JPS60263663A - Surface polishing method and device - Google Patents

Abstract

PURPOSE:To improve dimensional accuracy of a work by its stable contact pressure, by correcting a locus to polish the work by a fixed pressure in accordance with a program containing a moving instruction in which a detection signal of elastic change in X, Y, Z axis directions of a wheel rotary shaft is converted by a computer. CONSTITUTION:A fixed pressure polishing head under a condition of polishing time X4-X7 detects a change corresponding to a resultant displacement preset value E0 as a displacement detection signal, and the displacement detection signal, being distributed by a distributor into each axis component and compared with a command register of each axis, corrects an instruction value of the work processing program previously input to a computer. That is, the surface of a wheel draws a moving locus S2, in which a correction part DELTAE1-DELTAE4 is added to or subtracted from a moving locus S1, as a result holding a contact pressure P to a fixed level b'. Accordingly, work surface accuracy is improved by polishing a work under stable application of the fixed contact pressure.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a surface polishing method and apparatus,
More specifically, the present invention relates to a method and apparatus for constant-pressure polishing of the surface of a workpiece in a numerically controlled machine tool connected to a computer.

Conventionally, when manufacturing a workpiece with a free-form curved surface, such as a mold, first rough finishing is performed using a machine tool such as a copy milling machine or a machining center, and then processing is performed using a manual tool such as a hand grinder, so-called polishing processing. It is common to apply For rough finishing, we use highly liberalized numerically controlled machine tools and copying machine tools, making it possible to perform extremely highly efficient automatic machining. However, the reality is that polishing relies on manual finishing using hand tools, and it has been recognized that this is an obstacle that cannot be overlooked when trying to automate the polishing process and improve the dimensional accuracy of workpieces. .

In order to achieve automation of such a polishing process, various measures have been proposed so far. As an example, a method is known in which a grindstone is attached to the main shaft of a machining center and the surface of the workpiece is polished by rotation of the main shaft. However, in this method, the locus of movement of the grinding wheel rotation axis is defined in the cutting program of the workpiece, which is input into the computer in advance, and simply moving the grinding wheel according to the cutting program can provide sufficient dimensional accuracy. The reality is that a polished surface cannot be obtained.

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The reasons why practically sufficient dimensional accuracy cannot be obtained in polishing the surface of a workpiece using the above-mentioned numerically controlled machine tool include the following factors.

■ Grinding wheels generally have lower rigidity than cutting tools, and the amount of wear on them is an order of magnitude greater. For this reason, even if the polishing tool is given the same movement locus as the cutting tool, it often ends up in an empty polishing state due to wear and changes in the shape of the grindstone.

■ Chips are discharged from the grinding surface only by applying a predetermined contact pressure between the grinding wheel surface and the workpiece and moving them relative to each other. In order to maintain this chip evacuation function, it is necessary to maintain the contact pressure between the surface of the grinding wheel and the workpiece at a constant level. However, the grindstone itself is an elastic body, and the shape of the grindstone changes irregularly as the grindstone wears. The purpose of polishing is to improve the surface roughness while maintaining the dimensional accuracy of the workpiece obtained in the rough finishing process, and for this purpose, the above contact pressure must always be maintained at a constant level. This is a necessary condition. However, when polishing a free-form surface of a workpiece using a conventional numerically controlled machine tool, the contact pressure between the workpiece and the grindstone constantly changes as the grindstone wears, and as a result, the dimensional accuracy of the workpiece decreases. It was severely damaged.

A main object of the present invention is to provide a surface polishing method and apparatus which can solve the above-mentioned problems observed in the known methods of polishing the surface of a workpiece using a numerically controlled machine tool.

Another main object of the present invention is to provide a numerical control device with an additional tracing function that can automatically correct the movement trajectory of the grindstone based on the displacement detection signal of the grindstone rotation axis transmitted from the constant pressure polishing head. The object of the present invention is to provide a surface polishing device with improved surface polishing properties.

