JP4886375B2 - Laminated core manufacturing method - Google Patents

Description

  The present invention relates to a method for manufacturing a laminated core in which a laminated core is produced by a progressive die, and more particularly to a technique for easily and reliably removing an unnecessary portion temporarily fixed by a caulking joint.

  Laminated iron cores are widely used for cores of electric motors, etc., but as a manufacturing method, a core punching plate formed by integrally forming an unnecessary part having a caulking joint and an iron core part using a progressive die Punched from core material, punched core punched plates are stacked in order in the die, and a semi-finished product is formed by temporarily fixing the stacked core punched plates by caulking joints every predetermined number of sheets, and the half is taken out from the progressive die It is known that an unnecessary part is removed after the iron core of the product is restrained by restraining means.

  For example, in Patent Document 1, “only one of the iron steel plates to be laminated is punched out, and the second and subsequent plates are provided with protrusions that are kept just before punching, and adjacent electric iron plates are formed by the protrusions. A technique is described in which, after fitting and binding, the temporary binding portion is removed after the main fixing.

  Further, Patent Document 2 describes “a method of forming a rotor (rotor). A mandrel hole is formed on the inner side of the shaft hole and a temporary core portion is formed by joining the shaft hole and a slight width. Then, after the end rings are formed by die casting on both sides of the iron core, a technique of removing the force in the axial direction of the shaft hole by applying it to the temporary core part is described.

  Further, Patent Document 3 states that “at least a part of a scrap portion such as a through hole or a slot hole of a core sheet is formed as a half punching portion for superposition and laminated and integrated, and then press-fitted or after press-fitting a shaft. The technique of “removing the half-cut portion” is described.

Patent Document 4 is an earlier patent filed by the present applicant. Patent Document 4 states that “the unnecessary removal portion of the thin plate is pushed back from half punching or complete punching and fitted into the punching hole of the thin plate in a press-fit state ( pushing). (Referred to as “ back” ), and a temporary fixing means is formed by caulking and bonding to an unnecessary removal portion, and the unnecessary removal portion temporarily fixed outside the mold after the lamination is integrated is described.

  Patent Document 5 is also a prior patent filed by the present applicant. Patent Document 5 states that “a relief hole is formed in an unnecessary removal portion to facilitate removal of the unnecessary removal portion, and the fitting hole side is formed. And a technique that makes it easy to remove a removal portion unnecessary at the time of external punching by pressing and deforming from the punch side prior to punching.

  Patent Document 6 describes a technique of “joining and joining the protruding portions from the core piece main body portion, then bonding and bonding the iron core plates to each other, and then removing the bonding portion”.

  Furthermore, Patent Document 7 states that “a plurality of core ribs formed on the core have an annular connecting portion having a central hole at the center, and the center side of the connecting portion is force-squeezed and laminated integrally. The technology of removing the caulking portion after the conversion is made is described.

Japanese Patent Laid-Open No. 55-13665 Japanese Patent Publication No.7-123343 JP-A-5-103449 Japanese Patent No. 3294348 Japanese Patent No. 3523330 Japanese Patent Laid-Open No. 11-308821 JP 2003-88009 A

  The prior arts according to these patent documents all use unnecessary parts that become scrap after punching the iron core part, and after temporarily fixing and integrating each iron core plate in a laminated state with a joining means such as caulking, This unnecessary portion is removed to obtain a laminated iron core, and since there is no coupling means such as a caulking coupling portion remaining in the laminated iron core as a product, an improvement in electrical performance can be realized.

  However, the removal operation for removing the unnecessary portion from the temporarily fixed laminated core is not easy, and in particular, when skew is provided for each core plate laminated in the mold, the unnecessary portion is similarly skewed. Since the inclination is formed, the removal operation becomes more difficult as compared with the case of the stacked stack in which the unnecessary portions of the iron core plates are aligned.

  For example, in the case of Patent Document 2, a force directed in the axial direction of the shaft hole is applied to remove unnecessary portions, but a large force is actually required to remove in a state where a large number of sheets are stacked. Become. In addition, since the joint portion may remain in a flash shape when removed, there is a risk of trouble when the shaft is attached to the shaft hole after removal. It was difficult to perform removal easily and reliably.

