Patent Grant
8702084
This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2010-001056 filed in Japan on Jan. 6, 2010, the entire contents of which are hereby incorporated by reference.
This invention generally relates to a multiple blade cutting machine for multiple cutoff machining of a rare earth magnet block. More particularly, it relates to a jig for fixedly holding the magnet block during machining by the multiple blade cutting machine. It also relates to a cutoff machining method.
Systems for manufacturing commercial products of rare earth magnet include a single part system wherein a part of substantially the same shape as the product is produced at the stage of press molding, and a multiple part system wherein once a large block is molded, it is divided into a plurality of parts by machining. These systems are schematically illustrated in
In contrast, the multiple part system illustrated in
Well-known methods for cutoff machining of rare earth magnet blocks include a wire cutting method using a wire having abrasive grains bonded to the surface thereof, an outer- and inner-diameter cutting methods using outer- and inner-diameter blades.
Tools for cutting rare earth magnet blocks include two types, a diamond grinding wheel inner-diameter (ID) blade having diamond grits bonded to an inner periphery of a thin doughnut-shaped disk, and a diamond grinding wheel outer-diameter (OD) blade having diamond grits bonded to an outer periphery of a thin disk as a core. Nowadays the cutoff machining technology using OD blades becomes the mainstream, especially from the aspect of productivity. The machining technology using ID blades is low in productivity because of a single blade cutting mode. In the case of OD blade, multiple cutting is possible.
When a rare earth magnet block is machined by a multiple blade assembly, the magnet block is generally secured to a carbon-based support by bonding with wax or a similar adhesive which can be removed after cutting. The bonding with wax is achieved by heating the carbon-based support and the magnet block, applying molten wax between the support and the magnet block, and cooling for solidification. In this state, the magnet block is cut into pieces. The cutting operation is followed by heating to melt the wax, allowing the magnet pieces to be removed from the support. Since wax is kept attached to the magnet pieces at this point, the wax must be removed using a solvent or the like.
The adhesive way of securing a magnet block with wax involves concomitant steps of heat bonding, heat stripping and cleaning in addition to the cutting step, rendering the process very cumbersome. As a result, the cost of the cutting process is increased. One solution to this problem is a means for holding a magnet block without a need for wax, specifically a holding jig which is comb-shaped so as to allow passage of cutting blades during cutting.
For example, JP-A H06-304833 and JP-A 2001-212730 disclose a mechanism comprising a jig segment pivotally mounted for holding a workpiece on a support. Since the shape and size of a workpiece which can be held by the jig are limited, a jig must be separately prepared for a particular shape of workpiece.
In the jigs disclosed in JP-A 2007-044806 and JP-A 2000-280160, the cutting direction is set vertical. The cutting distance is limited to the distance of downward movement of a cutting blade assembly. This inhibits an efficient arrangement wherein a plurality of workpieces are arranged in tandem in the cutting direction.
Most of the foregoing patent documents relate to a mechanism for clamping a workpiece by a comb-shaped jig. As discussed for the respective documents, they have problems such as the limited shape of a magnet block, cumbersome loading/unloading operation, and the limited number of division. In fact, these mechanisms are difficult to hold a workpiece or magnet block in place until the completion of cutting. It is likely that immediately after cutting, magnet pieces are attractively moved aside under the influence of the rotating cutting blades and separated apart from the jig, and come in contact with the rotating cutting blades which are being retracted at the end of cutting. Then the magnet pieces may be abraded, resulting in dimensional degradation, and the interference between magnet pieces and cutting blades can cause magnet piece fissure and/or cutting blade damage.
Patent Document 1: JP-A H06-304833
Patent Document 2: JP-A 2001-212730
Patent Document 3: JP-A 2007-044806
Patent Document 4: JP-A 2000-280160
An object of the invention is to provide a jig for holding a rare earth magnet block in place when the block is cut into pieces by multiple cutting blades, which is effective for preventing the magnet pieces from moving sideways during and immediately after cutting, thus maintaining the magnet pieces at an improved dimensional accuracy after cutting; a rare earth magnet block cutting machine comprising the jig; and a cutting method using the jig.
The inventors have found that a magnet holding jig as defined below prevents a workpiece from moving sideways during cutting and ensures to hold the workpiece in place. The jig may be advantageously used in cutting of a rare earth magnet block by multiple outer-diameter cutoff abrasive blades. When the multiple cutoff abrasive blades are rotated with the peripheral cutting parts of the cutoff abrasive blades inserted into the guide paths, the jig prevents the workpiece from moving sideways. This ensures cutting operation at a high accuracy and high speed.
In one aspect, the invention provides a jig for holding a rare earth magnet block in place when the block is cut in a transverse direction by a cutting machine having multiple cutting blades, comprising a platform on which the magnet block is rested, the platform having opposed sides in the transverse direction, a first holder disposed on one side of the platform and constructed integral with or separate from the platform, and a second holder disposed on the other side of the platform and constructed separate from the platform. At least a top portion of the platform is provided with channels, at least upper portions of the first and second holders are comb-shaped to define digits and slits, the channels and the slits are aligned to together define guide paths for permitting entry of the cutting blades therein, the upper portions of the first and second holders are also configured as digitate hooks each having an inward projecting tip, the platform, first and second holders are assembled such that the hook tips of the first and second holders are in contact with an upper portion of the magnet block resting on the platform. The jig further comprises pusher means for pushing inward the first and second holders at their lower portions, the first and second holders being configured such that the tip of each digit of the hook of one holder is in pressure abutment with the magnet block at a higher level than the tip of each digit of the hook of the other holder for thereby holding the magnet block in place on the platform.
