The geometric parameters of milling cutter have a significant impact on the deformation of metal, milling force, cutting temperature and wear of milling cutter during milling, and thus affect the processing quality, service life and production efficiency of milling cutter. In order to give full play to the cutting performance of the milling cutter, in addition to the correct selection of the material of the milling cutter, the geometric parameters of the milling cutter should also be reasonably selected according to the specific milling conditions.
1. Selection principle of milling cutter diameter and tooth number
(1) The selection principle of milling cutter diameter: the diameter of milling cutter is large, the heat dissipation condition is good, the rigidity of milling cutter rod is good, and the allowable milling speed and cutting amount are large. However, when the diameter of the milling cutter is large, the cutting length of the milling cutter increases, the working time is long, the milling torque is large, and the tool material consumption is also large.
(2) Selection principle of the number of teeth of milling cutter: milling cutter has coarse teeth and fine teeth. Rough tooth milling cutter has high tooth strength and large chip holding space, but the number of teeth involved in cutting at the same time is small, the working stability is poor, and the vibration is large, which is suitable for rough milling; Fine tooth milling cutter, with a large number of teeth involved in cutting at the same time, small feed per tooth, stable milling, suitable for fine milling.
2. Selection principle of front corner
Reasonably increasing the rake angle can reduce the plastic deformation of the cutting layer, the chip deformation is small, the arc radius of the tool tip is easy to reduce, the blade is sharp, and the cutting effect is strong. Therefore, it is beneficial to reduce the milling force, cutting heat and power, improve the machining accuracy and reduce the surface roughness value of the machined surface. However, if the rake angle is too large, the strength and heat dissipation conditions of the blade will be destroyed, which will reduce the durability of the milling cutter.
(1) High speed tool steel tools have good bending strength and impact toughness, and larger rake angle can be taken; The bending strength and impact toughness of cemented carbide tools are poor, so smaller rake angle should be taken.
(2) During rough machining, in order to ensure better strength and heat dissipation conditions, the front corner should be smaller; When finishing, in order to ensure the quality of the machined surface and make the blade sharp, a larger rake angle should be selected.
(3) The strength and hardness of the workpiece material are high, and the front corner should be smaller. When processing plastic materials, choose a larger front angle; Machining brittle materials, select a smaller front angle.
3. Selection principle of rear corner
Increasing the back angle can reduce the friction between the back of the tool and the transition surface of the workpiece, and make the edge sharp. However, too large back angle will destroy the strength and heat dissipation conditions of the blade part, reduce the durability of the tool, and even cause blade collapse. The selection principle of the rear corner is as follows:
(1) High speed tool steel has high bending strength and impact toughness, and its rear angle can be larger than that of cemented carbide tools.
(2) During rough milling, the cutting resistance of the tool is large. In order to ensure the strength of the cutting edge, the back angle should be smaller; During finish milling, in order to reduce friction, make the cutting edge sharp and improve the quality of the machined surface, a larger back angle should be taken.
(3) When milling materials with large plasticity and elastic deformation, a larger back angle should be taken to reduce the friction behind; For materials with high milling strength and hardness, a smaller back angle should be taken to ensure the strength of the cutting edge. When the tool has adopted a negative rake angle and the edge strength has been strengthened, a larger rake angle can also be used to improve the sharpness of the tool.
4. Selection principle of principal deflection angle
Reduce the main deflection angle, increase the strength of the tool tip, and increase the length of the cutting edge, so as to reduce the thickness of the cutting layer, increase the tool durability, reduce the height of the residual area of the machining surface, flatten the knife grain, and reduce the surface roughness value. Under the condition of the same thickness of the cutting layer, the feed rate can be appropriately increased. However, a small main deflection angle increases the width of the cutting layer and the milling force, especially the axial force acting on the milling cutter and workpiece, which is easy to produce vibration.
5. Selection principle of secondary deflection angle
The function of the auxiliary deflection angle is mainly to reduce the friction between the auxiliary cutting edge, the rear of the auxiliary cutting edge and the machined surface of the workpiece. Properly reducing the secondary deflection angle can effectively reduce the height of the machining residual area and improve the machining surface quality. In addition, reducing the secondary deflection angle can increase the strength of the tool tip.
