Method for producing a sheet core, clamping system for a sheet stack and device for producing a sheet core

Abstract

Method for producing a stacked grain-oriented sheet core (O) for a transformer from a sheet stack (W), clamping system (9) and apparatus (1); the method provides for preparing a sheet stack (W) comprising one or more sheets (P) made of grain-oriented electrical steel; said sheet stack (W) is grabbed by a clamping system (9); the sheet stack (W) is placed on an assembly table (7; 7I; 7II; 7III; 7IV); during the placing step, the sheet stack (W) falls in free fall along a path (tx1).

Description

[0001] Cross-references to related applications

[0002] This patent application claims priority to Italian patent application No. 102020000003880, filed on February 25, 2020, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This patent application relates to a method for producing sheet cores, a clamping system for sheet stacking, and an apparatus (plant) for producing sheet cores, particularly a method for producing sheet cores of the type of grain-oriented sheet, a clamping system for sheet stacking, and an apparatus for producing sheet cores. Background Technology

[0004] For example, sheet cores with grain-oriented sheets are used, for instance, in the manufacture of power transmission and distribution transformers, i.e., transformers with a power output greater than 10 kVA.

[0005] Typically, the core of a grain-oriented sheet includes a lower yoke, an upper yoke, and multiple posts, each post connecting the lower yoke to the upper yoke.

[0006] The core of a grain-oriented sheet is a large and relatively heavy core, requiring suitable production equipment and handling facilities. It should be noted that, for example, for power distribution or electrical applications, the core column can have lengths ranging from 0.5 to 5 meters.

[0007] To manufacture sheet cores, it is known to produce and stack multiple sheets made of grain-oriented electrical steel through a process that essentially comprises three steps:

[0008] - We offer multiple strips of different widths made of grain-oriented electrical steel;

[0009] - Cut the strip into different lengths to obtain multiple metal sheets with different widths and / or lengths;

[0010] - Assemble metal sheets to form a core by manufacturing stacked sheets, each of which corresponds to a yoke or pillar.

[0011] The material typically used to manufacture sheet cores, namely grain-oriented electrical steel, is a sufficiently thick material that cannot be excessively bent, otherwise it would lead to degradation of the silicon composition. Therefore, sheet cores are manufactured by combining and stacking multiple flat sheets that have never been bent.

[0012] Most importantly, special care must be taken in handling the sheets to ensure coplanarity and prevent unwanted creases or indentations.

[0013] Downstream of the sheet cutting station where sheets are cut from steel strip, sheet stacks are known to be automatically formed. Such sheet stacks can be formed from a variable number of sheets, according to the plan.

[0014] For example, a sheet stack can be formed by stacking ten sheets together.

[0015] Each sheet stack is then manually or via a clamping system gripped and conveyed on the assembly table, where it is combined with other sheet stacks to form a core. Typically, the assembly table is horizontal, i.e., parallel to a horizontal support plane. The assembly table usually has reference pins, each of which protrudes vertically from the assembly table at a corresponding predetermined position.

[0016] Typically, each sheet has a hole at a predetermined location. Therefore, each sheet stack has one or more slots formed by connecting the corresponding holes of all the stacked sheets to form the sheet stack.

[0017] In order to place the sheet stacks on the assembly table, each pin of the assembly table must pass through the corresponding slot of the sheet stack.

[0018] Therefore, during the conveying and stacking of sheets on the assembly table, it is necessary to ensure the alignment of the sheets forming the stack to prevent unwanted jamming or deformation of the sheets during sliding on the corresponding pins.

[0019] Typically, the conveying and positioning (centering and insertion on pins) of sheet stacks is done manually by the operator.

[0020] However, the downside of doing this is that it requires a longer processing time and specialized operators to handle the sheet stacking and core production operations.

[0021] It is also known to use automated clamping systems to move and produce sheet stacks.

[0022] However, known types of clamping systems suffer from excessive rigidity, thus failing to compensate for any misalignment between the pins and the holes in the sheet. This can cause jamming and potentially damage the sheet, reducing production speed and increasing costs (due to discarding and replacing damaged sheets). Summary of the Invention

[0023] The object of this invention is to provide a clamping system that allows for overcoming the aforementioned drawbacks. In particular, the object of this invention is to provide a clamping system that allows for the automatic and accurate production of cores without jamming or interruption.

