EP3680065B1

EP3680065B1 - Method for making outer blade cutting wheels

Info

Publication number: EP3680065B1
Application number: EP20160891.6A
Authority: EP
Inventors: Harukazu Maegawa
Original assignee: Shin Etsu Chemical Co Ltd
Current assignee: Shin Etsu Chemical Co Ltd
Priority date: 2017-06-09
Filing date: 2018-06-04
Publication date: 2023-12-27
Anticipated expiration: 2038-06-04
Also published as: EP3412409B1; JP2018202591A; CN109015430A; JP2022113768A; JP7087284B2; EP3412409A1; EP3680065A1; PH12018000160A1; CN109015430B; US20180354099A1

Description

TECHNICAL FIELD

This invention relates to a method for preparing an outer-diameter blade cutting wheel suited for cutting rare earth sintered magnets.

BACKGROUND

A method for cutoff machining a rare earth sintered magnet block using an outer-diameter (OD) blade cutting wheel is well known. The method is implemented by mounting an outer blade cutting wheel on a common sawing machine, and has many advantages including good dimensional accuracy, high machining speed and improved mass productivity. Owing to these advantages, the OD blade cutting method is widely used in the cutting of rare earth sintered magnet blocks.
OD blade cutting wheels for cutting rare earth permanent magnets are typically constructed by furnishing a cemented carbide base, processing its periphery, and bonding diamond or CBN abrasive grains thereto by metal or resin bonding. Since diamond or CBN abrasive grains are bonded to the cemented carbide base, the base is improved in mechanical strength over prior art alloy tool steel or high-speed steel, and an improvement in machining accuracy is achieved. The cemented carbide base allows the blade to be thinned, leading to improvements in manufacturing yield and machining speed.
Cemented carbides obtained by sintering WC along with Ni or Co are extremely high rigidity materials having a Young's modulus of 450 to 700 GPa, as compared with iron alloy materials having a Young's modulus of the order of 200 GPa. A high Young's modulus implies a reduced deformation of the blade under the cutting force (or resistance) thereto. For the identical cutting resistance, the blade is less deflected. For the identical deflection of the blade, cutting at the identical accuracy is possible even when the thickness of the blade is reduced. On use of a blade using a cemented carbide base, although the cutting resistance per unit area of the blade remains substantially unchanged, the cutting resistance on the overall blade becomes less by a thickness reduction of the blade. This is advantageous in the case of a multiple blade assembly having a plurality of blades wherein one or more magnet blocks are cutoff machined into a plurality of pieces at a time because the total cutting resistance on the overall blade assembly is reduced. For a motor of identical power, the number of blades in a multiple blade assembly can be increased. For the identical number of blades, the cutting resistance is reduced, the dimensional accuracy of cutting is improved, and motor power is saved. When the motor power has a margin relative to the cutting resistance, the feed of the cutting wheel can be accelerated to reduce cutting time.
As discussed above, the use of high rigidity cemented carbide base contributes to a significant improvement in productivity of OD blade cutoff machining. Yet the market imposes an ever increasing demand for rare earth sintered magnets. Since productivity is improved as the machining speed is accelerated, it would be desirable to have an outer blade cutting wheel capable of cutoff machining at a higher speed and higher accuracy than the currently available cutting wheels of cemented carbide bases.

Citation List

Patent Document 1: JP-A H09-174441
Patent Document 2: JP-A H10-175171
Patent Document 3: JP-A H10-175172
Patent Document 4: JP-A 2009-172751
Patent Document 5: JP-A 2013-013966 ( EP2543478 )
Patent Document 6: JP-B S52-15834
Patent Document 7: WO 00/30810 ( EP1050375 ) Document EP2543478 discloses a method for preparing an outer blade cutting wheel by effecting electroplating of a base sandwhiched between a pair of jig segments, however said jigs do not present flanges with protrusions spaced apart from the base periphery.

