JPH0112601B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement of a guide bushing portion in a guide bush type lathe. example
The guide bush of an NC automatic lathe will be explained with reference to FIG. FIG. 1 is a sectional view of a conventional guide bush structure used in an automatic lathe.
The workpiece 4 is chucked to the main shaft 3 and rotated by a rotational driving force transmitted to the main shaft 3 from the outside. The main spindle 3 is rotatably attached to the headstock 2, and is regulated in the radial and axial directions by bearings within the headstock 2. The headstock 2 is disposed on the base 1 so as to be slidable in the directions of arrows A and B, and controls the movement of the workpiece 4 in the longitudinal direction by an NC command signal. On the other hand, a part conventionally called a guide bush generally includes a guide bush holder 9 fixed to the base 1, a sleeve 5 fixed to the guide bush holder 9 and having a tapered part 5' on the inside diameter, and a part adjusted in the radial direction by the tapered part 5'. It consists of a three-part bush 6 that can be fitted together, and a nut 7 that engages with a threaded portion 6'' of the three-part bush 6 for the purpose of fixing the three-part bush 6 to the sleeve 5 and adjusting the inner diameter thereof, By tightening the nut 7, the three-piece bushing deforms inwardly along the tapered portion 5' and is drawn toward the nut.
By appropriately adjusting this tightening amount, it is possible to provide a clearance 6' that matches the diameter of the workpiece material in order to suppress the deflection of the workpiece 4 due to cutting resistance without hindering the rotation and longitudinal movement of the workpiece 4. . The feature of the guide bush type lathe is that the cutter 8 is placed near the guide bush (in this case, near the end of the tapered part 5' of the three-part bush 6), and the position of the guide bush and the cutter 8 is kept constant so that the workpiece 4 can be moved along the shaft length. Since cutting is performed by moving in the direction, the guide bushing can prevent the material of the workpiece 4 from deflecting due to cutting resistance. However, for example, when machining while automatically feeding workpieces in an automatic cycle, it is impossible to adjust the gap 6' to suit the diameter of each workpiece material, and adjusting it to match the larger diameter of the workpiece material will compensate for the cutting force. There was a problem that rigidity could not be obtained, and that if it was fitted to the smaller diameter of the material, it would seize.
In addition, the three-split bush 6 provides an oil lubrication effect because the cutting oil flows into the gap 6' from the three-split part without providing a special pipe for oil supply, but the workpiece The dynamic pressure effect of floating the workpiece 4 by circulating the oil in the gap 6' when the workpiece 4 rotates cannot be expected because the streamline is interrupted at the cut-in part, and it is difficult to improve the rotation accuracy. I've reached my limit. The present invention aims to improve the rotation accuracy of a workpiece, prevent seizure between the workpiece and the guide bushing, strengthen the workpiece supporting force, and enhance the dynamic precision of the workpiece by using a static pressure bearing in the guide bushing.

