Accuracy analysis when turning shaft workpieces (2)

4) The remaining blank is not enough for the blank itself to be bent without alignment, and the center hole is deflected.

Second, the geometric accuracy and mutual positional accuracy can not meet the requirements of the main reasons 1) The ellipticity occurs. The ellipticity of the spindle journal is directly reflected on the workpiece. If it is a sliding bearing, then the load size and direction are unchanged. At the time, the main journal is pressed against a certain position on the bearing surface under load (due to the gap between the main shaft and the bearing). When the spindle rotates through 90°, the center position of the spindle changes, so that the spindle has two center positions during one rotation, and the back knife of the turning tool changes, which causes the workpiece to have an ellipticity. The ellipticity of the bearing bore has no effect on the workpiece.

The remaining amount of the blank is uneven, and there is a gap between the main shaft and the bearing, and the amount of the backing knife changes during the cutting process.

The front and rear center holes do not match (the two center holes are at an angle to the center of the workpiece), and the center hole and the tip are only in contact with one side, and the uneven wear causes axial swaying to form an elliptical front swing.

2) The busbar guide and the spindle centerline are not correctly positioned, especially at the level, due to the fact that the busbar is not straight (bending, convex, saddle) and taper. If the guide rail is bent, the workpiece is convex or concave, and the guide rail is not parallel to the center line of the main shaft to produce a taper or the like.

The front and rear centerline lines are not parallel to the bed rails, creating a taper.

As the temperature of the workpiece increases, the shaft bends. For example, when a heavy-duty lathe is used to machine a long shaft, when the temperature rises to a certain value, the workpiece is elongated, but since the distance between the two tips is not changed, the workpiece is bent due to the inability to elongate in the longitudinal direction. Therefore, when the axle is long, try to lower the temperature, and you must always retreat the rear tip.

The effect of stress in the workpiece. Internal stress often exists inside the workpiece. During the cutting process, due to the plastic deformation of the surface layer, internal stress is also generated. This internal stress is balanced inside the workpiece to keep the workpiece in a certain shape. But when the workpiece is unloaded from the fixture or lathe When it is down, it is necessary to produce deformation. To solve this problem, the aging treatment method is generally adopted.

3) The cause of the radial runout is the tip pulsation of the front; the center hole is not round or has debris such as chips; of course, the surface of the workpiece with ellipticity also causes radial runout.

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