Method for assembling a stack of sheet metal parts made of an electrical steel strip or sheet to form a laminated core

Abstract

The invention relates to a method for assembling a stack of sheet metal parts (2) made of an electrical steel strip or sheet (5) to form a laminated core (3). To prevent leakage, the invention proposes that stacking takes place such that in the stack (22) all sheet metal parts (2) are arranged with a rotational angle offset, in the circumferential direction (U) of the stack (22), to their respective adjacent sheet metal part (2) or adjacent sheet metal parts (2).

Description

[0001] METHOD FOR PACKAGING SHEET METAL PARTS FROM AN ELECTRICAL STRIP OR SHEET TO FORM A SHEET METAL PACK

[0002] Technical area

[0003] The invention relates to a method for bundling sheet metal parts made of an electrical strip or sheet to form a sheet metal package, in which the sheet metal parts, which each have a particularly thermosetting hot-melt adhesive lacquer layer, in particular a baking varnish layer, over their entire surface on both of their flat sides, are stacked on top of one another in such a way that in the stack of stacked sheet metal parts at least one sheet metal part is arranged offset in the circumferential direction of the stack with respect to an adjoining other sheet metal part in terms of its angle of rotation, and subsequently the stacked sheet metal parts are bonded to one another over their entire surface to form a sheet metal package using their hot-melt adhesive lacquer layers.

[0004] State of the art

[0005] A reduced size and increased power density in laminated laminated cores requires cooling with a coolant, for example, using cooling channels through the laminated core and / or by flowing around it - which requires a gap-free arrangement between the layers, each containing a single sheet metal part or several sheet metal parts arranged side by side. For this purpose, it is known, for example, to bond stacked sheet metal parts together with a hot-melt adhesive layer between the layers. However, due to parameter fluctuations in the stacking process used to produce the laminated core, undesirable impairment of the properties of the hot-melt adhesive layer, or other negative influencing factors, the formation of gaps between the layers cannot be completely ruled out - especially when high fluid pressure is applied to the laminated core.Such laminated cores are therefore often not suitable for use in high-performance applications with intensive cooling requirements.

[0006] In order to compensate for geometric deviations in the laminated core, it is also known to arrange stack sections with several stacked sheet metal parts at an offset angle relative to other sheet metal parts in the circumferential direction of the stack.

[0007] Description of the invention

[0008] It is therefore the object of the invention to modify the design of a laminated core of the type described at the outset in such a way that it can be stably subjected to liquid cooling even with high hydraulic pressure and is thus universally applicable.

[0009] The invention solves the problem by the features of claim 1.

[0010] By stacking the sheets according to the invention in such a way that all sheet metal parts are arranged in the stack at an angle of rotation offset from their respective adjacent sheet metal parts in the circumferential direction, it was surprisingly possible to significantly increase the stability of the sheet stack against fluid penetration between its layers. This angular offset can prevent the formation of large gaps between the adjacent hot-melt adhesive layers – presumably because the angular offset can cause the corrugations of the adjacent hot-melt adhesive layers, which in most cases run parallel, to intersect.This avoids continuous gaps, which can ensure that gap-free laminated cores can withstand high hydraulic pressures, such as those required for internal cooling of a stator and / or rotor laminated core in the high-performance range. This process step also eliminates complex handling steps, which can lead to the reproducible production of leak-free laminated cores.

[0011] The laminated core according to the invention is therefore not only robust and usable even at high hydraulic pressures, but can also be produced cost-effectively and reproducibly.

[0012] A rotation angle offset in the circumferential direction of the stack can be carried out in a handling-friendly manner by rotating the sheet metal part to be stacked on another sheet metal part in the circumferential direction of the stack to achieve the rotation angle offset in the stack.

[0013] Alternatively or additionally, it is also conceivable that the stack is rotated around its circumferential direction.

[0014] Preferably, a rotation angle in the range of 20 to 160 degrees is used for the rotation angle offset in order to be able to reliably interrupt parallel ripples.

