JP2014018875A - Magnetic polishing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic polishing method capable of performing mirror polishing to the whole surface including a concave surface evenly without moving a polishing tool along a surface of a workpiece (mainly upward and downward movement from planar surface to concave surface) even if the workpiece has the concave surface.SOLUTION: The magnetic polishing method for the workpiece W having the concave surface uses a polishing device 1 that includes: a polishing fluid containing a magnetic particle, a non-magnetic abrasive grain and a magnetic fluid; a polishing tool 3 formed of a magnetic material; and a coil 2 having a through-hole in an axial direction thereof, where the polishing tool 3 is inserted through the through-hole of the coil 2. The magnetic polishing method performs mirror polishing by maintaining a clearance between the polishing tool 3 and the workpiece W at 1.0-1.5 mm while rotating the polishing tool 3 in a state where the coil 2 is energized with a pulse voltage.

Description

  The present invention relates to a magnetic polishing method in which a concave surface of an object to be polished is mirror-polished using a polishing tool.

In recent years, surface polishing of a miniature mold represented by a molding lens for a camera lens mounted on a mobile phone has been required to be mirror-polished with high accuracy. Further, for surface polishing of semiconductors and magnetic recording devices, a polishing technique that provides excellent surface roughness and flatness is required. Various types of magnetic polishing methods have been conventionally proposed for polishing such products (objects to be polished).

For example, in Patent Document 1, a magnetic fluid (polishing liquid) containing nonmagnetic abrasive grains, magnetic particles, and a dispersion medium is applied to a magnetic polishing tool wound with a coil, and the polishing tool is rotated. At the same time, a magnetic polishing method is disclosed in which the object to be polished is polished while rotating the concave object to be polished while keeping the distance between the polishing tool and the object to be polished constant. Further, the voltage applied to the coil can be switched between ON (ON) and OFF (OFF) in conjunction with the position of the object to be polished. By using this magnetic polishing method, a highly accurate polished surface can be obtained.

Further, in Patent Document 2, a polishing tool having a polishing tool (magnetic iron core) wound with a coil in the presence of a polishing liquid containing nonmagnetic abrasive grains, magnetic particles, and a surfactant is used. A magnetic polishing method is disclosed in which a workpiece is polished while rotating a (magnetic iron core) while maintaining a processing gap between the polishing tool and the workpiece to be 0.7 mm. In addition, the voltage applied to the coil can be a direct voltage (DC). By using this magnetic polishing method, an extremely high polished surface (R _max = 0.1 μm) can be obtained.

Furthermore, in Patent Document 3, using a polishing apparatus having a polishing tool having a magnetic field generating source such as a permanent magnet, a non-magnetic abrasive such as alumina, a magnetic particle such as iron powder, and a dispersion medium such as kerosene A magnetic polishing method is disclosed in which a polishing tool and a workpiece are moved relatively while rotating a polishing tool in a state where a magnetic fluid (polishing processing liquid) containing is applied. By using this magnetic polishing method, concentric cutting and mirror polishing can be performed simultaneously.

Further, the inventors applied a pulse voltage of 0.1 Hz to a rotating polishing tool using a polishing apparatus equipped with a polishing tool that penetrates the central portion of the coil in a magnetic polishing method using magnetism. In this state, a magnetic fluid containing alumina (nonmagnetic abrasive grains), iron powder (magnetic particles), and kerosene (dispersion medium) is applied to the object to be polished while a magnetic field (pulse magnetic field) is generated. It has been announced that there is a certain polishing effect by polishing the surface of the polished product (see Non-Patent Documents 1 and 2).

JP 2006-224227 A Japanese Patent Laid-Open No. 5-8169 JP 2006-82213 A Hitoshi Nishida, Kunio Shimada, Koji Imon, "Effect of pulsed magnetic field on surface polishing using magnetic functional fluid", 2010 JSPE Spring Conference, March 17, 2010 Hitoshi Nishida, Kunio Shimada, Koji Imon, “Effects of Magnetic Clusters on Polishing Using Magnetic Functional Fluid”, 22nd Electromagnetic Force-Related Dynamics Symposium, May 20, 2010, p. 374-375

However, in the magnetic polishing method described in Patent Document 1, when polishing an object to be polished having a concave surface, the tip of the polishing tool is placed on the object to be polished while maintaining a constant distance between the polishing tool and the object to be polished. It is necessary to incline the object to be polished along the concave surface. That is, even if the polishing tool is only rotated, it is necessary to move the object to be polished three-dimensionally (relative to the polishing tool), and the apparatus for fixing the object to be polished has a complicated structure. It was.

