METHOD FOR STACKING SHEET METAL PARTS MADE FROM AN ELECTRICAL STEEL STRIP OR SHEET TO FORM LAMINATION STACKS

Abstract

The subject of the disclosure is a method for stacking sheet metal parts (4) composed of an electrical steel strip (3) or sheet in order to form lamination stacks (2), each with a stack height (hp) within a tolerance range (Δh) from a predetermined desired stack height (hs).

Claims

1. A method for stacking sheet metal parts made from an electrical steel strip or sheet in order to form lamination stacks each having a stack height within a tolerance range from a predetermined desired stack height, comprising: stacking the sheet metal parts, which have a hot-melt adhesive varnish layer on at least one of their flat sides, onto one another, preheating the hot-melt adhesive varnish layers of the stacked sheet metal parts to a first temperature, which is above a glass transition temperature of the hot-melt adhesive varnish and below a baking temperature of the hot-melt adhesive varnish, and in this preheated state, putting the hot-melt adhesive varnish layers of the stacked sheet metal parts under pressure, then determining the stack height of the individual lamination stacks composed of the stacked sheet metal parts using a measuring procedure and when this determined stack height falls below the tolerance range, placing at least one additional sheet metal part onto an end surface of the relevant lamination stack so as to adjust the stack height to a height within the tolerance range from the predetermined desired stack height, and then finally heating the hot-melt adhesive varnish layers of each lamination stack to a second temperature, which is greater than or equal to the baking temperature of the hot-melt adhesive varnish, and as a result, the sheet metal parts of each lamination stack are baked onto one another by the hot-melt adhesive varnish layers.

2. The method according to claim 1, wherein at least one sheet metal part is placed onto the hot-melt adhesive varnish layer on the lamination stack and/or the at least one sheet metal part is heated before it is placed onto the lamination stack and/or is placed onto the hot-melt adhesive varnish layer under pressure.

3. The method according to claim 1, wherein the first temperature is in a range from 90° C. to 150° C., and/or the second temperature is in a range from 180° C. to 250° C.

4. The method according to claim 1, wherein the determination of the stack height and/or the adjustment of the stack height is/are carried out in the preheated state of the hot-melt adhesive varnish layers.

5. The method according to claim 1, wherein the heating of the hot-melt adhesive varnish layers to the first temperature takes place in a stacking unit, which follows a stamping tool that exerts pressure on the hot-melt adhesive varnish layers in the stacking unit.

6. The method according to claim 1, wherein the heating of the hot-melt adhesive varnish layers to the first temperature takes place in a first furnace into which the lamination stacks composed of the stacked sheet metal parts are conveyed.

7. The method according to claim 6, wherein the adjustment of the stack height takes place in a stack-controlling device and/or the baking of the sheet metal parts takes place in a second furnace.

8. The method according to claim 1, wherein all of the lamination stacks are placed under the same high pressure and/or the pressure is in the range from 2 to 10 N/mm.sup.2.

9. The method according to claim 1, wherein a thickness of each sheet metal part is between 0.1 and 0.5 mm and/or a thickness of the hot-melt adhesive varnish layer of each sheet metal part is between 2 and 12 μm.

10. The method according to claim 1, wherein each lamination stack has more than 100 sheet metal parts.

11. The method according to claim 1, wherein in the event that the determined stack height of the lamination stack exceeds the desired stack height, the number of sheet metal parts in the stacking of the sheet metal parts for the respective lamination stack is reduced by at least one.

12. The method according to claim 1, wherein in the event that the determined stack height of the lamination stack falls below the desired stack height, the number of sheet metal parts in the stacking of the sheet metal parts for the respective lamination stack is increased by at least one.

13. The method according to claim 1, wherein the number of sheet metal parts that are stacked to form a lamination stack is always selected in such a way that the determined stack height falls below the desired stack height of the lamination stack by at least a thickness of one sheet metal part of the stacked sheet metal parts.

14. The method according to claim 1, wherein the adjustment of the stack height occurs by placing one to five sheet metal parts onto the end surface of the lamination stack.

15. The method according to claim 1, wherein before the lamination stack is formed, at least one of the sheet metal parts is separated out prior to the stacking and is used for adjusting the stack height.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0031] The subject of the invention is shown in greater detail by way of example based on several exemplary embodiments. In the drawings:

[0032] FIG. 1 shows a schematic depiction of a first apparatus for carrying out the method according to the invention,

[0033] FIG. 2 shows a schematic depiction of a second apparatus for carrying out the method according to the invention,

[0034] FIG. 3a shows stacked sheet metal parts in accordance with a method according to the prior art,

[0035] FIG. 3b shows stacked sheet metal parts in the method according to the invention,

[0036] FIG. 4a shows a height curve of lamination stacks that have been stacked in accordance with a method according to the prior art, and

[0037] FIG. 4b shows a height curve of lamination stacks that have been stacked in accordance with the method according to the invention.

