JPH0420741B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION A. Object of the Invention Industrial Application Field The present invention relates to a constant pressure polishing device, and more specifically, it is used for polishing a polishing tool body mounted on the main shaft of a machine tool, particularly a grindstone rotating shaft thereof. Supported so as to be freely displaceable in directions perpendicular to the axis of the tool body (X-axis, Y-axis direction) and in the axis direction of the polishing tool body (Z-axis direction), and between the grindstone rotating shaft and the body of the polishing tool. The present invention relates to a constant pressure polishing device that has an automatic origin return mechanism.

Conventional technology When processing a workpiece with a free-form surface, for example, when manufacturing a mold, a rough finish is first performed using a machine tool such as a copy milling machine or a machining center, and then a smoothing process is performed using a manual tool such as a hand grinder. , surface polishing is applied.
Since highly liberalized machine tools are used for rough finishing, extremely efficient automatic processing is possible. On the other hand, the reality is that surface polishing relies on manual finishing by workers, and there is a strong desire to automate the surface polishing process to improve work efficiency and product dimensional accuracy. It was hot. Naturally, various measures have been proposed in response to the request for liberalization of the surface polishing process. One example is a method in which a polishing tool is attached to the main shaft of a numerically controlled machine tool, and the surface of a workpiece, for example, the mold, is polished by rotation of the main shaft.

Problem to be Solved by the Invention In polishing the surface of a workpiece using the numerically controlled machine tool mentioned above, the movement command for the grinding wheel rotation axis of the polishing tool is input in advance into the machining program of the workpiece. For the reasons explained in detail in Section 1, it is not possible to obtain a polished surface with practically satisfactory dimensional accuracy simply by moving the grindstone rotation axis as instructed by the machining program. First, grindstones generally have lower rigidity than cutting tools, and the wear rate of grindstones is orders of magnitude higher than the wear rate of general-purpose cutting tools. For this reason, even if the polishing tool is given the same movement locus as the cutting tool, the shape of the grindstone changes over time due to wear, often resulting in a substantially empty polishing state. In addition, in a polishing mechanism that uses a grindstone, the chip discharge function is only guaranteed by moving the grindstone relative to the surface of the workpiece while applying contact pressure between the surface of the grindstone and the surface of the workpiece. . Therefore, ideally, it is desirable to adjust the polishing conditions so that a constant contact pressure always acts between the grinding wheel and the workpiece, but as mentioned above, the grinding wheel itself has considerable elasticity, and it also prevents wear. Since the shape of the grindstone changes irregularly as it progresses, it is practically impossible to maintain the contact pressure constant.

The main purpose of the present invention is to always maintain the contact pressure applied between the workpiece and the grindstone at a constant level, and perform constant pressure polishing without reducing the dimensional accuracy of the workpiece obtained in the pre-processing process as much as possible. The object of the present invention is to provide a new polishing device.

B. Means for Solving Problems in the Structure of the Invention The present invention includes a polishing tool body 1 mounted on the main shaft of a machine tool, and a polishing tool body 1 that is movable in the axial direction of the polishing tool body 1. , and a holder 7 attached with constant pressure biased in the direction of the tip;
It consists of a whetstone rotating shaft 2 mounted on the holder 7, and the whetstone rotating shaft 2 is attached to the body of the whetstone rotating shaft 2.
A disk-shaped flange 5 extending in a direction perpendicular to the axis of the flange 5 is formed, and a conical ball receiving surface 8 is provided on the side surface of the flange 5 on the grinding wheel side with its axis aligned with the grinding wheel rotating shaft 2. A holder 7 is attached to both sides of the flange 5 by steel balls 8b and 8a.
The ball is held movably in a direction perpendicular to the axis of the ball and at least three spring-loaded steel balls 9 arranged at equal intervals are brought into contact with the conical ball receiving surface 6 at a constant pressure. This article focuses on polishing equipment.

