JP7583556B2 - Magnetic functional polishing fluid - Google Patents

Description

This disclosure relates to a magnetic functional polishing fluid.

In the field of precision machining, polishing using a fluid that responds to a magnetic field (magnetic functional fluid) is known. In polishing using a magnetic functional fluid, polishing is performed by magnetic force using a magnetic functional polishing processing liquid containing abrasive grains. When a magnetic field is applied to the magnetic functional polishing processing liquid, the magnetic particles form aggregates (clusters) and are pressed against the processing surface together with the abrasive grains. The clusters slide when the magnetic field is moved, and the abrasive grains polish the processing surface.

A magnetic functional polishing processing liquid is known that uses a magnetic fluid in which nanometer-sized magnetic particles are dispersed in a dispersion medium such as kerosene as a base solution. Micrometer-sized magnetic particles such as carbonyl iron and non-magnetic abrasive grains such as alumina are added to the base solution. In addition, a fibrous cluster reinforcing material is added as necessary (see, for example, Patent Document 1).

JP2006-82213Publication

However, when polishing is performed using conventional magnetic functional polishing fluids, not only is the surface smoothed, but the fine structure is also removed, resulting in the problem that the shape of the workpiece being polished cannot be adequately maintained.

The objective of this disclosure is to realize a magnetic functional polishing liquid that can both smooth the polished object and retain its shape.

One aspect of the magnetic functional polishing liquid disclosed herein includes a dispersion medium, first magnetic particles having an average particle size of 15 nm or less, second magnetic particles having an average particle size of 20 nm or more and 200 nm or less, third magnetic particles having an average particle size of 0.5 μm or more and 50 μm or less, non-magnetic abrasive grains, and a cluster reinforcing material, the cluster reinforcing material being a non-magnetic fibrous material.

The magnetic functional polishing liquid disclosed herein can achieve both smoothing of the polished object and retention of its shape.

FIG. 2 is a diagram showing a magnetic functional polishing liquid according to an embodiment. FIG. 1 is a diagram showing an example of a polishing device that can use a magnetic functional polishing liquid according to an embodiment. FIG. 1 is a diagram showing a cluster of a conventional magnetic functional polishing liquid. FIG. 2 illustrates a cluster of a magnetic functional polishing fluid according to an embodiment. 2 is a graph showing a flow curve of the magnetic functional polishing liquid of Example 1. FIG. 2 is a diagram showing the structure of an object to be polished. FIG. 2 is a diagram showing shape characteristics before and after polishing using the magnetic functional polishing liquid of Example 1. 6 is a photograph showing the surface state before and after polishing with the magnetic functional polishing liquid of Example 1. FIG. 1 is a diagram showing shape characteristics before and after polishing using the magnetic functional polishing liquid of Comparative Example 1. 6 is a photograph showing the surface state before and after polishing with the magnetic functional polishing liquid of Comparative Example 1.

As shown in FIG. 1, the magnetic functional polishing processing liquid (hereinafter referred to as the processing liquid) of the present disclosure has first magnetic particles 101, second magnetic particles 102, third magnetic particles 103, non-magnetic abrasive grains, and cluster reinforcement material 105 dispersed in a dispersion medium 106, each having a predetermined average particle size. The average particle sizes of the first magnetic particles 101, second magnetic particles 102, third magnetic particles 103, and non-magnetic abrasive grains can be measured by dynamic light scattering or laser diffraction/scattering.

The first magnetic particle 101, the second magnetic particle 102, and the third magnetic particle 103 can be formed from various magnetic materials. Specifically, iron, iron oxide, iron nitride, iron carbide, carbonyl iron, chromium dioxide, low carbon steel, nickel, cobalt, etc. can be used. In addition, iron alloys such as aluminum-containing iron alloys, silicon-containing iron alloys, cobalt-containing iron alloys, nickel-containing iron alloys, vanadium-containing iron alloys, molybdenum-containing iron alloys, chromium-containing iron alloys, tungsten-containing iron alloys, manganese-containing iron alloys, and copper-containing iron alloys can also be used. Paramagnetic, superparamagnetic, or ferromagnetic compound particles made of gadolinium or gadolinium organic derivatives, and particles made of mixtures thereof can also be used.

In order for the first magnetic particles 101 to exhibit the properties of a magnetic fluid when dispersed in a dispersion medium, the average particle diameter is preferably 15 nm or less, more preferably 12 nm or less, and is preferably 5 nm or more, more preferably 8 nm or more.