[0038] FIGS. 1 and 2 show apparatuses 1a, 1b that are used to produce lamination stacks 2 whose stack height hp is within a tolerance range from a predetermined desired stack height. The lamination stacks 2 are preferably used for electromagnetic components, for example for electric machines.

[0039] To achieve this, the apparatus 1a—as shown in FIG. 1—cuts out multiple sheet metal parts 4 from an electrical steel strip 3.

[0040] The electrical steel strip 3 is coated with a preferably epoxy resin-based thermosetting hot-melt adhesive varnish layer 7, for example a backlack layer. The thermosetting or heat-setting hot-melt adhesive varnish layers 7 can consist of backlack. For example, a catalytic backlack can be used, e.g.: a backlack with a depot coating for achieving a more rapid complete reaction.

[0041] The cutting out of the sheet metal parts 4 is carried out with a stamping tool 5, which can also be part of a progressive stamping tool, not shown. It is also conceivable to use other devices for cutting out sheet metal parts 4, for example lasers.

[0042] Preferably, the thickness of each sheet metal part 4 is between 0.1 and 0.5 mm and the thickness of each hot-melt adhesive varnish layer 7 is between 2 and 12 μm.

[0043] The stamping die 5a of the stamping tool 5 pushes the sheet metal parts 4 into a stacking unit 6. The sheet metal parts 4, which have a hot-melt adhesive varnish layer 7—namely a backlack layer—on at least one of their flat sides 4a, are stacked in this stacking unit 6. Two of these stacked sheet metal parts 4 are shown in FIG. 3a. All of the stacked sheet metal parts 4 exit the stacking unit 6 in lamination stacks 2 or are separated into lamination stacks 2 as they exit the stacking unit 6, which has not been shown in detail.

[0044] The lamination stacks 2 then undergo other processing steps—namely, the lamination stack 2 is conveyed into a first furnace 8 in order to thus preheat the hot-melt adhesive varnish layers 7 of the stacked sheet metal parts 4 to a first temperature t1, which is above a glass transition temperature T.sub.g of the hot-melt adhesive varnish 7 and below the baking temperature of the hot-melt adhesive varnish. Preferably, the first temperature t1 is 90° C. (90 degrees Celsius).

[0045] In a next step, the lamination stack 2 is conveyed into a press 9, which uses a pressing die 9a to exert pressure an axial pressing force P on the lamination stack 2—see pressing force P in FIG. 3a.

[0046] This pressing force P smooths out irregularities, for example in the bonding of the hot-melt adhesive varnish 7 to a sheet metal part 4 or also to a hot-melt adhesive varnish 7 of an adjacent sheet metal part 4—see FIG. 3b in this regard.

[0047] The press 9 places all of the lamination stacks 2 under the same high pressure, which is in the range from 2 to 10 N/mm.sup.2, preferably from 3 to 5 N/mm.sup.2, namely 4 N/mm.sup.2. This pressing force P can be sufficient, for example, to bring about a complete bonding of the hot-melt adhesive varnish layers 7 in order to thus eliminate the open regions between the hot-melt adhesive varnish layers 7, as shown in FIG. 3a. This can also significantly improve the bonding of the sheet metal parts 4 to one another, which further increases the durability of the lamination stacks 2 produced by means of the method according to the invention.

[0048] In addition, as shown in FIG. 1, the lamination stack 2 or more specifically, its hot-melt adhesive varnish layer 7, is kept at the first temperature t1 during the pressing.

[0049] This achieves all of the prerequisites for exact measurements of the stack height hp. For this purpose, in another step after the press 9, the lamination stack 2 is conveyed to a measuring device 10, which determines the stack height hpm. A wide variety of measuring methods can conceivably be used for this purpose, for example optical methods, manual methods, etc. or also methods in which the position of the pressing die 9a of the press 9 during or after the exertion of pressure on the lamination stack 4 is used as the basis for inferring its stack height hpm.

[0050] Preferably, the stack height hpm of the lamination stack 2 is determined when its hot-melt adhesive varnish layers are in the preheated state, which makes it possible to further increase the precision of the measuring method.

[0051] Based on this determined stack height hpm, an adjustment of the stack height hp is then carried out if need be—namely if this determined stack height hpm falls below a tolerance range Δh from a predetermined desired stack height hs.

[0052] In this case, in a stack-controlling device 11 situated after the measuring device 10, an additional sheet metal part 4 is placed onto the lamination stack 2 at one end 2a of the relevant lamination stack 2 in order to adjust the stack height hp to a height within the tolerance range Δh. In the examples, the tolerance range Δh corresponds largely (i.e. +/−) to the thickness d of one sheet metal part 4, i.e. +d/2 and −d/2, starting from the desired stack height hs.