  The present invention has been made in view of such a background, and even in the case of a laminated core in which a skew is imparted to each iron core plate, a laminated layer that can easily and reliably remove unnecessary portions temporarily fixed by caulking joints. An object is to provide an iron core manufacturing method.

The method for manufacturing a laminated core according to the invention of claim 1 uses a progressive die to punch an iron core punched plate formed by integrally forming an unnecessary portion having a caulking joint portion and an iron core portion from a band-shaped core material, and punching the core. A punched plate is sequentially laminated in the die, and a semi-finished product is formed by temporarily fixing the laminated core punched plate at a predetermined number of times by a caulking joint, and the iron core portion of the semi-finished product taken out from the progressive die is restrained A method of manufacturing a laminated core by removing unnecessary portions after restraining, the step of half-cutting or punching the unnecessary portions with a progressive die, and pushing back the unnecessary portions to the core portion look including the step of fitting the unnecessary portion by pressure contact to the core portion by, the unnecessary portion includes a plurality of separate pieces tip is fitted to the core portion, the proximal end of the separation protrusions from each other And an annular connecting portion which forms an, said when removing the unnecessary portion, characterized in that the separation of the separation piece from the core portion by deforming in the form of reduced diameter of the annular connecting portion in the radial direction.

According to a second aspect of the present invention, an iron punching plate formed by integrally forming an unnecessary portion having a caulking coupling portion and an iron core portion is punched from a belt-like core material using a progressive die, and the punched iron core punching plate is die-molded. After sequentially laminating inside, forming a semi-finished product by temporarily fixing the laminated core punched plate with a caulking joint at a predetermined number of times, and constraining the core part of the semi-finished product taken out from the progressive die by restraining means, A method of manufacturing a laminated core by removing unnecessary portions, wherein the unnecessary portions are half-punched or punched with a progressive die, and the unnecessary portions are pushed back to the core portions. A step of fitting a portion with the iron core portion in a press-contact state, and the unnecessary portion includes a plurality of separation pieces whose front ends are fitted to the iron core portion, and an annular connection that connects the base ends of the separation pieces to each other With the door, said when removing the unnecessary portion, characterized in that the separation of the separation protrusions from the core portion by deforming bending the separating piece in the rotational direction.

According to a third aspect of the present invention, an iron core punching plate is formed by punching an iron core punching plate formed by integrally forming an unnecessary portion having a caulking joint portion and an iron core portion from a belt-shaped core material using a progressive die. After sequentially laminating inside, forming a semi-finished product by temporarily fixing the laminated core punched plate with a caulking joint at a predetermined number of times, and constraining the core of the semi-finished product taken out from the progressive die by restraining means, A method of manufacturing a laminated iron core by removing unnecessary portions,
Including half-cutting or punching the unnecessary portion with a progressive die, and fitting the unnecessary portion into the iron core portion in a press-contact state by pushing back the unnecessary portion to the iron core portion. The unnecessary portion is composed of a plurality of separation pieces in which a tip is fitted to the iron core portion and the caulking coupling portion is formed, and when the unnecessary portion is removed, the separation pieces are displaced inward in the radial direction. The separation piece is separated from the iron core by the above.

According to a fourth aspect of the present invention, in the laminated core manufacturing method according to the first or second aspect, the caulking coupling portion is provided on at least one of the separation piece and the annular coupling portion. To do.

The invention of claim 5 is the laminated iron core manufacturing method according to any one of claims 1 to 4, wherein the restraining means is a main fixing means for main fixing the iron core portion. And

The invention of claim 6 is the laminated core manufacturing method according to any one of claims 1 to 4 , wherein the restraining means is a restraining jig for temporarily restraining the iron core. It is characterized by.

The invention according to claim 7 is the method for manufacturing a laminated core according to claim 6, wherein the restraining jig restrains the core part until the core part is permanently fixed .

  According to the method of manufacturing a laminated core according to the present invention, the caulking joint portion does not exist in the laminated iron core by removing unnecessary portions. Therefore, when applied to a laminated core such as a core of an electric motor, the electrical and magnetic performance is improved. Can be made. In addition, since the unnecessary portion is merely fitted in a pressed state to the iron core portion by the separation processing portion pushed back, the removal operation is extremely easy, and even when skew is given to each iron core portion, It can be removed reliably.