[0024] According to the present invention, a method for producing sheet cores is provided, as claimed in the appended claims.

[0025] According to the present invention, a clamping system is provided as claimed in the appended claims.

[0026] According to the present invention, an apparatus for producing sheet cores of transformers is provided, as claimed in the appended claims. Attached Figure Description

[0027] The invention will now be described with reference to the accompanying drawings, which illustrate some examples of non-limiting embodiments of the invention, wherein:

[0028] - Figure 1A This is a schematic diagram of a stacked sheet core with grain-oriented sheets used in power transmission and distribution transformers;

[0029] - Figure 1B An example of a grain-oriented sheet according to the present invention is shown schematically;

[0030] - Figure 2 This is a plan view of the device according to the present invention;

[0031] - Figure 3 This is a perspective view of the clamping system according to the present invention;

[0032] - Figure 4 It is flipped Figure 3 A three-dimensional view of the clamping system;

[0033] - Figure 5 This is a perspective view showing details of the clamping system according to the present invention;

[0034] - Figure 6 and Figure 7 They are Figure 5 Detailed side and bottom views;

[0035] - Figure 8 and Figure 9 These are perspective views with corresponding different angles showing further details of the clamping system according to the present invention;

[0036] - Figures 10 to 18 The clamping system according to the invention is shown in corresponding different operating configurations;

[0037] - Figure 19 A variation of the device according to the invention is shown. Detailed Implementation

[0038] exist Figure 1AIn this diagram, O represents the entire sheet core, specifically for use in power distribution or power transformers, i.e., transformers for power transmission and distribution, i.e., transformers with a power rating greater than 10 kVA. The core O comprises, in a known manner, a lower yoke GI and an upper yoke GS that are laterally connected to each other by a plurality of posts C. According to the illustrated example, there are three posts: two lateral posts indicated by C1 and C3, and a central post indicated by C2. Each yoke GI, GS is connected to the corresponding end of each post C1, C2, and C3.

[0039] Each yoke GI, GS and each pillar C1, C2, C3 is composed of multiple grain-oriented sheets P stacked together. The sheets P are typically made of grain-oriented electrical steel. Advantageously, the sheets P are initially obtained from a single strip B, which is then appropriately processed (e.g., stamped and / or cut).

[0040] The connection between each yoke GI, GS and each post C1, C2 and C3 is achieved through a shaped joint, particularly a herringbone joint.

[0041] according to Figure 1B In the example shown, sheet P may have holes J arranged in predetermined positions. In this case, as... Figure 1A As shown, the core O obtained from this type of sheet P has grooves H, each of which is configured to accommodate a corresponding structural bolt F during use.

[0042] In a known manner, each groove H is formed by joining mutually aligned holes J of the corresponding laminated sheet P. According to a variant not shown, sheet P has no holes J; in this case, core O has no groove H.

[0043] The apparatus 1 includes a supply system 2 configured to supply at least one strip B of ferromagnetic metallic material, particularly strip B made of grain-oriented electrical steel. Preferably, the supply system 2 of the apparatus 1 is similar in type to that shown in International Patent Application No. WO2018 / 220585A1, the teachings of which are incorporated herein by reference for illustrative purposes. In particular, the supply system 2 is configured to supply multiple strips B in parallel, thereby eliminating downtime required for changing the dimensions of the strips.

[0044] The apparatus 1 also includes a processing unit 3, shown schematically in a known manner, which in turn has one or more stamping and / or cutting tables α, for example, making holes J (if provided) along the stamping and / or cutting tables α and further processing each sheet P to have a predetermined shape and separating each sheet P from the strip B.

[0045] The device 1 also includes a stacking unit 4, which is arranged downstream of the processing unit 3 in the forward direction v relative to the sheet P.

[0046] At stacking unit 4, multiple sheets P are stacked on the corresponding loading plane 5 to form sheet stack W.

