Plane machining methods include planing, milling, drawing, grinding, etc. Planing and milling are commonly used as rough and semi-finishing planes, and grinding is used as plane finishing. There are also scraping, grinding, super finishing, polishing and other finishing methods. Which kind of processing method is adopted is more reasonable, and it needs to be determined according to the shape, size, material, technical requirements, production type, and existing plant equipment.
First, planing
Planing is the most commonly used processing method for single-piece and small-batch production. The machining accuracy can reach IT9~IT7, and the surface roughness is Ra12.5~1.6μm. Planing can be done on a planer or a planer, as shown in Figure 8-3. The main motion of planing is variable speed reciprocating linear motion. Because of the inertia at the time of shifting, it limits the increase of the cutting speed, and it does not cut at the return stroke, so the efficiency of the planing process is low. However, the required machine tools and cutting tools are simple in structure, easy to manufacture and install, easy to adjust, and versatile. Therefore, it is widely used in single-piece and small-batch productions, especially for processing narrow flat surfaces.
At present, the use of a wide-edged knife fine planer instead of scraping is widely used to achieve good results. The use of wide blade planer, low cutting speed (2 ~ 5m/min), small machining allowance (pre-planar allowance 0.08 ~ 0.l2mm, final plan allowance 0.03 ~ 0.05mm), the workpiece heat deformation is small, can Obtained a small surface roughness (Ra0.8 ~ 0.25μm) and higher processing accuracy (straightness 0.02/1000), and the productivity is also high. Figure 8-4 is a wide-blade precision planer with a rake angle of -10? to -15?, with a squeeze effect; a relief angle of 5?, which increases the back support and prevents vibration; the angle of inclination is 3? to 5?. Kerosene is used as a cutting fluid during processing.
Second, milling
Milling is the most common method used in plane machining. Milling of planes, grooves, arcs, spiral grooves, gears, cams, and special surfaces can be performed using various milling machines, milling cutters, and attachments, as shown in Figure 8-5. As shown. After rough milling and fine milling, the dimensional accuracy can reach lT9~1T7 and the surface roughness can reach Ra12.5~0.63μm.
The main motion of milling is the rotary motion of the milling cutter, and the feed motion is the linear motion of the workpiece. Figure 8-6 shows the cutting motion of a cylindrical cutter and a face milling cutter.
(I) Milling process characteristics and application range
The milling cutter is composed of a plurality of cutter teeth. Each cutter tooth is sequentially cut, there is no idle stroke, and the cutter rotates at a high speed. Therefore, compared with planing, the milling productivity is higher than that of planing, and the milling plane is often used in the middle batch and above production.
When processing large-size planes, the relevant planes can be machined simultaneously with several milling cutters on a gantry milling machine. In this way, the mutual positional accuracy between the planes can be ensured and higher productivity can be obtained.
Milling process features:
1. High production efficiency but unstable
Since milling is a multi-blade cut and a larger cutting speed can be selected, the milling efficiency is higher. However, due to various reasons, it is easy to cause uneven load of the cutter teeth and inconsistent wear. As a result, the vibration of the machine tool may be caused, resulting in unstable cutting and directly affecting the surface roughness of the workpiece.
2. Intermittent cutting
Milling cutters produce impacts when cutting in or out, which on the one hand reduces the life of the tool and on the other causes periodic shocks and vibrations. However, due to the intermittent cutting of the cutter teeth, the working time is short, and the cooling time in the air is long, so the heat dissipation conditions are good, which is conducive to improving the durability of the cutter.
3. Semi-closed cutting
Because the milling cutter is a multi-tooth tool, the space between the teeth is limited. If the chips cannot be discharged smoothly or have enough chip flutes, the milling quality will be affected or the damage of the milling cutter will be affected. The flutes are considered as an important factor.
(b) Four Elements of Milling Consumption
As shown in Figure 8-7, the following four factors are used for milling:
l. Milling speed Cutting speed when the cutter rotates.
Type vc - milling speed (m/min);
D0 - diameter of milling cutter (mm);
n - cutter speed (r/min).
2. Feed amount refers to the distance that the workpiece moves relative to the milling cutter. It is represented by three methods: f, fz, and vf.
(1) Feed per rotation f refers to the relative displacement of the workpiece and the milling cutter per revolution, in mm/r;
(2) The feed per tooth fz refers to the relative displacement of the workpiece and the milling cutter along the feeding direction in each revolution of the cutter, in mm/z;
(3) Feed speed vf refers to the relative displacement of the workpiece and the milling cutter along the feeding direction in unit time. The unit is mm/min. In general, the feed rate during the milling process refers to the feed rate vf.
The relationship between the three is:
Where z is the number of cutter teeth;
n - number of milling cutter revolutions (r/min).
3. Milling depth ap refers to the dimension of the cutting layer measured parallel to the milling cutter axis direction.
4. Milling width ac refers to the size of the cutting layer measured perpendicular to the axis of the milling cutter and perpendicular to the feed direction.
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