4. Configuration of the Invention The present invention provides a grindstone rotating shaft (2) in gf polishing of a work surface by a polishing tool (1) mounted on the main shaft (26) of a numerically controlled machine tool. ) is converted into a movement command for the grinding wheel rotation axis (2) by a computer connected to the numerically controlled machine tool, and the workpiece processing including the movement command is performed. The first aspect is a surface polishing method for polishing the surface of a workpiece under constant pressure while correcting the movement locus of the grindstone rotating shaft according to the nib program.

The present invention also includes a floating support mechanism (S) that supports a grindstone rotating shaft (2) mounted on a main shaft (26) of a numerically controlled machine tool so as to be elastically displaceable in the X-axis, Y-axis, and Z-axis directions; The second gist is a surface polishing device in which a constant pressure polishing mechanism is formed by a detection mechanism (D) for the amount of elastic displacement of the grindstone rotating shaft (2) and a computer connected to the numerically controlled machine tool. .

The basis of the present invention is a constant-pressure polishing head, in other words, a polishing tool, which has a built-in device for detecting the polishing resistance acting on the grinding wheel rotating shaft (2) in the main shaft (26) of a general-purpose numerically controlled machine tool, such as a machining center. The main body (1) is attached, and the workpiece surface is F-shaped while automatically correcting the movement locus of the polishing tool according to the elastic displacement detection signal from the detection device in a numerical control program preset as a workpiece nib program.
It is placed on fF polishing.

FIG. 1 is a partial longitudinal cross-sectional view illustrating the main structure of a surface polishing apparatus according to the present invention, and FIG. 2 is a schematic explanatory diagram of the method of the present invention.

In FIG. 1, reference number (1) designates the constant pressure Q-polishing head, ie, the body of the polishing tool. The main body of the polishing tool is
By manufacturing the tool shank portion (not shown) to match the shape of the main shaft (26) of the numerically controlled machine tool, it can be mounted on any numerically controlled machine tool having the same main shaft structure. Inside the main body (1) of the polishing tool, for example, an air motor type (vane tamp) whetstone rotating shaft (2) is installed.
It is floatingly supported so as to be elastically displaceable in the axial, Y-axis, and Z-axis directions. At the base end of the grindstone rotation shaft, there is an air introduction port (3) for introducing high-pressure compressed air supplied from a compressed air source outside the system into the inside of the grindstone rotation shaft to rotate the grindstone (4) at high speed.
is provided. The side body of the grinding wheel rotation shaft (2) has a flange (
5), and a conical pressure receiving surface (6) is formed at the base end of the flange on the grindstone (4) side over its entire circumference. A plurality of steel balls (8a) arranged so that they can be positioned on the same circumference within the holder (7) are a plurality of steel balls (8a) arranged opposite to the steel balls (8a) with the flange (5) in between. The flange (5) is sandwiched between the steel ball (8b) and a part of the floating support mechanism (S) of the grindstone rotating shaft (2). That is, by floatingly supporting the flange (5) by the opposingly arranged steel balls (8a) and (8b), the grindstone rotating shaft (2) is allowed to freely elastically displace within the XY plane. On the other hand, the holder (7) has a steel ball (
A retainer (lO) is attached as a holding member of 9). A steel ball (9) biased by a coil spring (11) is placed at a Z angle with respect to the conical pressure receiving surface (6).
The remaining part of the floating support mechanism (S) of the grindstone rotation shaft (2) is formed in cooperation with the second coil spring (13) and the holder (7) described later so as to apply a negative direction pressing force of the shaft. ing. Therefore, the grindstone rotating shaft (2) is constantly pressed in the negative direction of the Z-axis by the compression reaction force of the coil spring (11) and steel ball (9), and can automatically return to a mechanically stable zero point. It is endowed with self-recovery capabilities. When the grindstone (4) comes into contact with the workpiece (W) during polishing and a reaction force of the polishing load is applied, the pressure receiving surface (6) is elastically displaced within the XY plane, and along with the elastic displacement, the steel ball (9) ) and the coil spring (11) are compressed and move in the positive direction of the Z axis. In this way, the grinding wheel rotation shaft (2) has the inclination angle of the conical pressure receiving surface (6) and the coil spring (1).
A movement resistance uniquely defined by the compression reaction force (1) occurs.