[0047] Typically, a sheet stack W comprises approximately ten overlapping sheets P. Without loss of generality, the number of sheets P in a sheet stack W can vary, and it is also possible that the sheet stack W can be formed from a single sheet P.

[0048] Advantageously, the stacking unit 4 includes an assembly unit 6 configured to move each sheet stack W from its corresponding loading plane 5 onto the assembly table 7. In particular, the assembly unit 6 is configured to place each sheet stack W onto the assembly table 7 in a predetermined order.

[0049] Specifically, assembly unit 6 is configured to form yokes GI, GS and pillars C1, C2 and C3 on assembly stage 7, thereby forming core O.

[0050] according to Figure 2 In the example shown, stacking unit 4 includes two parallel loading planes 5I, 5II. According to variations not shown, device 1 may include multiple loading planes 5, different from those shown. For example, device 1 may include a single loading plane 5 or three or more loading planes 5. Advantageously, the parallel presence of multiple loading planes 5I, 5II allows for ensuring production continuity and eliminating (or significantly reducing) waiting time during the formation of sheet stacks W. In this way, advantageously, sheet stack W can be formed while assembly unit 6 picks up and places another sheet stack W that has already been formed.

[0051] Each loading plane 5I, 5II is configured to receive a single sheet P leaving the processing unit 3 by falling, thereby forming a corresponding sheet stack W (in Figures 10 to 18 (Illustrated schematically).

[0052] according to Figure 2 The example shown includes an assembly unit 6 and four assembly tables 7 (in...). Figure 2 In the following text, assembly stations 7 (identified by Roman numerals I-IV) are evenly distributed around assembly units 6. In this way, a single assembly unit 6 can simultaneously form multiple cores O, each core O on its respective assembly station 7. Optionally, device 1 may include a plurality of assembly units 6 and assembly stations 7, different from the one illustrated.

[0053] Without loss of generality, and for illustrative purposes only, according to Figure 19 The variant shown includes two parallel assembly units 6, each configured to grip a stack of sheets W from either loading plane 5I or 5II of the supply unit. Figure 19As shown, each assembly unit 6I, 6II is configured to supply sheet stacks W to any assembly station 7 among multiple assembly stations 7I-7IV. According to Figure 19 In the example shown, there are four assembly stations 7I-7IV and two assembly units 6. The number of assembly stations 7 may vary depending on the variant not shown.

[0054] Each assembly stage 7 is horizontal, i.e., parallel to the horizontal support plane. When the core O to be manufactured has a groove H, the corresponding assembly stage 7 has a vertical reference pin 13 (in...). Figures 15 to 19 (As shown in detail below), in order to place the sheet stack W onto the assembly table 7, the corresponding reference pin 13 needs to pass through the slot H of the sheet stack W (it should be noted that if slot H exists, the number of slots H is typically two for each sheet stack W). In a known manner, the assembly table 7 has multiple housings k, each of which is configured to accommodate the corresponding reference pin 13. Depending on the type of core O to be manufactured, the reference pin 13 is mounted in the corresponding predetermined housing k. This operation is typically performed manually by the operator during the preparation step of the assembly table 7. Advantageously, the parallel existence of multiple assembly tables 7 allows the preparation step (i.e., setting the reference pin 13 onto the assembly table 7) to be performed during the masking time.

[0055] Advantageously, the assembly unit 6 includes a conveying system 8 and a clamping system 9. The conveying system 8 is configured to move the clamping system 9 in space according to a predetermined trajectory.

[0056] according to Figure 2 and Figure 19 In the example shown, the conveyor system 8 is an anthropomorphic robot. According to variations not shown, the conveyor system 8 may be a Cartesian machine or an equivalent system.

[0057] Advantageously, the clamping system 9 is configured to grip the sheet stack W from the loading plane 5 and place it in a predetermined position on the assembly table 7. Advantageously, the clamping system 9 is configured to allow proper alignment and positioning of the sheet stack W. Advantageously, the clamping system 9 is configured to allow the sheet stack W to slide properly on the corresponding reference pin 13 (if present), in this way preventing the sheet P from jamming and being damaged.

