JP3160274B2 - Method of processing rare earth alloy and method of manufacturing rare earth magnet using the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method of processing a rare earth alloy, and more particularly to a method of grinding and cutting a rare earth alloy suitably used as a material for a magnet.

[0002]

2. Description of the Related Art Rare earth alloys are used, for example, as materials for strong magnets. A rare earth magnet obtained by magnetizing a rare earth alloy is suitably used, for example, as a material for a voice coil motor used for positioning a magnetic head of a magnetic recording device.

[0003] As a method of cutting a rare earth magnet, Japanese Patent Application Laid-Open No. 9-174441 discloses an outer peripheral blade (also referred to as a "grinding wheel" or a "grinding wheel") in which a diamond-based abrasive is applied to a cutting portion at 10 to 80%. ) Is disclosed.

[0004] The applicant of the present invention has disclosed Japanese Patent Application Laid-Open No. 61-264.
No. 106 proposes a method of processing an R-Fe-B-based rare earth alloy in a non-oxidizing oil with a diamond grinding wheel or the like in order to prevent oxidation of the rare earth alloy surface.

[0005]

However, as a result of various studies by the present inventor on a method of processing a rare earth alloy, it has been found that the conventional processing method has the following problems. In particular, a hard main phase that mainly causes brittle fracture and a boundary layer that causes ductile fracture, such as a rare earth alloy manufactured by a sintering method (hereinafter, referred to as a “rare earth sintered alloy”). In order to efficiently process rare earth alloys with high processing accuracy and high efficiency, heat generated during processing is efficiently radiated,
That is, it was found that it was necessary to cool the processed part.

For example, even if the grinding wheel disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 9-174441 is used, unless the processing portion is cooled efficiently, the temperature of the grinding end rises abnormally, and Wear and abnormal shedding of diamond abrasive grains occur. When abnormal wear or abnormal shedding occurs, there is a problem in that the processing accuracy is reduced and the life of an expensive grinding wheel is shortened, so that the processing cost is increased.
This publication does not refer to a method of cooling the processing portion.

When the method disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 61-264106 is adopted, although the oxidation is suppressed by the non-oxidizing oil, the grinding wheel using diamond abrasive grains is sufficiently cooled. Difficult to do.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to provide a processing method for efficiently processing a rare earth alloy with high processing accuracy and a method for manufacturing a rare earth magnet using the same. And

[0009]

According to the present invention, there is provided a method for processing a rare earth alloy, comprising the steps of preparing a block of a rare earth alloy and rotatably supporting a grinding wheel having a grinding end including diamond abrasive grains on its outer periphery. Process and the grinding edge of the grinding wheel has a surface tension of 25 mN / m to 60 mN.
/ M (25 dyn / cm to 60 dyn / cm) while grinding the rare earth alloy block by bringing the rotating grinding end into contact with the block while supplying a cooling liquid of 25 dyn / cm to 60 dyn / cm. This achieves the above object.

Alternatively, the method for processing a rare earth alloy according to the present invention comprises the steps of: preparing a block of the rare earth alloy; rotatably supporting a grinding wheel having a grinding end including diamond-based abrasive grains on its outer periphery; The grinding edge of the grinding wheel has a coefficient of kinetic friction with the rare earth alloy of 0.
Grinding the block of rare earth alloy by contacting the rotating grinding end with the block while supplying cooling fluid of 1 to 0.3 to the grinding end, whereby the Objective is achieved.

Preferably, the cooling liquid is a cooling liquid containing water as a main component. The cooling liquid preferably contains an antifoaming agent. Preferably, the cooling liquid has a pH of 9 to 11. Further, the cooling liquid preferably contains a rust preventive.

The grinding end of the grinding wheel further contains a phenol resin, and has a volume ratio of 10 to 80%.
It is preferable to include the above-mentioned diamond-based abrasive grains. Further, it is preferable that the grinding wheel has a disk-shaped base plate, the grinding end is provided on an outer periphery of the base plate, and the base plate is formed of a cemented carbide.

[0013] The rare earth alloy may be an R-Fe-B rare earth sintered alloy.

It is preferable that the cooling liquid is discharged toward the grinding end.

The method for processing a rare earth alloy according to the present invention includes a step of collecting sludge containing grinding dust of the rare earth alloy and the cooling liquid generated in the grinding step, and a step of collecting sludge from the collected sludge. Separating the rare earth alloy grinding waste with a magnet.

In the method for processing a rare earth alloy according to the present invention, the grinding step includes a step of moving the grinding wheel relatively to the block, thereby cutting the block into small pieces. be able to.

In the grinding step, a tangential force Fx of the grinding wheel applied to the block and a radial force Fz of the grinding wheel applied to the block are within predetermined ranges. As described above, it is preferable that the rotation speed and the cutting speed of the grinding wheel and the jet pressure of the coolant are set.

It is preferable that the grinding step further includes a step of monitoring the Fx and Fz, and a step of determining whether or not the Fx and Fz are within the predetermined range.