[0015] This is especially true when the angle of rotation is 90 degrees.

[0016] A rotation angle offset can be selected more independently of the process if the stacked sheet metal parts are axially symmetrical with respect to a longitudinal axis running through the center of the stack.

[0017] Preferably, the hot-melt adhesive layers of the sheet metal parts to be stacked are in B-condition, which can further facilitate the packaging of leak-free sheet metal packages.

[0018] If each sheet metal part has hot-melt adhesive layers with different Martens hardnesses on its two opposite flat surfaces, this hardness difference can further help smooth out waviness at the interfaces between the hot-melt adhesive layers. This can further improve the leak-free integrity of the laminated core.

[0019] The Martens hardness HM is determined according to DIN EN ISO 14577 using a force penetration depth method at a maximum force Fmax (depth hardness). A pyramid-shaped indenter with a square base (Vickers indenter) is pressed into the test specimen surface with a constant increase in force. The indentation force and indentation depth are measured, and the Martens hardness is calculated from this. The indentation force is increased in the form of an increasing force ramp up to a certain maximum force Fmax within a specified time period in seconds. The maximum force Fmax is determined according to the Bückle rule, which states that the maximum penetration depth of the indenter must not exceed 10% of the coating thickness. A mean curve is calculated from at least five measurements at different points on the surface, from which the characteristic values ​​and standard deviation are calculated.

[0020] Preferably, the sheet metal parts are stacked in such a way that the hot-melt adhesive layers between two adjacent sheet metal parts have different Martens hardnesses. This ensures that a softer hot-melt adhesive layer always contacts a harder hot-melt adhesive layer, which can ensure a more stable, gap-free interface.

[0021] Preferably, the hot-melt adhesive layer on the first flat side of each sheet metal part has a Martens hardness HM in the range of 50 to 700 MPa. Preferably, the hot-melt adhesive layer on the first flat side of each sheet metal part has a Martens hardness HM in the range of 100 to 500 MPa.

[0022] Preferably, the hot-melt adhesive layer on the second flat side of each sheet metal part has a Martens hardness HM in the range of 50 to 700 MPa. Preferably, the hot-melt adhesive layer on the second flat side of each sheet metal part has a Martens hardness HM in the range of 100 to 500 MPa.

[0023] Gap-free interfaces can be more reliably guaranteed if the Martens hardness HM of the hot-melt adhesive layers on the first and second flat sides of each sheet metal part differ by at least 50 MPa. Preferably, the Martens hardness of the hot-melt adhesive layers on the first and second flat sides of each sheet metal part differs by at least 50 MPa.

[0024] The above can be further improved if, during pressurization, at least the hot-melt adhesive with the lower Martens hardness (HM) has a temperature higher than its glass transition temperature. For this purpose, the hot-melt adhesive with the lower Martens hardness preferably has a temperature in the range of 80 to 220 °C.

[0025] The Martens hardness (HM) is preferably determined at a test temperature in the temperature range between the lowest glass transition temperature Tg of the hot melt adhesive layers and the highest glass transition temperature Tg of the hot melt adhesive layers. For example, this temperature is above room temperature, although a range from 45 to below 80 degrees Celsius is conceivable. This further contributes to the compensation of waviness at the interfaces between the hot melt adhesive layers. This is especially true when the sheet metal parts are bonded by thermal activation of the hot melt adhesive layers.

[0026] In addition, the gap-free state between the individual laminations can be achieved by applying pressure to the stacked sheet metal parts in the longitudinal direction L of the stack. This pressure can also more reliably compensate for surface waviness in layers of hot-melt adhesive with different Martens hardnesses (HM). Preferably, the stacked sheet metal parts in the longitudinal direction L of the stack are subjected to pressure in the range of 0.5 to 10 N / mm 2 This preferably occurs under pressure when bonding the sheet metal parts.