[0058] like Figures 3 to 9 As shown in more detail, the clamping system 9 further includes a support assembly 12 configured to secure the clamping system 9 to the conveying system 8. The clamping system 9 also includes an electromagnetic system 10 (in... Figures 5 to 7 (shown in more detail below) and support system 11 (in Figure 8 and Figure 9 (As shown in more detail below). As will be better explained below, the electromagnetic system 10 is configured to selectively generate an electromagnetic field E (in... Figures 11 to 14(Schematally shown in the diagram) The electromagnetic field E is adapted to attract the entire sheet stack W during use, and the support system 11 is configured to adjacently support the entire sheet stack W and facilitate positioning the sheet stack W above the assembly table 7, particularly above the reference pin 13. Figures 15 to 18 ).

[0059] like Figure 3 As shown, the support assembly 12 includes a flange 14 with a symmetry axis X and a robotic arm 15.

[0060] Flange 14 is configured to be fixed to the free flange end (of a known type and not shown) of the conveying system 8 in a known manner and not shown (typically by bolts). For example, flange 14 is configured to be fixed to the flanged free end of an anthropomorphic robot.

[0061] The robotic arm 15 is connected to the flange 14 via a proximal end β. The robotic arm 15 is a rigid body and is substantially parallel to the axis of symmetry X of the flange 14. The robotic arm 15 also has a flanged proximal end γ.

[0062] Electromagnetic system 10 is connected to robotic arm 15. According to the example shown, electromagnetic system 10 is fixed in a predetermined position relative to robotic arm 15. In the example shown, electromagnetic system 10 is fixed to the flanged distal end γ of robotic arm 15.

[0063] According to a variant not shown, the electromagnetic system 10 and the robotic arm 15 are connected to form a reciprocating movable system.

[0064] Advantageously, the clamping system 9 includes a transport assembly 16 that connects the support system 11 to the support assembly 12. According to the example shown, the clamping system 9 includes a drive assembly 16 configured to move the support system 11 relative to the robotic arm 15.

[0065] According to the example shown in the figure, the drive assembly 16 includes a vertical drive unit 18 and a horizontal drive unit 19. The vertical drive unit 18 is configured to reciprocate the robotic arm 15 and the support system 11 along the axis of symmetry X. The horizontal drive unit 19 is configured to reciprocate the robotic arm 15 and the support system 11 along the axis Z. The axis Z is transverse, and in particular perpendicular to the axis of symmetry Z.

[0066] The vertical drive unit 18 includes two parallel cylindrical members, hereinafter referred to as the left vertical cylindrical member 18I and the right vertical cylindrical member 18II, respectively. The robotic arm 15 is positioned between the left vertical cylindrical member 18I and the right vertical cylindrical member 18II of the vertical drive unit 18.

[0067] The horizontal drive unit 19 includes two parallel cylindrical members, hereinafter referred to as the left horizontal cylindrical member 19I and the right horizontal cylindrical member 19II, respectively. The robotic arm 15 is located between the left horizontal cylindrical member 19I and the right horizontal cylindrical member 19II of the horizontal drive unit 19.

[0068] Advantageously, the central position of the robotic arm 15 relative to both the vertical drive unit 18 and the horizontal drive unit 19 ensures the rigidity and stability of the clamping system 9 (in this respect, it is important to emphasize the size and weight that the sheet stack W can achieve).

[0069] according to Figures 5 to 7 As shown, the electromagnetic system 10 includes a support 20 having a longitudinal axis Y substantially transverse to the longitudinal axis X of the robotic arm 15. The support 20 is configured to adhere at one or more points to a flat surface, particularly a surface flat against a horizontal plane π, such as a loading plane 5 or an assembly table 7. Figure 10 The support 20 has a plurality of windows 21 distributed along the longitudinal axis Y. The shape and / or size and / or position of each window 21 along the axis Y depends on the type of assembly table 7 on which the clamping system 9 must place the sheet stack W. In particular, each window 21 is configured to accommodate a reference pin 13 in use, the reference pin 13 protruding from the corresponding housing k of the assembly table 7.

