Method for connecting sheet-metal parts to form at least one lamination stack

Abstract

The invention relates to a method for connecting sheet-metal parts (2) to form at least one lamination stack (3). In order to create especially precise and stable lamination stacks, according to the invention, the sheet-metal parts (2) are adhesively bonded to one another at most in regions in the entry region (18a) of the stacking device (17), in order to avoid deformation, more particularly dishing in, of the sheet-metal parts (2) in the entry region (18a).

Description

[0001] Method for joining sheet metal parts to form at least one sheet metal package

[0002] Technical area

[0003] The invention relates to a method for joining sheet metal parts to form at least one sheet stack, in which an electrical strip or sheet is provided which has a preferably thermally activatable hot-melt adhesive lacquer layer, in particular a baked enamel layer, on at least one, in particular on both, of its flat sides, sheet metal parts are separated from the electrical strip or sheet using a punch and a die of a punching stage, in particular a progressive die, and the sheet metal parts are introduced into an inlet area of ​​a shaft of a stacking device, in which stacking device the sheet metal parts are stacked and are bonded over the entire surface to form the sheet stack in a bonding area of ​​the shaft of the stacking device following this inlet area by activating the hot-melt adhesive lacquer layer.

[0004] State of the art

[0005] In order to bond sheet metal parts to form sheet metal packages, for example by adhesive packaging, which involves punching and packaging sheet metal parts, it is known to punch these sheet metal parts out of an electrical steel strip or sheet coated with a baking varnish and to bond them over the entire surface by thermally activating the baking varnish, which is present as a hot-melt adhesive layer on one flat side of the electrical steel strip and consequently also on the separated sheet metal part. For this purpose, the sheet metal parts are separated using a punching stage, which also uses the punch to insert the separated sheet metal parts into its die, which is connected to an inlet area of ​​a stacking device. In the bonding area of ​​the stacking device following the inlet area, the hot-melt adhesive layers between the sheet metal parts are then activated and the sheet metal parts are thus bonded over the entire surface to form sheet metal packages.To achieve a specified dimensional accuracy on the sheet metal stack, the sheet metal parts are often guided to the wall of the stacking device with no play. In addition to the residual stresses in the sheet metal part that arise during punching, this can disadvantageously lead to cupping of the sheet metal parts in the entry area of ​​the stacking device. This cupping of the sheet metal parts, which can occur either against or in the direction of the stack depending on the process, endangers, among other things, the dimensional accuracy of the subsequently produced sheet metal stacks. In addition, pressure is temporarily applied to the stack when the sheet metal parts are inserted into the stacking device, which can lead to the stack of cupped sheet metal parts bouncing back and forth, with the risk of scratches on them. However, scratches can lead to reduced strength in the fully bonded sheet metal stack - and also impair its electromagnetic properties.

[0006] Description of the invention

[0007] The invention therefore has the object of modifying a method described above for joining sheet metal parts to form sheet metal packages in such a way that sheet metal packages can be produced precisely, reproducibly and without damage.

[0008] The invention solves the problem by the features of claim 1.

[0009] If the sheet metal parts in the entry area of ​​the stacking device are only glued together in specific areas, it can be ensured that the stacked sheet metal parts in the entry area do not bulge, especially in a bowl-like manner - thus maintaining the flat longitudinal extension across the shaft. Even a comparatively small material bond between the sheet metal parts in the entry area of ​​the stacking device can be sufficient to prevent the springing of the stack or cupping known from the prior art - thus preventing damage to the sheet metal parts caused by this. The relative movement of the stacked sheet metal parts can also be reduced in this way. This ensures that the position of the bonded sheet metal parts relative to one another is stabilized - which is beneficial for the quality of the connection when bonded to form a sheet metal stack and also for the dimensional accuracy of the sheet metal stack.Furthermore, the effort required for gluing sections in a specific area is comparatively low and only marginally impacts the process. According to the invention, this gluing in a specific area results in the advantages of a particularly dimensionally accurate laminated core, whose damage-free sheet metal parts – finally bonded together over their entire surface in the bonding area of ​​the stacking device – ensure particularly high stability of the laminated core.

[0010] The above can be further improved if the bonding of the sheet metal parts takes place in regions with respect to their center point at most in the outer third and / or the inner third of their flat side surface.