THE INVENTION

When a rare earth sintered magnet is cut by an outer blade cutting wheel, a grinding fluid or coolant is generally supplied during the cutting step. For the outer blade cutting wheel, a high dimensional accuracy with respect to cut pieces is required. For the purpose of improving the dimensional accuracy of cutting by the outer blade cutting wheel, it is effective to efficiently supply the grinding fluid to the grinding or cutting site to cool the site, to discharge sludge from the grinding site, and to prevent the wheel from chipping.
An aim herein is to provide a method for preparing new and useful outer blade cutting wheels capable of cutoff machining at high speed and high accuracy, thereby enabling good or improved yields and reduced costs of machining.
With respect to an outer blade cutting wheel comprising an annular thin disc base and a blade section of bonded abrasive grains formed on the periphery of the base, the inventor has found that desired aims can be attained when the blade section is formed so as to include a widthwise side portion (side face) provided with channels extending in the direction from an inner perimeter to an outer perimeter of the blade section. The resulting outer blade cutting wheel is found capable of cutoff machining at a high speed and high accuracy for thereby achieving improved yields and reduced costs of machining.
It has been found that such an outer blade cutting wheel can be advantageously prepared by clamping the base at its planar surfaces between a pair of jig segments so as to cover a portion, exclusive of the periphery, of the base where the blade section is not to be formed, and attaching a mesh member to the jig segments to define a cavity extending along and surrounding the base periphery, the mesh member having openings sufficient to allow passage of gas and liquid, but insufficient to allow passage of abrasive grains, filling the cavity with abrasive grains and closing the cavity, immersing the base, jig segments and mesh member in a plating solution, and electroplating with the base made cathode and allowing the plating metal to precipitate for thereby bonding the abrasive grains along with the plating metal onto the base periphery. The jig used herein consists of jig segments each including a flange which is spaced apart from the base periphery and defines the cavity in part and which is provided with protrusions for forming the channels.
The inventive method is set out in claim 1.

ADVANTAGEOUS EFFECTS

We find that the outer blade cutting wheels prepared by the invention are capable of cutoff machining at a high feed speed while maintaining a high accuracy and a low cutting load. Thus improved yields and reduced costs of machining are achievable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B schematically illustrate an outer blade cutting wheel, not part of the invention as defined in the appended claims, FIG. 1A being a side view, FIG. 1B being a cross-sectional view taken along a plane passing the rotational axis of the wheel.
FIGS. 2A, 2B and 2C are side views of the outer blade cutting wheel prepared in different embodiments, the cutting wheel not being part of the invention as defined in the appended claims.
FIGS. 3A and 3B schematically illustrate a jig and a mesh member used in the preparation of the outer blade cutting wheel according to the method of the invention,
FIG. 3A being an exploded side view, FIG. 3B being a cross-sectional view.
FIG. 4A is a photo showing the blade section of the outer blade cutting wheel in Example 1, and FIG. 4B is a photo showing the blade section of the outer blade cutting wheel in Comparative Example 1, the cutting wheels not being part of the invention as defined in the appended claims.
FIG. 5 is a diagram showing the average load current across the spindle motor versus the feed speed of the cutting wheel when rare earth sintered magnets are cut by the outer blade cutting wheels of Example 1 and Comparative Example 1.
FIG. 6 is a diagram showing the average thickness of magnet pieces versus the feed speed of the cutting wheel when rare earth sintered magnets are cut into pieces by the outer blade cutting wheels of Example 1 and Comparative Example 1.
FIGS. 7A and 7B schematically illustrate a jig and a mesh member not part of the invention, used in Comparative Example 1, FIG. 7A being an exploded side view and FIG. 7B being a cross-sectional view.

In the following description, like reference characters designate like or corresponding parts throughout the several views shown in the figures.