[0070] The electromagnetic system 10 also includes a plurality of electromagnets 22, each of which is fixed to the support 20 so as to face the sheet stack W in use. Each electromagnet 22 is configured to be electrically activated or deactivated to selectively generate an electromagnetic field E capable of attracting the sheet stack W. When an electromagnet 22 is electrically activated, it generates an electromagnetic field E. When an electromagnet 22 is deactivated, the electromagnetic field E is interrupted. The number and arrangement of the electromagnets 22 depend on the shape and size of the type of sheet stack W to be processed.

[0071] like Figure 8 and Figure 9 As shown, the support system 11 is configured relative to the electromagnetic system 10 from the rest position X1 ( Figure 3 , Figure 4 , Figure 10 , Figure 11 Selectively move to the grab position X2 ( Figures 13-17 ),vice versa.

[0072] The support system 11 is comb-shaped, comprising a plurality of parallel and mutually parallel fork teeth 23, i.e., rods (or equivalent structural elements). The support system 11 also includes a connecting structure 24 that supports all the fork teeth 23 such that the fork teeth 23 are substantially parallel to each other on the virtual plane πi. The connecting structure 24 is fixed to the drive assembly 16. Therefore, the drive assembly 16 can change the relative position between the support 20 and the fork teeth 23 via the connecting structure 24.

[0073] According to the example shown, the connection structure 24 is comb-shaped, and the support system 10 as a whole has a structure similar to a rake.

[0074] Adjacent fork teeth 23 are spaced apart by corresponding spaces 26. The size and distribution of the fork teeth 23 and spaces 26 depend on the type of assembly table 7 to which the clamping system 9 must cooperate.

[0075] According to the example shown, each fork tooth 23 is thin, i.e., flat, so as to have two relevant dimensions (width and length) and a reduced thickness (a few millimeters). Each fork tooth 23 has two substantially flat and parallel side surfaces, which are designated hereinafter as upper 25I and lower 25II, respectively. It is understood that the terms "lower" and "upper" are used with reference to... Figure 8 The clamping system 9 shown is used in the following orientation. The lower surface 25II of each fork tooth 23 is coplanar with the virtual plane πi.

[0076] The following describes a method for producing the sheet core O according to the present invention.

[0077] In use, the stacking unit 4 forms a sheet stack W above the corresponding loading plane 5 in a known but not shown manner. It should be noted that the method for producing core O according to the invention can also be applied to the conveying of a single sheet P. In this case, the sheet stack W should be understood as being formed from a single sheet P.

[0078] The sheet stack W can be formed from sheet P having holes J. When the sheet stack W has holes J (typically there are two holes J aligned with each other at a predetermined distance), the stacking unit 4 forms the sheet stack W such that the holes J of the sheet P are aligned to form corresponding grooves H. Alternatively, the sheet stack W can be formed from sheet P without holes (this variation is not shown in the figure).

[0079] Before gripping the sheet stack W, the support system 11 is in (optionally) a stationary position X1, so that the electromagnetic system 10, in particular the support 20, can directly face and adhere to the sheet stack W.

[0080] Then, the conveying system 8 moves the clamping system 9 to position the support 20 of the electromagnetic system 10 above and in contact with the sheet stack W. Preferably, the support 20 is aligned with a predetermined virtual line and references the positioning of the sheet stack W on the loading plane 5 and / or the arrangement of the slots H. The relative positions between the sheet stack W and the support 20 are known.

[0081] When the sheet stack W is provided with slots H, advantageously, the support 20 is positioned such that each slot H of the sheet stack W is centered (or falls into the corresponding window 21) by means of the corresponding window 21 of the support 20. In this way, advantageously, as will be better explained below, the pin 13 can be inserted and passed through the corresponding slot H and the corresponding window 21 of the support 20 without encountering any obstruction. Figure 16 and Figure 17 ).

[0082] When the support 20 comes into contact with the sheet stack W, the electromagnetic system 10 is activated, thereby generating an electromagnetic field E.

