KR20130059295A - Saw blade and method for multiple sawing of rare earth magnet - Google Patents

Abstract

PURPOSE: A cutting blade and a method for multi-cutting a rare earth magnet are provided to reduce resistance between the cutting blade and a magnet block using the cutting blade in a resinoid wheel. CONSTITUTION: A cutting blade(23) comprises a core(21) and a surrounding cutting unit(22). The core has a thin disk shape or a thin doughnut disk shape. The surrounding cutting unit is equipped on the outer surrounding edge of the core. The surrounding cutting unit cuts a rare earth magnet block into a plurality of pieces by rotating a plurality of cutting blades. The surrounding cutting unit reduces the friction between the cutting unit and the magnet block when cutting. The surrounding cutting unit includes an abrasive material(24), a resin binder, and lubricant. The lubricant is selected from a group comprised of boron nitride, carbon, molybdenum disulfide, tungsten disulfide, fluorination graphite, and poly tetra fluoro ethylene.

Description

Saw Blade and Method for Multiple Sawing of Rare Earth Magnet}

The present invention generally relates to a method of cutting a magnetic block into a plurality of pieces. More specifically, this relates to a cutting edge for use in cutting a rare earth magnetic block into a plurality of pieces.

Systems for the production of commercial products of rare earth magnets include a single part system in which parts of substantially the same shape as the product are manufactured at the stage of press molding, and a plurality of parts which, once large blocks are molded, divide them into a plurality of parts by machining. Parts system. Single part systems include press forming, sintering or heat treatment, and finishing steps. Molded parts, sintered or heat treated parts, and finished parts (or products) are substantially the same in shape and size. As long as the normal sintering is carried out, a sintered part of a near-real shape is obtained and the burden of the finishing step is relatively low. However, when it is desired to manufacture small sized parts or parts with reduced thickness in the magnetization direction, the order of press forming and sintering is difficult to form sintered parts of normal shape, and leads to low production yield, which is the worst. In this case, such a part cannot be formed.

In contrast, a multi-part system eliminates the above mentioned problems and allows the press forming and sintering or heat treatment steps to be performed with high productivity and flexibility. This is now the mainstream of rare earth magnet manufacturing. In a multi-part system, the molded blocks and the sintered or heat treated blocks are substantially the same in shape and size, but subsequent finishing steps require cutting or cutting steps. Cutting blocks in the most efficient and least wasteful way is the key to the production of finished parts.

Tools for cutting rare earth magnetic blocks are of two types: diamond grinding wheel ID blades with diamond grit bonded around the inside of a thin donut-shaped disc, and a thin disc as a core. Diamond grinding grindstone outer diameter (OD) blades having diamond grit bonded around the outside. Nowadays, cutting technology using OD blades is the mainstream, especially from the viewpoint of productivity. Cutting technology using ID blades is less productive due to the single blade cutting method. In the case of OD blades, multi-cutting is possible. 1 includes a plurality of cutting blades 11 coaxially mounted to a rotating shaft (not shown), alternating with spacers 12, each blade 11 having a thin donut disk shaped core ( 11b) and an exemplary multi-blade assembly 1 comprising a cut or abrasive grain layer 11a at the outer peripheral edge of the core 11b. This multi-blade assembly 1 is capable of multi cutting, ie cutting a block into multiple parts at once.

For the production of OD abrasive blades, diamond grains are generally bonded by three typical bonding systems including resin bonding with resin binders, metal bonding with metal binders, and electroplating. These abrasive blades are often used for cutting rare earth magnetic blocks.

When a cutting abrasive blade is used to machine a rare earth magnet block of a certain size into a number of parts, the relationship of the cutting (axis) width of the cutting blade is critically correlated with the material yield of the workpiece (magnetic block). It is important to maximize the production and productivity of the material by using the cutting part with the minimum width, machining with high accuracy to minimize the machining allowance and reduce the chip, and increase the number of available parts .