FURTHER EXPLANATIONS, OPTIONS AND PREFERENCES

An outer blade cutting wheel prepared by the invention comprises an annular disc base and a blade section disposed on the periphery of the base. FIG. 1 illustrates one exemplary outer blade cutting wheel, FIG. 1A being a side view, FIG. 1B being a cross-sectional view taken along a plane passing the rotational axis of the wheel. The outer blade cutting wheel 10 is illustrated as comprising a base 1 in the form of an annular thin disc having a pair of planar surfaces, a center bore 1a, and an (outer) periphery, and a blade section 2 composed of abrasive grains and a bond and formed on the periphery of the base 1, the blade section 2 having inner and outer perimeters. The wheel is adapted to rotate about an axis a (FIG. 1B).
The base is preferably made of cemented carbide. Examples of the cemented carbide include those in which powder carbides of metals in Groups IVB, VB, and VIB of the Periodic Table such as WC, TiC, MoC, NbC, TaC and Cr₃C₂ are cemented in a binder matrix of Fe, Co, Ni, Mo, Cu, Pb, Sn or a metal alloy thereof, by sintering. Among these, typical WC-Co, WC-Ti, C-Co, and WC-TiC-TaC-Co systems are preferred. Also, those cemented carbides which have an electric conductivity susceptible to plating or which can be given electric conductivity with palladium catalysts or the like are preferred. The base is in the form of an annular thin disc typically having an outer diameter of at least 80 mm, preferably at least 100 mm, and up to 200 mm, preferably up to 180 mm, defining the periphery, an inner diameter of at least 30 mm, preferably at least 40 mm, and up to 80 mm, preferably up to 70 mm, defining the center bore 1a, and a thickness of at least 0.1 mm, preferably at least 0.2 mm, and up to 1.0 mm, preferably up to 0.8 mm, between a pair of planar surfaces.
It is noted that the disc has an axis (or center bore) and a periphery as shown in FIGS. 1A and 1B. The terms "radial" and "axial" are used relative to the center and axis of the disc. Often, the width (or thickness) is an axial dimension, and the length (or height) is a radial dimension.
The blade section is formed by bonding abrasive grains with a bond to the periphery of the base. The abrasive grains used herein are preferably selected from diamond grains (naturally occurring diamond, industrial diamond), CBN (cubic boron nitride) grains, and a mixture of diamond grains and CBN grains. Preferably abrasive grains have an average grain size of 10 to 500 µm although the grain size depends on the thickness of the base. If the average grain size is less than 10 µm, there may be left smaller voids between abrasive grains, allowing problems like glazing and loading to occur during the cutting operation and losing the cutting ability. If the average grain size is more than 500 µm, faults may arise, for example, magnet pieces cut thereby may have rough surfaces.
The bond may be either a metal (inclusive of alloy) bond or a resin bond. The preferred bond is a metal bond, especially a plating metal resulting from electroplating or electroless plating because the blade section of the desired shape is readily formed on the base periphery. The metal bond used herein may be at least one metal selected from Ni, Fe, Co, Sn and Cu, an alloy of two or more of the foregoing metals, or an alloy of at least one metal selected from the foregoing metals with at least one non-metal element selected from B, P and C.
Preferably the blade section contains abrasive grains in a fraction of at least 10% by volume, more preferably at least 15% by volume and up to 80% by volume, more preferably up to 75% by volume. Less than 10 vol% means a less fraction of abrasive grains contributing to cutting whereas more than 80 vol% of abrasive grains may increase unwanted loading during the cutting operation. Either situation increases resistance during the cutting operation and so the cutting speed must be reduced. Although the blade section typically consists of abrasive grains and bond, a suitable ingredient other than the abrasive grains and bond may be mixed in a fraction of up to 10% by volume, especially up to 5% by volume for the purposes of adjusting the hardness, stress and modulus of the blade section.
The abrasive blade section of the outer blade cutting wheel includes widthwise side portions (side faces) each of which is provided with channels extending from the inner perimeter to the outer perimeter of the blade section. FIGS. 2A, 2B and 2C are side views of the outer blade cutting wheel in different embodiments, the cutting wheels not being part of the invention as defined in the appended claims.