The method of manufacturing a rare earth magnet according to the present invention comprises the steps of preparing a block of a rare earth alloy, rotatably supporting a grinding wheel having a grinding end including diamond abrasive grains on its outer periphery, The ground end of the wheel has a surface tension of 25 mN / m to 60 mN / m (25 dy / m).
n / cm to 60 dyn / cm), and moving the grinding wheel relative to the block while bringing the rotating grinding end into contact with the block. A grinding step of cutting the block into small pieces by grinding a block of the alloy and a step of magnetizing the rare earth alloy are included, thereby achieving the above object. The method for manufacturing a rare earth magnet according to the present invention is carried out by using the method for processing a rare earth alloy.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a method for processing a rare earth alloy and a method for manufacturing a rare earth magnet according to embodiments of the present invention will be described.

The method for processing a rare earth alloy according to the present invention comprises the steps of preparing a block of a rare earth alloy, rotatably supporting a grinding wheel having a grinding end including diamond-based abrasive grains on its outer periphery, and a grinding wheel. 2 on the ground end of
Surface tension at 5 ° C. is about 25 mN / m to about 60 mN
/ M (about 25 dyn / cm to about 60 dyn / cm) of a coolant (sometimes referred to as a “grinding fluid”) while bringing the rotating grinding end into contact with the block to form a block of the rare earth alloy. Grinding. A coolant having a dynamic friction coefficient of 0.1 to 0.3 at 25 ° C. with respect to the rare earth alloy may be used as the coolant.

In the method for processing a rare earth alloy according to the present invention,
In the step of grinding the rare earth alloy using a grinding wheel having a grinding end including a diamond-based abrasive grain on the outer periphery,
The coolant supplied to the grinding end has a surface tension at 25 ° C. of about 25 mN / m to about 60 mN / m (about 25 dyn /
cm to about 60 dyn / cm), so that the ground end can be efficiently cooled. The coolant having a surface tension within the above range has excellent permeability (wettability or conformability) to the grinding edge containing diamond-based abrasive grains as compared with water, so that the grinding portion (the rare earth alloy and the grinding edge come into contact with each other) It is considered that the coolant efficiently penetrates into the portion where the rare earth alloy is ground. The coolant suitably used in the grinding step can be selected according to the kinetic friction coefficient for the rare earth alloy. The coolant having the kinetic friction coefficient at 25 ° C. in the range of about 0.1 to about 0.3 is The same operation and effect as the cooling liquid having the surface tension within the above range can be exhibited. The surface tension is considered to be an index indicating the permeability of the coolant to the grinding edge, while the kinetic friction coefficient is considered to be an index of the lubricity provided by the coolant to the grinding edge. It is known that there is a qualitative correlation between the surface tension and the dynamic friction coefficient.

The surface tension of the coolant is measured using a well-known Dunui surface tensiometer. In addition, the dynamic friction coefficient of the coolant against rare earth alloys is based on Masuda's "four-ball friction tester" which is widely used as a basic tester in Japan.
It is measured using In this specification, the value at 25 ° C. is adopted as a value characterizing the coolant.

The dynamic friction coefficient shown in the following examples is
It is a value obtained by a four-ball friction tester using an iron ball. R-Fe-B based rare earth alloys (for example, Nd
_Since the alloy containing 2Fe ₁₄ B intermetallic compound as the main phase has the highest iron content, the kinetic friction coefficient of the coolant determined using iron balls is a good approximation and is adopted as the kinetic friction coefficient for rare earth alloys. can do. Rare earth alloy compositions and methods of manufacture are described, for example, in U.S. Pat. No. 4,770,723 and U.S. Pat. No. 4,792,368.

Further, the coolant used in the processing method of the present invention is specified by using the surface tension or the coefficient of kinetic friction at 25 ° C., but the temperature of the coolant when actually used is 25 ° C.
It is not limited to C. However, in order to obtain the effects of the present invention,
It is preferable to use a cooling liquid whose temperature is controlled within the range of 20 ° C to 30 ° C. As is well known, the surface tension and the kinetic friction coefficient of the coolant depend on the temperature, so if the temperature of the coolant actually used is out of the above temperature range, the surface tension and the kinetic friction coefficient of the coolant will decrease. Each of the states is very similar to a state outside the above numerical range, and the cooling efficiency is reduced.

By using the above-mentioned cooling liquid, an abnormal increase in the temperature of the grinding end can be suppressed, so that abnormal wear of the grinding end and abnormal shedding of diamond-based abrasive grains can be suppressed.
Can be prevented. As a result, a reduction in processing accuracy is prevented, and a grinding wheel can be used for a longer period than before, so that processing costs can be reduced.