Also contemplated herein is a machine for cutting a rare earth magnet block comprising the jig defined above. Typically the cutting machine further comprises a multiple blade assembly comprising a plurality of cutoff abrasive blades coaxially mounted on a rotating shaft at axially spaced apart positions, each said blade comprising a core in the form of a thin disk or thin doughnut disk and a peripheral cutting part on an outer peripheral rim of the core.
In a further aspect, the invention provides a method for cutting a rare earth magnet block using the cutting machine and the jig defined above, comprising the steps of:
holding the magnet block in place by the jig,
providing as the cutting machine a multiple blade assembly comprising a plurality of cutoff abrasive blades coaxially mounted on a rotating shaft at axially spaced apart positions, each said blade comprising a core in the form of a thin disk or thin doughnut disk and a peripheral cutting part on an outer peripheral rim of the core,
relatively moving the jig and the multiple blade assembly in the transverse direction of the magnet block, while rotating the cutoff abrasive blades, for thereby machining the magnet block, and
repeating the machining step one or more time until the magnet block is cutoff machined into pieces,
the final machining step of dividing the magnet block into pieces includes starting machining on the side of the one holder having the hook digit tip in pressure abutment with the magnet block at a higher level and continuing machining until the side of the other holder.
When a rare earth magnet block is cut by multiple cutoff abrasive blades, the magnet block can be held in place by the jig without a need for wax bonding. The jig which is simple as compared with prior art jigs prevents the workpiece from moving sideways during the cutting operation and ensures cutting operation at a high accuracy and high speed. The jig is of great worth in the industry.
These and other features, aspects, and advantages of the present invention will become better understood when the following detailed description is read with reference to the accompanying drawings in which like characters represent like parts throughout the drawings, wherein:
In the following description, the singular forms “a,” “an” and “the” include plural referents unless the context clearly dictates otherwise. As used herein, terms such as “upper”, “lower”, “outward”, “inward”, and the like are words of convenience, and are not to be construed as limiting terms. For example, the term “inward” as used herein refers to a direction toward a longitudinal axis of a magnet block, and the term “outward” refers to a direction away from the axis of the magnet block and is interchangeable with “backward”. The term “axial” is used with respect to the center of a circular blade (or the axis of a shaft) and a direction parallel thereto, and the term “radial” is used with respect to the center of a circular blade.
Jig
The magnet holding jig of the invention is used to hold a rare earth magnet block, typically a sintered rare earth magnet block, in place when the magnet block is cutoff machined into pieces of desired size by a cutting machine such as wire saw or OD cutoff abrasive wheel blade machine. The magnet block is cut in a transverse direction.
The jig comprises a platform, a first holder, and a second holder. The platform is a base plate on which the magnet block is rested. The first and second holders are disposed on opposite sides of the platform as viewed in the transverse direction of the magnet block. The first holder is disposed on one side of the platform and constructed integral with or separate from the platform. The second holder is disposed on the other side of the platform and constructed separate from the platform. The first and second holders clamp the magnet block from the opposite sides in the transverse direction to hold the magnet block in place on the platform.
Referring to
At least upper portions of the first and second holders are comb-shaped to define digits and slits. The upper portions of the first and second holders are also configured as digitate hooks each having an inward projecting tip (facing the magnet block). The first and second holders are constructed such that the tips of hooks may come in contact with an upper portion (upper side surface or top surface) of the magnet block on the platform.
Specifically, in the jig of
At least a top portion of the platform is provided with channels while at least upper portions of the first and second holders are comb-shaped to define digits and slits as mentioned above. The channels in the platform are aligned with the slits in the first and second holders to together define guide paths for permitting entry of the cutting blades therein when the magnet block is cut.
Specifically, in the jig of
When a magnet block is held in place by the jig comprising the platform and the first and second holders, the magnet block is first rested on the platform. The first and second holders are set so that the hooks at their tip may contact with the upper portion of the magnet block. In the embodiment wherein the first holder is constructed integral with the platform, the magnet block is rested on the platform so that the hook of the first holder at its tip may contact with the one side of the magnet block, after which the second holder is moved so that the second holder hook at its tip may contact with the opposite side of the magnet block.
The jig further comprises pusher means for pushing inward the first and second holders at their lower portions, thus pressing the first and second holders against the magnet block. Then the hooks of the first and second holders are elastically deformed and moved backward or warped outward. The digitate hooks abut against the magnet block. The elastic deformation creates a stress, and the restoring force due to the stress causes the digitate hooks to abut against the magnet block for thereby holding the magnet block in place on the platform.
Specifically, the jig of
The jig of the invention is characterized in that the first and second holders are configured such that the tips of the hooks of the holders are in abutment with the magnet block at different levels. Specifically, as shown in
Under the inward pressing force, the hook of the holder is elastically deformed and moved backward, taking an outward warped posture. It is then believed that the contact between the magnet block and the holder is line or point contact at the lower edge of the tip surface of the hook rather than surface contact (see
When a thick magnet block is cutoff machined, spinning does not occur until the magnet block is completely divided into discrete pieces. Immediately before and after the magnet block is divided into discrete pieces, spinning may be induced by any external force. Spinning of a magnet piece can cause a reduction of dimensional accuracy. If magnet pieces are removed from the jig after cutting and contact with the cutting blades, the magnet pieces and/or the cutting blades can be damaged.