Suitable channels formed in the blade section encompass channels 21 penetrating through the blade section 2 at both the inner and outer perimeters as shown in FIG. 2A, and channels 21 penetrating through the blade section 2 at the inner perimeter (open at the inner perimeter, or open radially inwardly) and closed (or discontinuing) at the outer perimeter as shown in FIG. 2B. In the embodiments of FIGS. 2A and 2B, the channels 21 extend radially. In another embodiment of FIG. 2C, the channels 21 extend at an angle relative to a radial direction. The angle or inclination of channels is preferably up to 60°, especially up to 45° relative to a radial direction. Further the channels may or may not reach the base or an underlay formed on the surface of the base if any.
The prior art outer blade cutting wheel includes a blade section having widthwise side portions which are configured planar and parallel to the planar surfaces of the base. We note that such planar side faces are not effective to retain grinding fluid. In contrast, the cutting wheel prepared by the invention is characterized in that the blade section includes a widthwise side portion (side face) provided with channels extending from the inner perimeter to the outer perimeter of the blade section. The channels are recesses with generally radial extent. The grinding fluid is retained within the channels. Also, the contact area between the blade section and a work to be cut is accordingly reduced, and the cutting resistance therebetween is reduced. This enables cutoff machining at a high speed and improves the accuracy of high speed cutoff machining over the prior art. The channels may be of any desired shape and need not be of a specific shape. For example, linear, arcuate or elliptic curve channels of rectangular, semicircular or semi-elliptic shape in cross section having a width (transverse distance) of 1 to 10 mm are preferred. Direction can be with reference to radially-extending side edges of the channels. Also the channels need not be regularly arranged although they are typically arranged at equal intervals or evenly distributed around the circumference. The channels are multiple; the number is not particularly limited, usually 10 or more or 20 or more. A proportion/extent of the channels in the blade section is preferably such that the total area of channels is 10 to 50% of the total area of the blade section in a side view (FIGS. 2A-2C) when the blade section is viewed in an axial or widthwise (onto the side face) direction.
As shown in FIG. 1B, the blade section 2 consists of a pair of clamp legs which straddle the distal or peripheral portion of the base 1 and a body which extends radially outward beyond the distal portion of the base 1 so that the thickness of the blade section 2 is greater than the thickness of the base 1. Each of the clamp legs sandwiching the distal portion of the base 1 preferably has a length of at least 0.5 mm, more preferably at least 1 mm and up to 4 mm, more preferably up to 3 mm and a thickness of at least 0.05 mm, more preferably at least 0.1 mm and up to 0.5 mm, more preferably up to 0.25 mm. The body of the blade section 2 preferably has a length of at least 0.05 mm, more preferably at least 0.1 mm and up to 5 mm, more preferably up to 2.5 mm, depending on the size of abrasive grains.
The outer blade cutting wheel is prepared by forming the specified blade section on the periphery of the base with a metal bond method of using a metal bond and molding the blade section of metal-bonded abrasive grains. The metal bond method is an electroplating method. The electroplating solution may be any of well-known plating solutions capable of forming the metal bond while standard plating conditions for a particular solution may be applied. The anode may be either soluble or insoluble, with the insoluble anode being preferred. The insoluble anode may be any of prior art well-known anodes used in electroplating such as Pt and Ti electrodes.
When the blade section is formed on the base periphery by the metal bond method, an underlay may be pre-formed on the base periphery. The underlay may be made of a material as exemplified above as the metal bond and formed by either brazing or plating. Also in order to enhance the bond strength established when abrasive grains are bound to the base periphery by the metal bond method, the abrasive grains may be coated by sputtering, electroless plating or the like, prior to use.
Specifically, the blade section of the outer blade cutting wheel is prepared by the method of claim 1.