As the cooling liquid, it is preferable to use a cooling liquid containing water as a main component. First, since water has a relatively high specific heat, the cooling efficiency is high. Furthermore, when a water-based coolant is used, the surface tension and the kinetic friction coefficient can be easily adjusted within the above ranges by adjusting the type and amount of the surfactant to be added. By adding a synthetic lubricant called "synthetic" to water instead of the surfactant, the surface tension and the coefficient of dynamic friction in the above ranges can be obtained. Also, when using a cooling liquid containing water as a main component, the viscosity is relatively low,
Rare earth alloy chips can be easily separated from the sludge generated by grinding using a magnet, and the coolant can be reused. Further, it is possible to prevent the disposal of the cooling liquid from adversely affecting the natural environment.
Since the time during which the rare earth alloy is exposed to the coolant is relatively short, the characteristics of the rare earth alloy do not deteriorate due to oxidation during the time.

If grinding is performed while rotating the grinding wheel at a high speed, the cooling liquid may foam and the cooling efficiency may decrease. By using a cooling liquid containing an antifoaming agent, a decrease in cooling efficiency due to foaming of the cooling liquid can be suppressed. Further, by using a coolant having a pH in the range of 9 to 11, corrosion of the rare earth alloy can be suppressed. In addition, by using a cooling liquid containing a rust inhibitor, oxidation of the rare earth alloy can be suppressed. These may be appropriately adjusted in consideration of the type of rare earth alloy, processing conditions, and the like.

As the grinding wheel, one having a grinding end containing diamond-based abrasive grains is used. As the binder for bonding the diamond abrasive grains to the outer periphery of the disk-shaped base plate of the grinding wheel, those using a resin can be suitably used. That is, a grinding wheel having a grinding end formed from a resin and diamond-based abrasive grains can be suitably used. Among them, it is preferable to use a grinding wheel having a grinding end containing a phenolic resin as a resin and containing 10 to 80%, preferably 10 to 50% by volume of diamond-based abrasive grains. The phenol resin has a high adhesive strength to the outer periphery of a disk-shaped base plate described later, and also has excellent wettability (permeability) to a cooling liquid described later. Further, by setting the volume fraction of the diamond-based abrasive grains within the above range, abnormal degranulation of the diamond-based abrasive grains is suppressed, and appropriate degranulation (degranulation of the abrasive grains with reduced grinding power) occurs. Stable grinding can be performed. As described above, by using a grinding wheel having a grinding end including a phenolic resin and an appropriate amount of diamond-based abrasive grains, good processing accuracy can be obtained, and the cooling effect of the cooling liquid is high. The rare earth alloy can be stably ground over the entire surface.

It is preferable to use a base plate made of cemented carbide as the base plate of the grinding wheel. For example, tungsten carbide cemented carbide has a high modulus of elasticity and is less deformed by force during processing, so that high processing accuracy can be realized. Further, since the thermal conductivity is high, the frictional heat at the grinding edge can be efficiently radiated. As described above, the grinding wheel including the base plate made of a cemented carbide is preferable from the viewpoint of processing accuracy and cooling efficiency.

The above-mentioned grinding wheel can be supplied from a general grinding wheel manufacturer (for example, Asahi Diamond Industrial Co., Ltd.) if the above-mentioned specifications are specified.

Further, as a base plate of a grinding wheel, a diamond sintered body using a hard alloy as a binder (see, for example, JP-A-8-109431) or a cubic boron nitride using a hard alloy as a binder A sintered body (for example, see JP-A-8-109432) can be used. In particular, the diamond sintered body (available from Reed Co., Ltd.) has a Young's modulus of about 550 GPa (about 55,
2,000 kgf / mm ² ), so that it is suitably used as a base plate for a grinding wheel. Furthermore, since this diamond sintered body has diamond powder on the surface,
A diamond sintered body can be used as a grinding end without separately providing a grinding end. At this time, the cooling effect by the above-described cooling liquid is sufficiently obtained.

The grinding wheel is generally rotated at high speed,
There is a flow of air around the periphery of the grinding wheel, which is referred to as “swirling flow”. When the coolant is discharged toward the grinding edge,
The coolant can be stably supplied to the grinding end without being hindered by the spiral flow. Therefore, the high-speed rotating grinding wheel can be efficiently cooled. Also,
Adopting the method of discharging the cooling liquid has an advantage that the cooling liquid can be supplied with a small or simple configuration, as compared with the method of immersing the grinding wheel in the bath of the cooling liquid.

The sludge containing the rare earth alloy grinding waste and the coolant generated in the grinding process is collected, and the rare earth alloy grinding waste is separated from the collected sludge by using a magnet, whereby the cooling fluid is separated. Can be reused (eg, used cyclically). As described above, the present invention is suitably applied when a water-based cooling liquid is used as the cooling liquid. Further, by separating the grinding dust of the rare earth alloy, it is possible to easily carry out the waste liquid treatment of the grinding liquid without damaging the environment.

Of course, the block can be cut into small pieces by grinding while moving the grinding wheel relatively to the rare earth alloy block. When the processing method according to the present invention is adopted, the rare earth alloy block can be cut with high accuracy and high efficiency. For example, a small rare earth alloy piece for a voice coil motor used for positioning a magnetic head can be manufactured with high accuracy and high efficiency. be able to.