[0011] Preferably, the sheet metal parts are bonded at specific points in order to maintain, for example, the homogeneity of the full-surface bonding between the sheet metal parts.

[0012] This area-by-area bonding can be achieved, for example, by activating the hot-melt adhesive layer of the electrical steel strip or sheet metal, or of the sheet metal parts. A laser, for example, is suitable for this purpose. This activation preferably takes place before the entry area of ​​a stacking device.

[0013] Alternatively, it is conceivable that adhesive is applied to the electrical strip or sheet or to the sheet metal parts for area-by-area bonding.

[0014] Before applying the adhesive, the hot-melt adhesive layer can be melted at the location designated for the adhesive application on the electrical strip or sheet metal or on the sheet metal parts. This can enhance the durability and strength of the adhesive bond. Alternatively, to achieve this advantage, it is conceivable that the hot-melt adhesive layer is removed at this location, preferably entirely. The use of a laser is conceivable for both of these variants, as this process step can be carried out reliably, precisely, and without contact.

[0015] This adhesive is preferably applied to the lower flat side of the electrical strip or sheet - for example, to keep the stamp free of adhesive residues or to avoid providing recesses on the stamp so that it does not come into contact with the adhesive.

[0016] It is conceivable that after the adhesive has been applied, the electrical strip or sheet is guided to the punching stage without contact in order to avoid stripping off the adhesive.

[0017] The risk of contamination on the punching tool or on the adhesive layer can be further reduced if the adhesive is applied directly before the punching stage.

[0018] The adhesive can preferably be a one-component adhesive. Furthermore, applying a one-component adhesive is technologically simple, which can further simplify the process.

[0019] Preferably, the tensile strength of the area-wise bonding [mPa] > the torsional residual stress [mPa] of the sheet metal part.

[0020] The process can be further simplified if the sheet metal parts are inserted into the die, which adjoins an entrance area of ​​the stacking device's shaft. It is also conceivable for the die to be part of the shaft's entrance area. Preferably, the sheet metal parts are inserted into the die using the punch.

[0021] Brief description of the drawings The figures show, for example, the subject matter of the invention in more detail using an embodiment variant.

[0022] Fig. 1 is a partially open side view of a schematically illustrated device for carrying out a method for joining sheet metal parts to sheet metal packages,

[0023] Fig. 2a is an enlarged partial view of Fig. 1, namely of the stacking device, Fig. 2b is a view of Fig. 2a without the inventive regional bonding of sheet metal parts in the stacking device and

[0024] Fig. 3 is a bottom view of a sheet metal part in the entrance area of ​​the stacking device according to Fig. 2a.

[0025] Way to implement the invention

[0026] According to the exemplary embodiment in Fig. 1, a device 1 for carrying out the method according to the invention is shown schematically. This device 1 serves to bundle individual sheet metal parts 2 into sheet metal packages 3 for electrical machines. For this purpose, an electrical steel strip 5 is unwound from a coil 4. This strip has a full-surface, thermally activated and thus curable hot-melt adhesive layer 8, 9 made of self-bonding varnish on one of its flat sides 6 or 7 or - as shown in Fig. 1 - on both of its flat sides 6, 7. An electrical steel sheet 5 typically comprises an iron-silicon alloy.

[0027] It is generally mentioned that such a thermally activated and thus heat-curing hot-melt adhesive layer 8, 9 or hot-melt adhesive layer is also known as a "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 electrical steel strip 5. 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 into the fully cross-linked C-stage – which is also referred to as caking.Typically, this partially cross-linked hot melt adhesive layer 8, 9 has a thickness of a few micrometers.

[0028] A plurality of sheet metal parts 2 are punched or separated from the bonded lacquer-coated electrical steel strip 5 using a punching tool 10, according to Fig. 1 using a progressive punching tool or progressive composite tool. Such punching can—as generally mentioned—be cutting, cutting off, notching, trimming, dividing by pressing, etc. However, pressing out sheet metal parts 2 is also conceivable. Preferably, the thickness of each sheet metal part 2 is between 0.09 and 0.49 mm (millimeters), and the thickness of each hot-melt adhesive layer 8, 9 is between 2 and 12 pm (micrometers).