Referring to FIGS. 3A and 3B, the method is described in detail. FIGS. 3A and 3B schematically illustrate a jig and a mesh member used in the preparation of the outer blade cutting wheel, FIG. 3A being an exploded side view, FIG. 3B being a cross-sectional view. In forming the blade section on the base periphery, there are first furnished a jig consisting of segments 51, 51 and a mesh member 52. The jig segments 51, 51 are sized to cover a portion of the base 1 excluding its periphery. The mesh member cooperates with the jig segments 51, 51 to define a cavity which extends along and surrounds the base periphery. The base 1 is clamped at its planar surfaces between the jig segments 51, 51 and the mesh member 52 is extended around and attached to the circumference of the jig segments 51, 51 to define a cavity c. The mesh member 52 used herein may be a metal mesh (e.g. stainless steel mesh) or resin mesh; its specific mesh or perforated character is not critical subject to retaining the abrasive grains.
Each jig segment 51 includes a flange 51a which is spaced apart from the base periphery and defines the cavity c in part. The flange 51a is provided with protrusions 511 for forming the channels in the blade section. The flange 51a is also provided with an inlet port 51b for feeding abrasive grains into the cavity c. Also shown in FIG. 3 are a plug 51c which fits in the inlet port 51b to constitute a part of the flange 51a, and a band 52a which is wound around to hold the mesh member 52 to the periphery of the jig segment 51.
This is followed by the step of filling the cavity c with abrasive grains and closing the cavity. When the jig segments 51, 51 as shown in FIG. 3 are used, abrasive grains may be fed through the inlet port 51b. Once the plug 51c is detached, a necessary amount of abrasive grains are fed into the cavity c, after which the plug 51c is fitted in the inlet port 51b again. Abrasive grains may be fed as such or as a slurry of abrasive grains in a liquid such as plating solution or water. In the latter case, extra liquid may be discharged through the mesh member 52.
Next, the base 1, together with the jig segments 51, 51 and mesh member 52, is immersed in a plating solution. Then the cavity c is filled with the plating solution that penetrates through the mesh member 52.
Next, electroplating is carried out with the base 1 acting as cathode. It is noted that a conductive layer or underlay is previously formed on the surface of the base 1 if the base 1 is made of non-conductive material. The plating metal is precipitated for thereby bonding the abrasive grains along with the plating metal onto the periphery of the base (cathode) 1. With the progress of electroplating, the plating solution is successively fed into the cavity c through the mesh member 52. In this way, the cavity c is gradually filled with abrasive grains and plating metal. Typically, the electroplating step is terminated when the cavity c is completely filled with the abrasive grains and the plating metal.
During electroplating, the base 1 is preferably placed with its planar surfaces kept horizontal. The horizontal setting ensures that abrasive grains, which are kept in contact with or in proximity to one surface of the base 1 under gravity, are bound by the plating metal. The base is turned upside down on the way of the electroplating step, which ensures that abrasive grains, which are kept in contact with or in proximity to the other surface of the base 1 under gravity, are bound by the plating metal. The step of turning the base upside down is not limited to once, and may be repeated several times. Once the plating metal is precipitated to such an extent that abrasive grains are bound to the base, the cavity c may then be opened. In this case, for example, the mesh member is detached, and the jig segments are replaced by non-flanged jig segments, after which electroplating step is restarted as the post-treatment.
On use of the outer blade cutting wheel prepared by the invention, various works may be cut thereby. Typical works are rare earth sintered magnets or permanent magnets including R-Co rare earth sintered magnets and R-Fe-B rare earth sintered magnets wherein R is at least one of rare earth elements inclusive of Y. R-Co rare earth sintered magnets include RCo₅ and R₂Co₁₇ systems. Of these, the R₂Co₁₇ magnets have a composition (in % by weight) comprising 20-28% R, 5-30% Fe, 3-10% Cu, 1-5% Zr, and the balance of Co. R-Fe-B rare earth sintered magnets have a composition (in % by weight) comprising 5-40% R, 0.2-8% B, up to 8% of an additive element(s) selected from C, Al, Si, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, Ag, Sn, Hf, Ta, and W for improving magnetic properties and corrosion resistance, and the balance of Fe or Fe and Co (Co is up to 30 wt% of Fe+Co).