In the grinding step, the tangential force Fx of the grinding wheel applied to the block and the radial force Fz of the grinding wheel applied to the block fall within a predetermined range. Rotation speed of grinding wheel,
By setting the cutting speed and the jet pressure of the cooling liquid, processing accuracy and / or processing efficiency can be improved. Further, grinding is performed while monitoring Fx and Fz, and it is determined whether or not Fx and Fz are within a predetermined range, so that the quality of the processed product is controlled and the time for replacing the grinding wheel is appropriately determined. It becomes possible to grasp, and the processing efficiency can be further increased.

In the grinding step, a tangential force Fx (typically in the horizontal direction) of the grinding wheel applied to the rare earth alloy block and a radial force Fz (typically in the horizontal direction) of the grinding wheel applied to the block. Can be measured using, for example, a known dynamometer using a quartz sensor (for example, available from Nippon Kistler Co., Ltd.).

As described above, the working method according to the present invention uses a rare earth sintered alloy which is difficult to work, especially R-Fe-B
It is suitably applied to processing of rare earth sintered alloys. By magnetizing the rare earth alloy processed by the processing method according to the present invention, a rare earth magnet is obtained. The magnetizing step may be performed before or after the grinding step. R-F
A rare earth sintered magnet manufactured using an eB-based rare earth sintered alloy is suitably used as a material for a voice coil motor used for positioning a magnetic head. The processing method according to the invention is described in particular in US Pat. No. 4,770,723 and US Pat.
No. 68, it is suitably used for processing an R-Fe-B-based rare earth sintered magnet (alloy). Among them, a hard main phase (iron-rich phase) composed of a tetragonal structure Nd ₂ Fe ₁₄ B intermetallic compound containing neodymium (Nd), iron (Fe) and boron (B) as main components; The present invention is suitably applied to processing and manufacturing of a rare earth sintered magnet (alloy) having a rich tough grain boundary phase (hereinafter, referred to as “neodymium magnet (alloy)”). A typical example of a neodymium magnet is NEOMA, manufactured by Sumitomo Special Metals Co., Ltd.
There is X.

[0039]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a method for processing a rare earth alloy (grinding method and cutting method) according to the present invention will be described below.

FIG. 1 is a schematic configuration diagram showing a cut state of a rare earth alloy block (also called a work) in one embodiment of the present invention.

FIG. 1 shows a state in which a rare-earth alloy block (work) 2 is cut by grinding with a grinding wheel 1.

As the block 2, a neodymium alloy having a height of about 20 mm (vertical direction in the figure), a length of about 40 mm (horizontal direction in the figure), and a width (direction perpendicular to the paper) of about 60 mm is used. The block 2 has an arcuate surface, and is ground and cut from the arcuate surface side.

The grinding wheel 1 has a disk-shaped base plate 1a.
And a ground end 1b mounted on the outer peripheral edge of the base plate 1a. Here, the base plate 1a is made of a cemented carbide such as tungsten carbide. More preferably, the Young's modulus is about 450 GPa to about 700 GPa (about 45,000 kgf / mm ² to about 70,000 kgf /
mm ² ) is used. Young's modulus is about 450GP
a (approximately 45,000 kgf / mm ² )
Bending or swelling occurs due to resistance at the time of cutting, about 700 GPa
If it exceeds (70,000 kgf / mm ² ), it becomes hard and brittle, so that it is easily broken. Further, for example, tungsten carbide cemented carbide is about 59 W / m · °
Since it has a high thermal conductivity of C (approximately 0.14 cal / cm · sec), there is also an advantage that the frictional heat generated at the grinding end 1b provided on the base plate 1a can be efficiently radiated. .

The particle size of the ground end 1b is 0.1 to 0.3 mm.
Of diamond-based abrasive grains (powder) of, for example, 10% by volume
It is formed by adhering to the outer peripheral edge of the base plate 1a using a resin so as to become 80%. The volume fraction of the diamond-based abrasive grains is more preferably 10 to 50%. As the abrasive powder, natural or synthetic industrial diamond abrasive powder is used. In addition, as abrasive powder,
It may be a mixture of cubic boron nitride (cBN).

Further, the ground end 1b preferably contains a phenol resin as a resin. In this embodiment, a grinding wheel 1 having a grinding end 1b containing diamond-based abrasive grains at a volume ratio of 10 to 50% and a phenol resin is used.
By including the phenol resin in this manner, the phenol resin is appropriately worn by heat at the time of grinding, so that abrasive grains can be cut with high cutting efficiency.

In this embodiment, for example, the grinding wheel 1
The diameter used was about 150 mm, the thickness of the base plate 1a was 0.5 mm, the thickness of the ground end 1b was 0.6 mm, and the width (length in the radial direction) of the ground end 1b was about 3 mm. FIG. 1 illustrates one grinding wheel 1. For example, six grinding wheels 1 are arranged at a pitch of 2 mm in parallel with each other (in a direction perpendicular to the paper surface), and the block 2 is divided into seven wheels. Can be cut into small pieces simultaneously.