The inventors have found that the freedom of spin is a main factor of causing magnet pieces to move aside immediately after cutoff machining. At an intermediate stage of cutoff machining when magnet pieces being cut are still connected by the uncut portion of the magnet block, they are considered one magnet block as a whole. Magnet pieces become discrete immediately after the cutoff machining. At this stage, each magnet piece is clamped between respective ones of the digits of the digitate hooks on the first and second holders in the jig. Since various forces including the grinding force of cutting blades and the pressure of cutting fluid injected during the cutting operation are applied to the magnet block or pieces immediately before and after the division, such external forces cause the magnet pieces to spin.
By contrast, in the jig of the invention, the first and second holders are configured such that the hooks of the holders abut against the magnet block at different levels, specifically, the tip of each digit of the hook of one holder is in pressure abutment with the magnet block at a higher level than the tip of each digit of the hook of the other holder. As shown in
Preferably the difference in height between the hook digit tips of the first and second holders is at least 10% of the height of a magnet block to be cut whereby the effect of staggered abutment to prevent magnet pieces from spinning is obtainable. Since a stronger holding force is available when both the hooks of the first and second holders are in abutment with the magnet block at its upper portion, the difference in height between the hooks is more preferably up to 20% of the height of the magnet block. Even more preferably, the height of the hook of one holder is up to ⅔ of the height of the hook of the other holder, the height being measured from the bottom of the magnet block.
It is acceptable for the jig that before the actuation of the pusher means, only some of the hook digits (111, 121) (some of 80 hook digits in the embodiment of
The pusher means may be a pneumatic cylinder or cam clamp, but is not limited thereto. It may also be a plunger utilizing pneumatic or hydraulic pressure or a mechanism utilizing screw engagement for maintaining a pressing force.
As described above, the jig is designed such that the magnet block is held in place by the pressing force resulting from backward movement of the hook formed on an upper portion of the holder. Before the first and second holders are pushed inward to bring the hooks in pressure abutment with the magnet block, the first and second holders except the hook tips are kept out of contact with the magnet block. Also before the first and second holders are pushed inward, the second holder is spaced apart from the platform in the embodiment wherein the first holder is constructed integral with the platform, or one or both of the first and second holders are spaced apart from the platform in the embodiment wherein the first holder is constructed separate from the platform. The spacing between the platform and the holder is such that when the holder is pushed toward the platform, the hook in an upper portion of the holder may be moved backward by a predetermined amount necessary to hold the magnet block in place.
The pusher means pushes inward the holder at such a position that the hook in an upper portion of the holder may be moved backward or outward. Specifically, a lower portion of the holder, more specifically a portion of the holder excluding the hook must be pushed from the outside. A provision must be made such that the holder itself may not turn over even when a lower portion of the holder is pushed inward. To this end, for example, the holder is configured such that the holder may come in pressure abutment with the platform (i.e., the spacing between the holder and the platform may become nil) when the hook in an upper portion of the holder is moved backward by a predetermined amount necessary to hold the magnet block in place. Also, if necessary, a spacer of a predetermined length may be disposed between the holder and the platform.
Alternatively, the first and second holders are restricted so that they may be movable only in the cutting transverse direction of the magnet block. For example, as shown in
In a preferred embodiment, one or both of the first and second holders are formed of a material having a Young's modulus of 5×103 MPa to 1×105 MPa. When the magnet block is held in place by clamping it between the hooks of the holders, the respective hooks are elastically deformed and moved backward (or warped outward) as shown in
Inversely, if the holders are formed of a rigid material allowing substantially no elastic deformation, there is a risk that the jig cannot accommodate magnet blocks of different size and fails to provide necessary holding. As discussed above, the hook of the holder is elastically deformed and moved backward, taking an outward warped posture. It is then believed that the contact between the magnet block and the holder is line or point contact at the lower edge of the tip surface of the hook rather than surface contact. With fine irregularities on the magnet block surface and the holder surface taken into account, the range of actual contact is further limited.
The magnet block or workpiece may have a dimensional variation of the order of at least several microns between different positions on the magnet block even thought it has been dimensionally finished. If the hook of the holder is formed of a material capable of adequate elastic deformation, digits of the digitate hook may come in pressure abutment with the magnet block to hold it in place while accommodating a dimensional variation of the magnet block. Even when a magnet block has a dimensional variation, the jig performs well in that the pusher means pushes the holders to elastically deform the hooks and move it backward (or warp it outward), for bringing the respective hook digits in pressure abutment with the magnet block while accommodating the dimensional variation of the magnet block. Due to the restoring force resulting from the stress of elastic deformation of the respective digits of the digitate hook, all the hook digits may come in pressure abutment with the magnet block.
