WO2020245921A1

WO2020245921A1 - Method for manufacturing sqirrel-cage rotor

Info

Publication number: WO2020245921A1
Application number: PCT/JP2019/022193
Authority: WO
Inventors: 宏織寺西; 晋也大石; 岡田　順二
Original assignee: 三菱電機株式会社
Priority date: 2019-06-04
Filing date: 2019-06-04
Publication date: 2020-12-10
Also published as: JPWO2020245921A1

Abstract

This method for manufacturing a squirrel-cage rotor (30) includes: a first step of forming an aluminum bar by filling aluminum into a slot formed in a rotor core (1) by aluminum die casting; a second step of twisting around the rotation axis (C) while pulling, in the extension direction of the rotation axis (C), the rotor core (1) in which the aluminum bar is formed in the slot; and a third step of twisting in a direction opposite to that in the second step while compressing the rotor core (1) in the extension direction of the rotation axis (C). In the second step, the central portion (1c) of the rotor core (1) in the extension direction of the rotation axis (C) is locally twisted while grasping one end portion (1a) and the other end portion (1b) of the outer circumferential surface of the rotor core (1) in the extension direction of the rotation axis (C).

Description

Manufacturing method of cage rotor

The present invention relates to a method for manufacturing a cage rotor.

The squirrel-cage rotor of an induction motor is equipped with a rotor core that rotates around a rotation axis and a secondary conductor. A plurality of slots are formed in the rotor core by arranging them in the circumferential direction. The secondary conductor is configured to include an aluminum bar formed by filling the slots with aluminum by die casting.

Due to the increasing demand for resource saving and high efficiency, reducing the loss of induction motors has become an issue. Induction motor losses include iron loss, primary copper loss, secondary copper loss, and mechanical loss, which can be reduced by using high-performance materials or by optimizing the core shape or coil. Efforts are being made to reduce it. In addition to these losses, there is a cross flow loss in which an unnecessary current flows through the rotor. Cross-flow loss is a loss caused by the flow of a current that should not flow due to a potential difference between the aluminum bar of the secondary conductor formed by aluminum die casting and the rotor core.

In Patent Document 1, the aluminum bar twists the rotor core formed in the slot to insulate between the aluminum bar and the rotor core, and the efficiency of the induction motor can be improved. A method for producing a child is disclosed.

International Publication No. 2014/102942

However, if the rotor core is twisted to the extent that it is evenly distributed in the extending direction of the rotating shaft, it may not be possible to improve the efficiency of the induction motor as intended.

The present invention has been made in view of the above, and an object of the present invention is to obtain a method for manufacturing a squirrel-cage rotor capable of improving the efficiency of an induction motor.

In order to solve the above-mentioned problems and achieve the object, the present invention is a method for manufacturing a cage rotor that rotates about a rotation axis, and aluminum is placed in a slot formed in a rotor core by an aluminum die cast. The first step of filling to form an aluminum bar, the second step of twisting the rotor core with the aluminum bar formed in the slot around the rotation axis while pulling it in the extending direction of the rotation axis, and twisting the rotor core around the rotation axis. It includes a third step of twisting in the direction opposite to the second step while compressing in the stretching direction. In the second step, one end and the other end of the outer peripheral surface of the rotor core in the extending direction of the rotating shaft are gripped, and the central portion of the rotor core in the extending direction of the rotating shaft is locally twisted.

The method for manufacturing a squirrel-cage rotor according to the present invention has the effect that the efficiency of the induction motor can be improved.