Specific embodiments of the present invention will be described below with reference to FIGS. 2 to 4. FIG. 2 is a cross-sectional view of a guide bush structure using the hydrostatic bearing of the present invention;
The figure is a sectional view of the hydrostatic bearing section of FIG. 2. The guide bush section consists of a guide bush holder 10 fixed to the base 1 and a sleeve 12 fixed to the guide bush holder 10.The guide bush holder 10 is made up of a sleeve 12 fixed to the guide bush holder 10, and a sleeve 12 is fixed to the guide bush holder 10 in order to generate a static pressure bearing force of pressure fluid against the workpiece 4. Although not shown in the drawing, the fluid supplied from an external pressure fluid supply source is
A pipe line 11 is formed for discharging through the pipe joint to the workpiece shaft support portion consisting of the throttle 13, the static pressure pocket 15, and the bearing gap 14', and the sleeve 12
A small bearing gap 14' is formed between the static pressure pocket 15, the static pressure pocket 15, and the workpiece 4, which allows the pressure fluid to flow out of the bearing. ing. However, in this embodiment, in order to facilitate the machining of the hydrostatic pocket, a part of the sleeve 12 is divided into two parts, and a static pressure pocket 15 is formed in advance as a bush 14 using an end mill, which is then fitted onto the sleeve 12 and integrated. be. As shown in FIG. 3, the static pressure pockets 15 are normally formed at multiple locations (four locations in this embodiment) along the circumference of the workpiece shaft.
If the diameter of the shaft becomes small, the number of pockets may be reduced to three or less, and if the diameter is small, there may be cases where no static pressure pocket is formed. In addition, when performing secondary processing, due to the characteristics of the automatic lathe described above, for example, the part machined to a diameter smaller than the workpiece material diameter may return to the guide bush, so the sleeve 12 should be cut at at least two locations in the longitudinal direction. Work shaft support part (aperture 1
3. It is better to form a static pressure pocket 15 and a bearing gap 14', and provide a fluid outlet in the middle of each work shaft support. The guide bush formed as described above has an orifice 13 like a known hydrostatic bearing.
The pressure fluid discharged from the static pressure pocket 15 is
A constant pressure distribution can be formed from the continuity of the flow rate until it is released to atmospheric pressure through the bearing gap 14', and the axial center of the workpiece 4 can be formed at the point where the pressures of the workpiece support surfaces facing in the circumferential direction are balanced. The position is determined. Therefore, the static pressure pocket 15 always has a restriction 13 for allowing pressure fluid to flow into the pocket.
openings are located. In addition, since the theory of hydrostatic bearings described above agrees well with reality, by calculation,
The shapes of the aperture 13 and the work shaft support can be determined so as to optimize the rigidity, etc. In reality, when supporting a small workpiece such as workpiece 4 with a material diameter of φ3 to φ32mm, static pressure alone is insufficient for the required rigidity, so dynamic pressure must be applied within the range where the frictional force due to the viscous resistance of the fluid does not become excessive. It is desirable to design it so that it produces an effect. In addition, in the experiment conducted with the workpiece 4 material diameter φ20, the clearance amount of the bearing clearance 14' was designed to be 30μm and the bearing characteristics were optimized. It was within the range. Therefore, the variation between rods was adjusted by changing the pressure of the pressure fluid supply source so that the rigidity was constant.However, in practice, even if the variation in the gap amount is not adjusted to the extent mentioned above, there is no problem in processing. .
In other experiments, when machining SUS304, a difficult-to-cut material with a complex shape, where the conventional guide bush structure had diameter variations of 5 to 7 μm, the diameter variations were reduced to less than 1 μm, and there was no seizure. Cutting oil was used as the pressure fluid in these experiments. The use of cutting oil is most desirable in practice because even if the used pressure fluid mixes with the cutting oil, the quality of the oil will not change.

FIG. 4 is a sectional view of a guide bush using a hydrostatic gas bearing according to another embodiment of the present invention. Second
In Fig. 3, there is a static pressure pocket 1 in the workpiece shaft support part.
However, in the case of a static pressure gas bearing, a static pressure pocket 15 is formed because the working fluid is compressible.
If there is, stable rotation cannot be obtained. Therefore, in this embodiment, the static pressure pocket 15 is not formed in the workpiece shaft support portion, but at least three or more throttles 13 are formed radially at the same longitudinal position of the sleeve 12, and the same effect as in FIG. 2 is obtained. It can be demonstrated.

In addition, regarding the longitudinal direction, since the same shape is formed, illustration is omitted.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a conventional guide bush structure used in lathes, FIGS. 2 to 4 show embodiments of the present invention, FIG. 2 is a sectional view of the guide bush structure of the present invention, and FIG. The figure is a sectional view taken along the line CC in FIG. 2, and FIG. 4 is a sectional view showing another embodiment of the present invention. 3...Spindle, 4...Workpiece, 12...Sleeve, 13
...Aperture, 14'...Bearing clearance, 15...Static pressure pocket.

Claims (1)

[Scope of Claims] 1. A spindle that grips and rotates a workpiece, a headstock that can slide in the longitudinal direction of the spindle, a control device that controls movement of the headstock in the longitudinal direction, and a control device that processes the workpiece. In an automatic lathe having a guide bush that is pivotally supported in the vicinity of a position, a pipe line for supplying pressure fluid to a workpiece shaft support part that pivotally supports the workpiece, and a pipe line that communicates with the pipe line and supplies pressure fluid to the workpiece shaft support part. The workpiece has a throttle for discharging, and the workpiece shaft support portion includes the throttle and a supporting portion around it, and is formed at two or more locations in the longitudinal direction of the axis on the inner circumferential surface of the sleeve provided on the guide bush. Automatic lathe guide bush structure. 2. The guide bush structure for an automatic lathe according to claim 1, characterized in that the workpiece shaft support portion has a static pressure pocket. 3. The guide bush structure for an automatic lathe according to claim 1 or 2, characterized in that cutting oil is used as the pressure fluid.