[0083] Advantageously, the electromagnet 22 of the support portion 20 is in contact with the sheet stack 20. Advantageously, the activation of each electromagnet 22 of the electromagnetic system 10 can be selected and adjusted according to the type of sheet stack W in contact with the support portion 20.

[0084] The electromagnetic system 10 generates an electromagnetic field E to attract the sheet stack W and cause the sheet stack W to adhere to one or more electromagnets 22.

[0085] In this regard, it should be emphasized that the sheet stack W according to the present invention can have a very large size and weight, with a length of approximately 0.5 to 5 meters.

[0086] When the electromagnetic device 10 is activated, the sheet stack W is adhered to the support portion 20 almost immediately by magnetic attraction.

[0087] Once the sheet stack W adheres to the support 20 under the action of the electromagnetic field E, the conveying system 8 will move the clamping system 9 from the loading plane 5 ( Figure 12 The clamping system 9 is raised and moved along a predetermined trajectory t. Figure 13 In order to move the sheet stack W from the loading plane 5 to the assembly table 7.

[0088] During the movement of the sheet stack W by the clamping system 9, the drive assembly 16 changes the relative position between the support system 11 and the support 20, causing the support system 11 to move from the rest position X1. Figure 11 ) to grab position X2 ( Figure 13 ).

[0089] According to the example shown, the support system 11 consists of a horizontal drive unit 19 ( Figure 12 It moves along axis Z and is moved along axis X by vertical drive unit 18. According to a variant not shown, support 20 moves relative to support system 11.

[0090] The change in the relative position between the support 20 and the support system 11 can occur during the operation or shutdown of the clamping system 9.

[0091] At the gripping position X2, the fork 23 is located below the support 20 so as to receive and support the sheet stack W placed by the electromagnetic system 10.

[0092] The clamping system 9 is positioned above the assembly table 7, depending on the sheet stack W carried by the clamping system 9 and forming the corresponding part of the core O.

[0093] When the sheet stack W has slots H, the clamping system 9 is positioned such that each slot H is aligned with the corresponding pin 13. In particular, the clamping system 9 is positioned such that the virtual plane πi on which the fork 23 of the support system 11 rests is substantially aligned with the tip of the pin 13.

[0094] Once the clamping system 9 is positioned above the corresponding location on the assembly table 7, the sheet stack W is placed by the electromagnetic system 10 and falls freely along the path tx1.

[0095] Advantageously, in order to place the sheet stack W onto the assembly table 7, the electromagnetic system 10 is disconnected to allow the sheet stack W to fall freely. Once the electromagnetic system 10 is disconnected, the sheet stack W falls onto the fork 23 of the support system 11 due to gravity g. Advantageously, the sheet P of the sheet stack W falls freely along the path tx1 (the distance along the axis X between the support 20 and the virtual plane πi, according to the illustrated example), especially the fact that it falls freely at the tip of the pin 13 (i.e., the initial path) allows for compensation of small alignment errors and ensures that the pin 13 passes through all the sheets P of the sheet stack W without jamming or forming creases on the sheets P. The path along which the sheet stack W can fall in a free-fall manner is variable and depends on the size of the sheets.

[0096] Free fall refers to the motion of an unrestrained object caused by gravity.

[0097] Then, the clamping system 9 is operated along the linear trajectory tx2 until the fork 23 is brought above the assembly table 7. Figure 16 Without making contact, the linear trajectory tx2 is basically parallel to pin 13 (especially the linear trajectory tx2 descends vertically, such as...). Figure 15 (As shown).

[0098] During movement along the linear trajectory tx2, the clamping system 9 can vibrate and / or make small possible movements and / or make continuous movements in any direction. In this way, advantageously, the sheet P in the sheet stack W is prevented from adhering to / being jammed by the pin 13.

[0099] Once above the assembly table 7, the moving support system 11 is used to place the sheet stack W. Advantageously, the sheet stack W is placed onto the assembly table 7 by descent (through a short path that is substantially a few millimeters thicker than the fork teeth themselves).

[0100] The same operation is repeated on different sheet stacks W at different positions on assembly table 7 until core O is produced.

[0101] When there is no hole J in sheet P of sheet stack W, clamping system 9 only activates electromagnetic system 10 to grip, move and place sheet stack W.