  The laminated iron core manufacturing method according to the present invention will be described in detail with reference to the accompanying drawings with some embodiments in which the present invention is applied to a rotor (rotor) of a rotating electrical machine (motor).

<First Embodiment>
FIG. 1 is a layout diagram of a progressive die according to the first embodiment, and FIG. 2 is a plan view showing a semi-finished product of a laminated core according to the first embodiment. In this embodiment, the steps shown in FIG. 1 are sequentially performed on the intermittently fed belt-shaped core material (hereinafter referred to as a hoop material) W, and a predetermined number of core punched plates A are laminated and temporarily fixed to FIG. The semi-finished product T1 shown is manufactured.

The hoop material W is processed in the first to seventh steps while being intermittently fed in the progressive die apparatus.
(1) First step: Punching of pilot hole P (2) Second step: Punching of three slots S for each core punching plate A (described later), and the first sheet to be laminated Punching of three measuring holes (caulking and coupling means) Kl to the core punching plate A (3) Third step ... punching of unnecessary center hole H (circular hole) for each core punching plate A (4) Fourth step: By punching an arc-shaped hole h whose outer diameter matches the inner diameter (shaft hole diameter) of the iron core portion 10 (described later) with respect to each iron punching plate A, the unnecessary portion center hole H and Between each arcuate hole h, formation of the inner annular portion D1, three separation pieces (separation processed portions) B1, and a narrow annular connection portion C1 for connecting these separation pieces B1 (5) Fifth Step: For each separated piece B1 of the second and subsequent iron core punched plates A to be laminated, Cutting and raising formation of crimping projections K2 (caulking coupling means) (6) Sixth step: After punching the outer end of the separation piece B1 with respect to each core punching plate A, push-back is performed and the annular connecting portion Formation of unnecessary portion R in which C1 and separation piece B1 are integrated (7) Seventh step: External cutting of iron punched plate A composed of unnecessary portion R and iron core portion 10, and caulking joint portion K ( Manufacture of semi-finished product T1 by temporary sticking in a die with a measuring hole K1 and caulking projection K2)

  As shown in FIG. 2, the iron core punching plate A is not formed by connecting the inner ring portion D1 and the iron core portion 10 including the three slots S and the three separated pieces B1 by the narrow ring connecting portion C1. Part R. Each separation piece B1 is pushed back to the inner annular portion D1 side after being punched, whereby the iron core portion 10 and the unnecessary portion R are fitted in a pressure contact state. Each separation piece B1 is formed with a caulking projection K2 (second and subsequent layers to be stacked) or a measuring hole Kl (first layer to be stacked) into which the caulking projection K2 is fitted as a caulking coupling portion K. ing.

  The semi-finished product T1 is formed by laminating each core punched plate A with the outer shape cut in the die by the punch and die provided in the seventh step, which is the final step of the progressive die, and caulking each core punched plate A adjacent vertically. It is formed by being separated by a predetermined number of sheets by an iron core punching plate A having a measuring hole Kl while being bonded and temporarily fixed by the projection K2.

  The pushback for the separation piece B1 is performed by the conventional technique whose operation principle is illustrated in FIG. 3A is a complete punching method in which the separation piece B1 on the unnecessary portion R side is once completely punched with respect to the inner annular portion D1, and then pushed back to the inner periphery of the inner annular portion D1. In the case of (b), it is a half punching method in which the separation piece B1 is punched out to about half the plate thickness with respect to the inner annular portion D1, and then pushed back to the inner periphery of the inner annular portion D1. As a result, the separation piece B1 and the inner annular portion D1 are fitted in a pressed state after being completely sheared.

  In either case, the separation piece B1 (that is, the unnecessary portion R) and the inner annular portion D1 (that is, the iron core portion 10) are fitted in pressure contact via the fitting surface (shear surface) F. Therefore, the removal operation of the unnecessary portion R thereafter is easy, and each core punching is performed by fitting the convex portion (caulking projection K2) on the lower surface side of the separation piece B1 and the concave portion on the upper surface side. Temporary fixing between the plates A is performed. Since burrs may occur during the punching process, it is desirable to form reliefs b1 and b2 on the inner circumference of the iron core portion 10 at the part facing the separation piece B1, as shown in FIG.