[0029] As can also be seen from Fig. 1, the punching tool 10 performs cutting with multiple strokes 11, in which its upper tool 12 interacts with its lower tool 13. For this purpose, the punching tool 10 has several punching stages 14, 15. With a first punch 14a of the pre-processing punching stage 14 on the upper tool 11, the electrical steel strip 5 is pre-machined for free punching, after which sheet metal parts 2 are punched out, i.e. separated, from the electrical steel strip 5 using a second punch 15a of the second and, in the exemplary embodiment, also last punching stage 15 on the upper tool 11. For this purpose, the punches 14a, 15a interact with the respective dies 14b, 15b of the respective punching stages 14, 15 on the lower tool 13. Such a subsequent cutting can be seen in Fig. 1, among other things, in that during pre-processing punching a part 16 is separated from the electrical steel strip 5 in order to prepare the electrical steel strip 5 for the free punching of the sheet metal parts 2.

[0030] The sheet metal parts 2 punched out by means of the punching stage 15 are forced into the die 15b by the pressure of the upper tool 11 or the punch 15a, and subsequently into a stacking device 17 adjoining the die 15b, and thus stacked. For this purpose, the stacking device 17 comprises a shaft 18 and a movable counterholder 19 in the lower tool 13. The shaft 18 can also have a known stack brake as an alternative to or in addition to the counterholder 19.

[0031] The shaft 18 is divided into an entry area 18a and a subsequent bonding area 18b. The counterholder 19 in the lower tool 13 brakes the sheet metal parts 2, whereby these sheet metal parts 2, under the pressure of the upper tool 11 and with the help of the hot-melt adhesive layers 8, 9 present between the sheet metal parts 2, form a physical and / or chemical bond or are joined together – namely by thermal activation of the hot-melt adhesive layers 8, 9 between the sheet metal parts 2 in the bonding area 18b of the shaft 18. This bonds the sheet metal parts 2 together over their entire surface. For this purpose, the hot-melt adhesive layers 8, 9 are brought to a temperature in the range of 180 °C to 250 °C and thus activated.

[0032] For this purpose, the stacking device 17 is actively heated in the bonding area 18b—the stacking device 17 has an electric heater 20 for this purpose. According to the arrangement of the electric heater 20, the shaft 18 is divided into the input area 18a and the bonding area 18b, with the two areas understandably merging into one another.

[0033] In addition, the laminated cores 3 can be subjected to at least one further curing step (not shown) after leaving the stacking device 17 in order to further cure the material connection between the sheet metal parts 2. Furthermore, it is possible to rotate the stacking device 17, for example, to form segmented laminated cores 3 from layers with several sheet metal parts 2 arranged side by side and stacked on top of one another—which is also not shown.

[0034] According to the invention, the sheet metal parts 2 are bonded together in the entry area 18a of the stacking device 17 at most in certain areas on their flat side surfaces 21 - as can be seen in Fig. 2a. The corresponding bonding points can be seen in Fig. 3 on the flat side surfaces 21. This bonding in certain areas ensures that the sheet metal parts 2 do not leave the flat position in the stacking device 17 and do not become dished or bulged, for example due to residual stresses.

[0035] Such a disadvantageous cupping or curvature can be seen, for example, in the sheet metal parts 2a of Fig. 2b. In this case, the curved sheet metal parts 2a also spring when the punch 15a applies pressure to the stack 22 of sheet metal parts 2a in the stacking device 17 – which can complicate bonding in the bonding area 18b of the shaft 18. Furthermore, a precisely formed sheet metal stack 3 cannot be expected due to these curved sheet metal parts 2a deviating from the flat extension.

[0036] The invention with the area-wise bonding avoids this - which makes the process particularly reproducible in the production of defect-free and dimensionally accurate sheet packages 3.

[0037] As can also be seen in Fig. 3, the sheet metal parts 2 are bonded in the outer third 23 and inner third 24 of their flat side surfaces relative to their center point M. According to Fig. 3, the bonding in the outer third 23 is carried out completely all the way around. The bonding in the inner third 24 is carried out at specific points.

[0038] This partial bonding can be achieved by activating the hot-melt adhesive layer 8, 9, for example with a laser, although other means releasing thermal energy are also conceivable.