The grinding wheel 1 is 1000 to 3000
The block 2 is rotated at a peripheral speed of m / min, in the direction indicated by an arrow (Z direction: typically a vertical direction) with respect to the block 2,
Cutting is performed at a cutting speed of 10 mm / min. Here, if the peripheral speed is less than 1000 m / min, abnormal wear occurs at the ground end 1b, and abnormal abrasive shedding occurs. On the other hand, if the peripheral speed exceeds 3000 m / min, the swirling flow becomes large, and it becomes difficult to supply the cooling liquid, and the device vibrates. The cutting speed is 3 mm / min.
If it is less than 10%, the production efficiency becomes poor and the cutting speed becomes 10
If it exceeds mm / min, abnormal wear of the grinding wheel occurs.

The cutting of the block 2 by the grinding wheel 1 is performed while supplying the cooling liquid 3. The cooling liquid 3 is supplied to the grinding end 1b by ejecting it from a nozzle 3a. In this way, by squirting the grinding end 1b,
The coolant 3 can be reliably supplied to the grinding end 1b, and abnormal temperature rise and abnormal wear at the grinding end 1b can be prevented.

The discharge pressure of the cooling liquid 3 from the nozzle 3a is about 20 kPa to about 150 kPa (2 kg / cm ²
１５15 kg / cm ² ), more preferably about 30 kPa〜
The pressure is set to about 70 kPa (3 kg / cm ^{2 to} 7 kg / cm ² ). If the discharge pressure is less than about 20 kPa (about 2 kg / cm ² ), the rotation of the grinding wheel 1 causes the air flow generated on the outer periphery of the grinding wheel 1 to blow off the coolant 3 and sufficiently supply the coolant 3 to the grinding end 1 b. However, this causes an abnormal rise in temperature at the grinding end 1b. When the discharge pressure exceeds about 150 kPa (about 15 kg / cm ² ), the coolant 3 causes the grinding wheel 1 to pulsate due to pump pulsation or the like.
Unnecessary vibration is given, and the processing accuracy of the block 2 is reduced. In addition, the discharge pressure is set to about 30 kPa to about 70
^{kPa (3kg / cm 2 ~7kg /} cm 2) With, with attained an extended service life of the grinding wheel 1, it is possible to improve the machining accuracy of the block 2. Also,
It is more preferable that the discharge direction of the nozzle 3a is a direction perpendicular to the grinding end 1b (that is, the radial direction of the grinding wheel 1).

The coolant 3 is a water-soluble lubricant containing water as a main component and containing a surfactant or a synthetic type synthetic lubricant, a rust inhibitor, a non-ferrous metal anticorrosive, a preservative, and a defoamer as components. Use agent. By using the cooling liquid 3 containing water as a main component in this way, the cooling effect can be enhanced, and an abnormal rise in the temperature at the grinding end 1b is less likely to occur. Further, by incorporating a surfactant or a synthetic type synthetic lubricant, the penetration effect can be enhanced, and the surface tension and the dynamic friction coefficient can be easily adjusted.

The surface tension of the cooling liquid is about 25 mN / m to about 60 mN / m (about 25 dyn / cm to about 60 dyn / c).
m) is preferable. The coefficient of dynamic friction between the grinding fluid and the block 2 is preferably 0.1 to 0.3.

Surfactants added to the grinding fluid containing water as a main component include, as anionic surfactants, fatty acid derivatives such as fatty acid soaps and naphthenic acid soaps, long-chain alcohol sulfates, and sulfated oils of animal and vegetable oils. Sulfonate type such as sulfonic acid type such as petroleum sulfonic acid salt, non-ionic polyoxyethylene type such as polyoxyethylene alkyl phenyl ether and polyoxyethylene monofatty acid ester, and polyhydric alcohol such as sorbitan monofatty acid ester Or an alkylolamide system such as a fatty acid diethanolamide. More specifically, the surface tension and the kinetic friction coefficient can be adjusted within a suitable range by adding about 2% by weight of a chemical solution type JP-0497N (manufactured by Castrol) to water.

As synthetic type synthetic lubricants, synthetic solution type, synthetic emulsion type and synthetic soluble type can be used.
Synthetic solution type is preferable, and specific examples thereof include Syntylo 9954 (manufactured by Castrol) and # 870 (manufactured by Yushiro Chemical Industries). In any case, by adding about 2% by weight to water, the surface tension and the kinetic friction coefficient can be adjusted within a suitable range.

Also, by adding a rust inhibitor, corrosion of the rare earth alloy can be prevented. Here, the PH is preferably set to 9 to 11. As a rust inhibitor, carboxylate such as oleate and benzoate, or amines such as triethanolamine as an organic type, and phosphate, borate, molybdate, tungstate as an inorganic type. Or carbonates.

As a non-ferrous metal anticorrosive, for example, a nitrogen compound such as benzotriazole is used.
A formaldehyde donor such as hexahydrotriazine can be used.

