Stator core manufacturing method

Abstract

The present invention provides a stator core manufacturing method that can keep core losses low.　The method comprises: a laminating step for forming a laminate 10 by laminating a plurality of iron core pieces 11 with resin injection holes such that the resin injection holes overlap each other; a pressurizing step for pressurizing the laminate 10 in the lamination direction at a mold clamping pressure between 1.0 MPa and 6.0 MPa; and a resin injecting step for injecting a resin 320 at a resin injection pressure between 2.5 MPa and 6.0 MPa into a resin injection part 6 formed by the resin injection holes overlapping each other in the laminate 10.

Description

Method for manufacturing a stator core

[0001] The present invention relates to a method for manufacturing a stator core that constitutes a stator of an electric motor.

[0002] A stator core of an electric motor is constituted by laminating a plurality of plate-shaped core pieces punched from an electromagnetic steel sheet into a predetermined shape, and fastening the core pieces adjacent to each other in the lamination direction.

[0003] As means for fastening core pieces adjacent to each other in the lamination direction, caulking and welding are known. Fastening means by caulking and welding are excellent in terms of cost and work efficiency, and have been widely adopted conventionally. On the other hand, when prioritizing reduction of iron loss of an electric motor, instead of caulking or welding, fastening of core pieces adjacent to each other in the lamination direction using resin has been performed (for example, refer to Patent Document 1).

[0004] Patent Document 1 discloses manufacturing a stator core by sandwiching a laminate in which a plurality of core pieces are laminated between an upper die and a lower die, applying a pressing force (die clamping pressure) to the sandwiched laminate, and injecting resin under pressure in the die-clamped state.

[0005] Japanese Patent Application Laid-Open No. 2015-6034

[0006] In the method for manufacturing a stator core described in Patent Document 1, when injecting resin under pressure, an excessively large die clamping pressure is applied to the laminate for die clamping. Therefore, even after removing the die clamping pressure, the strain remaining in the laminate becomes large, and as this residual strain increases, the iron loss increases.

[0007] The present invention has been made in view of the above problems, and an object thereof is to provide a method for manufacturing a stator core capable of suppressing iron loss to a low level.

[0008] The characteristic configuration of the stator core manufacturing method according to the present invention for solving the above problems is to include: a lamination step of stacking a plurality of iron core pieces having resin injection holes so that the resin injection holes overlap each other to form a laminate; a pressurizing step of pressurizing the laminate with a clamping pressure of 1.0 to 6.0 MPa in the lamination direction; and a resin injection step of injecting resin into the resin injection portions formed in the laminate by the overlapping of the resin injection holes with a resin injection pressure of 2.5 to 6.0 MPa.

[0009] According to the manufacturing method of the stator core with this configuration, an excessively large clamping pressure is not applied to the laminate formed in the lamination process, and the balance between the clamping pressure in the pressurization process and the resin injection pressure in the resin injection process is appropriately set. As a result, residual strain in the laminate after the clamping pressure is removed can be suppressed, and iron loss can be kept low.

[0010] In the method for manufacturing a stator core according to the present invention, it is preferable that the resin injection pressure be set to be equal to or greater than the mold clamping pressure.

[0011] According to the manufacturing method of the stator core with this configuration, the resin injection pressure in the resin injection process is set to be higher than or equal to the mold clamping pressure in the pressurization process, so that resin can be reliably injected into the molded laminate.

[0012] In the method for manufacturing a stator core according to the present invention, it is preferable to perform a heat treatment step to remove residual stress before performing the pressurization step.

[0013] According to the manufacturing method of the stator core with this configuration, the residual stress of the multiple iron core pieces constituting the laminate is removed in advance by the heat treatment process before the pressurization process is carried out. Therefore, residual strain caused by residual stress can be reduced, and iron loss can be kept to a lower level.

[0014] Figure 1 is a diagram illustrating the structure of a stator core manufactured by a method for manufacturing a stator core according to one embodiment of the present invention. Figure 2 is a flowchart showing the steps of the manufacturing process for the stator core. Figure 3 is a diagram showing the laminate mounted on a positioning jig. Figure 4 is a diagram illustrating the resin injection process using a transfer mold molding machine.