EXAMPLES

Examples of the invention are given below by way of illustration and not by way of limitation.

Example 1

An annular thin disc of cemented carbide K10 having an outer diameter of 131 mm, an inner diameter of 60 mm, and a thickness of 0.4 mm was used as a base. By previous nickel electroplating in a nickel plating solution containing 70 g/L of NiCl₂·6H₂O, 370 g/L of NiSO₄·6H₂O, 45 g/L of boric acid and 2 g/L of lubricant #82 (JCU Corp.) at a temperature of 55°C, a nickel coating was formed on the periphery of the base as an underlay.
Jig segments and a mesh member as shown in FIG. 3 were combined with the base having the underlay to define a cavity extending along and surrounding the base periphery. With the plug removed, a slurry of diamond abrasive grains (ASTM #230/270) dispersed in a plating solution (described below) was fed into the cavity through the inlet port, after which the plug was fitted to close the cavity. The flanges were spaced apart a distance of 0.6 mm so that the blade section might have a width of 0.6 mm, and each of clamp legs straddling the base periphery might have a thickness of 0.1 mm and a length of 3 mm. The distance from the base periphery to the mesh member was 2 mm so that the body might have a length of 2 mm. The flange was provided with protrusions such that 36 channels each having a width of 2 mm, a length of 2 mm, and a depth of 0.1 mm will be formed arranged at equal intervals around each side surface of the blade section, and the channels reaching through to the underlay on the base.
Next, the base together with the jig, mesh member and abrasive grains was immersed in a nickel plating solution containing 70 g/L of NiCl₂·6H₂O, 370 g/L of NiSO₄·6H₂O, 45 g/L of boric acid, 2 g/L of lubricant #82 (JCU Corp.), 20 g/L of #83 S (JCU Corp.) and 0.5 g/L of #81S (JCU Corp.) as brightener, with the planar surfaces of the base kept horizontal. Using the conductive underlay on the base as a cathode and a titanium case electrode as an anode, nickel electroplating was carried out at a temperature of 55°C and a constant voltage of up to 0.7 V for a total time of 420 minutes. During electroplating, hydrogen gas evolved from the plating site. During electroplating, the procedure of interrupting electric conduction, turning the base upside down, and restarting electric conduction was repeated 32 times, every electric amount to precipitate 1 to 3 AM/dm² of nickel.
It was confirmed that abrasive grains were bound to the base, after which the jig segments and mesh member were detached. It was confirmed that the cavity had been completely filled with abrasive grains and the plating metal, after which non-flanged jig segments were attached. Nickel electroplating under the same conditions as above was carried out for 120 minutes as post-treatment, yielding an outer blade cutting wheel. FIG. 4A is a photo showing the outer appearance of the blade section of the cutting wheel. As seen, the channels in this example were open radially inwardly but closed to the outer perimeter.

Comparative Example 1

An annular thin disc of cemented carbide K10 having an outer diameter of 131 mm, an inner diameter of 60 mm, and a thickness of 0.4 mm was used as a base. By previous nickel electroplating in a nickel plating solution containing 70 g/L of NiCl₂·6H₂O, 370 g/L of NiSO₄·6H₂O, 45 g/L of boric acid and 2 g/L of lubricant #82 (JCU Corp.) at a temperature of 55°C, a nickel coating was formed on the periphery of the base as an underlay.
Jig segments and a mesh member as shown in FIG. 7 were combined with the base having the underlay to define a cavity extending along and surrounding the base periphery. With the plug removed, a slurry of diamond abrasive grains (ASTM #230/270) dispersed in a plating solution (described below) was fed into the cavity through the inlet port, after which the plug was fitted to close the cavity. The flanges were spaced apart a distance of 0.6 mm so that the blade section might have a width of 0.6 mm, and each of clamp legs straddling the base periphery might have a thickness of 0.1 mm and a length of 3 mm. The distance from the base periphery to the mesh member was 2 mm so that the body might have a length of 2 mm. Since the parts in FIG. 7 are the same as in FIG. 3 except that the flange of each jig segment is not provided with protrusions for forming channels, their description is omitted.
Next, the base together with the jig, mesh member and abrasive grains was immersed in a nickel plating solution containing 70 g/L of NiCl₂·6H₂O, 370 g/L of NiSO₄·6H₂O, 45 g/L of boric acid, 2 g/L of lubricant #82 (JCU Corp.), 20 g/L of #83S (JCU Corp.) and 0.5 g/L of #81S (JCU Corp.) as brightener, with the planar surfaces of the base kept horizontal. Using the conductive underlay on the base as a cathode and a titanium case electrode as an anode, nickel electroplating was carried out at a temperature of 55°C and a constant voltage of up to 0.7 V for a total time of 480 minutes. During electroplating, hydrogen gas evolved from the plating site. During electroplating, the procedure of interrupting electric conduction, turning the base upside down, and restarting electric conduction was repeated 32 times, every electric amount to precipitate 1 to 3 AM/dm² of nickel.
It was confirmed that abrasive grains were bound to the base, after which the jig segments and mesh member were detached. It was confirmed that the cavity had been completely filled with abrasive grains and the plating metal, after which non-flanged jig segments were attached. Nickel electroplating under the same conditions as above was carried out for 120 minutes as post-treatment, yielding an outer blade cutting wheel. FIG. 4B is a photo showing the outer appearance of the blade section of the cutting wheel. The widthwise side surfaces of the blade section were planar and parallel to the planar surfaces of the base.

