction between the secondary cutting edge and the machined surface of the workpiece and also affects the workpiece’s surface roughness. A smaller secondary angle results in a lower surface roughness, but increases friction between the tool and the workpiece. Typically, the secondary angle ranges from 5° to 15°, with smaller values used for finish turning and larger values for rough turning.
The rake angle is the angle between the main cutting edge and the base surface. Its primary function is to control the direction of chip flow and influence tool strength. A positive rake angle allows chips to flow toward the surface being machined, preventing scratches on the machined surface and making it suitable for finishing. A negative rake angle allows chips to flow toward the machined surface, enhancing tool edge strength and making it suitable for roughing or machining hard materials. A rake angle of 0° causes chips to flow perpendicular to the main cutting edge and is suitable for general machining. The absolute value of the rake angle is generally between 0° and 10°. For machining high-strength steel or in applications with high impact loads, a negative rake angle of -5° to -10° can be used to improve the tool’s impact resistance.
The selection of tool cutting angles must adhere to certain principles. First, the workpiece material properties should be considered. When machining plastic materials (such as mild steel and aluminum alloys), larger rake and clearance angles should be used to minimize cutting deformation and friction, and to suppress built-up edge. When machining brittle materials (such as cast iron and bronze), smaller rake and clearance angles should be used to enhance tool edge strength and prevent chipping. Secondly, the selection should be based on the machining requirements. For roughing, smaller rake and clearance angles, along with larger lead angles and negative rake angles, should be used to enhance tool strength and durability. For finishing, larger rake and clearance angles, along with smaller lead angles and positive rake angles, should be used to ensure surface quality. Furthermore, the tool material properties must be considered. High-speed steel tools offer greater toughness, so a larger rake angle can be used. Carbide tools are more brittle, so a smaller rake angle should be used to enhance tool strength.
The selection of tool cutting angles also needs to be combined with specific processing conditions, such as machine tool rigidity, workpiece clamping method, etc. When the machine tool rigidity is poor, a larger main deflection angle should be selected to reduce radial cutting force and avoid vibration; when the workpiece clamping rigidity is poor, a larger main deflection angle and a smaller feed rate should also be selected to prevent workpiece deformation. For complex tools, such as forming cutters, gear hobs, etc., the selection of the cutting angle also needs to consider the tool structure and processing technology to ensure that the tool has sufficient strength and life. In actual applications, the selection of tool cutting angles often needs to be adjusted through trial cutting. According to the cutting force, tool wear and surface quality during the processing process, the cutting angle parameters are optimized to achieve the best processing effect. By reasonably selecting the tool cutting angle, the processing efficiency can be effectively improved, the cost can be reduced, and the processing quality can be guaranteed.