For the second magnetic particles 102, magnetic particles larger than the first magnetic particles 101 can be used. The average particle size of the second magnetic particles is 20 nm or more, preferably 50 nm or more, more preferably 80 nm or more, and 200 nm or less, preferably 150 nm or less, more preferably 120 nm or less. Although not particularly limited, magnetite particles, which are a composite oxide containing divalent iron and trivalent iron, and iron particles formed by an arc plasma method are preferred as the second magnetic particles 102 because they can be easily obtained with a suitable particle size.

The third magnetic particles 103 are magnetic particles of a size generally used in MR fluids. The average particle size of the third magnetic particles 103 is 0.5 μm or more, preferably 0.7 μm or more, more preferably 1 μm or more, and 50 μm or less, preferably 20 μm or less, more preferably 10 μm or less. Although not particularly limited, carbonyl iron particles are preferred as the third magnetic particles 103 due to their magnetic properties and ease of availability.

From the viewpoint of effective polishing, the non-magnetic abrasive grains 104 are preferably non-magnetic particles with high hardness and sharp edges. Specifically, abrasive grains made of alumina, silicon carbide, diamond, boron nitride, etc. can be used. The average particle size of the abrasive grains can be selected according to the purpose, but those of about 0.3 μm to 50 μm can be used.

A non-magnetic fibrous material can be used for the cluster reinforcement 105. Specifically, alpha-cellulose fibers with an average length of about 0.05 mm to 0.2 mm can be used.

The dispersion medium may be any liquid capable of dispersing the mixture of fine particles. For example, water, kerosene, silicone oil, fluorine oil, polyalphaolefin (PAO), paraffin, ether oil, ester oil, mineral oil, vegetable oil, or animal oil may be used. In addition, organic solvents such as toluene, xylene, hexane, and ethers, or ionic liquids (room-temperature molten salts) such as ethylmethylimidazolium salt, 1-butyl-3-methylimidazolium salt, and 1-methylpyrazolium salt may also be used. These may be used alone or in combination of two or more types.

The volume concentration of all solids (mixture of fine particles) in the processing liquid is not particularly limited, but is preferably 35 vol% to 45 vol%. The volume concentration of all magnetic particles in the processing liquid is not particularly limited, but is preferably 15 vol% to 25 vol%. The ratio of all magnetic particles to all components is not particularly limited, but is preferably 45 mass% to 55 mass%.

The ratio of the first magnetic particles 101 to the total magnetic particles (the total amount of the first magnetic particles, the second magnetic particles, and the third magnetic particles) is preferably 30% by mass or more, more preferably 35% by mass or more, preferably 50% by mass or less, and more preferably 45% by mass or less. The ratio of the second magnetic particles 102 to the total magnetic particles is preferably 30% by mass or more, more preferably 35% by mass or more, preferably 50% by mass or less, and more preferably 45% by mass or less. The ratio of the third magnetic particles 103 to the total magnetic particles is preferably 10% by mass or more, more preferably 15% by mass or more, preferably 30% by mass or less, and more preferably 25% by mass or less. The ratio of the non-magnetic abrasive grains 104 to the total components including the dispersion medium is preferably 10% by mass to 30% by mass. The ratio of the cluster reinforcing material to the total components is preferably 4% by mass to 10% by mass.

The machining liquid 100 of this embodiment can be used in a polishing device 200 as shown in FIG. 2, for example. The polishing device 200 is composed of a coil 202 to which a pulse current is applied from a pulse power source (not shown), a polishing tool 203 inserted into a through hole provided in the center of the coil 202 in the axial direction, a base (stand) 204 on which the workpiece W is placed, an O-ring 205 that fixes the workpiece W in the base 204, and a motor spindle 206 and a motor 207 that control the rotation speed of the workpiece W during polishing.

An appropriate amount of the processing liquid 100 is dropped onto the surface of the workpiece W, and a pulse voltage is applied to the coil 202. When the pulse voltage is applied to the coil 202, a magnetic field (pulse magnetic field) is generated in the polishing tool 203, and chain-like clusters are generated in the processing liquid 100 that is in contact with the tip of the polishing tool 203.