[0053] This feature ensures the production of particularly exact lamination stacks 2.

[0054] Preferably, the stack height (hp) of the lamination stack 2 whose hot-melt adhesive varnish layers 7 are in the preheated state is adjusted, which facilitates the bonding of the sheet metal part 4 to the lamination stack 2.

[0055] In a subsequent step, the lamination stack 2 is conveyed into a second furnace 12 and in the latter, the hot-melt adhesive varnish layers 7 of the lamination stack 2 are finally heated to a second temperature t2, which is greater than or equal to the baking temperature of the hot-melt adhesive varnish, in order to bake their sheet metal parts 4 onto one another under pressure exerted by a furnace die 12a with a sufficiently long baking time. For example, the second temperature t2 is 190° C. (190 degrees Celsius) and the baking time is 15 minutes.

[0056] The method according to the invention is thus extremely flexible and produces exact lamination stacks 2 with a high degree of reproducibility.

[0057] In particular, however, the method is distinguished by the fact that sheet metal parts 4 can be stacked into lamination stacks 2 that tend to be undersized because it is in fact possible to supplement such undersized lamination stacks 2 with an additional sheet metal part 4. It is therefore unnecessary to bring oversized lamination stacks 2 to the correct dimension by exerting pressure during the baking, which is only possible to a limited degree anyway. It is thus possible to prevent a squeezing-out 13 of hot-melt adhesive varnish, as shown in FIG. 3b, which could jeopardize the short-circuit safety between the sheet metal parts 4 of the lamination stack 2.

[0058] The apparatus 1b according to FIG. 2 differs from the apparatus 1a in FIG. 1 essentially due to the fact that the preheating and exertion of pressure on the hot-melt adhesive varnish layers 7 are not carried out in the lamination stack 2; instead, they occur in the stacking unit 6.

[0059] For this purpose, the stacking unit 6 is provided with a wall heating 6a, which heats the hot-melt adhesive varnish layers 7 to the first temperature t1. By contrast, the stamping die 5a pushes the cut-out sheet metal parts 4 into the stacking unit 6 in opposition to the countervailing force of a counter support 6b—which results in an axial force being exerted on the stacked sheet metal parts 4 and thus exerts pressure on the preheated hot-melt adhesive varnish layers 7.

[0060] This method is distinguished by a smaller number of method steps and thus results in reduced cycle times in the stacking of lamination stacks 2 that have exact stack heights hp.

[0061] FIG. 4a shows a method for stacking lamination stacks according to the prior art in which a trend analysis of the height H, depicted over twenty lamination stacks, is carried out. As is clear, in the lamination stacks with the numbers 7 to 13, an oversizing has occurred; these stacks are thus outside the upper limit of the tolerance range Δh from a desired stack height hs. This trend is detected by the trend analysis and the number of stacked sheet metal parts is reduced in such a way that the stack height hp once again lies within the required tolerance range Δh from a desired stack height hs. Since the stack height in the trend decreases inversely to the preceding lamination stacks, there is suddenly an undersizing in the lamination stack with the number 16. This cannot be corrected in the prior art and generates waste. The same is true at least for the lamination stacks with the numbers 7 to 13, whose oversizing can no longer be compensated for by pressure without the risk of short circuits due to the hot-melt adhesive varnish being squeezed out.

[0062] FIG. 4b shows the method according to the invention in which there is the option of adding at least one additional sheet metal part 4 as needed to lamination stacks 2 formed from stacked sheet metal parts 4. For this reason, the method according to the invention can also be carried out so that the number of stacked sheet metal parts 4 tends to be undersized relative to the tolerance range Δh. It is thus possible to disregard known trend analyses since—as mentioned above—the stack height hp can always be adjusted to within the tolerance range Δh from a desired stack height hs by adding sheet metal parts.

[0063] The number of added sheet metal parts 4 can remain low and can preferably total from one to five sheet metal parts 4 in order to ensure the reproducibility of the method. For example, according to FIG. 4b, the lamination stacks with the numbers 1, 2, 3, 4, 5, 15, and 19 are each missing two stacked sheet metal parts 4, lamination stack 16 is missing three stacked sheet metal parts 4, and the other lamination stacks are each missing one stacked sheet metal part 4, as is clear from the determined stack height hpm.

[0064] The stacking unit 6 adds the respectively missing sheet metal parts 4, which ensures that a produced stack height hp is within the tolerance range Δh from the desired stack height hs. The method according to the invention can therefore produce geometrically accurate lamination stacks 3 without waste.

[0065] This adjustment of the stack height hs after the stacking can also be integrated into the method in a comparatively unproblematic way. This is due simply to the fact that the cycle time is in any case essentially predetermined by the chronologically longer hardening time during the final heating.