In order to form cuts (or thinner cuts) with a minimum width in terms of material yield, the abrasive grindstone core must be thin. In the case of the OD blade 11 shown in FIG. 1, its core 11b is made of a common steel material in terms of material cost and mechanical strength. Of these steel materials, alloy tool steels classified as SK, SKS, SKD, SKT, and SKH according to JIS standards are often used in commercial practice. However, in attempts to cut hard materials, such as rare earth magnets, by thin OD blades, the cores of conventional alloy tool steels lack mechanical strength and deform or bend during cutting operations and lose dimensional accuracy.

One solution to this problem is to provide a core of cemented carbide, in which high-strength abrasive grains such as diamond and CBN are bonded into a bonding system such as resin bonding, metal bonding or electroplating, as described in JP-A H10-175172. A cutoff grindstone for use in containing rare earth magnet alloys. The use of cemented carbide as the core material mitigates buckling deformation by stress during machining, ensuring that the rare earth magnets are cut with high accuracy. However, if high friction resistance is applied between the cutting portion and the magnet during the cutting of the magnet, high accuracy machining is not expected. In particular, when substantial friction occurs between the side surface of the cutting portion (which does not directly contribute to the grinding operation) and the magnet, the grinding resistance becomes high. Then, even if a cemented carbide core is used, chipping and / or warping may occur, adversely affecting the machined state.

One solution to this problem is to add a lubricant, such as a fatty acid, to the grinding fluid or coolant. However, since the space between the cutting blade and the work piece or the rare earth magnet is extremely narrow, it is difficult to effectively supply coolant between the cutting blade and the magnet.

Japanese Patent Laid-Open No. 10-175172

It is an object of the present invention to be used in multi-cutting of a plurality of pieces of rare earth magnetic blocks, to reduce cutting resistance between the cutting blade and the magnetic block, and to cut at high accuracy and high speed even if the cutting blade is thinner than conventional blades. To provide a cutting blade in the form of a resinoid wheel that ensures processing. Another object is to provide a method of cutting a rare earth magnet block into a plurality of pieces.

The present invention relates to a multiple blade assembly comprising a plurality of cutting blades coaxially mounted to a rotating shaft in axially spaced positions. Multiple blade assemblies are used to cut a rare earth magnet block into multiple pieces by rotating a plurality of cutting blades. The cutting blade has a core in the form of a thin disk or a thin donut disk and peripheral cuts on the outer peripheral edge of the core. The inventors have developed a cutting edge in the form of a resinoid grindstone having a cut made of a composition comprising a lubricant or a component for reducing friction between the cut and the magnetic block during the cutting operation. When the magnetic block is cut by the cutting edge, the cutting operation suffers from reduced cutting resistance and achieves equivalent yield and accuracy, compared with the prior art, even if thinner cutting blades were used.

The present invention generally includes a plurality of cutting blades coaxially mounted to a rotating shaft at axially spaced locations that are used to cut a rare earth magnetic block into a plurality of pieces by rotating the plurality of cutting blades. It is associated with a multiple blade assembly. In one aspect, the present invention provides a cutting edge comprising a core in the form of a thin disc or a thin donut disc, and a peripheral cut on the outer periphery of the core, wherein the cutting portion reduces friction between the cut and the magnetic block during the cutting operation. To reduce, to a composition comprising an abrasive, a resin binder, and a lubricant.

In a preferred embodiment, the lubricant is selected from the group consisting of boron nitride, carbon, molybdenum disulfide, tungsten disulfide, graphite fluoride, and polytetrafluoroethylene, and mixtures thereof. Also preferably, the lubricant is in particulate form having a particle size in the range of 1 to 200 μm.

Typically, the cuts comprise 10 to 40 weight percent diamond and / or CBN as abrasive; SiC having a particle size of 1 to 100 μm, SiO ₂ having a particle size of 1 to 100 μm, Al ₂ O ₃ having a particle size of 1 to 100 μm, WC having a particle size of 0.1 to 50 μm, 1 to 20 to 60 weight percent matrix selected from the group consisting of Fe, Ni, and Cu, and mixtures thereof having a particle size of 200 μm; 10 to 50 wt% thermosetting resin as a binder; And 1 to 50% by weight of lubricant.