Further, in the magnetic polishing method described in Patent Document 2, polishing is performed in a state where the object to be polished is fixed without moving while rotating the polishing tool, so that the object to be polished having a concave surface is polished. However, there is a problem that it is difficult to uniformly polish the entire concave surface.

Furthermore, in the magnetic polishing method described in Patent Document 3, when the magnetic field generation source for the polishing tool is a permanent magnet, the magnetic field does not change, and therefore the magnetic fluid is not uniformly distributed at the tip of the polishing tool. (Magnetic polishing liquid) remains. Therefore, there is a problem that it is difficult to ensure the polishing accuracy of the object to be polished having a concave surface.

Therefore, in the present invention, even an object having a concave surface without moving the polishing tool along the surface of the object to be polished (mainly moving up and down from the flat surface in the depth direction of the concave surface) It is an object of the present invention to provide a magnetic polishing method capable of uniformly polishing the entire continuous plane.

  In order to solve the above-described problem, in the present invention, a polishing liquid containing magnetic particles, nonmagnetic abrasive grains and a magnetic fluid, a polishing tool made of a magnetic material, and a coil having a through hole in the axial direction, A method for magnetically polishing an object having a concave surface using a polishing apparatus in which a polishing tool is inserted into a through-hole of a coil, and polishing with a pulse voltage applied to the coil While rotating the tool, the distance between the polishing tool and the object to be polished was maintained at 1.0 mm to 1.5 mm, and the concave surface was mirror polished.

By applying a pulse voltage having a constant frequency to the coil by this method, the polishing tool is magnetized, and the polishing liquid containing magnetic particles and nonmagnetic abrasive grains forms a magnetic cluster. Depending on the frequency of the pulse voltage, the magnetic cluster undergoes “formation (a magnetic cluster is born along the lines of magnetic force)” and “decay (a magnetic cluster is destroyed by the disappearance of the magnetic field)” in a short time. Repeatedly, the polishing surface (concave surface) is polished by adhering to the magnetic cluster each time or by replacing the held nonmagnetic abrasive grains.

  The invention according to claim 2 is a magnetic polishing method for polishing an object to be polished in a state where the frequency of the pulse voltage applied to the coil is 0.1 Hz to 0.5 Hz. By this method, the interval (timing) between formation and decay of the magnetic cluster can be optimized.

The magnetic polishing method according to the present invention includes a polishing tool and a coil having a through hole in the axial direction, and a concave surface using a polishing apparatus in which the polishing tool is inserted into the through hole of the coil. A method for magnetically polishing an object to be polished, wherein the polishing tool and a concave surface of the object to be polished are held at an interval of 1 mm to 1.5 mm while rotating the polishing tool with a pulse voltage applied to the coil. As a result, the magnetic cluster repeatedly forms and collapses according to the frequency of the pulse voltage, and adheres to the magnetic cluster each time, or the held nonmagnetic abrasive grains are replaced, and the polished surface (concave surface) is polished. Therefore, without moving the polishing tool along the surface of the object to be polished (mainly moving up and down from the flat surface in the depth direction of the concave surface) (without controlling the distance between the polishing tool and the object to be polished) Even a polished object having a concave surface And an effect that the overall plan for continuous thereto can be uniformly mirror-polished.