Cross-sectional view of an induction motor including a squirrel-cage rotor manufactured by the manufacturing method according to the first embodiment of the present invention. The figure which shows the structural example of the rotor core provided in the cage rotor which concerns on Embodiment 1. External perspective view of the cage rotor according to the first embodiment Schematic diagram of the die-cast portion extracted from the cage rotor according to the first embodiment. The figure which shows an example of the induced current which flows in the die casting part when the rotor core and the aluminum bar are in electrical contact with each other near the center in the vertical direction in the rotor core which concerns on Embodiment 1. Schematic diagram for explaining the twisting process of the cage rotor according to the first embodiment. Schematic diagram for explaining the untwisting process of the cage rotor according to the first embodiment. Schematic diagram for explaining the method of twisting the rotor core according to the first embodiment. Schematic diagram showing the state after the twisting process of the rotor core according to the first embodiment. The schematic diagram which shows the state change of the region including the skew of a cage rotor in the twisting process which concerns on Embodiment 1. The figure which shows the state change by the twisting process of the region including the aluminum bar in the central part in the vertical direction of the cage rotor which concerns on Embodiment 1. Side view of a cage rotor in a state where the shaft according to the first embodiment is connected. The figure which shows the relationship between the rotation speed and torque of the induction motor using the squirrel-cage rotor which concerns on Embodiment 1. The figure which shows the relationship between the rotation speed and efficiency of the induction motor using the squirrel-cage rotor which concerns on Embodiment 1. Schematic diagram showing the side surface of the squirrel-cage rotor before the twisting process according to the first embodiment. A schematic view showing a state in which the die-cast portion of the cage rotor shown in FIG. 15 is twisted as a whole. Schematic diagram showing a state in which both ends of the outer peripheral surface of the rotor core in the state before aluminum die casting according to the first embodiment are gripped by gripping portions and the rotor core is twisted. Schematic diagram showing a state in which the cage rotor according to the first embodiment is twisted as a whole. Schematic diagram showing a state in which one end and the other end of the cage rotor according to the first embodiment are gripped. Schematic diagram showing the side surface of the squirrel-cage rotor in the state where the twisting step according to the first embodiment is completed.

The method for manufacturing a cage rotor according to the embodiment of the present invention will be described in detail below with reference to the drawings. The present invention is not limited to this embodiment.

Embodiment 1.
FIG. 1 is a cross-sectional view of an induction motor including a cage rotor manufactured by the manufacturing method according to the first embodiment of the present invention. The induction motor 50 shown in FIG. 1 is fixed to the squirrel-cage rotor 30, the stator 40 arranged at positions where the inner circumferences of the squirrel-cage rotor 30 face each other at intervals from the outer circumference, and the squirrel-cage rotor 30. The shaft 11 is provided.

The cage rotor 30 is formed by filling a rotor core 1 formed by arranging a plurality of slots 6 along the circumferential direction, a plurality of slots 6 formed in the rotor core 1, and a skew 5. It is equipped with an aluminum bar 7. A through hole 8 is formed in the center of the rotor core 1, and the shaft 11 is inserted into the through hole 8. The cage rotor 30 can rotate with the axis of the shaft 11 as the rotation axis C.

FIG. 2 is a diagram showing a configuration example of a rotor core included in the cage rotor according to the first embodiment. As shown in FIG. 2, the rotor core 1 is formed by laminating a plurality of electromagnetic steel sheets 2 punched into the same shape. Holes forming the slots 6 and the through holes 8 are formed in each of the electrical steel sheets 2. Further, in the electromagnetic steel plate 2, a groove is formed from the hole forming the slot 6 to the outer periphery of the electromagnetic steel plate 2.

By laminating the electromagnetic steel plates 2 while shifting them in the circumferential direction, a skew 5 is formed in the rotor core 1 so as to extend the above-mentioned grooves diagonally with respect to the rotation axis C. The electromagnetic steel sheets 2 are connected to each other by caulking. Teeth 3 are formed between slots 6 of the rotor core 1.

FIG. 3 is an external perspective view of the cage rotor according to the first embodiment. As shown in FIG. 3, the squirrel-cage rotor 30 includes the rotor core 1 and the die-cast portion 17 described above. The die-cast portion 17 is formed by performing aluminum die-casting on the rotor core 1. The die casting portion 17 includes the above-mentioned aluminum bar 7 and first end rings 15 and second end rings 16 provided on both sides of the rotor core 1 in the direction of the rotation axis C. In FIG. 3, the second end ring 16 is hidden behind the rotor core 1 and is invisible.

Here, the cross flow loss will be explained. Since there is no insulating film on the fracture surface of the rotor core 1, the rotor core 1 and the aluminum bar 7 are in a conductive state by aluminum die casting. Therefore, when a potential difference occurs between the aluminum bars 7 which are secondary conductors, a part of the current flows through the rotor core 1 and a cross flow loss occurs. It is known that such cross flow loss occurs locally in the vicinity of the center in the vertical direction of the rotor core in the induction motor. In the induction motor 50, the vertical direction is the stacking direction of the electromagnetic steel sheets 2 on the rotor core 1 and the stretching direction of the rotating shaft C. Hereinafter, the laminating direction of the electromagnetic steel sheet 2 may be described as the laminating direction of the rotor core 1.