[0015] The present invention will be described below with reference to the drawings. However, the present invention is not intended to be limited to the embodiments and configurations described below or shown in the drawings. In Figures 1, 3, and 4, it is shown that the stator core manufactured by the manufacturing method of the present invention is composed of multiple layers, but the thickness relationships of each layer have been exaggerated or simplified as appropriate for the sake of ease of understanding the drawings, and do not strictly reflect the relative thicknesses (scale) of each layer in an actual stator core. Also, the number of layers forming the stator core does not necessarily directly reflect the actual product.

[0016] <Overall Structure> Figure 1 is an explanatory diagram of the structure of a stator core 1 manufactured by a method for manufacturing a stator core according to one embodiment of the present invention. Figure 1(a) is a plan view of the stator core 1, and Figure 1(b) is a front view of the stator core 1. The stator core 1 shown in Figures 1(a) and (b) comprises a cylindrical portion 2, a toothed portion 3, a protruding portion 4, a through portion 5, a resin injection portion 6, and a resin 7.

[0017] The cylindrical portion 2 is formed to extend cylindrically along the axis S (see Figure 1(b)), with the axis S being a vertical line passing through the center O shown in the plan view of Figure 1(a). The teeth portion 3 is the part around which a winding (not shown) is wound, and is integrally provided in large numbers on the inner circumference side of the cylindrical portion 2, projecting toward the center O (axis S) at predetermined pitches in the circumferential direction of the cylindrical portion 2. Multiple projections 4 are integrally provided on the outer circumference side of the cylindrical portion 2, projecting toward the center O (axis S) in multiple numbers (three in this example), and are arranged at equal angles (every 120° in this example) in the circumferential direction of the cylindrical portion 2. The through portion 5 is drilled in a circular cross-section so as to penetrate the center of each projection 4 along the direction in which the axis S extends. The resin injection portion 6 is drilled in a rectangular cross-section so as to penetrate the cylindrical portion 2 along the direction in which the axis S extends. Multiple resin injection sections 6 are arranged around the circumferential direction of the cylindrical section 2 at equal angles (60° intervals in this example) (6 sections in this example). Resin 7 is filled into each resin injection section 6. The number and arrangement of the teeth section 3, protrusion section 4, and resin injection sections 6 are not particularly limited and can be provided as appropriate.

[0018] Next, a method for manufacturing the stator core 1 with the above configuration will be described. Figure 2 is a flowchart showing the steps of the manufacturing process for the stator core 1. As shown in Figure 2, the stator core 1 is manufactured through a preparation step, a lamination step, a heat treatment step, a mold setting step, a pressurizing step, a resin injection step, and a recovery step. Of these, the lamination step, the pressurizing step, and the resin injection step are essential steps in this invention. Each step will be described in order below.

[0019] <Preparation Process> First, multiple plate-shaped iron core pieces 11 (see Figure 3) are punched out from electrical steel sheets into a predetermined shape, and a positioning jig 100 (see Figure 3) is prepared.

[0020] <Lamination Process> Figure 3 shows the laminated body 10 mounted on the positioning jig 100. Figure 3(a) is a plan view, and Figure 3(b) is a cross-sectional view taken along the line A-A in Figure 3(a). As shown in Figures 3(a) and (b), the laminated body 10 is formed by laminating multiple iron core pieces 11 while positioning them using the positioning jig 100.

[0021] Here, as shown in Figure 3(a), the core piece 11 has an annular piece 12, teeth pieces 13, protruding pieces 14, through holes 15 and resin injection holes 16. The annular piece 12 is formed to extend in an annular shape around the center O shown in the plan view of Figure 3(a). The teeth pieces 13 are integrally projected in large numbers from the annular piece 12 toward the center O at a predetermined pitch in the circumferential direction of the annular piece 12 on the inner circumference side of the annular piece 12. In the core piece 11, a central opening 20 is formed on the inner side of the numerous teeth pieces 13. The protruding pieces 14 are integrally projected in large numbers (three in this example) from the annular piece 12 on the outer circumference side of the annular piece 12 and are arranged at equal angles (every 120° in this example) in the circumferential direction of the annular piece 12. The through holes 15 are drilled in a circular cross-section so as to penetrate the center of each protruding piece 14. The resin injection holes 16 are drilled in a rectangular cross-section so as to penetrate the annular piece 12. Multiple resin injection holes 16 are arranged around the annular piece 12 at equal angles (60° intervals in this example) (6 holes in this example). The number and arrangement of the teeth 13, protruding pieces 14, and resin injection holes 16 are not particularly limited and can be provided as appropriate.