Inversely, if the hooks of the holders are formed of a rigid material allowing substantially no elastic deformation, only some digits of the digitate hook come in contact with the magnet block, or only some digits of the digitate hook come in pressure abutment with the magnet block, while the remaining digits do not fully abut against the magnet block. Even in this state, some digits of the digitate hook hold the whole magnet block in place until the magnet block is cut into pieces. However, immediately before and after the magnet block is separated into magnet pieces by cutting, despite the need to hold discrete magnet pieces, those magnet pieces corresponding to the remaining digits not in contact with the magnet block are not in pressure abutment or not fully pressed. Then those magnet pieces may be moved aside or removed from the jig, for example, under the pressure of cutting fluid injected to the magnet block during the cutting operation. Any shifting of magnet pieces may cause a lowering of dimensional accuracy. If magnet pieces removed from the jig after cutting contact with the cutting blades, the magnet pieces and/or the cutting blades can be damaged.
The material of which the first and second holders are formed should preferably have a fully high yield strength or proof stress in order that the hooks of the holders tightly clamp the magnet block to hold it in place and the distance of backward movement of the hook by elastic deformation be sufficient. In particular, with the above-described dimensional variation between different positions on the magnet block taken into account, when the holders are pushed to bring all digits of the digitate hooks in pressure abutment with the magnet block, even those digits undergoing the greatest deformation should be kept within the elastic deformation region. A low yield strength or proof stress is undesired for the reason that once the hooks are largely deformed, they are kept deformed, due to a transition from the elastic deformation region to the plastic deformation region. Then, a restoring force necessary to hold the magnet block in place is not available. Therefore, one or both of the first and second holders are preferably formed of a material having a yield strength or proof stress of at least 2×102 MPa. From the standpoint of repeated use of the jig, one or both of the first and second holders are preferably formed of a material having a fatigue strength of at least 8×101 MPa.
Although the material of which the holders are formed is not particularly limited, high strength engineering plastics and metal or alloy materials such as iron, stainless steel, aluminum and brass are preferred.
From the standpoint of the dimensional variation between different positions on the magnet block, when a magnet block which has been dimensionally finished is cut, the holders are preferably formed such that elastic deformation may be maintained over a range of deformation amount before and after backward movement (or outward warp) of the hook which is from 0.01 mm to 1 mm, preferably from 0.01 mm to 0.1 mm, calculated as the total of the first and second holders. Specifically, the deformation amount may be represented by a distance of movement in the transverse direction of the hook in abutment with the magnet block.
When a magnet block immediately after sintering and prior to dimensional finishing is cut, which has a larger dimensional variation, the holders are preferably formed such that elastic deformation may be maintained over a range of deformation amount before and after backward movement (or outward warp) of the hook which is from 0.1 mm to 2 mm, preferably from 0.5 mm to 1.5 mm, calculated as the total of the first and second holders. In order to maintain elastic deformation in the specified range, physical properties of the material of the holders, especially hooks are selected, and the height or width (in the direction of outward warp of the hook) of the holders, especially hooks is determined as appropriate.
Notably, the setting of deformation amount and the design of hook shape may also be performed by a general linear static analysis. An appropriate deformation amount is an amount corresponding to a dimensional variation of a magnet block. The deformation amount may be slightly larger than the amount corresponding to a dimensional variation of a magnet block, insofar as it does not exceed the yield strength or proof stress of the hook-forming material. An extra deformation beyond that level is unnecessary because excess deformation produces a stress which exceeds the yield strength or proof stress, leading to breakage of the hooks.
One of the hooks of the first and second holders, specifically the hook of one holder in abutment with the magnet block at a higher level is preferably configured to a shape and/or size to undergo more backward warp by elastic deformation than the other. When one holder is more susceptible to elastic deformation, the one holder provides a sufficient elastic deformation amount to accommodate a dimensional variation of a magnet block or workpiece, and the other holder providing a less elastic deformation amount functions as the support point for holding. This enables to hold the magnet block in place consistently at any stage before and after cutting of the magnet block.
The jig is provided with guide paths for receiving cutting blades. When outer-diameter cutoff abrasive wheel blades are used, for example, the guide paths are arranged in alignment with the outer peripheral parts of the cutoff abrasive blades. The cutoff abrasive blades are inserted into the guide paths in a straight and parallel relationship. Accordingly, the width of the guide path is configured to a width corresponding to the width of the abrasive portion of the cutoff abrasive blade.
During cutting of a magnet block, a cutting fluid is fed. The cutting fluid is contacted with the outer peripheral portions of the cutoff abrasive blades, entrained on the surfaces (outer peripheral portions) of the cutoff abrasive blades, introduced into the guide paths in the jig, transported onto the magnet block, and delivered to points of cutoff machining. Then the guide path has a width which must be greater than the width of the cutoff abrasive blade (i.e., the width W of the outer cutting part). If guide paths have too large a width, the cutting fluid may not be effectively fed to the cutoff abrasive blades. Provided that the peripheral cutting part of the cutoff abrasive blade has a width W (mm), the width of the guide path (i.e., spacing between hook digits) in the jig is preferably more than W mm, and more preferably from (W+0.1) mm to (W+6) mm.
The length of the guide path in the transverse direction is preferably in the range of 1 mm to 100 mm, and more preferably 3 mm to 100 mm, as measured from the magnet block which is held in place by the jig. If the guide path has a length of less than 1 mm, the guide path is less effective in preventing scattering of the cutting fluid or accommodating the cutting fluid when the cutting fluid is delivered to the workpiece or magnet block. If the guide path has a length of more than 100 mm, the effect of delivering the cutting fluid to the machining area is no longer enhanced, and the overall machining apparatus becomes large sized without merits. The depth of each guide path is selected appropriate depending on the height of the magnet block. Since the magnet block must be cut throughout, the guide paths are preferably formed in the jig components slightly deeper than the lower surface of the magnet block held by the jig, specifically to a depth of at least 1 mm, more specifically at least 5 mm.
