Machine tool spindle error on parts machining accuracy have what effect?

The machine tool spindle is a major component of the machine tool, because the machine tool spindle is used to install the tool or workpiece, so it is the relative position of the tool or workpiece reference and motion reference. Machine tool spindle rotary accuracy is one of the main precision indicators of the machine tool, directly affecting the machining accuracy and surface roughness of the machined parts. Machine tool spindle rotary error is a comprehensive error, is the spindle in the rotary process of the actual rotary axis relative to the theoretical rotary axis drift. The following mainly analyzes the spindle pure radial runout on the impact of parts processing.

A spindle pure radial runout causes

The spindle pure radial runout refers to the spindle actual axis of rotation around the average axis of parallel rotary motion.

The main cause of pure radial runout of the spindle is the spindle journal and bearing accuracy errors. Bearing used on the machine tool is divided into two categories of sliding bearings and rolling bearings, bearing type is different, the impact of pure radial runout is also different.

1, the use of plain bearings on the spindle pure radial runout

Sliding bearings are used as a support, the spindle to its journal in the bearing hole rotation. For lathe type machine tools, in the process of machining, the spindle force direction is certain, the spindle journal is cutting force is pressed to the surface of the bearing hole in a fixed place. At this time, different parts of the spindle journal and a fixed part of the bearing hole contact, so the journal roundness error will make the spindle rotary pure radial runout, while the shape of the bearing hole error on the spindle rotary accuracy of the impact is very small. For boring machine tools, the cutting force acting on the spindle is rotating with the rotation of the boring tool, a fixed part of the journal in contact with different parts of the surface of the bearing hole, so the roundness error of the bearing hole will cause pure radial runout of the boring machine spindle, while the boring machine spindle journal shape error has little effect on the spindle rotary accuracy.

2, the use of rolling bearings on the spindle pure radial runout

Spindle using rolling bearings for support, caused by the spindle pure radial runout of the factors in addition to the accuracy of the bearings themselves, but also with the precision of the bearing mating parts.

(1) the influence of rolling bearing precision

Rolling bearing outer ring and inner ring raceway shape accuracy and positional accuracy on the spindle pure radial runout and the influence of the sliding bearing is similar. Turning, the inner ring raceway accuracy has a greater impact; boring, the outer ring raceway accuracy has a greater impact.

The shape error and size inconsistency of the rolling body will cause the pure radial runout of the spindle. When the rolling body with larger diameter is located on the left, it will make the inner ring move right, that is, the spindle position moves right: on the contrary, when the rolling body with larger diameter is located on the right, it will make the inner ring position move left, that is, the spindle position moves left. Since the speed of the rolling body cage is lower than that of the inner ring, the frequency of pure radial runout caused by it is lower.

The clearance of the rolling bearing also has an effect on the pure radial runout of the spindle. Set the bearing load area on the right, this time the inner ring right shift, when a rolling body is located in the horizontal position, the right shift of the inner ring is smaller than when the rolling body is not in the horizontal position, so that the spindle produces pure radial runout, this pure radial runout frequency is much higher than the speed of the inner ring.

(2) and rolling bearing mating parts of the impact

bearing inner ring is a thin-walled parts, easily deformed after the force, the spindle journal roundness error will lead to deformation of the inner ring caused by pure radial runout of the spindle. Similarly, the outer ring of the bearing is also a thin-walled parts, mounted to the box hole, the box hole roundness error will also cause the outer ring raceway deformation, resulting in pure radial runout of the spindle.

Two, the spindle pure radial runout on the impact of parts processing

1, the impact of the boring process

In the boring machine on the boring hole, boring tool with the boring machine spindle with the rotary movement. When the spindle for pure radial runout, will make the axis line along a fixed direction for simple harmonic motion. The shape of the hole is determined by the trajectory of the tip of the boring tool in the inertial coordinate system. Set the boring tool tip in the dynamic coordinate system position: M = R, N = 0, where R is the radius of the processed hole.

2, the impact of turning

In the lathe machining cylindrical or boring, the workpiece with the lathe spindle for rotary motion. Therefore, the geometry of the machined surface of the workpiece is determined by the relative trajectory of the tool in the dynamic coordinate system. Internal and external turning on the lathe, the spindle radial runout mainly affects the coaxiality error of the workpiece, the impact of the roundness error of the workpiece is negligible.

Third, the conclusion

Through the analysis of pure radial runout of the spindle can be seen, the spindle rotary error on the machining accuracy of the part has a great impact. Therefore, in machining, effective measures should be taken to reduce the impact of spindle rotary error on parts machining accuracy. The measures taken can be considered from two aspects. The first is to improve the rotary accuracy of the spindle. Spindle bearings are the key parts affecting the rotary accuracy of the spindle, for precision machine tools can be used for precision rolling bearings, but also the use of multi-oil wedge dynamic bearings and hydrostatic bearings. At the same time, we also need to improve the accuracy of the parts that are compatible with the bearings. Secondly, to reduce the spindle rotary error on the impact of parts processing. Can be used to separate the movement and positioning of the spindle structure, so that the rotary accuracy of the workpiece in the machining process is not affected by the machine tool spindle rotary error, so that the spindle rotary error is not reflected in the workpiece.