Embodiment FIG. 1 is a partial vertical cross-sectional view of a constant pressure polishing apparatus according to the present invention, and FIG. 2 is a schematic explanatory diagram of a state in which a workpiece surface is polished by a circular grindstone. In FIG. 1, reference number 1 indicates the main body of the polishing tool, and the tool shank portion (not shown) is fitted to the shape of a tool fitting hole formed in the main shaft of a machine tool, for example, a machining center. Can be attached to the main shaft. The illustrated grindstone rotating shaft 2 is composed of a hollow cylindrical body 4', and a rotating shaft 4'' having a whetstone 4 at its tip rotatably positioned inside the cylinder 4'. A drive mechanism for driving the rotating shaft 4'' is built into the cylindrical body 4'.
A compressed air inlet 3 is opened at the proximal end of the cylinder. The compressed air introduced into the cylinder 4' from the compressed air inlet 3 causes the rotating shaft 4'', which has a grinding wheel 4 fixed to its tip, to rotate at high speed.By adopting this type of drive mechanism, The grindstone 4 is driven at a high speed of 10,000 RPM or higher, and transmits the polishing load to the free-form surface of the workpiece (not shown). A disk-shaped flange 5 is formed extending in a perpendicular direction, and a conical ball receiving surface 6 is connected to the grindstone-side side surface of the flange with its axis aligned with the grindstone rotating shaft 2. The front surface 14 and rear surface 15 of the flange 5 are fitted with a plurality of steel balls 8b, which are loosely supported in the holder 7 and arranged at approximately equal intervals on the same circumference, and the flange 5. The grindstone rotating shaft 2
In addition, it allows free movement within the XY plane orthogonal to the axis of the polishing tool body 1.

On the other hand, on the conical ball receiving surface 6, three or more steel balls 9 are arranged on the same circumference at approximately equal intervals.
is located. These steel balls 9 are constantly pressed against the ball receiving surface 6 of the flange 5 by the compressive reaction force of a retainer 10 that is slidably mounted on the holder 7 and a coil spring 11 fitted within the retainer. There is. As can be understood from the above explanation, the grindstone rotating shaft 2 is automatically positioned at a dynamically stable point (zero point) by the pressing force of the steel balls 9 acting on the ball receiving surface 6. Therefore, when a compressive reaction force due to contact with the workpiece surface acts on the grinding wheel 4 during polishing, the conical receiving surface 6 of the grinding wheel rotating shaft 2 will move in the XY direction perpendicular to the axis of the polishing tool body 1.
The coil spring 11 fitted in the steel balls 9 and the retainer 10 is compressed or expanded depending on the direction of movement in a plane. That is, at this point, a movement resistance corresponding to the inclination angle of the receiving surface 6 and the compression reaction force of the coil spring 11 is generated on the grindstone rotating shaft 2. Further, the holder 7 is configured to be able to move linearly in a direction parallel to the axis of the polishing tool body 1, that is, in the Z-axis direction, by means of a linear guide element 12 such as a ball slide, and is constantly moved by a coil spring 13. 1 is pressed in the direction of the tip. Therefore, when a contact reaction force is generated on the grindstone 4 toward the rear end of the polishing tool body 1, the entire grindstone rotating shaft 2 is guided by the linear guide element 12 and rotates in the Z-axis direction within the grindstone tool body 1. retreat to.

Note that the grindstone rotating shaft 2 includes a pin 16 installed on the side surface of the holder 7 and a pin 16 installed on the side surface of the flange 5.
Rotation is prevented by a mechanism consisting of a hole 17 with a slightly larger diameter than the pin 16, into which the pin 16 is inserted. Further, a similar rotation prevention mechanism is provided between the holder 7 and the grindstone tool main body 1.

As is clear from the above explanation, a self-restoring force that always tries to return to the zero position acts on the grindstone rotating shaft 2 when polishing a workpiece, and the grinding wheel rotating shaft is It is configured to be able to move in any direction of XYZ depending on its size.

In addition, since a reaction force proportional to the amount of deflection of the coil springs 11 and 13 is generated, there is a difference between the load applied to the grinding wheel 4 and the displacement of the grinding wheel rotating shaft 2, regardless of the polishing conditions. A linear relationship is established.