The width of each hook digit (dimension perpendicular to the transverse direction of a magnet block) is less than or equal to the width of each magnet piece cut from the magnet block. A difference between the hook digit width and the magnet piece width is preferably up to 1 mm, more preferably up to 0.5 mm. The difference is preferably as small as possible because a smaller difference is effective for inhibiting the cutoff abrasive blades from axial runout. With respect to the height of each hook digit (i.e., the height of the holder), since more effective holding is possible by clamping the magnet block at a higher position between the hooks, the hook digit may have a top high enough, but not contacting the rotating shaft of the cutoff blade assembly during the cutting operation. A magnet block is preferably cut by cutoff abrasive blades having a possible cut distance (distance from the rotating shaft to the outer periphery) which is set somewhat longer than the height of the magnet block because this setting is more effective for inhibiting the cutoff abrasive blades from axial runout during the cutting operation. Therefore, the height of the top of the hook digits (or the holder) is equal to the height of the magnet block or within a range of ±10 mm relative to the height of the magnet block.
The guide paths in the jig components may be pre-formed. Alternatively, they may be formed in the first cycle of cutoff machining by cutoff machining a magnet block or dummy workpiece which is properly held until grooves are formed in the holders and platform, which process is known as co-machining.
In the jig, at least one of the first and second holders is preferably provided with a stop means for restricting the backward movement (or outward warp) of the hook when the hook is elastically deformed and moved backward, so that the stress of elastic deformation may not exceed the yield strength or proof stress of the material of which the holder is formed. The stop means should be configured to a shape and/or size which is less susceptible to elastic deformation than the hook.
The stop means may be formed in one or both of the first and second holders below the hook. Specifically, as shown in
Provision of a stop for limiting further backward movement of the hook inhibits the deformation of the hook from transiting from the elastic deformation region to the plastic deformation region. The stop is thus effective for preventing breakage of the holder and application of any excessive pressing force to the magnet block.
In a further preferred embodiment, a plurality of jigs each comprising a platform, a first holder, and a second holder as defined above are arranged in tandem in the transverse direction of a magnet block to construct a multiple jig arrangement. In the embodiment, when the hooks are elastically deformed and moved backward by a predetermined amount, the backsides of the hooks of two adjacent jigs come in abutment with each other for thereby restricting the backward movement of the hooks so that the stress of elastic deformation may not exceed the yield strength or proof stress of the material of which the hooks (or the holders) are formed.
Such a multiple jig arrangement is illustrated in
In the multiple jig arrangement illustrated in
In such a multiple jig arrangement, jigs may be arranged such that first holders adjoin each other or second holders adjoin each other. However, an arrangement wherein first and second holders are alternately arranged is preferred because a plurality of magnet blocks can be held by an equal force and the stops can exert an equivalent function.
Where the function of a stop is applied, advantageously one of the first holder hook and the second holder hook is configured to a shape and/or size capable of more backward movement (or outward warping) by elastic deformation than the other holder hook. If one holder is more susceptible to elastic deformation than the other, the distance of permissible backward movement of the hook until the backward movement of the hook is limited by the stop may be set in a broader range. In the case of a multiple jig arrangement, the other holder less susceptible to elastic deformation can function as a stop for the one holder. This is advantageous in that after a magnet block is cut into magnet pieces, the holding state of adjacent magnet pieces cut in the transverse direction has no substantial impact.
The magnet block which can be held by the jig of the invention is not limited to the rectangular parallelepiped one illustrated in the foregoing embodiments. The magnet block may be of a generally half-tubular shape (arch in cross section) having curved surfaces as shown in
Particularly when the upper surface of a magnet block to be cut is a curved or slant surface rather than a horizontal surface as in the embodiment of a generally half-tubular magnet block shown in
It is understood that in
In the prior art, when a rare earth magnet block is machined into multiple magnet pieces by a multiple blade assembly, the magnet block is generally held to a carbon-based support by bonding with wax or a similar adhesive which can be removed after cutting. In contrast, using a jig adapted to hold a magnet block by clamping it between holders, the invention obviates the bonding, stripping and cleaning steps of the prior art process and saves the laborious operation. When a magnet block is held by the jig, the jig prevents the magnet block from moving sideways during the cutting operation, achieving precise cutoff machining.
The magnet holding jig is best suited to hold a magnet block when it is cut by a magnet cutoff machine.
When a rare earth magnet block is machined into multiple magnet pieces, a multiple blade assembly is used in combination with the jig. First the magnet block is held in place by the jig. The multiple blade assembly is set such that cutoff abrasive blades are inserted into guide paths. The cutoff abrasive blades are then brought in contact with the magnet block. The blade assembly and the magnet block (or the jig) are moved relatively whereby the magnet block is cut into pieces.