[0102] Advantageously, the methods and clamping systems of the above type allow for the automated transport of sheet stacks W of considerable size and the production of sheet stacks W on assembly table 7, thereby preventing problems of deformation or jamming when the sheet stacks W pass through the corresponding pins 13 of assembly table 7.

[0103] Advantageously, the methods and clamping systems of the type described above allow for the automatic transport of sheet stacks W of considerable size and the correct production of sheet stacks on the assembly table 7, even when the slot H is not aligned with the center of gravity of the sheet stack W.

[0104] In fact, in this case, the above-described method and clamping system 9 prevent the sheet P from getting stuck in the pin 13 of the assembly table 7.

[0105] Advantageously, the clamping system 9 of the above type can also be used to transport sheet stacks W without slots H, in which case only the electromagnetic system 10 is activated. Thus, the clamping system 9 ensures maximum adaptability and the possibility of transporting a large number of different sheet stacks W that differ from each other in type (with or without slots H) and size.

Claims

1. A method for producing a stacked sheet core (O) of a transformer by sheet stacking (W); the method comprising the following steps: - Provide a sheet stack (W), the sheet stack (W) comprising one or more sheets (P) made of grain-oriented electrical steel; - The sheet stack (W) is gripped by the clamping system (9); - Place the stack of sheets (W) on the assembly table (7; 7I; 7II; 7III; 7IV); The method is characterized in that, during the placement step, the sheet stack (W) falls freely along the path (tx1), wherein the clamping system (9) includes: an electromagnetic device (10) configured to selectively generate an electromagnetic field (E) adapted to attract the sheet stack (W) when in use; and a support device (11) configured to support the sheet stack (W); wherein, during the gripping step, the electromagnetic device (10) is activated to attract the sheet stack (W), wherein, during the placement step, the support device (11) is located between the sheet stack (W) and the assembly table (7; 7I; 7II; 7III; 7IV); wherein the placement step includes disconnecting the electromagnetic device (10) so that the sheet stack (W) falls freely onto the support device (11).

2. The method according to claim 1, wherein the assembly table (7; 7I; 7II; 7III; 7IV) is horizontal, i.e., parallel to the support plane, and includes one or more pins (13), each of which protrudes perpendicularly to the assembly table (7; 7I; 7II; 7III; 7IV); wherein the support device (11) is comb-shaped, including two or more forks (23); the support device (11) has a space (26) between two adjacent forks (23); wherein, During the placement step, the support device (11) slides vertically along the pin (13).

3. The method according to claim 2, wherein, During the placement step, the support device (11) vibrates and / or moves continuously in one or more directions.

4. A clamping system for producing a stacked sheet core (O) for a transformer by means of a stack (W) comprising one or more sheets (P) made of grain-oriented electrical steel; the clamping system (9) includes an electromagnetic device (10) configured to selectively generate an electromagnetic field (E) adapted to attract and / or place the stacked sheet (W) in use; the clamping system (9) includes a support device (11) configured to support the stacked sheet (W), wherein, The electromagnetic device (10) and the support device (11) are reciprocally movable from a rest position (X1) to a gripping position (X2) and vice versa; wherein the support device (11) is comb-shaped and includes two or more forks (23); the support device (11) has a space (26) between two adjacent forks (23); the clamping system (9) grips the sheet stack (W) and places the sheet stack (W) on an assembly table (7; 7I; 7II; 7III; 7IV), wherein the forks (23) are configured such that in the gripping position (X2), the forks (23) are between the electromagnetic device (10) and the assembly table (7; 7I; 7II; 7III; 7IV).

5. The clamping system according to claim 4, wherein, The electromagnetic device (10) is configured such that in the rest position (X1), the electromagnetic device (10) is in direct contact with the sheet stack (W).

6. An apparatus for producing stacked sheet cores (O) for transformers; the apparatus (1) includes a supply unit configured to provide a sheet stack (W) comprising one or more sheets (P); the apparatus includes a clamping system (9) according to claim 4 and is configured to perform the method according to claim 1.

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