In another aspect, the present invention provides a multi-blade assembly comprising a plurality of the aforementioned cutting blades coaxially mounted to a rotating shaft at axially spaced positions, and rotating the plurality of cutting blades. Provided is a method for cutting a rare earth magnetic block into a plurality of pieces, comprising.

Resinoid grindstone cutting blades are useful for multi-cutting multiple pieces of rare earth magnet blocks. Compared with the prior art, although the cutting blade is thinner than the conventional blade, the cutting blade reduces the cutting resistance, improves the cutting accuracy, and ensures the cutting at high accuracy and high speed. The day is very valuable in the industry.

1 illustrates a multiple blade assembly in one embodiment of the present invention, FIG. 1A is a perspective view and FIG. 1B is a sectional view.
2 is an enlarged cross-sectional view of the periphery of the cutting blade.

The term "axis" means the axis of the rotating shaft and "radial" means the circular blade in the assembly. The width of the cutting portion corresponds to the axial size in this respect.

The multiple blade assembly is constructed by coaxially mounting the plurality of cutting blades to the rotating shaft at axially spaced locations (as shown in FIG. 1). Multiple blade assemblies are manipulated by rotating a plurality of cutting blades, thereby cutting the rare earth magnet block into multiple pieces simultaneously. The cutting blade 23 in the form of a resinoid grindstone according to the present invention includes a core 21 in the form of a thin disk or a thin donut disk and a peripheral cutting portion 22 on an outer peripheral edge of the core 21. 2 is shown. The cut 22 is made of a composition comprising an abrasive 24, a resin binder and a lubricant to reduce the friction between the cut and the workpiece (or magnet block) during the cutting operation.

Examples of lubricants used herein include boron nitride, carbon (including graphite and amorphous carbon), molybdenum disulfide, tungsten disulfide, graphite fluoride, and polytetrafluoroethylene (PTFE), alone or in combination of two or more. It can be used as a mixture. Although conventional cutting operations are difficult to reduce the friction between the cut side surface and the workpiece by providing a coolant supply for lubrication, the inclusion of lubricant in the cut may reduce the friction between the cut side surface and the workpiece. It is effective to reduce, thereby preventing the cutting edges from falling on-axis during the cutting operation. This allows the cutting portion to transfer its grinding force only in the radial direction and uses a thin core with low drag force to ensure high accuracy cutting operation even with the cutting edge.

If less lubricant is used, the effect of reducing the friction on the side surface is reduced. If a large amount of lubricant is used, since the lubricant lacks the strength of the structural matrix, not only the strength of the cutting portion of the blade is reduced, but also the frictional force of the grinding surface is reduced, resulting in a reduced grinding rate. The lubricant should preferably be used in an amount of 1 to 50% by weight of the composition from which the cut is made. As a preferred amount of each type (% by weight based on the composition), boron nitride is 1 to 40% by weight, carbon (including graphite and amorphous carbon) is 1 to 40% by weight, and molybdenum disulfide is 1 to 40% by weight. Tungsten disulfide is 5-50 wt%, graphite fluoride is 5-40 wt% and PTFE is 5-40 wt%. More preferably, boron nitride is 5 to 30% by weight, carbon (including graphite and amorphous carbon) is 5 to 30% by weight, molybdenum disulfide is 5 to 30% by weight, and tungsten disulfide is 10 to 40% by weight. , Graphite fluoride is 10 to 30% by weight, PTFE is 10 to 30% by weight. When a mixture of two or more lubricants is used, the total amount should preferably be in the range of 1 to 50% by weight, more preferably 5 to 40% by weight.

Lubricants are typically available in particulate form. Since the cut has a width of 0.2 to 2 mm, particle sizes exceeding 0.2 mm (200 μm) are inadequate. Too fine particles have an increased volume, which impairs the strength of the cut. The lubricant preferably has a particle size of 1 to 200 μm, more preferably 10 to 150 μm.