Multiple Blade Assembly
The jig of the invention is advantageously used to hold a rare earth magnet block when the magnet block is subjected to multiple cutoff machining using a multiple blade assembly. A typical multiple blade assembly comprises a plurality of cutoff abrasive blades mounted on a rotating shaft at axially spaced apart positions, each said blade comprising a core in the form of a thin disk or thin doughnut disk and a peripheral cutting part on an outer peripheral rim of the core. While the cutoff abrasive blades are rotated, the multiple blade assembly is moved relative to the magnet block, achieving multiple cutoff machining.
Any prior art well-known multiple blade assembly may be used in the multiple cutoff machining process. As shown in
The dimensions of the core are not particularly limited. Preferably the core has an outer diameter of 80 to 200 mm, more preferably 100 to 180 mm, and a thickness of 0.1 to 1.0 mm, more preferably 0.2 to 0.8 mm. The core in the form of a thin doughnut disk has a bore having a diameter of preferably 30 to 80 mm, more preferably 40 to 70 mm.
The peripheral cutting part or abrasive grain-bonded section has a width W in the thickness or axial direction of the core, which is from (T+0.01) mm to (T+4) mm, more preferably (T+0.02) mm to (T+2) mm, provided that the core has a thickness T. An outer portion of the peripheral cutting part or abrasive grain-bonded section that projects radially outward from the outer peripheral rim of the core has a projection distance which is preferably 0.1 to 10 mm, more preferably 0.3 to 8 mm, depending on the size of abrasive grains to be bonded. An inner portion of the peripheral cutting part or abrasive grain-bonded section that radially extends on the core has a coverage distance which is preferably 0.1 to 10 mm, more preferably 0.3 to 8 mm.
The spacing between cutoff abrasive blades may be suitably selected depending on the thickness of magnet pieces after cutting, and preferably set to a distance which is slightly greater than the thickness of magnet pieces, for example, by 0.01 to 0.4 mm.
For machining operation, the cutoff abrasive blades are preferably rotated at 1,000 to 15,000 rpm, more preferably 3,000 to 10,000 rpm.
When a rare earth magnet block is machined into multiple magnet pieces, a multiple blade assembly is used in combination with the jig. First the magnet block is held in place by the jig. The multiple blade assembly is set such that peripheral cutting parts of cutoff abrasive blades are inserted into guide paths. While a cutting fluid is fed, the multiple bladed assembly is operated such that the peripheral cutting parts of rotating cutoff abrasive blades come in contact with the magnet block. The blade assembly and the magnet block (or the jig) are moved relatively in a transverse direction of the magnet block (which may be a width or longitudinal direction of the block) whereby the magnet block is cut into pieces.
More specifically, after a rare earth magnet block is held in place by the jig, either one or both of the multiple blade assembly and the jig are relatively moved in the transverse direction of the magnet block. While the multiple blade assembly is rotated, the magnet block is cut by the outer peripheral parts of cutoff abrasive blades. The multiple blade assembly is further moved to a position out of contact with the magnet block, shifted perpendicular to the transverse direction, and then moved relative to the jig to carry out cutoff machining in the transverse direction. This machining operation may be repeated one or more times.
Around the cutoff abrasive blades which rotate at a high velocity, air streams are produced. The air streams form so as to surround the peripheral cutting parts of the cutoff abrasive blades. Thus if cutting fluid is directly injected toward the peripheral cutting parts of the cutoff abrasive blades, the cutting fluid impinges with the air streams and is scattered away thereby. That is, the air layer obstructs the contact of cutting fluid with the cutting parts and hence an efficient supply of cutting fluid. In contrast, in the setting that the outer peripheral portions of the cutoff abrasive blades are inserted into the guide paths in the jig, the air streams are blocked by the jig body (slit-defining digits) so that the cutting fluid may contact with the outer peripheral portions of the cutoff abrasive blades without obstruction by the air layer.
Accordingly, the cutting fluid that has contacted with the outer peripheral portions of the cutoff abrasive blades is entrained by the surfaces (outer peripheral surface and radially outer portions of side surfaces) of the cutoff abrasive blades being rotated and, under the centrifugal force due to rotation of the cutoff abrasive blades, transported toward the peripheral cutting parts of the cutoff abrasive blades. The cutting fluid that has reached the peripheral cutting parts is transported to points of cutoff machining on the magnet block as the cutoff abrasive blades rotate. This ensures that the cutting fluid is efficiently delivered to the points of cutoff machining. This, in turn, permits to reduce the amount of cutting fluid fed. Additionally, the areas of machining can be effectively cooled.
Referring to
In the process of cutoff machining a magnet block, the last portion of the block remaining uncut tends to be disintegrated by fissure immediately before cutting, leaving burrs. If burrs contact with the cutting blade which travels forward while rotating, the cutting blade applies a rotational force to the magnet piece in the same direction as the rotating direction of the blade. To overcome the problem of such a force, the distance between two contact points on the holder hooks restricting spinning of the magnet piece is prolonged, and the contact point remote from the last portion to be cut is disposed far apart from the last portion to be cut which is likely to form burrs. Then the distance between two contact points is increased, and hence, the magnet block is more effectively held against spinning. As shown in
In a further preferred embodiment, the holders are configured to such a shape and/or size that one hook is moved more backward through elastic deformation than the other hook, and the cutoff abrasive blade is rotated in the (counterclockwise) direction of
Fluid Feed Nozzle
During multiple cutoff machining of a rare earth magnet block, a cutting fluid is typically fed to the cutoff abrasive blades to facilitate machining. To this end, one preferred embodiment of the invention uses a cutting fluid feed nozzle having a cutting fluid inlet at one end and a plurality of slits formed at another end and corresponding to the plurality of cutoff abrasive blades such that an outer peripheral portion of each cutoff abrasive blade may be inserted in the corresponding slit.