[0022] As shown in Figures 3(a) and (b), the positioning jig 100 comprises a base portion 101, a main positioning member 102, and a sub-positioning member 103. The base portion 101 is composed of a rectangular plate-shaped member in plan view on which the iron core piece 11 can be placed. The main positioning member 102 is a cylindrical member that can be inserted through the central opening 20 of the iron core piece 11 and is integrally erected in the center of the base portion 101. The sub-positioning members 103 are round bar-shaped members that can be inserted through the through holes 15 of the iron core piece 11 and are arranged in multiples (three in this example) around the main positioning member 102 at equal angles (every 120° in this example), and are integrally erected on the base portion 101 to correspond to each through hole 15 in the iron core piece 11 when the main positioning member 102 is inserted through the central opening 20.

[0023] In the lamination process, a main positioning member 102 is inserted through the central opening 20 of the core piece 11, and each sub-positioning member 103 is inserted through each through-hole 15 of the core piece 11, thereby sequentially laminating multiple core pieces 11 on the base portion 101. The number of layers of core pieces 11 is not particularly limited, but is usually set to about 2 to 30 layers. As a result, multiple core pieces 11 are laminated with their resin injection holes 16 overlapping, forming a laminate 10 having resin injection sections 6 formed by the overlapping resin injection holes 16. In the laminate 10, a cylindrical section 2 is formed by the overlapping of annular pieces 12, a toothed section 3 is formed by the overlapping of toothed pieces 13, a protruding section 4 is formed by the overlapping of protruding pieces 14, and a through-hole 5 is formed by the overlapping of through-holes 15. Furthermore, in the lamination process, it is preferable to perform a roll stacking operation in which multiple core pieces 11 are stacked while relatively shifting the angles of the core pieces 11 to be stacked in the circumferential direction (shifted by 120° in this example). By performing such a roll stacking operation, the thickness deviation of the core pieces 11 can be canceled out, thereby improving the flatness, parallelism, and perpendicularity of the laminate 10.

[0024] <Heat Treatment Process> Next, the laminate 10 mounted on the positioning jig 100 is subjected to heat treatment. Specifically, the laminate 10 is heated to 700-900°C using a heating device (not shown), and then slowly cooled to about 180°C. This removes residual stress from the multiple iron core pieces 11 constituting the laminate 10 before the pressurization process described later. Note that this heat treatment process also serves as the preheating process in the transfer molding method using the transfer molding machine 300 described later. In this way, the manufacturing process can be streamlined.

[0025] Figure 4 is an explanatory diagram of the resin injection process using the transfer mold molding machine 300. Figure 4(a) is a diagram showing the state before resin injection by the transfer mold molding machine 300. Figure 4(b) is a diagram showing the state during resin injection by the same molding machine 300.

[0026] <Mold Setting Process> As shown in Figure 4(a), the laminate 10 that has undergone the heat treatment process is set in the mold 200 for resin filling. Here, the mold 200 comprises a lower mold 201 on which the laminate 10 is placed together with a positioning jig 100, and an upper mold 203 positioned above the lower mold 201. The upper mold 203 has resin flow channels 210 that communicate with each resin injection section 6 in the laminate 10. The mold 200 configured in this way is set in a transfer mold molding machine 300. The transfer mold molding machine 300 comprises a heating upper plate 301 with a heater function having a housing section 301a that communicates with the resin flow channels 210 of the upper mold 203, a plunger 303 that can reciprocate in the housing section 301a, and a heating lower plate 305 with a heater function that supports the lower mold 201 from below.