In addition to the lubricant, the composition from which the cut is made contains abrasive grains, a resin binder, and a structural matrix. Preferred examples of the matrix are SiC having a particle size of 1 to 100 μm, SiO ₂ having a particle size of 1 to 100 μm, Al ₂ O ₃ having a particle size of 1 to 100 μm, particle sizes of 0.1 to 50 μm. WC, Fe, Ni, and Cu having a particle size of 1 to 200 μm, which may be used alone or in a mixture of two or more. The role of the matrix is to increase the strength of the cutting part, to prevent the cutting part from deforming in the direction perpendicular to the feed direction of the cutting edge during the cutting operation, to prevent the cutting edge from falling axially during the cutting operation, It allows the transfer of its grinding forces only in the radial direction and ensures high accuracy cutting operations even with cutting blades using thin cores with low drag forces. The matrix is available in particulate form. Too fine particles have an increased volume and fail to provide a cut with strength. If the particle size is large, there is only one particle per width of the cut, which also results in reduced strength. Thus, the matrix preferably has a particle size in the above range. More preferably, the particle size of SiC is 2-50 μm, SiO ₂ is 2-50 μm, Al ₂ O ₃ is 2-50 μm, WC is 1-30 μm, Fe, Ni, and Cu Is 10 to 150 m.

The matrix should preferably be used in an amount of 20 to 60% by weight of the composition, more preferably 25 to 50% by weight. Outside this range, smaller amounts of matrix may be less effective, while larger amounts may impair the strength of the cut.

The abrasive grains can be any well known abrasives, preferably diamond and CBN. The abrasive grains preferably have a particle size of 10 to 200 μm, more preferably 50 to 200 μm. Particle sizes above 200 μm may exceed the width of the cut, while smaller particle sizes may hinder grinding efficiency, cutting speed, and productivity. The abrasive should preferably be used in an amount of 20 to 60% by weight, more preferably 20 to 40% by weight of the composition. Outside this range, smaller amounts of abrasives can result in lower grinding rates, while larger amounts can impair the strength of the cut.

The binder combines diamond or CBN, lubricant and matrix together to have a high strength, so that a cutting portion having a high stiffness is formed despite being thin. Thermosetting resins are preferred as binders. Especially, phenol resin, formaldehyde resin, and urea resin are more preferable. Phenol formaldehyde resins obtained by condensation of phenol and formaldehyde are most preferred because they have excellent heat resistance and water resistance and can firmly bond the abrasive and the matrix. Melamine resins made from melamine and formaldehyde are also advantageous. The binder should preferably be used in an amount of 10 to 50% by weight of the composition. Outside this range, smaller amounts of binder may be weaker to combine other components, while larger amounts of binder may result in less amount of other components, resulting in a lack of strength, grinding rate, and lubrication.

The core supporting the cut is preferably made of cemented carbide. Any of the cemented carbides described in patent document 1 can be used.

Workpieces intended for cutting herein are rare earth magnetic blocks. The rare earth magnet as the work piece is not particularly limited. Suitable rare earth magnets include sintered rare earth magnets of the R-Fe-B system, where R is at least one rare earth element, including yttrium.

Suitable sintered rare earth magnets of the R-Fe-B system are 5-40% by weight of R, 50-90% by weight of Fe, and 0.2-8% by weight of B, and optionally improve the properties and corrosion resistance of the magnet. One or more additive elements selected from C, Al, Si, Ti, V, Cr, Mn, Co, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Ag, Sn, Hf, Ta, and W These magnets contain. The amount of added element added is the same as conventional, for example, 30 wt% or less of Co, and 8 wt% or less of other elements. If the additional element is added in an extra amount, it rather adversely affects the magnetic properties.

Suitable sintered rare earth magnets in R-Fe-B systems are, for example, weighing and melting source metal materials, casting in alloy ingots, and casting alloys with an average particle size of 1 to 20 μm. , Ie, finely divided into sintered R-Fe-B magnet powders, the powder is compacted in a magnetic field, the compact is sintered at 1000 to 1200 ° C. for 0.5 to 5 hours, and heat treated at 400 to 1000 ° C. .

Any well known process can be used when cutting the rare earth magnet block into multiple pieces by the multiple blade assembly of the cutting blade.

Example

Examples and comparative examples are given below to further illustrate the present invention, but the present invention is not limited thereto.