  The semi-finished product T1 formed by the progressive die is taken out from the die, transported to the next process, and the unnecessary portion R is removed by a removal jig, whereby the laminated core 100 composed of a predetermined number of core portions 10 and Become. At this time, if the unnecessary portion R is simply removed from the core punching plate A, each core punching plate A temporarily fixed by the caulking protrusion K2 is scattered.

  Therefore, when forming the rotor (rotor) of the rotating electrical machine (motor), it is necessary to constrain the iron core portion 10 (that is, the laminated iron core 100) before removing the unnecessary portion R. In the case of the first embodiment, the iron core 10 is constrained (bound) by the coil winding 11. In addition to the coil winding 11, various means such as die-cast molding, welding, coating, and the like can be used as the main fixing means of the iron core portion 10.

  Unnecessary portion R pushes back separation piece B1 by using a removal jig provided with a plurality of pressing gripping pieces movable in the radial direction and pulling it inward (center side) via annular connecting portion C1. It can be removed by separating from the fitted surface F. For example, as shown in FIG. 4, using a removal jig J1 having six pressure arms Ja that can be gripped by reducing the diameter in the radial direction, inside the inner annular portion D1 and outside the annular coupling portion C1. Each pressure arm Ja is inserted into the formed space 12, and the shoulder portions located on both sides of each separation piece B1 are pressurized toward the center. As a result, the annular connecting portion C1 formed in a narrow width is deformed in a reduced diameter shape, and each separation piece B1 is forcibly peeled from the inner side of the inner annular portion D1, so that the unnecessary portion R is removed from the iron core portion 10. It is removed and the laminated iron core 100 shown in FIG. 5 is obtained.

  Since this laminated iron core 100 does not have the caulking joint portion K (K1, K2) to which the iron core punched plate A has been temporarily fixed, the electrical and magnetic performance can be improved. Moreover, since the separation piece B1 is merely fitted in the inner annular portion D1 in a pressure contact state by pushback, the removal work is extremely easy, and a skew is imparted to each iron core portion 10. But it can be removed easily and reliably.

Second Embodiment
FIG. 6 is a plan view showing a semi-finished product of the laminated core according to the second embodiment, and FIG. 7 is a layout diagram of a progressive die according to the second embodiment.

  In the semi-finished product T2 according to the second embodiment, the three separated pieces B2 that are narrow and radially extend in the radial direction are connected by the annular connecting portion C2, and the caulking joint portion K (K1, K2) is annularly connected. It is provided in the part C2.

  Moreover, in the layout of the progressive die which concerns on 2nd Embodiment, the punching process of the pilot hole P of the process (1B) of FIG. 7, the punching process of the slot S in a process (2B), and the iron core part of a process (7B) However, in the step (2B), the measuring hole Kl is punched more to the axial center side, and in the step (3B), the unnecessary portion central hole H is formed in the center of the iron core portion 10 inside the measuring hole Kl. Is stamped.

  Further, in the step (4B), the portions that form the separation piece B2 are left at three places, and fan-shaped arc-shaped holes h whose outer shape matches the inner diameter of the iron core portion 10 are punched into three places, and unnecessary portion center holes H and An annular connecting portion C2 for connecting the separation pieces B2 is formed between the inner annular portion D2 and the annular connecting portion C2, and a space 12 into which the removal jig J1 can be inserted is formed.

  Further, in the step (5B), the caulking protrusion K2 of the second and subsequent iron core portions 10 to be laminated with respect to the annular connecting portion C2 is cut and formed, and in the step (6B), it is fitted to the inner periphery of the inner annular portion D2. After punching with the punches to be joined, the unnecessary portion R composed of each separation piece B2 and the annular connecting portion C2 is half-punched or punched, and then the outer end of each separation piece B2 is in pressure contact with the inner annular portion D2. The unnecessary portion R is pushed back so as to be fitted.

  As shown in FIG. 6, the semi-finished product T <b> 2 includes the unnecessary portion R including the caulking joint portion K (K <b> 1, K <b> 2) after the coil winding 11 is applied to the iron core portion 10 as in the case of the first embodiment. In the case of the second embodiment, the separation piece is formed in a narrow width using a removal jig (not shown) provided with a pressure arm that can be inserted into the space 12 and rotated in the circumferential direction. When the B2 is forcibly peeled while being deformed, the separation pieces B2 are separated from the inner annular portion D2, and the laminated iron core 100 shown in FIG. 5 is obtained.