Further, the holder (7) is supported by a linear guide element (12) such as a pole slide so as to be linearly movable in the Z-axis direction, and is constantly pressed in the positive direction of the Z-axis by a coil spring (13). Therefore, if a contact reaction force occurs in the negative direction of the Z-axis on the grinding wheel (4), the grinding wheel rotation axis (
2) The entire body is guided by the linear guide element (12) and retreats in the negative direction of the Z axis. As can be understood from the above explanation, the grinding wheel rotation shaft (2) has a self-righting property that automatically returns to a mechanically stable zero position when a polishing load is applied, and moreover, It is configured so that it can be elastically displaced in any direction depending on the direction and magnitude of resistance. Further, the coil springs (11) and (1)
3), a reaction force proportional to the amount of deflection is generated, so the grinding wheel (
A proportional relationship exists between the polishing load applied to 4) and the elastic displacement generated in the grindstone rotating shaft (2).

In this way, the polishing resistance applied to the grinding wheel rotation shaft (2) is detected as the elastic displacement of the grinding wheel rotation shaft, so the elastic displacement is recorded in the workpiece grinding program that is input into the computer in advance to show the movement trajectory of the grinding wheel rotation shaft. By transmitting it as a correction parameter, it is possible to form a constant pressure polishing mechanism that can always maintain a constant contact pressure regardless of the amount of wear of the grindstone (4). The elastic displacement detection mechanism (D) of the grindstone rotating shaft (2) will be described below. Reference number (14
) is the holder of the elastic displacement detector and the body of the polishing tool (1
) is fixed in an appropriate manner. Detector holder (1
4) includes three displacement detectors for detecting the elastic displacement of the right rotation shaft (2) along the X-axis, Y-axis, and Z-axis directions;
For example, a differential transformer is fixed. first detector
(15) is a detection means for detecting the elastic displacement of the grinding wheel rotation shaft (2) in the X-axis direction, and detects the elastic displacement of the grinding wheel rotation shaft (2) in the The first measuring element (1) is in contact with the reference ring (20) formed on the body 1.
9) and a displacement conversion lever (17), the displacement is converted into a displacement in the X-axis direction and detected.

The displacement conversion lever (17) is swingably supported around a pin (18) as a center of rotation, and uses the swinging motion to convert a radial displacement of the grindstone rotation shaft (2) into a displacement in the X-axis direction. Convert. The measuring element indicated by reference number (16) is a second measuring element fixed to the tip of the first detector (15).

The elastic displacement of the grindstone rotating shaft (2) along the Y-axis direction is also detected by a second detector (not shown) having the same structure as the first detector (15). However, the second detector is arranged such that its angular position is offset by approximately 90° with respect to the first detector (15). The third detector, designated by the reference number (21), is located at the grinding wheel rotation axis (2
) is provided for the purpose of detecting the elastic displacement along the X-axis direction of the detector.
2) is brought into contact with the holder (7) to detect the displacement of the holder in the X-axis direction, that is, the elastic displacement of the grindstone (4) along the X-axis direction.

On the other hand, the main body (1) of the polishing tool is equipped with electrical signals transmitted from three displacement detectors for detecting the elastic displacement of the grinding wheel rotation shaft (2) along the X-axis, Y-axis, and X-axis directions. A signal extraction device is attached for sending out to the computer. To explain in more detail, FIG. 1 shows the constant pressure polishing head (1) connected to the main shaft (26) of the machining center, and the reference number (23) is the one attached to the main body (1) of the polishing tool. A projecting arm is shown, and reference number (24) indicates a signal emitting rod extending in a direction substantially perpendicular to the axis of said arm (23). Electrical signals transmitted from the displacement detectors (15), (21), etc. are transmitted to the electric connector (25) attached to the arm (23) and the signal sending rod (24). On the other hand, around the main shaft (26), a main shaft cap (27) fixed to the front surface of a main shaft head (not shown) is provided, and the main shaft cap includes a signal extraction block (28) and an electrical The connector (29) is installed in a positioned state. Therefore, at the same time as the constant pressure polishing head (1) is mounted on the spindle (26) from the tool magazine by a known automatic tool changer, the electric signal cables extending from the three displacement detectors are connected to the machining center. It will automatically be connected to a connection terminal of a computer (not shown). Air motor model grinding wheel rotation shaft (2)
Similarly to the electrical signal system mentioned above, the compressed air supply route to
The communication state is acquired at the same time as the constant pressure polishing head (1) is attached to the main shaft (26).