[0027] The cooling of the laminated core can be improved if the sheet metal parts have a channel recess and are stacked on top of each other in such a way that their channel recess defines a cooling channel extending in the laminated core, which is arranged eccentrically to a longitudinal axis of the laminated core running through the center of the laminated core.

[0028] The productivity of leak-free sheet stacks can be further increased by using an electrical strip or sheet with hot melt adhesive layers covering the entire surface of both flat sides, and then separating the sheet parts to be stacked from the electrical strip or sheet.

[0029] Short description of the drawing

[0030] The figures show, for example, the subject matter of the invention in more detail using several embodiments.

[0031] Fig. 1 is a schematic view of an apparatus for producing sheet packages from first or second sheet metal parts,

[0032] Fig. 2 is an enlarged partial view of the device according to Fig. 1,

[0033] Fig. 3a is a plan view of the uppermost sheet metal part of a stack shown in Fig. 2 after rotation by a counterholder of the device according to Fig. 1,

[0034] Fig. 3b a top view of the stack with a new separated sheet metal part,

[0035] Fig. 4a a detailed view of Fig. 3b and

[0036] Fig. 4b is an enlarged sectional view along lines l-ll of Fig. 4a.

[0037] Way to implement the invention

[0038] According to the exemplary embodiment shown in Fig. 1, a device 1 for carrying out the method according to the invention is shown schematically. This device 1 serves to bundle laminated sheet metal parts 2 into stacks. For this purpose, an electrical steel strip 5 (or an electrical steel sheet in the case of a sheet) is unwound from a coil 4. This strip has a full-surface hot-melt adhesive layer 8, 9, namely a self-bonding varnish, in the B-stage on both flat sides 6 and 7 (only indicated in Fig. 1). The layer thickness is 4 pm (micrometers) each. The electrical steel strip 5, with a grade NO25-13 Y420, has a strip thickness of 0.3 mm (millimeters).

[0039] For example, it is mentioned that such a thermally activated and thus heat-curing hot-melt adhesive layer (often also referred to as a hot-melt adhesive layer) is known under the term "baking varnish." For example, the hot-melt adhesive can be based on an epoxy resin. The hot-melt adhesive is preferably a bisphenol-based epoxy resin system with a hardener, for example, a dicyandiamide-based one. In particular, the hot-melt adhesive mentioned can be a bisphenol A-epichlorohydrin resin system with dicyanamide as the hardener. This two-stage curing epoxy resin system is in the B-stage on the sheet or sheet metal strip. This makes the partially cross-linked hot-melt adhesive reactive. By applying heat, the hot-melt adhesive in the B-stage reacts further and can thus be converted to the fully cross-linked C-stage – which is also referred to as caking or final curing.Typically, this partially cross-linked hot melt adhesive layer has a thickness of a few micrometers.

[0040] From the adhesive-coated electrical steel strip 5, several sheet metal parts 2 are separated, specifically punched, using a punching tool 11—in the exemplary embodiment, a progressive punching tool. Such punching can—as generally mentioned—be performed by cutting, trimming, notching, trimming, dividing by pressing, etc. Laser cutting is also conceivable, although this is not shown.

[0041] As can be further seen from Fig. 1, the punching tool 11 performs a cutting operation with multiple strokes 12. For this purpose, the cutting edges 13a, 13b in the upper tool 11a of the punching tool 11 interact with the respective dies 14a, 14b of the lower tool 11b of the punching tool 11, thus forming two punching stages 15a, 15b in the punching tool 11.

[0042] With the first cutting edge 13a of the upper tool 11a, several channel recesses 16 are introduced, namely punched, into the electrical steel strip 5—which can be seen in Fig. 1 by the punched-out remnants 17. The channel recesses 16 are provided in the electrical steel strip 5 for each individual sheet metal part 2 in order to enable several cooling channels 18a, 18b through the entire sheet stack 3. A central recess 19 is also introduced to accommodate a rotor shaft (not shown in detail).