[0039] This area-by-area bonding can be achieved more quickly and easily by applying an adhesive 25 to the hot-melt adhesive layer 8, 9 of the electrical steel strip 5 and thus to the sheet metal parts 2. This single-component adhesive is applied to the lower flat side 7 of the electrical steel strip 5 using a coating device 26 with nozzles (not shown). The coating device 26 can also include a laser (not shown) to melt the hot-melt adhesive layer at the location on the electrical steel strip or sheet intended for application of the adhesive, or to remove it entirely, before the adhesive is applied. This can be beneficial to the quality and durability of the adhesive bond between the sheet metal parts 2.

[0040] This coating device 26 is arranged immediately before the last punching stage 22, namely in the lower tool 13 according to the embodiment.

[0041] In order to prevent the applied adhesive 25 from spreading over the lower tool 13, after the adhesive 25 has been applied, the electrical strip 5 is guided to the punching stage 22 without contact, as can be seen in Fig. 1.

[0042] In addition, according to Fig. 1, a stacked separating element 27 can be seen, which facilitates the separation of the sheet metal parts 2, which are fully glued or baked together, into sheet metal packages 3.

[0043] 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

P a t e n t a n s p r ü c h e: 1 . Method for joining sheet metal parts (2) to form at least one laminated core (3), in which an electrical strip (5) or sheet is provided which has a preferably thermally activatable hot-melt adhesive lacquer layer (8, 9), in particular a baked enamel layer, on at least one, in particular on both, of its flat sides (6, 7), sheet metal parts (2) are separated from the electrical strip (5) or sheet using a punch (15a) and a die (15b) of a punching stage (15), in particular a progressive die, and the sheet metal parts (2) are introduced into an inlet region (18a) of a shaft (18) of a stacking device (17), in which stacking device (17) the sheet metal parts (2) are stacked and, in a bonding region (18b) of the shaft (18) of the stacking device (17) following this inlet region (18a), are bonded over the entire surface to form the laminated core (3) by activating the hot-melt adhesive lacquer layer (8, 9), characterized in thatthat the sheet metal parts (2) in the entrance area (18a) of the stacking device (17) are glued to one another at most in certain areas in order to avoid a warping, in particular a bowl-like warping, of the sheet metal parts (2) in the entrance area (18a).

2. Method according to claim 1, characterized in that the partial bonding of the sheet metal parts (2) with respect to their center point (M) takes place at most in the outer third (23) and / or in the inner third (24) of their flat side surface (21).

3. Method according to claim 1 or 2, characterized in that the bonding of the sheet metal parts (2) takes place in a point-by-point manner.

4. Method according to one of claims 1 to 3, characterized in that for the region-wise bonding, the hot-melt adhesive layer (8, 9) of the electrical strip (5) or sheet or of the sheet metal parts (2) is activated, in particular by a laser.

5. Method according to one of claims 1 to 4, characterized in that for the partial bonding, adhesive (25) is applied to the electrical strip (5) or sheet or to the sheet metal parts (2).

6. Method according to claim 5, characterized in that before the application of the adhesive (25), the hot-melt adhesive lacquer layer (8, 9) is melted or, in particular completely, removed at the location intended for the application of the adhesive (25) on the electrical strip (5) or sheet or the sheet metal parts (2), in particular with the aid of a laser.

7. Method according to claim 5 or 6, characterized in that the adhesive (25) is applied to the lower flat side (7) of the electrical strip (5) or sheet.

8. Method according to claim 7, characterized in that after the application of the adhesive (25) the electrical strip (5) or sheet is guided to the punching stage without contact.

9. Method according to one of claims 5 to 8, characterized in that the adhesive (25) is applied directly before the punching step.

10. Method according to one of claims 5 to 9, characterized in that the adhesive (25) is a one-component adhesive.

11. Method according to one of claims 1 to 10, characterized in that the tensile strength of the regional bonding [mPa] > the torsional residual stress [mPa] of the sheet metal part (2).

12. Method according to one of claims 1 to 11, characterized in that the sheet metal parts (2), in particular with the aid of the punch (15a), are introduced into the die (15b) which is connected to an inlet region (18a) of the shaft (18) of the Stacking device (17) or which is part of the entrance area (18a) of the shaft (18).

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