Shaft workpieces encounter problems such as lack of accuracy and surface roughness during turning. According to the specific process of turning, carry on the analysis. First, the size of the accuracy of the reasons for not meet the requirements and their solutions As the operator is not careful, measuring children when mistakes, or wrong dial and improper use, so when measuring, it is necessary to carefully, the correct use of the dial is very important The dials for various types of lathes are not the same as for the middle handle dials. Each small dial can be calculated using the following formula: Scale shift distance = tool travel distance = pallet screw distance / The total number of lines (mm) of the dial After knowing the scale value of each grid, be careful when using it. Because there is a gap between the screw and the nut, sometimes the dial rotates, but the turning tool does not necessarily move. After turning, the lathe moves. Therefore, when using, if the scale turns over the number of grids, it is not allowed to reverse only a few squares, but to reverse one rotation and then realign the scale. If there is any error in the measuring tool itself or if the measuring tool is not used before use, check and adjust it carefully. Due to the change of temperature, the size of the workpiece is changed. During cutting, the chips are deformed, and the molecules of the chips move relative to each other. When they move, they rub and generate a lot of heat. In addition, due to the friction between the chip and the turning tool, the friction between the back surface of the turning tool and the workpiece surface also generates heat, which directly affects the tool and the workpiece. Of course, the highest heat is chip (about 75%), followed by lathe (about 20%) and workpiece (about 4%, and 1% in air). When the workpiece is heated, the diameter increases (about 0.01 to 0.05 mm, and the change of cast iron is larger than that of steel), and the diameter shrinks after cooling, resulting in waste products. Therefore, it cannot be measured when the workpiece temperature is high. If it is necessary to measure the amount of fluid, sufficient fluid is poured during turning to prevent the temperature of the workpiece from rising; More than half of the blank is not enough because the blank itself is not straightened, and the central hole is misaligned. Second, the geometric accuracy and mutual position accuracy can not meet the requirements of the main reason for the occurrence of ellipticity The ellipticity of the spindle journal is directly reflected on the workpiece, if it is a sliding bearing, then when the load size and direction of the same, The main journal is pressed at a certain position on the bearing surface under load (due to the clearance between the main shaft and the bearing). When the main shaft rotates through 90°, the center position of the main shaft changes, so that the main shaft has two center positions in the course of one rotation, and the amount of the back knife of the turning tool changes, and the ellipticity of the workpiece is generated. The ellipticity of the bearing bore has no effect on the workpiece. The rough stock is not uniform, plus there is a gap between the spindle and the bearing, and the amount of the back knife changes during the cutting process. The front and rear center holes are not coincident (the two center holes are at an angle to the center of the workpiece). The center hole and the top contact only one side, and uneven wear causes the axial turbulence to be elliptical and the top tip oscillates. The reason that the generatrix is not straight (education, convexity, saddle shape) and taper is that the positions of the lathe guide rail and the centerline of the spindle are not correct, especially in the horizontal direction. If the guide rail is bent, the workpiece is convex or concave, and the guide rail is not parallel to the centerline of the spindle to produce a taper. Before and after the top centerline and the bed rail is not parallel, producing taper. As the workpiece temperature increases, the shaft will bend. For example, when machining a long axis on a heavy-duty lathe, the workpiece will stretch when the temperature rises to a certain level. However, since the distance between the two tips does not change, the workpiece may bend due to its inability to extend in the longitudinal direction. Therefore, in the axle of the car, try to reduce the temperature, and you must always retreat back to the top. The effect of stress on the workpiece. The internal stress of the workpiece often exists. During the cutting process, due to the plastic deformation of the surface layer, internal stress is also generated. This internal stress is in an equilibrium state inside the workpiece, so that the workpiece maintains a certain shape, but when the workpiece is unloaded from the fixture or lathe When it is time, it is necessary to generate distortions. To solve this problem, the aging method is generally used. The cause of radial runout is the pulsation of the former term; the center hole is not round or there are dirt such as chips; of course, the workpiece surface with an ellipticity will also cause radial runout. Third, the surface roughness does not meet the requirements of the main reason is the lack of rigid lathe, such as dragging the plug iron loose, vibration caused by unbalanced transmission. Of course, unstable lathe installation will cause vibration, due to vibration caused by the workpiece surface roughness. The lack of rigidity of the turning tool causes the use of rough arbors as much as possible to reduce the length of the turning tool; the lack of rigidity of the workpiece also causes vibration. Therefore, when turning the slender shaft, the center frame must be used or replaced with a clamp. Two top clips. The incorrect geometric parameters of the turning part of the turning tool are based on the cutting characteristics of the workpiece material, and a reasonable and appropriate cutting angle is selected to reduce the surface roughness. Due to the build-up of the built-up edge, the surface roughness of the workpiece is reduced. The built-up edge of the built-up edge is very strong. Due to the involvement of the built-up edge, the surface of the workpiece may be napped or grooved. This should be avoided when turning. Combined with the above reasons, the process should be done as early as possible to prevent early, eliminate the problem in the bud, improve the accuracy of the workpiece to meet the design requirements.
