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Analysis of the precision of turning shaft workpiece
Source: China Bearing Network Time: 2014-07-25
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First, the reason why the scale accuracy does not meet the demand and its disposal method1. Because the operator is not careful; the child is making mistakes; perhaps the dial is wrong and improperly used, so when measuring; be careful; the correct use of the dial is very important; in the middle of the handle dial; The dials of the type lathes are not the same; each small grid dial can be calculated by the following formula: the scale is turned into a grid cutter movement interval = the carriage screw spacing / the dial is a total of the number of grid lines (mm) know each grid scale Value in the future; in the application should pay attention to because there is a gap between the screw and the nut; sometimes the dial is changed; but the turning tool will be moved; when the gap is turned, the turning tool will move. So when it is used; If the scale is over the grid, it is too much; it is not allowed to reverse only a few grids; instead, it should be reversed and turned forward;
2. The measuring tool itself has errors or is not used before the application of the measuring tool; it must be carefully checked and adjusted;
3. Because of the change in temperature; the scale of the workpiece changes during cutting; the chip is deformed; the molecules of the chip move with each other; and they have a lot of heat when they move in conflict; in addition; because the chip conflicts with the front of the turning tool The back of the turning tool and the appearance of the workpiece conflict with the heat; this heat directly affects the tool and the workpiece. Of course; the highest heat is the chip (about 75%); followed by the turning tool (about 20%) and the workpiece (about 4%; 1% in the air). When the workpiece is heated, the diameter increases (about 0.01 to 0.05 mm; the cast iron changes more than the steel); the diameter is shortened after cooling; the waste is formed. Therefore, it is not possible to measure when the workpiece temperature is very high. If it is necessary to measure the amount; fill the satisfactory cutting fluid during turning; do not increase the temperature of the workpiece, and then use the method of separating the coarse and fine cars.
4. The blanks are not covered by the blanks themselves, and the straight holes are not straightened;
Second, the main reason for the shape accuracy and mutual orientation accuracy can not meet the demand. The cause of the onset of ovality.
a. The ellipticity of the spindle journal is directly reflected on the workpiece; if it is a plain bearing; then when the load is small and the direction is constant; the main journal is pressed against the bearing's outer orientation under the load effect (because the main shaft and the bearing There is a gap between them. When the spindle rotates through 90°; the middle orientation of the spindle changes; so that the spindle has two intermediate orientations during the one-rotation process; the back knife of the turning tool has changed; and the workpiece has an ovality. The ellipticity of the bearing bore has no effect on the workpiece.
b. The blank margin is not uniform; there is a gap between the main shaft and the bearing; the amount of back-feeding changes during the cutting process.
c. The front and rear intermediate holes do not conform to each other (the two intermediate holes are at a point of view with the middle of the workpiece); the intermediate hole and the tip only contact one side; the uneven wear forms an axial yaw to form an ellipse d. Front top swing. 2. The cause of the busbar is not straight (cultivation, convex, saddle) and the cause of the taper a. The orientation between the lathe guide and the center line of the main shaft is incorrect; especially in the horizontal. For example, the guide rail is meandered; the workpiece is convex or concave; the guide rail and the main shaft of the main shaft are not parallel and taper.
b. The front and rear centerline are not parallel to the bed rail; the taper is attacked.
c. Because the temperature of the workpiece rises; the axis will be tortuous. For example; when the long axis is processed on a heavy-duty lathe; the temperature rises to a certain time; the workpiece will elongate; but because the two tip intervals are not changed; the resulting workpiece cannot be in the length direction Stretching and attacking and twisting. Therefore; in the long axis of the car; try to lower the temperature; together must always retreat the back top.
d. The influence of the internal stress of the workpiece. There is often internal stress inside the workpiece; in the cutting process; because the outer layer is plastically deformed; the internal stress is also attacked; this internal stress is in equilibrium inside the workpiece; the workpiece adheres to a certain shape. However, when the workpiece is removed from the fixture or lathe; deformation occurs. Dispose of this problem; usually use the aging method.
3. The edge that causes the radial runout is pulsated by the front tip, the middle hole is not round or there are dirt such as chips, and of course the appearance of the workpiece with ellipticity will also cause radial runout.
Third, the main reason for the roughness of the appearance is not up to the demand. The lack of rigidity of the lathe is caused by the looseness of the plug iron and the unbalanced transmission. Of course; the instability of the lathe device can also cause oscillation; the roughness of the workpiece is reduced due to the oscillation.
2. If the rigidity of the turning tool lacks oscillation, so use the rough shank as much as possible; reduce the length of the turning tool and the lack of rigidity of the workpiece will cause oscillation; therefore, use the intermediate frame when turning the slender shaft; or replace it with a clip and a top. Two top clips.
3. Some parameters of the turning tool are incorrect. According to the cutting characteristics of the workpiece data, a reasonable and suitable cutting viewpoint is selected; the roughness of the outer surface is lowered.
4. Because of the onset of built-up edge; the roughness of the surface of the workpiece is reduced; the built-up edge is very strong; the cutting is due to the participation of the built-up edge; the appearance of the workpiece is rough or a groove mark; the turning should be prevented as much as possible. Analyze the above reasons; in the processing should be early to prevent early prevention; to eliminate the problem in the germination situation; improve the accuracy of the workpiece; satisfactory depiction of demand.
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