FIG. 4 is a schematic view of a die-cast portion extracted from the cage rotor according to the first embodiment. As shown in FIG. 4, the die casting portion 17 includes a plurality of aluminum bars 7, a first end ring 15 connected to one end of each aluminum bar 7, and a second end connected to the other end of each aluminum bar 7. It includes a ring 16.

When a current flows through the stator winding provided on the stator 40, an induced magnetic field is generated in the rotor core 1. Due to such an induced magnetic field, an induced current flows through the aluminum bar 7 which is a secondary conductor. As shown in FIG. 4, the induced current is applied to one of the two adjacent aluminum bars 7 by the aluminum bar 7, the first end ring 15, the other aluminum bar 7, the second end ring 16, and one aluminum bar 7. It flows in a loop in the order of.

Since an alternating current is applied to the stator winding, the direction of the current flowing through the stator winding is repeatedly reversed with the passage of time. The direction in which the induced current flows corresponding to the current flowing in the stator winding also repeatedly reverses with the passage of time.

When the rotor core 1 and the aluminum bar 7 are in electrical contact near the center of the rotor core 1 in the vertical direction, a lateral current may be generated near the center in the vertical direction and the rotational torque may decrease. is there. FIG. 5 is a diagram showing an example of an induced current flowing through the die casting portion when the rotor core and the aluminum bar are in electrical contact with each other near the center in the vertical direction of the rotor core according to the first embodiment. ..

When the magnetic field formed by the stator winding is non-uniformly formed between the upper side and the lower side in FIG. 5 and a potential difference occurs, the positive and negative values are positive and negative between the upper side and the lower side when the current of the stator winding is switched between positive and negative. The inversion timing shifts. Therefore, as shown in FIG. 5, a lateral current is generated near the center in the vertical direction, which is the stacking direction of the rotor core 1, and a short loop current in the opposite direction flows between the upper side and the lower side. The rotation torque may decrease due to the flow of these short loop currents.

Therefore, in the first embodiment, the rotor core 1 is twisted to peel off the aluminum bar 7 which is a secondary conductor from the rotor core 1, and the electrical resistance between the rotor core 1 and the aluminum bar 7 is increased. By doing so, the generation of short loop current is suppressed. The short loop current is generated when the current of the stator winding is switched between positive and negative, and is likely to be generated vertically symmetrically, and the lateral current is likely to be generated near the center of the rotor core 1 in the stacking direction. Therefore, it is desirable that the aluminum bar 7 is peeled off from the rotor core 1 mainly in the vicinity of the center in the vertical direction of the rotor core 1.

Therefore, in the first embodiment, by locally twisting the central portion of the rotor core 1 which is greatly affected by the transverse flow loss, the aluminum bar 7 from the rotor core 1 is located near the center of the rotor core 1 in the vertical direction. Focus on peeling off. As a result, the eddy current loss and the drifting load loss of the induction motor 50 incorporating the squirrel-cage rotor 30 can be suppressed, and the characteristics of the induction motor 50 can be improved. Further, an insulation treatment can be applied between the rotor core 1 and the aluminum bar 7 by a simple procedure of applying an impact due to twisting to the rotor core 1.

The peeling process consists of a twisting process in which the central portion of the rotor core 1 in the vertical direction is locally twisted in a state where the aluminum bar 7 is solid after aluminum die casting, and a twisting process in which the rotor core 1 is twisted after the twisting process. Includes untwisting step. In the following, the twisting process may include the processing in the twisting process and the processing in the untwisting process.

FIG. 6 is a schematic diagram for explaining the twisting process of the cage rotor according to the first embodiment. FIG. 7 is a schematic view for explaining the untwisting step of the squirrel-cage rotor according to the first embodiment. FIG. 8 is a schematic view for explaining a method of twisting the rotor core according to the first embodiment. FIG. 9 is a schematic view showing a state after the twisting step of the rotor core according to the first embodiment.

In the twisting process of the cage rotor 30, as shown in FIG. 6, the skew 5 is positioned along the rotation axis C at one end and the other end of the rotor core 1 of the cage rotor 30. This is done by rotating the rotation axis C in opposite directions with respect to each other. Further, in the untwisting step of the cage rotor 30, as shown in FIG. 7, a direction in which one end and the other end of the outer peripheral surface of the rotor core 1 of the cage rotor 30 are rotated in the twisting step. It is done by rotating in the opposite direction.