Hereinafter, a method for polishing the surface of a workpiece using the apparatus of the present invention will be explained based on FIG. In the following description, in order to facilitate understanding, the case where a circular grindstone is used will be explained. For simplification, Figure 2 schematically shows the case where elastic displacement occurs only in the XZ plane in the constant pressure polishing head shown in Figure 1, that is, the main body (1) of the polishing tool. It is something. The constant pressure polishing head (1) is elastically supported by two coil springs having spring constants (Kx) and (Kz). Kz) and the spring constant (Ky) in the Y-axis direction are adjusted to be equal to each other. Reference symbol (Su
) displays the surface of the workpiece (W) that has been roughly finished with a cutting tool such as a ball end mill in the previous process. A locus (LO) with an offset equal to the radius (r) of the grindstone (4) in the normal direction to the surface (Su
) on the workpiece while rotating the grindstone (4), the contact pressure acting between the grindstone and the workpiece is almost zero, so that no polishing is actually performed. Therefore, in this state, the output signals of the displacement detectors (15) and (21) become almost zero.

Here, in order to apply the contact pressure necessary for polishing between the grinding wheel (4) and the workpiece (W), the roughly finished surface of the workpiece (
Su') is given a pushing amount of resultant displacement E = Jrrr 100 T1 (where, Ex is the elastic displacement along the X-axis direction of the grinding wheel rotation axis (2), and Ez is the elastic displacement along the
), and the grindstone (4) is moved so that the envelope of the surface of the grindstone (4) becomes (So). In this way, the surface of the workpiece is polished while maintaining the contact pressure corresponding to the resultant displacement (E).

The following three technical issues should be considered at this time.

■ The setting accuracy of the pushing amount to apply a constant contact pressure, that is, the resultant displacement (E), ■ The measurement accuracy of the grindstone radius (r), and ■ The increase in the amount of grindstone wear over time.

All of the above three items are factors that cannot be ignored when setting the contact pressure, but since it is difficult to understand them quantitatively, conventional polishing processes rely on the operator's experience and rely on trial and error. Therefore, it was necessary to correct the contact pressure each time. In other words, since the grinding wheel (4) itself is an elastic body, the measurement accuracy of the diameter (2r) is not necessarily high, and the change in the diameter and shape of the grinding wheel due to wear is not uniform, so it is difficult to quantify it. Due to this inability to maintain contact pressure at a constant level, conventional polishing processes have experienced major obstacles.

By adopting the method of the present invention, the above problems are solved at once, and constant contact is maintained between the grinding wheel (4) and the workpiece surface (Su) without being affected by the elastic displacement or amount of wear of the grinding wheel. The pressure can be maintained.

Below, the movement locus of the envelope of the grinding wheel surface in Fig. 2 (S
Fig. 3 is an orthogonal coordinate diagram in which o) is subdivided and displayed in minute sections (ΔX) along the X-axis direction, and the resultant displacement (E) of the grinding wheel rotation axis (2) at that time and the contact pressure P The features of the present invention will be described in detail with reference to FIG. 4, which is a graph schematically showing the relationship between (= and -E). In the conventional surface polishing method, the front side of the workpiece (W) is imprinted on the computer.
Since the movement locus of the grinding wheel (4) is defined by the grinding wheel program in Fig. 3, the grinding wheel (4) has the reference number (So
) to move it to display. Assuming that the amount of wear gradually increases as the grindstone (4) moves from position X4 to X7, the actual movement trajectory of the grindstone surface is (S1)
Therefore, the resultant displacement and the contact pressure P change as shown in FIG. 4(a) and (b) in response to the amount of wear, and normal polishing is not performed.