1 is a schematic diagram of a polishing apparatus 1 used in a magnetic polishing method according to the present invention. FIG. 2 is an enlarged schematic view of a tip portion of a polishing tool 3 in the polishing apparatus 1 of FIG. 1. It is a schematic diagram showing the distribution state of the magnetic particle and nonmagnetic abrasive grain in a magnetic fluid between a polishing tool and a to-be-polished object. It is a graph of the surface state before and behind grinding | polishing of a to-be-polished object at the time of applying a pulse voltage to the coil of a grinding | polishing apparatus. It is a graph of the surface state before and behind grinding | polishing of a to-be-polished object when a DC voltage is applied to the coil of a grinding | polishing apparatus. It is a graph of the surface state of the to-be-polished object before and after grinding | polishing when the distance of the grinding | polishing tool front-end | tip part and the to-be-polished object surface at the time of applying a pulse voltage to the coil of a grinding | polishing apparatus is 0.5 mm. It is a graph of the surface state of the to-be-polished object before and after grinding | polishing when the distance of the polishing tool front-end | tip part and the to-be-polished object surface at the time of applying a pulse voltage to the coil of a grinding | polishing apparatus is 1.0 mm. It is a graph of the surface state of the to-be-polished object before and after grinding | polishing when the distance of the polishing tool front-end | tip part and the to-be-polished object surface at the time of applying a pulse voltage to the coil of a grinding | polishing apparatus is 1.5 mm. It is a graph of the surface state of the to-be-polished object before and after grinding | polishing when the distance of the polishing tool front-end | tip part and the to-be-polished object surface at the time of applying a pulse voltage to the coil of a grinding | polishing apparatus is 2.0 mm.

An embodiment of a magnetic polishing method according to the present invention will be described with reference to the drawings. FIG. 1 is a schematic view of a polishing apparatus 1 used in a magnetic polishing method according to the present invention, and FIG. 2 is an enlarged schematic view of a tip portion of a polishing tool 3 in the polishing apparatus 1 of FIG. As shown in FIG. 1, a polishing apparatus 1 used in a magnetic polishing method according to the present invention includes a coil 2 to which a pulse voltage is applied from a pulse power source (not shown), and a through hole provided in the central portion of the coil 2 in the axial direction. A polishing tool 3 inserted through the base, a base (base) 4 on which the object to be polished W is installed, an O-ring 5 for fixing the object to be polished W in the base 4, and the number of rotations of the object to be polished W during polishing. The main shaft 6 and the motor 7 of the motor to be controlled are configured. Further, as shown in FIG. 2, the workpiece W has a concave surface (concave portion) having a depth d from the plane F, and maintains a distance δ between the tip surface of the polishing tool 3 and the plane F of the workpiece W. In this state, the concave surface and the flat surface F continuous thereto are polished.

Next, a magnetic polishing method using the polishing apparatus 1 will be described. After fixing the object to be polished W having a concave surface to the main shaft 6 of the motor by screwing with an O-ring 5, an appropriate amount of polishing liquid containing magnetic particles, nonmagnetic abrasive grains and magnetic fluid is dropped on the surface of the object to be polished W. Then, a pulse voltage is applied to the coil 2. When a pulse voltage is applied to the coil 2, a magnetic field (pulse magnetic field) is generated in the polishing tool 3, and the chain-like magnetic cluster shown in FIG. 3 is formed by the magnetic particles in the polishing liquid in contact with the tip of the polishing tool 3. Will occur.

As shown in FIG. 3, the magnetic cluster is formed between the surface of the tip of the polishing tool and the surface of the object to be polished, the magnetic particles are distributed along the lines of magnetic force, and the non-magnetic abrasive grains are mainly polished. Many gather on the surface side of things. The magnetic cluster has a chain shape, and is elongated and elastic due to dispersed particles of magnetic fluid and α-cellulose between the magnetic particles and the nonmagnetic abrasive grains. Thereafter, the polishing tool is rotated at a predetermined number of revolutions, and at the same time, the polishing of the surface of the object to be polished is started while the object to be polished is also rotated. That is, the surface of the object to be polished is polished by relatively moving the polishing tool and the object to be polished. As for the relative movement mode between the polishing tool and the object to be polished, the polishing tool is moved in parallel with the surface of the object to be polished without rotating the object to be polished while only the polishing tool is rotated, or the polishing tool. There is a form in which the object to be polished is moved in the horizontal direction in a state in which is fixed, and the same effect as when polishing is performed with both the polishing tool and the object to be rotated can be obtained.