As shown in FIG. 8, in the twisting step and the untwisting step of the cage rotor 30, one end 1a and the other end 1b of the outer peripheral surface of the rotor core 1 are gripped by gripping

portions

61 and 62 such as chucks. It is performed by rotating one grip portion 61 and the other grip portion 62 in opposite directions with respect to the rotation axis C. Since the rotor core 1 can be gripped and twisted by the gripping

portions

61 and 62 such as chucks, the production line for manufacturing the squirrel-cage rotor 30 can be miniaturized and in-lined. One grip portion 61 may be fixed and only the other grip portion 62 may be rotated around the rotation shaft C, or the other grip portion 62 may be fixed and one grip may be centered on the rotation shaft C. Only the portion 61 may be rotated.

In the twisting process of the cage rotor 30, as shown in FIG. 9, the central portion 1c of the rotor core 1 in the vertical direction, which is greatly affected by the transverse flow loss, is locally and the skew 5 is along the rotation axis C. By twisting until it reaches the position, the aluminum bar 7 and the rotor core 1 are actively peeled off. The position where the skew 5 is along the rotation axis C is, for example, a position where the skew angle is 90 degrees, and can be rephrased as a position where the skew 5 disappears. The skew angle is the angle of the skew 5 with respect to the direction perpendicular to the rotation axis C.

During the twisting process, the rotor core 1 extends in the stretching direction of the rotating shaft C, so that a force is applied to the aluminum bar 7 to separate it from the electromagnetic steel sheet 2 in the vertical direction. Therefore, in the twisting process of the cage rotor 30, the rotor core 1 is twisted while pulling the rotor core 1 in the extending direction of the rotation shaft C. As a result, it is possible to prevent an excessive load from being applied to the aluminum bar 7, and it is possible to prevent damage to the aluminum bar 7.

FIG. 10 is a schematic view showing a state change of a region including skew of a cage rotor in the twisting step according to the first embodiment. As shown in FIG. 10, the twisting process causes the aluminum bar 7 to tilt in the rotational direction, and a gap is created between the aluminum bar 7 and the electromagnetic steel sheet 2. The gap between the aluminum bar 7 and the electromagnetic steel plate 2 increases the contact resistance between the aluminum bar 7 and the electromagnetic steel plate 2, and it is possible to suppress an unnecessary current flowing from the aluminum bar 7 to the rotor core 1. .. Note that if the rotor core 1 is twisted until the skew 5 exceeds the position along the rotation axis C in the twisting process, the aluminum bar 7 may be damaged and the aluminum bar 7 may be cracked. is there.

During the untwisting process of the cage rotor 30, the rotor core 1 contracts in the extending direction of the rotating shaft C, contrary to the twisting process. Therefore, in the untwisting step, the rotor core 1 is twisted in the direction opposite to the twisting step while compressing the rotor core 1 in the extending direction of the rotating shaft C. As a result, it is possible to return to the same skew angle as before the twisting process.

FIG. 11 is a diagram showing a state change due to a twisting process of a region including an aluminum bar in the central portion in the vertical direction of the cage rotor according to the first embodiment. As shown in FIG. 11, a gap 9 is created between the aluminum bar 7 and the electrical steel sheet 2 by the twisting process of the cage rotor 30. The gap 9 generated between the aluminum bar 7 and the electromagnetic steel plate 2 is, for example, in the range of 0.1 mm to 0.2 mm. Note that hatching is omitted in FIG.

FIG. 12 is a side view of a squirrel-cage rotor in a state where the shaft according to the first embodiment is connected. The shaft 11 shown in FIG. 12 may be connected to the cage rotor 30 either before the twisting process or after the twisting process, but when the twisting process is performed after the shaft 11 is connected, the shaft It is desirable to pay attention to the decrease in the connection strength between the 11 and the cage rotor 30.

FIG. 13 is a diagram showing the relationship between the rotation speed and the torque of the induction motor using the squirrel-cage rotor according to the first embodiment. In FIG. 13, the horizontal axis represents the rotation speed of the induction motor 50, and the vertical axis represents the torque of the induction motor 50. As shown in FIG. 13, the torque curve 20 of the induction motor 50 having the twisted squirrel-cage rotor 30 is more than the torque curve 21 of the induction motor having the untwisted squirrel-cage rotor. It is possible to confirm a larger torque increase.