[0043] The cutting edge 13b separates the sheet metal part 2 from the electrical steel strip 5. This is done with the help of the punching stage 15b, which punches the sheet metal parts 2 free, and pushes them into a stacking device 20 by the pressure of the upper tool 11a, where they are stacked to form a stack 22. For this purpose, the stacking device 20 has a guide in the lower tool 11b. A counterholder 10, partially shown in Fig. 1, is also provided in the guide.

[0044] The stacking device 20 is actively heated to thermally activate the bonding lacquer layer of the sheet metal parts 2 and to create an adhesive bond, i.e., a material bond, between the sheet metal parts 2. In this way, the hot-melt adhesive lacquer 8 is baked and thus converted from the B-state to the C-state, which laminates the sheet metal parts 2 into a sheet stack 3.

[0045] The cooling channels 18 are each arranged eccentrically to a longitudinal axis L of the laminated core 3 running through the center of the laminated core 3, and thus do not run centrally through the laminated core 3, as can be seen in Fig. 1. In the exemplary embodiments, the longitudinal axis L is the central longitudinal axis of the laminated core 3, i.e. a longitudinal axis L running through the center of the laminated core 2. In the exemplary embodiment, this longitudinal axis L is also, for example, an axis of symmetry of the laminated core. A receptacle 21 in the laminated core 3 runs centrally through the laminated core, since the laminated core 3 is used as a rotor for an electrical machine 100 and the receptacle 21 serves for a rotor shaft. However, it is also conceivable that the laminated core 3 is used as a stator, and the receptacle 19 is provided to accommodate a rotor (not shown).According to the invention, all sheet metal parts 2 in the stack 22 are arranged in the circumferential direction U of the stack 22 with a rotational angle offset from their respective adjacent sheet metal part 2 or adjacent sheet metal parts 2. This is achieved by rotating the stack 22 by a 90-degree rotation angle before another, individual sheet metal part 2 is applied. However, it is also conceivable that the sheet metal part 2 to be newly stacked on top of the other sheet metal parts 2 is rotated in its circumferential direction U, which has not been illustrated in detail.

[0046] This rotation is also unproblematic with respect to the cooling channels 18a, 18b, since the stacked sheet metal parts 2 are axially symmetrical with respect to a longitudinal axis L running through the center M of the stack 21. Thus, even after rotation of the stack, the channel recesses 16 are aligned with the corresponding cooling channels 18a, 18b.

[0047] This angular offset of all sheet metal parts 2 of the stack 22 results in, as shown in Fig. 3b, a reliable interruption of the continuous gap formation between the layers 3a, 3b of the laminated core 3, as shown, for example, in Fig. 2. After the angular offset, the surface wave troughs 23a, 23b, which run almost parallel on each sheet metal part 2, intersect. This reliably interrupts the wave troughs 23a, 23b by superimposing their wave fronts, as shown in Figs. 4a and 4b.

[0048] Leakage through two adjacent hot melt adhesive layers cannot occur, so that the laminated core according to the invention can withstand liquid cooling even with high hydraulic pressure.

[0049] This is further improved by the fact that for each sheet metal part 2, the hot melt adhesive layers 8, 9 on the opposite flat sides 6, 7 have a different Martens hardness HM compared to each other.

[0050] Thus, the hot-melt adhesive layer 8 on the flat side 6 has a Martens hardness HM of 400 MPa (megapascals), whereas the hot-melt adhesive layer 9 on the opposite flat side 7 has a Martens hardness HM of 300 MPa. The hot-melt adhesive layers 8, 9 on the first and second flat sides 7, 8 therefore differ in Martens hardness HM by 100 MPa.