As shown in
The feed nozzle 6 is combined with the multiple blade assembly 5 such that an outer peripheral portion of each cutoff abrasive blade 51 may be inserted into the corresponding slit 61 in the feed nozzle 6. Then the slits 61 are arranged at a spacing which corresponds to the spacing between cutoff abrasive blades 51, and the slits 61 extend straight and parallel to each other.
The outer peripheral portion of each cutoff abrasive blade which is inserted into the corresponding slit in the feed nozzle functions such that the cutting fluid coming in contact with the cutoff abrasive blades is entrained on the surfaces (outer peripheral portions) of the cutoff abrasive blades and transported to points of cutoff machining on the magnet block. Then the slit has a width which must be greater than the width of the cutoff abrasive blade (i.e., the width W of the outer cutting part). Through slits having too large a width, the cutting fluid may not be effectively fed to the cutoff abrasive blades and a more fraction of cutting fluid may drain away from the slits. Provided that the peripheral cutting part of the cutoff abrasive blade has a width W (mm), the slit in the feed nozzle preferably has a width of from more than W mm to (W+6) mm, more preferably from (W+0.1) mm to (W+6) mm.
The slit portion 61a of the feed nozzle 6 is defined by a wall having a certain thickness. A thin wall has a low strength so that the slits may be readily deformed by contact with the blades or the like, failing in a stable supply of cutting fluid. If the wall is too thick, the nozzle interior may become too narrow to define a flowpath and the outer peripheral portion of the cutoff abrasive blade which is inserted into the slit may not come in full contact with the cutting fluid within the feed nozzle. Then the slit portion 61a of the feed nozzle 6 has a wall thickness which varies depending on the material of which it is made, and preferably is 0.5 to 10 mm when the wall is made of plastics, and 0.1 to 5 mm when the wall is made of metal materials.
The slit has such a length that when the outer peripheral portion of the cutoff abrasive blade is inserted into the slit, the outer peripheral portion may come in full contact with the cutting fluid within the feed nozzle. Often, the slit length is preferably about 2% to 30% of the outer diameter of the core of the cutoff abrasive blade. It is also preferred that when the outer peripheral portion of the cutoff abrasive blade is inserted into the slit, the slit be substantially blocked with the blade, but without contact with the blade. For the purpose of injecting part of the cutting fluid directly to the cutoff abrasive blade, the magnet block being machined, and the magnet holding jig, the slit may have such a length that when the outer peripheral portion of the cutoff abrasive blade is inserted into the slit, a proximal portion of the slit is left unblocked.
The feed nozzle 6 is combined with the multiple blade assembly 5 as shown in
In the setting that the multiple blade assembly, feed nozzle and magnet block are disposed as described above, while the cutoff abrasive blades are rotated, either one or both of the multiple blade assembly combined with the feed nozzle and the magnet block are relatively moved (in the width or longitudinal direction of magnet block) with the cutting parts kept in contact with the magnet block, whereby the magnet block is machined. When the magnet block is machined in this way, a high accuracy of cutoff machining is possible since the slits serve to restrict any axial runout of the cutoff abrasive blades being rotated.
In the setting that the outer peripheral portions of cutoff abrasive blades are inserted into slits of the cutting fluid feed nozzle, when it is intended to bring the peripheral portions in contact with the cutting fluid in the interior of the nozzle, the air streams are blocked by the feed nozzle housing (slit-defining portion) so that the cutting fluid may contact with the peripheral portions of the cutoff abrasive blades without obstruction by the air layer. When both the cutting fluid feed nozzle and the magnet holding jig are used, their cooperation ensures to deliver the cutting fluid to points of cutoff machining.
Where the cutting fluid feed nozzle is used, the feed nozzle and the jig are preferably combined to provide fluid communication between the slits in the feed nozzle and the guide paths in the jig. With respect to the distance between the slits in the feed nozzle and the guide paths in the jig, a relatively short distance is advantageous for the delivery of the cutting fluid by entrainment on the surfaces of cutoff abrasive blades. However, a too close distance may become an obstruction against the movement of the multiple blade assembly and magnet block, the injection and draining of the cutting fluid, or the like. Then the preferred distance between the slits in the feed nozzle and the guide paths in the jig is 1 mm to 50 mm, as measured between the feed nozzle and the top of the jig or the top of the magnet block at the end of cutting operation (for example, the feed nozzle is positioned 1 to 50 mm above the top of the jig at the end of cutting operation).
The workpiece which is intended herein to cutoff machine is a rare earth magnet block, typically a sintered one. Although the rare earth magnet as the workpiece is not particularly limited, suitable rare earth magnets include sintered rare earth magnets of R—Fe—B systems wherein R is at least one rare earth element inclusive of yttrium.
Suitable sintered rare earth magnets of R—Fe—B system are those magnets containing, in weight percent, 5 to 40% of R, 50 to 90% of Fe, and 0.2 to 8% of B, and optionally 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, for the purpose of improving magnetic properties and corrosion resistance. The amounts of additive elements added are conventional, for example, up to 30 wt % of Co, and up to 8 wt % of the other elements. The additive elements, if added in extra amounts, rather adversely affect magnetic properties.