As an antifoaming agent, a silicone emulsion can be used. By containing an antifoaming agent, foaming of the cooling liquid 3 is reduced, permeability of the cooling liquid 3 is improved, a cooling effect is enhanced, a temperature rise at the grinding end 1b is prevented, and a grinding end of the grinding wheel 1 is formed. Abnormal temperature rise and abnormal wear in 1b are unlikely to occur.

In the state shown in FIG. 1, the grinding portion (contact portion) between the grinding wheel 1 and the block 2 is, as shown in FIG.
Grinding resistance (cutting resistance) F in the circumferential direction of the grinding wheel 1
x, a grinding resistance (cutting resistance) Fz acts in the cutting direction. The cutting resistance Fx and the cutting resistance Fz were measured using a quartz four-component dynamometer 5 manufactured by Nippon Kistler Co., Ltd. An appropriately sized pedestal (for example, a steel plate) 4 a is provided on the upper surface of the dynamometer 5.
And 4b are arranged, and the block 2 is arranged thereon.
Force applied to block 2 (cutting resistance Fx and Fz)
Is transmitted to the dynamometer 5 via the pedestals 4a and 4b and measured.

An example of the results of evaluating the cutting resistances Fx and Fz using the cooling liquids 3 having different surface tensions and dynamic friction coefficients will be described. Table 1 below shows the values of the surface tension and the dynamic friction coefficient of the coolant used for the evaluation. The coolants A and B are synthetic type, the coolants C and D are chemical solution type, and the coolant E is tap water. Although the illustrated cooling liquid C has a relatively low dynamic friction coefficient with respect to the value of the surface tension, there is a general correlation between the surface tension and the dynamic friction coefficient.

[Table 1] Coolant ABCDE Surface tension (mN / m) 29 32 34 54 72 Dynamic friction coefficient 0.17 0.17 0.12 0.21 0.45 Here, the peripheral speed of the grinding wheel 1 is 3000 m / mi.
FIG. 2 shows an example of a change in the cutting resistance Fx when the surface tension of the cooling liquid 3 is changed, and FIG. 3 shows an example of a change in the cutting resistance Fz. The cutting speed of the grinding wheel 1 is 3 m
The measurement was performed at m / min, 5 mm / min, and 10 mm / min.

When the surface tension is low, the coolant 3 easily penetrates into the grinding end 1b and the block 2, and when the surface tension is high, the cooling liquid 3 hardly penetrates into the grinding end 1b and the block 2. Therefore, in the case of a coolant having a small surface tension, a large amount of coolant is supplied to the contact portion between the grinding wheel 1 and the block 2, and in the case of a coolant having a large surface tension, the grinding wheel It becomes difficult to supply the coolant to the contact portion between 1 and the block 2.

First, a cutting speed of 10 mm / mi shown in FIG.
Focusing on the characteristics of n, the cutting resistance Fx becomes minimum when the surface tension is about 40 mN / m (about 40 dyn / cm),
The cutting resistance Fx shows a characteristic that the cutting resistance Fx increases regardless of whether the surface tension is smaller or larger than about 40 mN / m. If the surface tension is larger than about 40 mN / m, the resistance is increased because the grinding is performed in a state where the coolant is not sufficiently supplied between the grinding end 1 b and the block 2. This tendency increases as the cutting speed increases. on the other hand,
The reason why the surface tension becomes smaller than about 40 mN / m and Fx increases despite the sufficient supply of the cooling liquid is that the cooling liquid is supplied too much and the grinding edge 1b slips and the grinding can be performed. This is a phenomenon that is becoming difficult. This situation is considered to be because the grinding wheel 1 is deflected and the side surface of the grinding wheel 1 is in friction with the side surface of the grinding groove formed in the block 2.

Next, a cutting speed of 5 mm / min shown in FIG.
Looking at the characteristics of the above, the surface tension of the coolant is about 30 mN / m
About 40 mN / m (about 30 dyn / cm to about 40 dyn /
cm), the cutting resistance Fx decreases. Also,
Looking at the characteristics of the cutting speed of 3 mm / min shown in FIG. 2, the surface tension is about 50 mN / m to about 60 mN / m (about 50 dy / m).
The cutting resistance Fx decreases around n / cm to about 60 dyn / cm.

Accordingly, although the minimum range of the cutting resistance Fx varies with the change of the cutting speed, the surface tension is about 25 mN /
If it is not more than m (about 25 dyn / cm), the dynamic friction coefficient, which is substantially correlated, is not more than 0.1, and the abrasive grains slide up between the abrasive grains and the rare earth alloy block, so that effective grinding cannot be performed. Further, the surface tension is about 60 mN / m (about 60 dyn
/ Cm), the cutting resistance tends to increase due to insufficient supply of the cooling liquid. From this, the surface tension of the coolant is about 25 mN / m to about 60 mN / m (25 dyn / c
m to 60 dyn / cm).