Example  One

The OD blade provides a donut-shaped disc core of a cemented carbide (consisting of 90 wt% WC / 10 wt% WC) of cemented carbide having an outer diameter of 120 mm, an inner diameter of 40 mm, and a thickness of 0.3 mm, and the composition is coated with the outer periphery of the core. It was produced by thermocompression bonding to the rim to form a resinoid grinding grindstone portion or cutting portion. The composition comprises 10% by weight graphite with a particle size of 5-30 μm as lubricant, 40% by weight # 800 SiC (GC powder) as matrix, 25% by weight phenol formaldehyde resin as binder, and an average particle of 150 μm. It contained 25 weight percent synthetic diamond grains with size. Subsequent finishing operations completed the OD blade (or cutting abrasive blade). The axial extension of the cut from the core was 0.05 mm on each side, ie the cut had a width (in the thickness direction of the core) of 0.4 mm. The radial extension or length of the cut was 2.5 mm, ie the blade had an outer diameter of 125 mm.

Using an OD blade, a cutting test was performed on the workpiece, which is a sintered Nd-Fe-B magnet block. The multi blade assembly was constructed by coaxially mounting 41 OD blades to the shaft at axial spacing of 2.1 mm with spacers therebetween, as shown in FIG. 1. Each spacer had an outer diameter of 85 mm, an inner diameter of 40 mm, and a thickness of 2.1 mm. The multi blade assembly was designed to cut the magnetic block into a magnetic strip having a thickness of 2.0 mm.

The sintered Nd-Fe-B magnet block was cut using a multi-blade assembly consisting of 41 ODs and 40 spacers alternately mounted on the shaft. The sintered Nd-Fe-B magnetic block had a length of 101 mm, a width of 30 mm, and a height of 17 mm, and polished all six surfaces with an accuracy of ± 0.05 mm by a vertical double-disk polishing tool. By multi-blade assembly, the magnetic block was longitudinally divided into multiple magnetic strips 2.0 mm thick. Specifically, one magnetic block was cut into 40 magnetic strips.

The cutting operation feeds 30 l / min of grinding fluid or coolant from the feed nozzle, rotates the OD blade at 7,000 rpm (circumferential speed of 46 m / sec), and transfers the multi-blade assembly at a speed of 20 mm / min. Was performed.

After the magnetic strips were cut using the OD blades configured as above, they were measured in micrometers at the center for the thickness between the machined surfaces. The strip was rated “pass” when the measured thickness was within a cutting size tolerance of 2.0 ± 0.05 mm. If the measured thickness was outside the tolerance, the multi-blade assembly was customized by adjusting the thickness of the spacer so that the measured thickness fell within the tolerance. If spacer adjustments were repeated more than once on the same OD day, this OD day was assessed to have lost stability and was replaced with a new OD day. Under these conditions, 1000 magnetic blocks were cut. The evaluation results of the cut state are shown in Table 1.

Comparative example  One

The sintered rare earth magnet block was cut by the same process as in Example 1 except that the cut portion composition was changed. In this way, 1000 magnetic blocks were cut and the cut condition was evaluated. The evaluation results are also shown in Table 1.

The composition of the cutout in Comparative Example 1 was 45% by weight # 800 SiC (GC powder) as matrix, 30% by weight phenol formaldehyde resin as binder, and 25% by weight synthetic diamond with an average particle size of 150 μm. Grain contained.

Number of strips After 200 block cuts After cutting 400 blocks After cutting 600 blocks After cutting 800 blocks After cutting 1000 blocks A B A B A B A B A B Example 1 40 0 0 0 0 0 0 0 0 0 0 Comparative Example 1 40 10 0 16 2 25 7 39 18 69 27

A: Number of adjustment of spacer

B: Number of replacements of OD blade

As shown in Table 1, the multi-cutting method of the present invention is successful in maintaining consistent dimensional accuracy of the product over a long period of time despite reduced blade thickness, and reducing the number of adjustments of spacers and replacement of OD blades. . An increase in productivity is then achieved.