Using the polishing apparatus shown in FIG. 1, a polishing test was performed to polish a concave surface of an object having a concave surface in a state where a direct voltage (DC) and a pulse voltage (frequency 0.1 Hz) were applied to the coil. The test results will be described with reference to FIGS. The polishing test was performed by rotating a brass workpiece (diameter 30 mm, thickness 10 mm, concave surface diameter 8 mm, concave surface depth 0.5 mm) at a rotational speed of 200 rpm while rotating the polishing tool at a rotational speed of 500 rpm. However, the distance between the tip of the polishing tool and the plane of the object to be polished was maintained at 1.0 mm. Further, the distance (offset distance) between the center axis of the polishing tool and the center of the object to be polished is maintained at 5 mm, and the object to be polished is moved (oscillated) at a speed of 40 mm per minute while moving (oscillating) a width of 8 mm. It was. In addition, the rotation direction (rotation direction) of the object to be polished and the polishing tool was set so as to be in a reverse rotation relationship as shown in FIG. 1, and the polishing time was 80 minutes.

FIG. 4 is a graph of the surface state before and after polishing of the object to be polished when a pulse voltage is applied to the coil of the polishing apparatus, and FIG. 5 is a surface of the object to be polished before and after polishing when a DC voltage is applied to the coil of the polishing apparatus. It is a graph of a state. 4 and 5 of the surface state of the object to be polished are graphs in which the surface state of the object to be polished is measured by a surface profile measuring device in the range of about 14 mm (total measurement distance: 28 mm) from the center of the concave surface to the left and right. It is. In both graphs, the graphs before and after polishing were superimposed on each other at a measurement start position (diameter direction measurement distance: 0 mm) and a measurement end position (diameter direction measurement distance: 28 mm).

When a pulse voltage is applied to the coil of the polishing apparatus, as shown in FIG. 4, the shape after polishing for 80 minutes is the boundary portion between the flat surface and the concave surface, the inclined portion that forms the concave surface, and the bottom surface portion of the concave surface. There is almost no difference from the shape before polishing. Moreover, both the concave part and the surface of the flat part are in a mirror state.

On the other hand, when a DC voltage is applied to the coil of the polishing apparatus, as shown in FIG. 5, the shape after polishing for 80 minutes is the boundary portion between the flat surface and the concave surface, the inclined portion forming the concave surface, and the concave surface Differences from the shape before polishing occurred at all locations on the bottom surface of the substrate. Specifically, the shape after polishing exhibits a shape that is inclined as the plane of the object to be polished approaches the concave surface side, and in the inclined portion that forms the concave surface, the surface is polished deeper as it approaches the bottom surface portion. At the bottom surface, the distance from the smooth surface increased in the depth direction by about 10 μm. The polished surface is in a mirror state on both the concave and flat surfaces.

From the above results, the magnetic polishing method according to the present invention moves the polishing tool along the surface of the object to be polished even when the object has a concave surface (up and down movement from the plane to the concave direction), The mirror surface could be uniformly polished while maintaining the shape of the entire surface (shape accuracy).

Next, in order to clarify the influence of the interval on polishing, the distance between the tip of the polishing tool and the plane of the object to be polished (frequency in FIG. 2) with a pulse voltage applied to the coil (frequency = 0.1 Hz). A polishing test was conducted while changing δ). The test results will be described with reference to FIGS. The polishing test was performed using the same polishing apparatus as in Example 1, but the object to be polished was only a flat surface having no concave surface, and the object to be polished was fixed without rotating during polishing. A polishing test was performed in the state. Further, the polishing tool is rotated at a rotation speed of 500 rpm as in the first embodiment, and the center axis of the polishing tool and the center of the object to be polished are made the same to polish the object to be polished without moving the object to be polished. (Polishing time: 80 minutes).

FIG. 6 shows the surface state of the workpiece before and after polishing when the distance between the tip of the polishing tool and the plane of the workpiece is 0.5 mm, and FIG. 7 shows the distance between the tip of the polishing tool and the plane of the workpiece. FIG. 8 shows the surface state of the object before and after polishing when the distance between the tip of the polishing tool and the plane of the object is 1.5 mm. FIG. 9 shows the surface state of the object before and after polishing when the distance between the tip of the polishing tool and the plane of the object is 2.0 mm. 6 to 9, the alternate long and short dash line represents the polishing center position.

Each of the graphs in FIGS. 6 to 9 is a graph in which the surface state of an object to be polished is measured by a surface profile measuring device within a range of 14 mm (total measurement distance: 28 mm) from the polishing center position. In addition, the graphs of FIGS. 6 to 9 are displayed by superimposing the graphs before and after polishing on the measurement start position (measurement distance in the diameter direction: 1 mm) and the measurement end position (measurement distance in the diameter direction: 29 mm). .