On the other hand, in the method of the present invention, as shown in FIG. is detected as a displacement detection signal, and by distributing the displacement detection signal into each axis component by a distributor (not shown) and comparing it with the command register of each axis, the command value of the workpiece machining program that is input into the computer in advance is determined. In other words, the surface of the grindstone (4) draws a movement trajectory '7a (S2) that is the movement trajectory (S+) plus or subtracted by corrections ΔE1 to ΔE4, and as a result, the contact pressure CP'') will be held at a constant level as indicated by reference numeral (b'') in FIG.

FIG. 5 is a flowchart illustrating the signal flow of the correction operation in FIG. 4, in which the signal flow indicated by the thin arrow is a movement command for the grinding wheel rotation axis (2) given by a standard Canadian program. Furthermore, the signal flow indicated by the bold line arrow is the sending path of the movement command for the grindstone rotating shaft (2) corrected by the method of the present invention.

C8 Effects of the invention As can be understood from the above explanation, by inputting the detection signal of the elastic displacement of the grinding wheel rotating shaft transmitted from the constant pressure polishing hand to the computer connected to the numerically controlled machine tool, the grinding wheel and the workpiece can be Surface polishing conditions are obtained in which the contact pressure between the two surfaces is maintained at a constant level. According to the present invention, the grinding program of the workpiece, especially the movement locus of the grinding wheel rotation axis, is automatically corrected in response to wear or changes in the shape of the grinding wheel, so that the grinding process can be carried out under the action of a stable and constant contact pressure. is carried out. Therefore, the dimensional accuracy of the workpiece surface can be greatly improved by reducing the pressure to the conventional polishing method.Furthermore, by monitoring the detection signal of the above-mentioned elastic displacement, the contact pressure acting between the grinding wheel and the workpiece can be reduced. (★It becomes possible to quantitatively control the wear amount of the grinding wheel.Also, by using the external work offset mechanism and tool diameter offset mechanism of the known numerical control device, constant pressure grinding can be performed on general-purpose numerically controlled machine tools. Numerical control copying VR polishing can be performed simply by attaching the head.

[Brief explanation of the drawing]

FIG. 1 is a partial vertical cross-sectional view illustrating the main structure of a surface polishing apparatus according to the present invention (2r), and FIG. 2 is a schematic explanatory diagram of the method of the present invention. Also, Figure 3 shows the movement of the envelope of the grinding wheel surface in Figure 2 above! 1iILis is an orthogonal coordinate diagram that subdivides and displays it in minute sections (ΔX) along the X-axis direction, and FIG. 4 is a graph that schematically displays the relationship between the resultant displacement of the grinding wheel rotation axis and the contact pressure. be. Further, FIG. 5 is a flowchart illustrating the signal flow of the correction operation in FIG. 4. (1) - Polishing tool, (2) - Grinding wheel rotation axis, (S)
- Floating support mechanism for grinding wheel rotating shaft, (D) - Elastic displacement detection mechanism, (26) - Main shaft of numerically controlled machine tool.

Claims (1)

[Claims] (11) In polishing the surface of a workpiece using a tool attached to the main shaft of a numerically controlled machine tool,
A computer connected to the numerically controlled machine tool converts the detection signals of elastic displacement in the Y-axis and Z-axis directions into a movement command for the grindstone rotation axis, and the movement trajectory of the grindstone rotation axis is determined according to the workpiece machining program including the movement command. A surface polishing method characterized by polishing the surface of a workpiece under constant pressure while correcting the path. (2) a floating support mechanism that supports a grindstone rotating shaft attached to the main shaft of a numerically controlled machine tool such that it can be elastically displaced in the X-axis, Y-axis, and Z-axis directions; and a detection mechanism for detecting the amount of elastic displacement of the grindstone rotating shaft; . A surface polishing apparatus characterized in that a constant pressure polishing mechanism is formed by a computer connected to the numerically controlled machine tool.