(1) Selection of milling cutter type
According to the geometry of the parts to be processed, the types of cutting tools are selected as follows:
1) When machining curved surface parts, in order to ensure that the cutting edge of the cutter is tangent to the machining contour at the cutting point, the high-speed computer gong machining is used to avoid the interference between the cutting edge and the workpiece contour. Generally, ball end cutter is used for rough machining, and four edge milling cutter is used for semi finishing and finishing machining, as shown in Fig. 4.
2) When milling large plane: in order to improve the production efficiency and surface roughness, insert type disc milling cutter is generally used, as shown in Fig. 5.
3) When milling small plane or step surface, general milling cutter is generally used, as shown in Fig. 6.
4) In order to ensure the accuracy of keyway milling, use the cutter as shown in Figure 7.
5) During hole processing, drill bit, boring cutter and other hole processing tools can be used
Milling cutter is generally composed of blade, positioning element, clamping element and cutter body. There are many kinds of positioning and clamping methods for the blade on the cutter body, and the structure of the positioning element of the blade has different types. Therefore, there are many kinds of structure forms and classification methods of milling cutter. When selecting, it can be mainly according to the arrangement of blades. The arrangement of blades can be divided into two categories: flat mounting structure and vertical mounting structure.
Flat structure (radial arrangement of blades)
The flat structure milling cutter (as shown in Fig. 9) has a good structure and is easy to process. It can also use a non hole blade (the blade price is low and can be reground). Due to the need for clamping elements, a part of the blade is covered, the chip holding space is small, and the cemented carbide section in the direction of cutting force is small, so the flat structure milling cutter is generally used for light and medium milling.
Vertical installation structure (blade tangential arrangement)
The blade of end mounted structure milling cutter (as shown in FIG. 10) is fixed on the cutter groove with only one screw, which is simple in structure and convenient in rotation. Although there are few tool parts, it is difficult to process the cutter body, so it is necessary to process it with five coordinate machining center. Since the blade is clamped by cutting force, the clamping force increases with the increase of cutting force, so the clamping element can be omitted and the chip holding space is increased. Because the blade is installed in tangential direction, the section of cemented carbide in the direction of cutting force is large, so it can be used for large cutting depth and large cutting distance. This kind of milling cutter is suitable for heavy and medium milling.
The angle of milling cutter includes front angle, back angle, main deflection angle, auxiliary deflection angle, edge inclination angle, etc. In order to meet the different processing needs, there are a variety of angle combination types. The main deflection angle and rake angle are the most important in the processing of high-speed computer gongs.
Main deflection angle KR
The main deflection angle is the angle between the cutting edge and the cutting plane, as shown in FIG. 11. The main deflection angles of milling cutter are 90 °, 88 °, 75 °, 70 °, 60 ° and 45 ° etc.
The main deflection angle has a great influence on the radial cutting force and cutting depth. The size of radial cutting force directly affects the cutting power and anti vibration performance of cutting tools. The smaller the main deflection angle of the milling cutter is, the smaller the radial cutting force is, the better the vibration resistance is, but the cutting depth is also reduced.
The main deflection angle of 90 ° is selected when milling the plane with shoulder, but it is not used for pure plane machining. This kind of tool has good versatility (not only can process step surface, but also can process plane), so it can be selected in single piece and small batch processing. Because the radial cutting force of this kind of cutting tool is equal to the cutting force, the feed resistance is large, and it is easy to vibrate. When machining the plane with shoulder, the milling cutter with 88 ° main deflection angle can also be selected. Compared with the milling cutter with 90 ° main deflection angle, its cutting performance is improved to some extent.
The main deflection angle of 60 ° to 75 ° is suitable for rough machining of plane milling. Due to the obvious reduction of radial cutting force (especially at 60 degrees), its vibration resistance is greatly improved, and the cutting is smooth and light. Therefore, it should be preferred in plane machining. 75 ° main deflection angle milling cutter is a general-purpose tool with wide application range; 60 ° main deflection angle milling cutter is mainly used for rough milling and semi finishing milling on boring and milling machines and machining centers.
The radial cutting force of this kind of milling cutter with 45 ° main deflection angle is greatly reduced, which is approximately equal to the axial cutting force. The cutting load is distributed on the longer cutting edge, and has good vibration resistance. It is suitable for the machining occasions with longer spindle overhang of boring and milling machine. When machining plane with this kind of cutting tool, the damage rate of blade is low and the durability is high; when machining iron castings, the edge of the workpiece is not easy to break.
Anterior angle γ
The rake angle of milling cutter can be divided into radial rake angle γ F and axial rake angle γ P. the radial rake angle γ f mainly affects the cutting power; the axial rake angle γ P affects the chip formation and the direction of axial force. When γ P is positive, the chip will fly away from the machining surface. The discrimination between the positive and negative radial forward angle γ F and the axial forward angle γ P is shown in FIG. 12.
The common combination forms of front angle are as follows:
The milling cutter with double negative rake angle and double negative rake angle usually adopts square (or rectangular) blade without back angle. The cutter has many cutting edges (generally 8), high strength and good impact resistance, which is suitable for rough machining of cast steel and cast iron. Because the chip shrinkage ratio is large, it needs a large cutting force, so the machine tool has higher power and higher rigidity. Because the forward angle of the shaft is negative, the chip can not flow out automatically. When cutting ductile materials, chip accretion and tool vibration are easy to occur.
It is suggested that the double negative rake angle milling cutter should be preferred in order to make full use of and save the blade. When double positive rake angle milling cutter is used to produce chipping edge (i.e. large impact load), the double negative rake angle milling cutter should also be preferred when the machine tool allows.
The milling cutter with double positive rake angle and double positive rake angle adopts a blade with back angle. The wedge angle of the cutter is small
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