Next, a cutting speed of 10 mm / mi shown in FIG.
Focusing on n, it shows a substantially constant cutting resistance value without affecting the change in the surface tension of the cooling liquid. That is, when the cutting speed is 10 mm / min, the cooling liquid hardly affects the cutting resistance Fz in the cutting direction. Here, looking at the characteristics of the cutting speed of 3 mm / min and the cutting speed of 5 mm / min, the surface tension is about 25 mN / m (25 dyn / cm).
When it becomes smaller, the cutting resistance becomes almost equal to the cutting resistance at a cutting speed of 10 mm / min. Therefore, the surface tension is about 2
When it is less than 5 mN / m (25 dyn / cm), the effect of the cooling liquid is hardly observed. On the other hand, the surface tension is about 4
0 mN / m to about 60 mN / m (40 dyn / cm to 60 mN / m)
(dyn / cm), the cutting resistance Fz is small.

Therefore, when the cutting speed is lower than 10 mm / min, the effect of the coolant can be seen in the cutting direction, but the surface tension is about 25 from the viewpoint of the cutting direction.
mN / m to about 60 mN / m (25 dyn / cm to 60 d
yn / cm).

Next, the peripheral speed of the grinding wheel 1 is set to 300
FIG. 4 shows the change in the cutting resistance Fx when the dynamic friction coefficient was changed by changing the surface tension of the coolant 3 to 0 m / min.
FIG. 5 shows the change in the cutting resistance Fz. In this case as well, the cutting speed of the grinding wheel 1 is 3 mm / min, 5 m
m / min, 10 mm / min.

Here, in the case of a coolant having a small surface tension, a large amount of the coolant penetrates into the grinding end 1b and the block 2, so that the dynamic friction coefficient becomes small. In the case of a coolant having a large surface tension, the coolant is less likely to penetrate into the grinding end 1b and the block 2, so that the dynamic friction coefficient is increased.

First, a cutting speed of 10 mm / mi shown in FIG.
Focusing on the characteristics of n, the dynamic friction coefficient is 0.15 to 0.2.
In the vicinity, the cutting resistance Fx becomes minimum and the dynamic friction coefficient is 0.1
The cutting resistance Fx shows a characteristic that the cutting resistance Fx increases even if it becomes smaller than 5 and the dynamic friction coefficient becomes larger than 0.2.

Next, focusing on FIG. 5, even if the cutting speed is different, the cutting resistance Fz is small when the dynamic friction coefficient is around 0.3. When the kinetic friction coefficient is smaller than 0.3, there is a tendency that the coolant is supplied too much and the slip increases. In particular, when the dynamic friction coefficient is close to 0.1, the cutting resistance value Fz approximates regardless of the cutting speed. That is, when the dynamic friction coefficient is smaller than 0.1, it can be seen that there is almost no grinding and slipping. On the other hand, when the kinetic friction coefficient exceeds 0.3, no significant change in the cutting resistance Fz is seen from the figure. Was done. From the above, the dynamic friction coefficient is preferably in the range of 0.1 to 0.3.

The processing accuracy was evaluated by measuring the thickness of a small piece of the rare earth alloy cut from the block 2 with a micrometer according to the processing method of the above embodiment.
As a result, the surface tension is about 25 mN / m to about 60 mN / m
(About 25 dyn / cm to about 60 dyn / cm), or when using a coolant having a dynamic friction coefficient of about 0.1 to about 0.3, the cutting speed is 3 mm / min, 5 mm / min, and 10 mm / min. Sufficient processing accuracy (for example, accuracy of ± 75 μm) was obtained. Also, the ground end 1b
Abnormal wear due to abnormal rise in temperature and abnormal shedding of diamond-based abrasive grains can be suppressed and prevented. For example, over a longer period than when water (surface tension is about 70 dyn / cm) is used. The grinding wheel 1 could be used. In particular, the surface tension of the coolant is about 25 mN / m or more.
About 40 mN / m (25 dyn / cm to about 40 dyn / c
The processing accuracy when the cooling liquid of m) was used was high, and the grinding wheel 1 could be used for a long period of time.

After the surface of the obtained rare earth alloy small piece was smoothed by mechanical polishing, a protective coating for preventing oxidation was applied and magnetized according to a conventional method to obtain a rare earth sintered magnet. This rare earth sintered magnet is suitably used as a material for a voice coil motor used for positioning a magnetic head. Of course, after the rare earth alloy is magnetized, it may be processed using the processing method of the present invention.

As described above, by adjusting the surface tension (index of permeability) and the coefficient of kinetic friction (index of lubricity) of the coolant within the above ranges, the cooling effect of the grinding end of the grinding wheel can be improved. I understand. The coolant shown in the above example has a surface tension of about 25 mN / m to about 60 mN / m.
mN / m and the dynamic friction coefficient is about 0.1 to
It was in the range of about 0.3. As described above, since there is a general correlation between the surface tension and the dynamic friction coefficient, it is possible to select the coolant based on one of the numerical values.
However, the correlation between the surface tension and the coefficient of dynamic friction varies depending on the properties of the cooling liquid (for example, the ease of foaming). Therefore, it is preferable that both the surface tension and the coefficient of kinetic friction are within the above ranges.