[0051] These Martens hardnesses (HM) were determined according to DIN EN ISO 14577 at room temperature in the range of 23 °C (degrees Celsius) and at 45% relative humidity using a force penetration depth method with a force ramp. A Fischerscope HM 2000 with a Vickers indenter was used as the measuring instrument. The following test parameters were used:

[0052] Maximum force Fmax: 10 mN (millinewtons). As well as continuously increasing the force to this maximum force Fmax, i.e., at time 0, F = 0 mN, and at time 20 s (seconds), the maximum force Fmax = 10 mN is reached.

[0053] Measurement time: 20 seconds

[0054] The penetration depth was chosen at 10% of the layer thickness.

[0055] To ensure a liquid-tight bond, it is particularly advantageous if the different Martens hardnesses HM are measured according to the method described above in accordance with DIN EN ISO 14577 at a higher test temperature, namely in the range from 45 to below 80°C (degrees Celsius), for example at 55°C. The test temperature thus lies in the temperature range between the lowest glass transition temperature Tg, namely 50°C, of ​​hot melt adhesive layer 9, and the highest glass transition temperature Tg, namely 60°C, of ​​hot melt adhesive layer 8.

[0056] In this case, the hot-melt adhesive layer 8 (Tg=60°C) also has a measured Martens hardness HM in the range of 400 MPa (megapascals). In contrast, the hot-melt adhesive layer 9 (Tg=50°C) has a Martens hardness HM of only 50 MPa. The difference (350 MPa) between the hot-melt adhesive layers 8, 9 is therefore more significant, which increases the suitability of the two hot-melt adhesive layers 8, 9 for compensating waviness at their interfaces and thus further improves the reproducibility of the process. The harder property of the hot-melt adhesive layer 8 on the flat side 6 of the sheet metal part 2 is achieved, for example, by using a reaction accelerator. For example, by spraying a reaction accelerator onto this hot-melt adhesive layer 8, which has the same composition as the hot-melt adhesive layers 8, 9. The reaction accelerator can also be contained in the hot melt adhesive layer 8 to achieve the same effect.As a reaction accelerator, for example, 2-ethyl-4-methylimidazole can be used in the case of baking varnish as a hot-melt adhesive layer 8.

[0057] The sheet metal parts 2 are now stacked in such a way that the hot-melt adhesive layers 8, 9 located between two adjoining sheet metal parts 2 have different Martens hardnesses HM.

[0058] In this way, any remaining gaps between the layers 3a, 3b can be reliably closed by forcing the softer hot-melt adhesive layer 9 into the troughs 23a of the harder hot-melt adhesive layer 8.

[0059] This is particularly effective when the softer hot-melt adhesive 9 is heated to a temperature above its glass transition temperature (Tg), namely 120 °C (degrees Celsius). This heating can occur, for example, during the baking of the sheet metal parts.

[0060] In addition, the pressure exerted on the stack 22 in its longitudinal direction L has a beneficial effect on ensuring the interruption of the wave troughs 23a, 23b. This applied pressure amounts to 2 N / mm 2 (Newtons per square millimeter), for example for 60 seconds.

[0061] In general, it is noted that "in particular" can be translated into English as "more particularly." A feature preceded by "in particular" is to be considered an optional feature that can be omitted and thus does not constitute a limitation, for example, of the claims. The same applies to "vorzugsweise," translated into English as "preferably."

Claims

Patent claims:

1. Method for bundling sheet metal parts (2) from an electrical strip or sheet (5) into a sheet stack (3), in which Sheet metal parts (2), each of which has a particularly thermosetting hot-melt adhesive lacquer layer (8, 9), particularly a baked enamel layer, over its entire surface on both of their flat sides (6, 7), are stacked on top of one another in such a way that in the stack (22) of stacked sheet metal parts (2), at least one sheet metal part (2) is arranged at an offset angle of rotation in the circumferential direction of the stack to another sheet metal part (2) adjoining it, and subsequently the stacked sheet metal parts (2) are fully bonded to one another to form the laminated core (3) using their hot-melt adhesive lacquer layers (8, 9), characterized in that they are stacked on top of one another in such a way that in the stack (22) all sheet metal parts (2) are arranged at an offset angle of rotation in the circumferential direction (U) of the stack (22) to their respectively adjoining sheet metal part (2) or adjoining sheet metal parts (2).