FIG. 14 is a diagram showing the relationship between the rotation speed and the efficiency of the induction motor using the squirrel-cage rotor according to the first embodiment. In FIG. 14, the horizontal axis represents the rotation speed of the induction motor 50, and the vertical axis represents the efficiency of the induction motor 50. As shown in FIG. 14, the efficiency curve 22 of the induction motor 50 having the twisted squirrel-cage rotor 30 is higher than the efficiency curve 23 of the induction motor having the untwisted squirrel-cage rotor. It can be confirmed that the efficiency is improved.

Here, the effect of locally twisting the central portion 1c of the rotor core 1 in the vertical direction will be described more specifically. FIG. 15 is a schematic view showing a side surface of the squirrel-cage rotor before the twisting process according to the first embodiment. FIG. 16 is a schematic view showing a state in which the die-cast portion of the cage rotor shown in FIG. 15 is twisted as a whole. Since the die-cast portion 17 is a rigid body, if only the die-cast portion 17 is used, as shown in FIG. 16, the aluminum bar 7 can be straightened by twisting so that the skew 5 portion is absent.

FIG. 17 is a schematic view showing a state in which both ends of the outer peripheral surface of the rotor core in the state before aluminum die casting according to the first embodiment are gripped by gripping portions and the rotor core is twisted. The rotor core 1 is composed of a plurality of electromagnetic steel plates 2 laminated, and if slip occurs between specific electromagnetic steel plates 2 when the rotor core 1 is twisted, the dynamic friction force is lower than the static friction force. , As shown in FIG. 17, it may rotate only between the sliding electromagnetic steel sheets 2 and not rotate at other positions. Note that in FIG. 17, for convenience of explanation, only one skew 5 is shown.

FIG. 18 is a schematic view showing a state in which the cage rotor according to the first embodiment is twisted as a whole. Since the cage rotor 30 has a structure in which the rotor core 1 and the aluminum bar 7 are integrated, the state change due to the twisting process only for the aluminum bar 7 and the state change due to the twisting process for only the rotor core 1 can occur. The state changes as if it were synthesized.

That is, in the rotor core 1, the slip between the electromagnetic steel plates 2 is large in the grip portions of the

grip portions

61 and 62 in the vertical direction, and the slip between the electromagnetic steel plates 2 is small in the central portion 1c. Therefore, the cage rotor 30 is brought into the state as shown in FIG. 18 by the twisting process of the rotor core 1. In the state shown in FIG. 18, since the slip between the electromagnetic steel sheets 2 is small in the central portion 1c of the rotor core 1, the aluminum bar 7 and the rotor core 1 are formed in the central portion 1c of the rotor core 1 which is greatly affected by the cross flow loss. The peeling is insufficient.

Therefore, in the twisting step of the first embodiment, the one end 1a and the other end 1b of the outer peripheral surface of the rotor core 1 which are less affected by the cross flow loss are gripped by the gripping

portions

61 and 62, and the influence of the cross flow loss is exerted. The central portion 1c of the large rotor core 1 is locally twisted. FIG. 19 is a schematic view showing a state in which one end and the other end of the squirrel-cage rotor according to the first embodiment are gripped, and FIG. 20 is a state in which the twisting step according to the first embodiment is completed. It is a schematic diagram which shows the side surface of a cage rotor.

As shown in FIGS. 19 and 20, in the twisting step according to the first embodiment, one end 1a and the other end 1b of the outer peripheral surface of the rotor core 1 are gripped by the

grips

61 and 62. It is desirable that the length L2 of the rotor core 1 in the stacking direction of the central portion 1c of the central portion 1c to be twisted be in the range of 30% to 40% of the total length in the stacking direction of the rotor core 1. Therefore, it is desirable that the length L1 of one end portion 1a and the other end portion 1b in the stacking direction of the rotor core 1 is, for example, in the range of 30% to 35% of the total length in the stacking direction of the rotor core 1. As a result, the peeling at a position where the cross flow loss is large can be sufficiently performed.

It is sufficient that the rotor core 1 of the central portion 1c of the rotor core 1 to be twisted can be locally twisted, and the length L1 of one end 1a and the other end 1b is a stack of the rotor cores 1. It is not limited to the range of 30% to 35% of the total length in the direction. Further, in the twisting step, the cage rotor 30 is twisted so that the skew 5 is located along the rotation axis C. However, in the state where the skew 5 is located along the rotation axis C, FIG. The state shown in is included.