Cutting Test

From a R-Fe-B rare earth sintered magnet block of 40 mm long (cutting length direction of the cutting wheel) and 16 mm high (cutting depth direction of the cutting wheel), six magnet pieces of 2 mm thick were cut by using the outer blade cutting wheel of Example 1 or Comparative Example 1, and operating the cutting wheel at a rotational speed of 7,040 rpm, a cutting depth per pass of 1 mm, and a feed rate (moving rate in length direction) of 100 mm/min to 700 mm/min. During the cutting operation, the average load current across the motor for the rotating spindle of the cutting wheel was measured, with the results shown in FIG. 5. Each of the cut magnet pieces was measured for thickness at five points: 4 corners and the center, an average of which was computed. A cutting accuracy was evaluated in terms of thickness variations of magnet pieces, with the results shown in FIG. 6.

Claims

A method for preparing an outer blade cutting wheel comprising an annular disc base (1) having a pair of planar surfaces and a periphery, and a blade section (2) formed on the periphery of the base and composed of abrasive grains and a bond, wherein the blade section (2) includes side faces provided with channels (21) extending in a direction from an inner perimeter to an outer perimeter of the blade section,
the method comprising the steps of:
clamping the base (1) at its planar surfaces between a pair of jig segments (51) so as to cover a portion of the base other than the periphery where the blade section is not to be formed, and attaching a mesh member (52) to the jig segments to define a cavity extending along and surrounding the base periphery, the mesh member having openings sufficient to allow the passage of gas and liquid, but not the passage of the abrasive grains;

filling the cavity with abrasive grains and closing the cavity;

immersing the base (1), jig segments (51) and mesh member (52) in a plating solution, and

effecting electroplating with the base acting as cathode and allowing plating metal to deposit, thereby bonding the abrasive grains along with the plating metal onto the base periphery,

wherein the or each said jig segment (51) includes a flange (51a) which is spaced apart from the base periphery and defines the cavity in part, and the flange has protrusions (511) for forming the channels in the blade section.
A method of claim 1 wherein the protrusions (511) form the channels (21) to penetrate both the inner perimeter and the outer perimeter of the blade section (2).
A method of claim 1 wherein the protrusions (511) form the channels (21) to penetrate the inner perimeter while being closed at the outer perimeter.
A method of claim 1, 2 or 3 wherein the protrusions (511) form the channels (21) to extend in a radial direction of the base, or at an angle of not more than 60° relative to the radial direction.
A method of any one of the preceding claims wherein the protrusions (511) form the channels (21) to reach through the blade section to the base (1), or to an underlay on the base if any.
A method of any one of the preceding claims wherein the protrusions (511) form the channels (21) to be evenly circumferentially distributed around the cutting wheel.
A method of any one of the preceding claims wherein the protrusions (511) form the channels (21) to account for at least 10% of the area of the blade section as seen from the axial direction.
A method of any one of the preceding claims wherein the blade section (2) is formed to consist of a pair of clamp legs which straddle the distal peripheral portion of the base (1) and a body which extends radially outward beyond the peripheral portion of the base, and the thickness of the blade section is greater than the thickness of the base.
A method of any one of the preceding claims wherein the base is made of cemented carbide.
A method of any one of the preceding claims wherein the base (1) is in the form of an annular thin disc having an outer diameter defining the periphery of at least 100 mm, and up to 180 mm, an inner diameter defining a center bore (1a) of at least 40 mm, and up to 70 mm, and a thickness between the pair of planar surfaces of at least 0.2 mm and up to 0.8 mm.
A method of any one of the preceding claims wherein the plating metal forming the bond is at least one metal selected from Ni, Fe, Co, Sn and Cu, alloys of two or more of the foregoing metals, and alloys of at least one metal selected from the foregoing metals with at least one non-metal element selected from B, P and C.
A method of any one of the preceding claims wherein a metal underlay is formed on the base periphery before forming the blade section (2).