Suitable sintered rare earth magnets of R—Fe—B system may be prepared, for example, by weighing source metal materials, melting, casting into an alloy ingot, finely dividing the alloy into particles with an average particle size of 1 to 20 μm, i.e., sintered R—Fe—B magnet powder, compacting the powder in a magnetic field, sintering the compact at 1,000 to 1,200° C. for 0.5 to 5 hours, and heat treating at 400 to 1,000° C.
The dimensions of a rare earth magnet block, workpiece are not particularly limited. Appropriate blocks have a width (in a transverse or cutting direction) of 10 to 100 mm, a length (perpendicular to the cutting direction) of 10 to 100 mm, and a thickness of 5 to 50 mm.
Examples and Comparative Examples are given below for further illustrating the invention although the invention is not limited thereto.
OD blades (cutoff abrasive blades) were fabricated by providing a doughnut-shaped disk core of cemented carbide (composed of WC 90 wt %/Co 10 wt %) having an outer diameter 120 mm, inner diameter 40 mm, and thickness 0.35 mm, and bonding, by the resin bonding technique, diamond abrasive grains to an outer peripheral rim of the core to form an abrasive section (peripheral cutting part) containing 25% by volume of diamond grains with an average particle size of 150 μm. The axial extension of the abrasive section from the core was 0.05 mm on each side, that is, the abrasive portion had a width (in the thickness direction of the core) of 0.45 mm.
Using the OD blades, a cutting test was carried out on a workpiece which was a sintered Nd—Fe—B magnet block. The test conditions are as follows. A multiple blade assembly was manufactured by coaxially mounting 39 OD blades on a shaft at an axial spacing of 2.1 mm, with spacers interposed therebetween. The spacers each had an outer diameter 80 mm, inner diameter 40 mm, and thickness 2.1 mm. The multiple blade assembly was designed so that the magnet block was cut into magnet pieces having a thickness of 2.0 mm.
The workpiece was a sintered Nd—Fe—B magnet block having a length 100 mm, width 30 mm and height 17 mm, which was polished at an accuracy of ±0.05 mm by a vertical double-disk polishing tool. By the multiple blade assembly, the magnet block is transversely cut into a plurality of magnet pieces of 2.0 mm thick. Specifically, one magnet block is cut into 38 magnet pieces because two outermost pieces are excluded.
The workpiece, sintered Nd—Fe—B magnet block was held in place by the jig shown in
The first and second holders were pushed inward. While the first holder was fixedly secured to rails by bolts, a pneumatic cylinder was actuated to push the second holder inward. As a result, the magnet block was pressed from the opposite sides of the jig. The pressure of the pneumatic cylinder was increased so that the hooks of the first and second holders were deformed to a total deformation amount of 0.05 mm, thereby holding the magnet block in place.
For cutoff machining operation, a cutting fluid was fed at a flow rate of 30 L/min. First, the multiple blade assembly was positioned above the second holder and descended toward the magnet block until the peripheral cutting parts of cutoff abrasive blades were inserted into the corresponding guide paths by a distance of 2 mm from the blade periphery. While feeding the cutting fluid from the feed nozzle and rotating the cutoff abrasive blades at 7,000 rpm, the multiple blade assembly was moved at a speed of 100 mm/min toward the first holder for cutoff machining the magnet block in a transverse direction. At the end of this stroke, the assembly was moved back to the second holder side without changing its height. In this way, cutoff channels of 2 mm deep were formed in the magnet block.
Next, the multiple blade assembly above the second holder was descended toward the magnet block by a distance of 16 mm. While feeding the cutting fluid from the feed nozzle and rotating the cutoff abrasive blades at 7,000 rpm, the multiple blade assembly was moved at a speed of 20 mm/min toward the first holder for cutoff machining the magnet block in the transverse direction. At the end of this stroke, the assembly was moved back to the second holder side without changing its height, completing the cutoff machining of the magnet block into the predetermined number of magnet pieces. It is noted that machining was performed by rotating the multiple blade assembly in such a direction that the hook of the second holder was forced downward. The magnet pieces were measured for thickness at 5 points (i.e., center and four corners of rectangular cut section). A difference between the maximum and minimum thicknesses was computed and reported as a size variation, with the results shown in Table 1.
A magnet block was cut into pieces by the same procedure as in Example 1 except that the orientation of the jig relative to the multiple blade assembly was reversed and machining was performed by moving the multiple blade assembly from the first holder side to the second holder side and moving it back from the second holder side to the first holder side. A size variation was similarly evaluated. The results are also shown in Table 1.
According to the prior art method, a magnet block was secured to a carbon plate by bonding with wax. The magnet block was then cut into pieces by the same procedure as in Example 1. A size variation was similarly evaluated. The results are also shown in Table 1.
A magnet block was cut into pieces by the same procedure as in Example 1 except that the dimensions of components of the first and second holders are shown in
Japanese Patent Application No. 2010-001056 is incorporated herein by reference.
Although some preferred embodiments have been described, many modifications and variations may be made thereto in light of the above teachings. It is therefore to be understood that the invention may be practiced otherwise than as specifically described without departing from the scope of the appended claims.
| Number | Date | Country | Kind |
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