When the distance between the tip of the polishing tool and the plane of the object to be polished is 0.5 mm, the surface state of the object before and after polishing is as shown in FIG. ) To 2 mm, no change was observed in the depth direction before and after polishing because it was close to the center of rotation of the polishing tool. However, in the range from 2 mm to 5 mm from the polishing center (rotation center of the polishing tool), the depth is polished to the maximum depth of 3.5 μm, and in the range from 5 mm to 12 mm from the polishing center, the depth is about 0.8 μm. It was polished. That is, the amount of polishing in the depth direction varies depending on the measurement location in the diameter direction.

Further, the surface state of the object before and after polishing when the distance between the tip of the polishing tool and the plane of the object to be polished is 2.0 mm, the polishing center in the diametrical direction (15 mm in the figure) is shown in FIG. No change was observed in the depth direction before and after polishing in the range from 4 to 4 mm. However, in the range of 4 mm to 12 mm from the polishing center, the processing depth varied.

On the other hand, the surface state of the object before and after polishing when the distance between the tip of the polishing tool and the plane of the object to be polished is 1.0 mm is shown in FIG. In the range from the 15 mm position in the figure to 2 mm, there is no change in the depth direction before and after polishing, as in the case where the distance between the tip of the polishing tool and the plane of the workpiece shown in FIG. 6 is 0.5 mm. I couldn't. However, in the range of 2 mm to 12 mm from the center of polishing, the polishing amount was about 0.7 μm and there was little change, and in this range, polishing was almost uniform.

The surface state of the object before and after polishing when the distance between the tip of the polishing tool and the flat surface of the object to be polished is 1.5 mm is shown in FIG. In the range from 2 mm to 2 mm, the depth direction before and after polishing is the same as in the case where the distance between the tip of the polishing tool and the plane of the object to be polished shown in FIGS. 6 and 7 is 0.5 mm and 1.0 mm. There was no change. However, the polishing amount in the range from 2 mm to 12 mm from the polishing center was about 0.8 μm, and in this range, the polishing was almost uniform.

  From the above results, the magnetic polishing method in which the distance between the tip of the polishing tool and the plane of the object to be polished is 1.0 mm to 1.5 mm while rotating the polishing tool with a pulse voltage applied to the coil is as follows. It was found that the same surface properties were obtained in an equivalent wide polishing region. That is, by using the magnetic polishing method according to the present invention, an object to be polished having a concave surface in which the distance between the polishing tool and the processing surface changes in the range of 1.0 mm to 1.5 mm can be obtained by the characteristics of a long and elastic magnetic cluster. Thus, polishing can be performed without moving the polishing tool up and down in the depth direction. In addition, if the object to be polished has a concave surface whose distance from the plane is 0.5 mm (500 μm) or less by using the magnetic polishing method according to the present invention, the concave surface and the subsequent plane are maintained in a wide range and uniform shape accuracy. Can be polished. In addition, although the present Example performed the grinding | polishing test for the to-be-polished object which has a concave surface, even if it is the to-be-polished object which has the surface of fine complicated shapes, such as a groove shape and a hole shape of a micron unit, Needless to say, an effect can be obtained.

1 Polishing device 2 Coil 3 Polishing tool
DESCRIPTION OF SYMBOLS 10 Magnetic particle 11 Nonmagnetic abrasive grain 12 Magnetic fluid W To-be-polished object (delta) Interval of polishing tool and to-be-polished object

Claims (2)

A polishing liquid containing magnetic particles, non-magnetic abrasive grains and a magnetic fluid, a polishing tool made of a magnetic material, and a coil having a through hole in the axial direction, the polishing tool being the coil A method for magnetically polishing an object to be polished having a concave surface using a polishing apparatus inserted through a through-hole, wherein the polishing tool is rotated while a pulse voltage is applied to the coil. And polishing the concave surface of the object to be polished while maintaining the distance between the object and the object to be polished at 1.0 mm to 1.5 mm. The magnetic polishing method according to claim 1, wherein the concave surface of the object to be polished is polished in a state where the frequency of the pulse voltage is 0.1 Hz to 0.5 Hz.

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