An actual polishing example will be explained below. In order to facilitate understanding of the present invention, in the following description, an example of polishing using a cylindrical surface of a cylindrical grindstone will be explained. In FIG. 2, reference numeral S indicates the surface of the workpiece finished by a cutting tool such as a ball end mill in the previous process. Assuming that the grindstone 4 rotates along the locus L ₀ with an offset in the normal direction to the surface S of the workpiece by an amount corresponding to the radius r of the grindstone 4, the grindstone 4 and The contact pressure acting between the workpiece and the workpiece becomes almost zero, and normal polishing is not performed. In other words, the amount of offset (Δr) required to generate contact pressure from the radius r of the grinding wheel
(r-.DELTA.r) is defined as the offset amount of the polishing tool main body 1, and polishing is performed only by moving the grindstone rotating shaft 2 along a locus L defined by the offset amount. When the spring constant of the elastic deformation of the grindstone rotating shaft 2 is k, the contact pressure P during polishing is expressed by the following general formula: P=k·Δr (1). Center O of grindstone rotation axis 2
Alternatively, when polishing the surface S of the workpiece while moving O' along L, problems arise in setting the offset amount (Δr) for applying contact pressure and polishing the grindstone over time. Here, even if the optimal contact pressure is known experimentally in advance, it is the offset amount (Δr) that actually applies the contact pressure, so the general formula (1) is used to calculate the It is necessary to convert it into contact pressure P. However, the grinding wheel 4 is an elastic body with low rigidity compared to general-purpose cutting tools, and the spring constant k varies widely between individual grinding wheels, so it is logically unreasonable to set Δr uniformly. It is. On the other hand, when the grindstone 4 wears out, the radius of the grindstone decreases, so the contact pressure P decreases. Furthermore, the wear pattern of the grindstone 4 is not uniform over the entire circumference, and varies depending on the shape of the workpiece.

In the device of the present invention, the offset amount (Δr) for applying the above-mentioned contact pressure can be roughly set by allowing free elastic displacement of the grinding wheel rotating shaft 2, so that the contact pressure can be adjusted to the set value. Even when the contact pressure exceeds the above value, the contact pressure can be automatically corrected to a predetermined set value due to the self-returning property of the grindstone rotating shaft 2 to the zero position. Furthermore, wear of the grindstone 4 can be effectively counteracted by setting the depth of cut larger in advance by an amount corresponding to the amount of wear. The above explanation is for the case where the surface of the workpiece is processed with the cylindrical surface of the cylindrical grindstone, but when grinding is performed by pressing the spherical part at the tip of the grindstone 4 at right angles to the workpiece as shown in FIG. Polishing is performed by displacing the holder 7 in the Z-axis direction. Further, when the spherical portion of the grindstone 4 is pressed against the inclined or curved surface of the workpiece, the same polishing process is performed by the combined action of the displacements in the X, Y, and Z axis directions.

C. Effects of the Invention According to the present invention, it is possible to extremely easily set the amount of offset for generating contact pressure between the grindstone and the polished surface of the workpiece.

Therefore, the movement trajectory of the center of the grinding wheel, the wear of the grinding wheel,
Alternatively, a substantially constant contact pressure can be constantly generated between the grindstone and the polishing surface of the workpiece by utilizing the self-returning elastic displacement of the grindstone rotating shaft in order to respond to changes in the shape of the workpiece. Thus, by using the constant pressure polishing apparatus according to the present invention, the polishing accuracy of the work surface can be greatly improved, and the polishing process can be liberalized.

[Brief explanation of drawings]

FIG. 1 is a partial vertical cross-sectional view of a constant pressure polishing apparatus according to the present invention, and FIG. 2 is a schematic explanatory diagram of a state in which a workpiece surface is polished by a circular grindstone. 1... Polishing tool body, 2... Grindstone rotating shaft, 4...
... Grindstone, 5 ... Flange, 6 ... Conical ball receiving surface, 9 ... Spring-biased steel ball.

Claims (1)

[Claims] 1. A polishing tool body mounted on the main shaft of a machine tool; a holder movable in the axial direction of the polishing tool body and mounted in the polishing tool body so as to be constantly biased toward the tip; a whetstone rotating shaft attached to the holder, a disc-shaped flange extending in a direction perpendicular to the axis of the whetstone rotating shaft is formed on the body of the whetstone rotating shaft, and the whetstone side of the flange A conical ball receiving surface is connected to the side surface of the flange with its axis aligned with the grinding wheel rotation axis, and both sides of the flange are held movably in a direction perpendicular to the axis of the holder by steel balls. A constant pressure polishing device characterized in that three or more spring-biased steel balls arranged at equal intervals are brought into contact with the conical ball receiving surface.