2. Method according to claim 1, characterized in that for the rotation angle offset in the stack (22) the sheet metal part (2) to be stacked on another sheet metal part (2) is rotated in the circumferential direction (U) of the stack (22) and / or the stack (22) is rotated about its circumferential direction (U).

3. Method according to claim 1 or 2, characterized in that for the rotation angle offset a rotation angle (4>) in the range of 20 to 160 degrees is carried out.

4. Method according to claim 3, characterized in that the angle of rotation (((>) is 90 degrees.

5. Method according to one of claims 1 to 4, characterized in that the stacked sheet metal parts (2) are axially symmetrical with respect to a longitudinal axis (L) running through the center of the stack (22).

6. Method according to one of claims 1 to 5, characterized in that the hot-melt adhesive lacquer layers (8, 9) of the sheet metal parts (2) to be stacked are in the B-state.

7. Method according to one of claims 1 to 6, characterized in that each sheet metal part (2) has on its two mutually opposite flat sides (6, 7) hot-melt adhesive lacquer layers (8, 9) with mutually different Martens hardnesses (HM), determined according to DIN EN ISO 14577 using a force penetration depth method at a maximum force Fmax (depth hardness).

8. Method according to claim 7, characterized in that the sheet metal parts (2) are stacked in such a way that the hot-melt adhesive lacquer layers (8, 9) located between two adjoining sheet metal parts (2) have different Martens hardnesses (HM) from one another.

9. Method according to claim 7 or 8, characterized in that the hot-melt adhesive lacquer layer (8, 9) on the first and / or second flat side (7, 8) of each sheet metal part (2) has a Martens hardness (HM) in the range from 50 to 700 MPa, in particular from 100 to 500 MPa.

10. Method according to claim 7, 8 or 9, characterized in that the Martens hardnesses (HM) of the hot-melt adhesive lacquer layers (8, 9) on the first and second flat sides (7, 8) of each sheet metal part (3) differ by at least 20 MPa, in particular by at least 50 MPa. 11 . Method according to one of claims 7 to 10, characterized in that the Martens hardness (HM) at a test temperature in the temperature range between the lowest glass transition temperature (Tg) of the hot melt adhesive layers (8, 9) and the highest glass transition temperature (Tg) of the hot melt adhesive layers (8, 9), particularly in the temperature range from 45 to below 80 degrees Celsius.

12. Method according to one of claims 1 to 11, characterized in that the stacked sheet metal parts (2) are placed under pressure (D) in the longitudinal direction L of the stack (22).

13. Method according to claim 12, characterized in that when pressurized, at least the hot melt adhesive (8) with the lower Martens hardness (HM) has a temperature greater than its glass transition temperature (Tg), in particular in the range from 80 to 220 °C.

14. Method according to claim 12 or 13, characterized in that the sheet metal parts (2) stacked on top of one another in the longitudinal direction L of the stack (22) are bonded under pressure (D), in particular in the range of 0.5 to 10 N / mm 2 , be set.

15. Method according to one of claims 1 to 14, characterized in that the sheet metal parts (2) each have at least one channel recess (16) and are stacked on top of one another in such a way that their channel recess (16) delimits a cooling channel (18a, 18b) extending in the sheet metal stack (3), which is arranged eccentrically to a longitudinal axis (L) of the sheet metal stack (3) running through the center (M) of the sheet metal stack (3).

16. Method according to one of claims 1 to 16, characterized in that an electrical strip or sheet (5) is provided with the hot-melt adhesive lacquer layers (8, 9) covering the entire surface of the two flat sides (7, 8), and subsequently the sheet metal parts (2) to be stacked on top of one another are separated from the electrical strip or sheet (5).

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