<Third Embodiment>
FIG. 8 is a plan view showing a semi-finished product of the laminated core according to the third embodiment, and FIG. 9 is a layout diagram of a progressive die according to the third embodiment.

  In the semi-finished product T3 according to the third embodiment, three separation pieces B3 that are narrow and radially extend in the radial direction are connected by an annular connection portion C3, and the unnecessary portion R is connected in the same manner as in the second embodiment. Although it is formed, the caulking joint portion K (K1, K2) is formed inside the annular coupling portion C3 (that is, a portion corresponding to the unnecessary portion central hole in the second embodiment).

  Therefore, on the layout when manufacturing with the progressive die, after punching the pilot hole P in the step (1C) of FIG. 9, the punching of the slot S and the one to be stacked in the step (2C) A measuring hole Kl is punched into the center of the core 10 of the eye, and the part where the separation piece B3 is formed in step (3C) is left in three places, and the fan-shaped arc shape whose outer diameter matches the inner diameter of the core 10 The holes h are punched at three locations, and caulking protrusions K2 are cut and formed at the center of the second and subsequent iron cores 10 to be laminated.

  As a result, an annular connecting portion C3 for connecting each separation piece B3 is integrally formed on the outside of the caulking joint portion K (K1, K2) provided at the center portion, and between the inner annular portion D3 and the annular connecting portion C3. A space 12 into which the removal jig J1 can be inserted is formed.

  Further, in step (5C), punching is performed with a punch fitted to the inner annular portion D3, and the unnecessary portion R is half-punched or punched from the inner annular portion D3. Push-back is performed so that the inner annular portion D3 is fitted in a press-contact state, and the outer shape of the iron core is removed in the step (6C) to obtain the iron punched plate A.

<First Modification>
FIG. 10 is a plan view of a semi-finished product according to the first modification.
As shown in the figure, in the first modification, the unnecessary portion R is removed in a state where the outer periphery of the core portion 10 of the laminated core 100 is temporarily restrained by the restraining jig J2. The iron core portion 10 is restrained by the restraining jig J2 until the iron core portion 10 is fixed by the main fixing means such as coil winding. Further, the restraining jig may restrain a portion other than the outer periphery of the iron core portion 10, for example, the inner periphery or the outer periphery of the inner annular portion D.

<Second Modification>
FIG. 11 is a plan view of a semi-finished product according to the second modification.
As shown in the figure, in the second modification, the unnecessary portion R is separated for each of the three separation pieces B, but the iron core portion 10 is formed by the caulking joint portion K formed in each unnecessary portion R, as described above. In the same manner as in each of the embodiments described above. Therefore, the laminated core 100 can be obtained by removing each unnecessary portion R in a state where the iron core portion 10 is restrained by the main fixing means (coil winding, die-cast molding, etc.) or a restraining jig. In the case of restraining with a restraining jig, the restraining jig may be removed after the iron core 10 is permanently fixed by the fixing means.

  This is the end of the description of specific embodiments and modifications. However, aspects of the present invention are not limited to these. For example, in the above embodiment, the present invention is applied to a laminated iron core for a rotor (rotor) of a rotating electrical machine (electric motor), and the unnecessary portion R is fitted into the shaft hole of the rotating shaft in a pressure contact state. It may be applied to a laminated iron core for a stator (stator) of a rotating electrical machine, and the unnecessary portion R may be fitted into the loose fitting hole of the rotor in a pressure contact state. Further, the restraint of the iron core portion performed before the removal of the unnecessary portion R may be performed by a method of attaching a coil winding using a coil assembly (insulator). As described above, as described above, die casting molding, welding, Various methods such as coating may be used. If the method of constraining the iron core portion with a restraining jig as in the first modification is used, the coil winding is performed when the unnecessary portion is removed because the fixing is performed after the unnecessary portion is removed. And die-cast moldings are not damaged.

It is a layout figure of the progressive metal mold | die which concerns on 1st Embodiment. It is a top view which shows the semi-finished product of the laminated iron core which concerns on 1st Embodiment. It is explanatory drawing which shows the operation | movement principle of pushback. It is explanatory drawing which shows the process of removing an unnecessary part from a semi-finished product. It is a perspective view which shows the rotor for electric motors. It is a top view which shows the semi-finished product of the laminated iron core which concerns on 2nd Embodiment. It is a layout figure of the progressive die which concerns on 2nd Embodiment. It is a top view which shows the semi-finished product of the laminated iron core which concerns on 3rd Embodiment. It is a layout figure of the progressive die which concerns on 3rd Embodiment. It is a top view which shows the semi-finished product of the laminated iron core which concerns on a 1st modification. It is a top view which shows the semi-finished product of the laminated iron core which concerns on a 2nd modification.