[0073]

According to the present invention, there is provided a method for efficiently processing a rare earth alloy with high processing accuracy.

When the processing method of the present invention is used, the rare earth alloy can be cut with high processing accuracy, and therefore, the loss of expensive rare earth metal alloy material can be reduced. Therefore, the processing cost of the rare earth metal alloy is reduced, and a processed product, for example, a voice coil motor for a magnetic head can be manufactured at a low price. In addition, since the life of a relatively expensive grinding wheel can be extended,
Processing costs can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a cut state of a rare earth alloy block in one embodiment of the present invention.

FIG. 2 is a characteristic diagram showing a change in a cutting resistance Fx applied in a circumferential direction of the grinding wheel 1 shown in FIG. 1 when a surface tension is changed.

FIG. 3 is a characteristic diagram showing a change in a cutting resistance Fz applied to a cutting direction of the grinding wheel 1 shown in FIG. 1 when a surface tension is changed.

4 is a characteristic diagram showing a change in a cutting resistance Fx applied in a circumferential direction of the grinding wheel 1 shown in FIG. 1 when a dynamic friction coefficient is changed.

5 is a characteristic diagram showing a change in a cutting resistance Fz applied to a cutting direction of the grinding wheel 1 shown in FIG. 1 when a dynamic friction coefficient is changed.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Grinding wheel 1a Base plate 1b Grinding end 2 Rare earth alloy block 3 Coolant 3a Nozzle 4a, 4b Base 5 Dynamometer

Claims (15)

(57) [Claims] 1. A step of preparing a block of a rare-earth alloy, a step of rotatably supporting a grinding wheel having a grinding end including diamond-based abrasive grains on an outer periphery, and a surface provided on the grinding end of the grinding wheel. 25m tension
Grinding the block of the rare earth alloy by bringing the rotating grinding end into contact with the block while supplying a cooling liquid of N / m to 60 mN / m. . 2. A step of preparing a block of a rare earth alloy, a step of rotatably supporting a grinding wheel having a grinding end including diamond-based abrasive grains on an outer periphery, and a step of: Grinding the rare earth alloy block by bringing the rotating grinding end into contact with the block while supplying a cooling fluid having a coefficient of kinetic friction to the rare earth alloy of 0.1 to 0.3 to the grinding end; A method for processing a rare earth alloy, comprising: 3. The method for processing a rare earth alloy according to claim 1, wherein the cooling liquid is a cooling liquid containing water as a main component. 4. The method for processing a rare earth alloy according to claim 1, wherein the cooling liquid contains an antifoaming agent. 5. The method for processing a rare earth alloy according to claim 1, wherein the cooling liquid has a pH of 9 to 11. 6. The method for processing a rare earth alloy according to claim 1, wherein the coolant contains a rust preventive. 7. The grinding end of the grinding wheel further includes a phenol resin, and has a volume ratio of 10 to 80.
The method of processing a rare-earth alloy according to claim 1, wherein the method comprises: 8. The grinding wheel has a disk-shaped base plate, and the grinding end is provided on an outer periphery of the base plate,
8. The method according to claim 1, wherein the base plate is formed of a hard metal.
The method for processing a rare earth alloy according to any one of the above. 9. The method for grinding a rare earth alloy according to claim 1, wherein the rare earth alloy is an R—Fe—B based rare earth sintered alloy. 10. The rare earth alloy processing method according to claim 1, wherein the cooling liquid is discharged toward the grinding end. 11. A step of collecting sludge containing the rare earth alloy grinding chips and the cooling liquid generated in the grinding step, and magnetizing the rare earth alloy grinding chips from the collected sludge. The method for processing a rare earth alloy according to any one of claims 1 to 10, further comprising a step of separating using a rare earth alloy. 12. The grinding method according to claim 1, wherein the grinding step includes a step of moving the grinding wheel relatively to the block, wherein the block is cut into small pieces. Rare earth alloy processing method. 13. The tangential force Fx of the grinding wheel applied to the block in the grinding step.
And the rotational speed, the cutting speed, and the jet pressure of the coolant of the grinding wheel are set such that the radial force Fz of the grinding wheel applied to the block is within a predetermined range. The method for processing a rare earth alloy according to claim 1, wherein 14. The rare earth alloy according to claim 13, further comprising: a step of monitoring the Fx and Fz; and a step of determining whether or not the Fx and Fz are within the predetermined range. Method. 15. A step of preparing a block of a rare earth alloy, a step of rotatably supporting a grinding wheel having a grinding end including diamond-based abrasive grains on an outer periphery, and a step of: 25m tension
Supplying the coolant of N / m to 60 mN / m and moving the grinding wheel relative to the block while bringing the rotating grinding end into contact with the block; A method of manufacturing a rare earth magnet, comprising: a grinding step of cutting the block into small pieces by grinding the block; and a step of magnetizing the rare earth alloy.