The clusters are distributed along the magnetic field lines between the tip of the polishing tool 203 and the workpiece W. The surface of the workpiece W is polished by rotating the polishing tool 203 and the workpiece W and moving the polishing tool 203 and the workpiece W relative to each other. Note that, as long as the polishing tool 203 and the workpiece W can be moved relative to each other, the configuration is not limited to rotating both the polishing tool 203 and the workpiece W, and one of them may be fixed. Furthermore, the motion is not limited to rotational motion, and linear motion is also possible.

As shown in FIG. 3, when the second magnetic particles 102 are not included, the clusters are formed by the third magnetic particles 103 and the cluster reinforcing material 105, resulting in thick and relatively long clusters. The clusters also have high strength and a large processing force. However, these clusters cannot enter small gaps, and the precision of micromachining cannot be sufficiently improved. In addition, most of the non-magnetic abrasive grains 104 are present outside the clusters, and many of them are present in the dispersion medium. For this reason, polishing is mainly performed by the large clusters pressing the non-magnetic abrasive grains 104 in the dispersion medium against the processing surface.

On the other hand, in the cluster 110 of this embodiment, as shown in FIG. 4, the first magnetic particles 101 and the second magnetic particles 102 get into the gaps between the third magnetic particles 103 arranged along the magnetic flux, and the cluster 110 is reinforced by the fibrous cluster reinforcing material 105. Since the first magnetic particles 101 are small, even if they get into the gaps between the third magnetic particles 103, they do not significantly disrupt the packing. On the other hand, the intermediate-sized second magnetic particles 102 get into the gaps between the third magnetic particles 103, so the cluster 110 becomes thinner and relatively short in length. Therefore, the cluster 110 of this embodiment can get into small gaps.

Since the first magnetic particles 101 are present in large quantities in the dispersion medium, the dispersion medium is a magnetic fluid. Therefore, the non-magnetic abrasive grains 104 have diamagnetic properties under a magnetic field and form abrasive grain clusters. In this embodiment, the non-magnetic abrasive grains 104 are also non-magnetic and are therefore not easily incorporated into the clusters 110, but there are some gaps between the magnetic particles that form the clusters 110, so the non-magnetic abrasive grains 104 and the abrasive grain clusters can adhere to the surface of the clusters 110. In addition, magnetic buoyancy acts on the non-magnetic abrasive grains 104 that exist in the dispersion medium together with the magnetic particles, so that the non-magnetic abrasive grains 104 move to the processing surface where the magnetic field strength is small. Therefore, polishing is performed by the clusters 110 with the non-magnetic abrasive grains 104 attached to their surfaces coming into contact with the processing surface and the processing force of the clusters 110 acting on the non-magnetic abrasive grains present on the processing surface. Therefore, even if the size of the clusters is small, polishing can be performed efficiently.

There are no particular limitations on the workpiece W to be polished. In particular, by using the processing liquid of this embodiment, it is easy to maintain the shape precision of the surface structure, so that it is possible to suitably polish a workpiece having a fine structure on its surface.

Example 1
The following was used as the machining liquid. Kerosene, which is a dispersion medium, was mixed and dispersed at 23.7% by mass, first magnetic particles with an average particle size of 10 nm at 21.0% by mass, second magnetic particles with an average particle size of 100 nm at 19.7% by mass, third magnetic particles with an average particle size of 1 μm to 7 μm at 9.9% by mass, non-magnetic abrasive grains with an average particle size of 3 μm at 19.5% by mass, and cluster reinforcement at 6.2% by mass. The ratio of the first magnetic particles to the total amount of the first magnetic particles, second magnetic particles, and third magnetic particles was 41.4% by mass, the ratio of the second magnetic particles was 39.0% by mass, and the ratio of the third magnetic particles was 19.6% by mass. Magnetite particles were used as the first magnetic particles. Iron nanoparticles were used as the second magnetic particles. Carbonyl iron particles were used as the third magnetic particles. The non-magnetic abrasive grains were made of alumina, and the cluster reinforcement material was made of α-cellulose fibers having an average length of about 0.1 mm. The volume ratio of the total solid content in the processing liquid was 37.6 vol%.

Figure 5 shows the flow curve of the processing fluid of Example 1. When a magnetic field of 100 mT to 500 mT was applied, the shear stress increased significantly, indicating a sufficient value for the fluid to be used in polishing processing. Furthermore, when a magnetic field was applied, the flow curve changed smoothly, indicating sufficient dispersibility for the fluid to be used in polishing processing.