Example  2 to 10, and Comparative example  2

The OD blade was provided with a donut-shaped disc core of cemented carbide (consisting of 90 wt% WC / 10 wt% WC) of a cemented carbide having an outer diameter of 95 mm, an inner diameter of 40 mm, and a thickness of 0.3 mm, the composition shown in Table 2 It was produced by thermocompression bonding to the outer periphery of the core to form a cut. The axial extension of the cut from the core was 0.025 mm on each side, ie the cut had a width (in the thickness direction of the core) of 0.35 mm. The radial extension or length of the cut was 2.5 mm, ie the blade had an outer diameter of 100 mm.

Using an OD blade, a cutting test was performed on the workpiece, which is a sintered Nd-Fe-B magnet block. The multi blade assembly was constructed by coaxially mounting 38 OD blades to the shaft at axial intervals of 1.05 mm with spacers therebetween as shown in FIG. 1. Each spacer had an outer diameter of 70 mm, an inner diameter of 40 mm, and a thickness of 1.05 mm. The multi-blade assembly was designed to cut the magnetic block into magnetic strips having a thickness of 1.0 mm.

The multi-blade assembly, consisting of 38 OD blades and 37 spacers alternately mounted on the shaft, was placed on the sintered Nd-Fe-B magnet block so that the lowest end of the blade was 2 mm below the bottom surface of the magnetic block. Was set. The sintered Nd-Fe-B magnetic block had a length of 50 mm, a width of 30 mm, and a height of 12 mm, and polished all six surfaces with an accuracy of ± 0.05 mm by a vertical double-disk polishing tool. By multi-blade assembly, the magnetic block was longitudinally divided into multiple magnetic strips 1.0 mm thick. Specifically, one magnetic block was cut into 37 magnetic strips.

The cutting operation feeds 30 l / min of grinding fluid or coolant from the feed nozzle, rotates the OD blade at 7,000 rpm (circumferential speed of 37 m / sec), and transfers the multi-blade assembly at a speed of 20 mm / min. Was performed.

Each of the OD blades of Examples 2 to 10 and Comparative Example 2 was used to cut 1000 magnetic blocks. Magnetic strips were measured in micrometers at the center between the machined surfaces. The capability index (Cpk) of the measured thickness was calculated with a cutting size tolerance of 1.0 ± 0.075 mm. The results are shown in Table 2.

As shown in Table 2, the cutting blades containing lubricant ensure a high accuracy cutting operation even when they are as thin as 0.35 mm. The number of cutting strips is increased.

Claims (5)

In a multi-blade assembly comprising a plurality of cutting blades coaxially mounted to a rotating shaft at axially spaced locations used to cut a rare earth magnet block into a plurality of pieces by rotating the plurality of cutting blades,
A core in the form of a thin disk or a thin donut disk and a peripheral cut on the outer peripheral edge of the core, the cutting comprising abrasives, resin binders and lubricants to reduce friction between the cutting and magnetic blocks during the cutting operation. A cutting blade, characterized in that it is made of a composition. The cutting blade of claim 1 wherein the lubricant is selected from the group consisting of boron nitride, carbon, molybdenum disulfide, tungsten disulfide, graphite fluoride, and polytetrafluoroethylene, and mixtures thereof. The cutting blade of claim 1, wherein the lubricant is in the form of particulates having a particle size in the range of 1 to 200 μm. The method of claim 1, wherein the cutting portion,
10 to 40% by weight diamond and / or CBN as abrasive
SiC having a particle size of 1 to 100 μm, SiO ₂ having a particle size of 1 to 100 μm, Al ₂ O ₃ having a particle size of 1 to 100 μm, WC having a particle size of 0.1 to 50 μm, 1 to 20 to 60% by weight matrix selected from the group consisting of Fe, Ni, and Cu, and mixtures thereof having a particle size of 200 μm,
10 to 50% by weight thermosetting resin as a binder, and
A cutting blade, characterized in that it is made of a composition comprising from 1 to 50% by weight of lubricant. A method of cutting a rare earth magnet block into a plurality of pieces, the method comprising: a plurality of cutting edges coaxially mounted to a rotating shaft at axially spaced locations, each cutting edge having multiple blades as set forth in claim 1; Providing an assembly, and rotating the plurality of cutting blades.

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