Explanation of symbols

W Hoop material (banded core material)
B, B1-B3 Separation piece (separation processing part)
C1-C3 annular connecting part D, D1-D3 inner annular part J1 removing jig J2 restraining jig (constraining means)
K Caulking joint K1 Measuring hole (caulking joint)
K2 Caulking projection (caulking joint)
T1-T3 Semi-finished product A Iron punched plate F Fitting surface R Unnecessary part T Semi-finished product 10 Iron core 11 Coil winding (Main fixing means: Restraint means)
100 laminated iron core

Claims (7)

Using a progressive die, an iron core punching plate that is formed by integrally forming an unnecessary portion having a caulking joint and an iron core portion is punched from a belt-shaped core material, and the punched iron core punching plates are sequentially stacked in a die. A semi-finished product is formed by temporarily fixing a punched plate at a predetermined number of times at a joining portion, a core of a semi-finished product taken out from a progressive die is constrained by a restraining means, and then a laminated core is formed by removing unnecessary portions. A method of manufacturing
Seen containing a step of half blanking or stamping with progressive dies the unnecessary portion, a step of fitting at the pressed state the unnecessary portion to the core portion by pushing back the unnecessary portion in the core portion ,
The unnecessary portion includes a plurality of separation pieces whose front ends are fitted to the iron core portion, and an annular connection portion that connects the base ends of these separation pieces to each other,
In removing the unnecessary part, the separated piece is separated from the iron core part by deforming the annular connecting part in a radial direction to reduce the diameter . Using a progressive die, an iron core punching plate that is formed by integrally forming an unnecessary portion having a caulking joint and an iron core portion is punched from a belt-shaped core material, and the punched iron core punching plates are sequentially stacked in a die, and the laminated core A semi-finished product is formed by temporarily fixing a punched plate at a predetermined number of times at a joining portion, a core of a semi-finished product taken out from a progressive die is constrained by a restraining means, and then a laminated core is formed by removing unnecessary portions. A method of manufacturing
Including half-cutting or punching the unnecessary portion with a progressive die, and fitting the unnecessary portion into the iron core portion in a press-contact state by pushing back the unnecessary portion to the iron core portion.
The unnecessary portion includes a plurality of separation pieces whose front ends are fitted to the iron core portion, and an annular connection portion that connects the base ends of these separation pieces to each other,
In removing the unnecessary portion, the separated piece is separated from the iron core by bending and deforming the separated piece in the rotation direction. Using a progressive die, an iron core punching plate that is formed by integrally forming an unnecessary portion having a caulking joint and an iron core portion is punched from a belt-shaped core material, and the punched iron core punching plates are sequentially stacked in a die, and the laminated core A semi-finished product is formed by temporarily fixing a punched plate at a predetermined number of times at a joining portion, a core of a semi-finished product taken out from a progressive die is constrained by a restraining means, and then a laminated core is formed by removing unnecessary portions. A method of manufacturing
Including half-cutting or punching the unnecessary portion with a progressive die, and fitting the unnecessary portion into the iron core portion in a press-contact state by pushing back the unnecessary portion to the iron core portion.
The unnecessary portion is composed of a plurality of separation pieces in which a tip is fitted to the iron core portion and the caulking coupling portion is formed,
In removing the unnecessary portion, the separated piece is separated from the iron core portion by displacing the separated piece inward in the radial direction. The method of manufacturing a laminated core according to claim 1 or 2 , wherein the caulking joint portion is provided on at least one of the separation piece and the annular coupling portion . The method of manufacturing a laminated core according to any one of claims 1 to 4, wherein the restraining means is a main fixing means for main fixing the iron core portion . The laminated core manufacturing method according to claim 1, wherein the restraining means is a restraining jig that temporarily restrains the iron core portion . The laminated core manufacturing method according to claim 6, wherein the restraining jig restrains the iron core until the iron core is permanently fixed .

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