As described above, the method for manufacturing the cage rotor 30 that rotates around the rotating shaft C according to the first embodiment includes an aluminum bar forming step, a twisting step, and a twisting back step. In the aluminum bar forming step, the slot 6 formed in the rotor core 1 is filled with aluminum by aluminum die casting to form the aluminum bar 7. In the twisting step, the rotor core 1 having the aluminum bar 7 formed in the slot 6 is twisted around the rotating shaft C while being pulled in the extending direction of the rotating shaft C. In the untwisting step, the rotor core 1 is compressed in the extending direction of the rotating shaft C and twisted in the direction opposite to the twisting step. In the twisting step, one end 1a and the other end 1b of the outer peripheral surface of the rotor core 1 in the stretching direction of the rotating shaft C are gripped, and the central portion 1c of the rotor core 1 in the stretching direction of the rotating shaft C is localized. Twist to. By locally twisting the central portion 1c of the rotor core 1 in this way, it is possible to accurately twist the central portion 1c of the rotor core 1 which is greatly affected by cross flow loss, resulting in eddy current loss and stray load loss. It is possible to improve the efficiency of the induction motor 50 by suppressing the above. Further, an insulation treatment can be applied between the rotor core 1 and the aluminum bar 7 by a simple procedure of applying an impact due to twisting to the rotor core 1.

Further, the length of the central portion 1c in the extending direction of the rotating shaft C is in the range of 30% to 40% of the total length of the rotor core 1 in the extending direction of the rotating shaft C. As a result, insulation between the rotor core 1 and the aluminum bar 7 can be achieved in a region where the influence of cross flow loss is large, and the efficiency of the induction motor 50 can be appropriately improved.

Further, in the twisting step, a gap 9 is formed between the rotor core 1 and the aluminum bar 7 by twisting the rotor core 1. As a result, the contact resistance between the aluminum bar 7 and the electromagnetic steel plate 2 increases in the central portion 1c of the rotor core 1, and unnecessary current flowing from the aluminum bar 7 to the rotor core 1 can be suppressed.

The gap 9 is in the range of 0.1 mm to 0.2 mm. As a result, the unnecessary current flowing from the aluminum bar 7 to the rotor core 1 can be accurately suppressed in the central portion 1c of the rotor core 1.

Further, a skew 5 is formed on the rotor core 1, and the twisting step twists the rotor core 1 until the skew 5 is located along the rotation axis C. As a result, in the central portion 1c of the rotor core 1, the peeling at a position where the cross flow loss is large can be sufficiently performed.

The configuration shown in the above-described embodiment shows an example of the content of the present invention, can be combined with another known technique, and is one of the configurations without departing from the gist of the present invention. It is also possible to omit or change the part.

1 rotor core, 1a one end, 1b other end, 1c center, 2 electromagnetic steel plate, 3 teeth, 5 skew, 6 slots, 7 aluminum bars, 8 through holes, 9 gaps, 11 shafts, 15 1st end ring , 16 2nd end ring, 17 die cast part, 20, 21 torque curve, 22, 23 efficiency curve, 30 cage rotor, 40 stator, 50 induction motor, 61, 62 grip part, C rotation shaft.

Claims

A method for manufacturing a cage rotor that rotates around a rotation axis.
The first step of forming an aluminum bar by filling a slot formed in a rotor core with aluminum by die casting,
A second step of twisting the rotor core having the aluminum bar formed in the slot around the rotation axis while pulling the rotor core in the extending direction of the rotation axis.
A third step of twisting the rotor core in the direction opposite to the second step while compressing the rotor core in the extending direction of the rotating shaft is included.
The second step is
It is characterized in that one end and the other end of the outer peripheral surface of the rotor core in the extending direction of the rotating shaft are gripped and the central portion of the rotor core in the extending direction of the rotating shaft is locally twisted. How to manufacture a cage rotor.
The length of the central portion in the extending direction of the rotating shaft is
The method for manufacturing a cage rotor according to claim 1, wherein the range is 30% to 40% of the total length of the rotor core in the extending direction of the rotating shaft.
The second step is
The method for manufacturing a cage rotor according to claim 1 or 2, wherein a gap is formed between the rotor core and the aluminum bar by twisting the rotor core.
The method for manufacturing a cage rotor according to claim 3, wherein the gap is in the range of 0.1 mm to 0.2 mm.
A skew is formed on the rotor core.
The second step is
The method for manufacturing a cage rotor according to any one of claims 1 to 4, wherein the rotor core is twisted until the skew is located along the rotation axis.