[0027] <Pressing Process> The laminated body 10, which is placed on the lower mold 201 together with the positioning jig 100 in the mold setting process, is sandwiched between the upper mold 203 and the lower mold 201 in the stacking direction, and the sandwiched laminated body 10 is pressed with a predetermined clamping pressure in the stacking direction. Here, the clamping pressure is 1.0 to 6.0 MPa, preferably 1.1 to 5.6 MPa.

[0028] <Resin Injection Process> As shown in Figure 4(a), in transfer molding using the transfer molding machine 300, a resin tablet 310 made of thermosetting resin (for example, thermosetting epoxy resin) is preheated to about 85°C and then placed into the containment section 301a of the heating plate 301. The placed resin tablet 310 melts due to the heat of the heating plate 301 and becomes molten resin. Then, as shown in Figure 4(b), the plunger 303 pushes out the molten resin 320 in the containment section 301a, and the molten resin 320 is injected into the resin injection section 6 of the laminate 10 via the resin flow path 210 (see Figure 4(a)) at a predetermined resin injection pressure. Here, the resin injection pressure is 2.5 to 6.0 MPa, preferably 2.8 to 5.6 MPa. Furthermore, it is preferable that the resin injection pressure be set to be higher than or equal to the mold clamping pressure. By doing so, the molten resin 320 can be reliably injected into the mold-clamped laminate 10.

[0029] Then, by further heating the heating upper plate 301 and the heating lower plate 305, the filled molten resin 320 is heated to its curing temperature and cured. As a result, adjacent iron core pieces 11 in the lamination direction are fastened together by the cured resin 7 filled in the resin injection section 6.

[0030] <Recovery Process> After opening the mold 200, the laminate 10, i.e., the stator core 1, which is formed by filling the resin injection section 6 with resin 7, is removed together with the positioning jig 100, and the stator core 1 is removed from the positioning jig 100 for recovery.

[0031] In the manufacturing method of the stator core 1 of this embodiment, an excessively large clamping pressure is not applied to the laminate 10 formed in the lamination process, and the balance between the clamping pressure in the pressurization process and the resin injection pressure in the resin injection process is appropriately set. As a result, residual strain in the laminate 10 after the clamping pressure is removed can be suppressed, and iron loss can be kept low.

[0032] Furthermore, in the manufacturing method of the stator core 1 of this embodiment, the residual stress of the multiple iron core pieces 11 constituting the laminate 10 formed by the lamination process is removed in advance by the heat treatment process before the pressurization process is carried out. This makes it possible to further suppress residual strain caused by residual stress and to further reduce iron loss.

[0033] Although the method for manufacturing a stator core of the present invention has been described above based on one embodiment, the present invention is not limited to the configuration described in the above embodiment, and its configuration can be modified as appropriate without departing from the spirit of the invention.

[0034] In the above embodiment, an example was shown in which a heat treatment process is performed after the lamination process but before the pressurizing process. However, the embodiment is not limited to this, and there is also an example in which a heat treatment process is performed before laminating the iron core pieces 11 that have been punched out into a predetermined shape from the electromagnetic steel sheet, and the heat-treated iron core pieces 11 are laminated while being rolled to adjust the thickness (lamination process), and then the mold setting process, pressurizing process, resin injection process, etc. are performed sequentially.

[0035] The following describes examples of the method for manufacturing the stator core of the present invention. However, the present invention is not limited to the following examples.

[0036] <Examples 1-6 and Comparative Examples 1 and 2> Regarding the method for manufacturing a stator core of the present invention, Examples 1-6 and Comparative Examples 1 and 2 were carried out under the clamping pressure and resin injection pressure conditions shown in Table 1 below. The frequency of the change in magnetic flux density of the coil (not shown) formed by winding wire around the teeth portion 3 of the stator core 1 was changed, and the iron loss value was measured at each frequency (100 Hz, 200 Hz, 300 Hz, 400 Hz). The measurement results are shown in Table 1. As will be described later, in Comparative Example 1, when injecting molten resin 320 into the resin injection section 6, molten resin 320 leaked out from between adjacent iron core pieces 11 in the laminate 10. As a result, the molten resin 320 could not be injected and filled into the resin injection section 6, and the stator core 1 could not perform its function, so the iron loss value could not be measured.