A workpiece having a microstructure (groove) as shown in Figure 6 was polished, and the surface roughness and shape change of the microstructure before and after polishing were measured. The workpiece was a brass (C3604 JIS H3250:2012) disk with a diameter of 30 mm and a thickness of 10 mm, and the groove depth h was 0.2 mm, width w was 0.37 mm, and central angle was 60°. During polishing, an offset was provided between the central axis of the polishing tool and the central axis of the workpiece, and the polishing tool was oscillated. The offset value was 4 mm, the oscillating distance was 6 mm, and the speed was 40 mm/min. The polishing tool and the workpiece were rotated in opposite directions, the polishing tool rotation speed was 500 rpm, and the workpiece rotation speed was -200 rpm.

During polishing, the distance between the polishing tool and the workpiece was set to 0.5 mm, a pulse voltage of 0.1 Hz was applied to the coil, and a magnetic field of 240 mT was applied to the processing fluid.

The arithmetic mean surface roughness Ra in the range of 3.5 mm to 1.0 mm from the center of the workpiece was 0.193 before polishing, but improved to 0.067 after 80 minutes of polishing. The arithmetic mean surface roughness Ra was measured using a surface roughness and contour shape measuring instrument (Tokyo Seimitsu: Surfcom 1900DX).

Figure 7 shows the results of measuring the change in shape before and after polishing. The change in shape was measured using a surface roughness and contour shape measuring device (Tokyo Seimitsu: Surfcom 1900DX). The burrs that were present at the upper end A of the groove before polishing were removed by 80 minutes of polishing, while the edge of the upper end A was maintained, and the shape of the sidewall of the groove was also maintained.

Figure 8 shows micrographs of the positions of the upper end A and the bottom B of the groove in Figure 7 before and after polishing. At both the upper end A and the bottom B of the groove, the surface scratches have been reduced and smoothed by polishing.

(Comparative Example 1)
The composition of the processing liquid was 24.8% by mass of kerosene, 18.4% by mass of the first magnetic particles, 30.4% by mass of the third magnetic particles, 20.0% by mass of non-magnetic abrasive grains, and 6.4% by mass of cluster reinforcement material. The ratio of the first magnetic particles to the total amount of the first magnetic particles and the third magnetic particles was 37.7% by mass. The ratio of the third magnetic particles to the total amount of the first magnetic particles and the third magnetic particles was 62.3% by mass. The volume ratio of the total solid content in the processing liquid was 36.4 vol%.

Figure 9 shows the results of measuring the change in shape before and after polishing. The burrs that were present at the upper end A of the groove before polishing were removed by 80 minutes of polishing. Meanwhile, as shown in Figure 10, the ridges of the corners after polishing are rounded. The change in corner shape was even greater at the corners facing the groove. At part B, undulations occurred on the slope of the groove, causing a significant change in shape.

The processing fluid disclosed herein is capable of achieving both smoothing and shape retention, making it useful for polishing precision parts, etc.

REFERENCE SIGNS LIST 100 Machining liquid 101 First magnetic particles 102 Second magnetic particles 103 Third magnetic particles 104 Non-magnetic abrasive grains 105 Cluster reinforcement material 106 Dispersion medium 110 Cluster 200 Polishing device 202 Coil 203 Polishing tool 204 Base 205 O-ring 206 Spindle 207 Motor

Claims (2)

A dispersion medium;
first magnetic particles having an average particle size of 15 nm or less;
second magnetic particles having an average particle size of 20 nm or more and 200 nm or less;
third magnetic particles having an average particle size of 0.5 μm or more and 50 μm or less;
Non-magnetic abrasive grains;
and a cluster reinforcement material.
the cluster reinforcement material is a non-magnetic fibrous material;
a ratio of the first magnetic particles to a total amount of magnetic particles is 30% by mass or more and 50% by mass or less,
a ratio of the second magnetic particles to the total amount of the magnetic particles is 30% by mass or more and 50% by mass or less;
a ratio of the third magnetic particles to a total amount of magnetic particles is 10% by mass or more and 30% by mass or less;
The ratio of the cluster reinforcing material to the total components is 4% by mass or more and 10% by mass or less,
The cluster reinforcing material is α-cellulose fiber having an average length of 0.05 mm or more and 0.2 mm or less . The magnetic functional polishing liquid according to claim 1 , wherein the non-magnetic abrasive grains account for 10% by mass or more and 30% by mass or less of the total amount of all components.

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