[0037]

[0038] As shown in Table 1, Examples 1 to 6, which satisfy the conditions that the clamping pressure is 1.0 to 6.0 MPa and the resin injection pressure of the resin (molten resin 320) is 2.5 to 6.0 MPa, were able to keep the iron loss values ​​at each coil frequency (100 Hz, 200 Hz, 300 Hz, 400 Hz) lower than Comparative Example 2, which does not satisfy these conditions.

[0039] In Comparative Example 1, the molten resin 320 was injected into the resin injection section 6 at a resin injection pressure (11.9 MPa) that was more than twice the upper limit of the resin injection pressure (5.6 MPa) in Examples 1 to 6, compared to the lower limit of the clamping pressure (1.1 MPa) in Examples 1 to 6. As a result, resin leaked out from between adjacent iron cores 11 in the laminate 10, preventing the molten resin 320 from being injected and filled into the resin injection section 6, and thus preventing the stator core 1 from functioning properly.

[0040] In Comparative Example 2, the clamping pressure is set to more than four times the upper limit (5.6 MPa) of the clamping pressure in Examples 1 to 6, and also more than four times the lower limit (2.8 MPa) of the resin injection pressure in Examples 1 to 6. Thus, in Comparative Example 2, when injecting the resin under pressure, an excessively large clamping pressure is applied to the laminate 10 for clamping. As a result, even after the clamping pressure is removed, the residual strain in the laminate 10 becomes large, and as this residual strain increases, the iron loss is greater compared to Examples 1 to 6. Furthermore, while it is possible to inject molten resin 320 into the resin injection section 6 even at the lower limit (2.8 MPa) of the resin injection pressure in Examples 1 to 6, an excessively large resin injection pressure is applied to the resin injection section 6 to inject the molten resin 320, resulting in wasted energy in the resin injection process.

[0041] Therefore, in order to keep iron loss low and reduce the energy costs required for manufacturing the stator core 1, it is important to appropriately set the balance between the clamping pressure in the pressurizing process and the resin injection pressure in the resin injection process, without applying excessively large clamping pressure to the laminate 10 formed in the lamination process.

[0042] <Example 7> Next, the effects when a heat treatment process was performed between the lamination process and the pressurization process were verified. As shown in Table 2 below, with the mold clamping pressure and the resin injection pressure set to the same conditions as in Example 2, after performing the lamination process and before performing the pressurization process, the laminate 10 was heated to 700 to 900 °C and then further subjected to a heat treatment process of gradually cooling to about 180 °C (Example 7). Table 2 shows the measurement results of the iron loss values at each frequency (100 Hz, 200 Hz, 300 Hz, 400 Hz).

[0043]

[0044] As shown in Table 2, in Example 7, the iron loss values at each frequency (100 Hz, 200 Hz, 300 Hz, 400 Hz) could be reduced by about 18 to 25% compared to Example 2. Thus, it was confirmed that by performing a heat treatment process between the lamination process and the pressurization process, the iron loss could be further reduced.

[0045] The present invention can be used in the application of manufacturing a stator core of an electric motor.

[0046] 1 Stator core 6 Resin injection part 7 Resin 10 Laminate 11 Core piece 16 Resin injection hole

Claims

1. A method for manufacturing a stator core, comprising: a lamination step of stacking a plurality of iron core pieces having resin injection holes so that the resin injection holes overlap each other to form a laminate; a pressurizing step of pressurizing the laminate in the lamination direction with a clamping pressure of 1.0 to 6.0 MPa; and a resin injection step of injecting resin into resin injection portions formed in the laminate by the overlapping of the resin injection holes with a resin injection pressure of 2.5 to 6.0 MPa.

2. The method for manufacturing a stator core according to claim 1, wherein the resin injection pressure is set to be equal to or greater than the mold clamping pressure.

3. A method for manufacturing a stator core according to claim 1 or 2, wherein a heat treatment step is performed to remove residual stress before the pressurization step.

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