EP0028494B1

EP0028494B1 - Method for forming laminations for transformer cores

Info

Publication number: EP0028494B1
Application number: EP19800303829
Authority: EP
Inventors: Christoph Rossman; Sidney Hirst; William George French
Original assignee: Linton and Hirst Ltd
Current assignee: Linton and Hirst Ltd
Priority date: 1979-11-02
Filing date: 1980-10-28
Publication date: 1984-06-20
Also published as: EP0028494A1; DE3068319D1

Description

The invention relates to a method of forming a plurality of identical lamination parts for use in the magnetic cores of transformers, each part comprising a first limb, a second limb extending at right angles to the first limb at one end thereof and a third limb extending substantially parallel to the second limb and located intermediate the ends of the first limb so that said lamination parts are generally in the form of a letter "F", said lamination parts being adapted to be formed into stacks from which each transformer magnetic core may be formed by assembling two of the stacks with the "F"s of one stack inverted relative to the "F"s of the other stack and with said third limbs of said one stack lying alongside and in edge-to-edge engagement with said third limbs of said other stack, said third limbs thus forming a centre core portion of said magnetic core, said lamination parts being provided with projections and recesses which interlock with each other to hold the two stacks together when the core is assembled.
GB-A-1,118,546 (corresponding to US-A-3,587,020) in the name Waasner discloses such lamination parts and these have been in wide commercial use. In the Waasner laminations, the third limb tapers in width towards its free end so that, when the stacks of laminations are assembled to form a transformer magnetic core, the centre limb thereof contains a diagonal split. The advantage of the Waasner laminations is that because all of the laminations forming a core are identical and because they are provided with inter-engaging projections and recesses which hold the two stacks of laminations together, high speed assembly of transformers using these laminations may be achieved. The Waasner lamination is particularly suitable for small transformers particularly for domestic use. Prior to the introduction of the Waasner lamination, such transformer cores were conveniently made of laminations made up of E-shaped pieces and I-shaped pieces. Only low production rates were achievable with those laminations since firstly, to achieve acceptable magnetic properties of the core, it was necessary that alternate laminations were reversed relative to each other. Secondly, the finished core must be held together by clamps and bolts. The production rate achievable with the Waasner laminations is accordingly many times higher than that achieved with the conventional E and I-shaped laminations.
The main problem with the Waasner laminations is that it is wasteful of material. Typically, about 24% of the material used is wasted with the Waasner lamination.
Accordingly, the present invention is concerned with solving this problem of waste whilst preserving the high speed assembly possibilities. The solution provided by the invention is that lamination parts are cut from a strip of material having parallel edges in such a way that:

a) said second and third limbs are of equal length;
b) the longitudinal edges of said third limbs are parallel to each other so that the width of the third limb is substantially uniform along its length and is equal to that of the first and second limbs;
c) the lines along which the strip is cut define pairs of lamination parts with the parts of each pair being inverted relative to each other such that the second and third limbs of one part embrace the third limb of the other part of that pair, the pairs being arranged in a row extending along the length of the strip with each pair nested with the next pair and the first limbs inclined relative to the edges of the strip.

Preferably the lines along which the material are cut are arranged to form a plurality of said rows of nested pairs of "F"s, wherein adjacent rows are fitted together so as to leave substantially no waste material therebetween. Typically, if two rows of "F"s are provided, the waste may be 8% to 10% of the material whereas if four rows are provided, the waste may be reduced to 4% to 5% of the material. This is a significant improvement, as will be immediately recognized, on the Waasner lamination. All of this is achieved without any loss in the speed of assembly.
The invention is described further by way of example with reference to the accompanying drawings in which:

Figure 1 is a plan view of a two part lamination;
Figure 2 shows the lines of cut on a strip of material for forming a plurality of laminations as shown in Figure 1 with a minimum of waste;
Figure 3 is a view similar to Figure 1 showing an alternative and preferred form of lamination;
Figure 4 is a view similar to Figure 2 showing the lines of cut for forming the lamination of Figure 3;
Figure 5 illustrates stamping operations which may be carried out by a progression tool on a strip of material for forming the laminations of Figure 3 with the arrangement of Fs as shown in Figure 4; and
Figure 6 is an enlarged fragmentary view of a modification of the projections shown in Figures 1 and 3.

The lamination shown in Figure 1 is made up of two parts 2a and 2b. The part 2a comprises a pair of parallel limbs 4a and 6a and a limb 8a arranged in the shape of a "F", the limb 8a forming the stem of the F and the limbs 4a and 6a forming the cross members of the F. The limbs 4a and 6a are of equal length and their longitudinal edges 10a, 12a, 14a and 16a are all parallel to each other so that the limbs 4a and 6a are substantially rectangular. The limb 4a is provided with a projection 18a at its free end. The lower corner 20a of the limb 6a is radiussed. A recess 22a is formed in the limb 8a near to the end opposite to the limbs 4a. The part 2b is identical to the part 2a and includes, therefore, features the same as those described with reference to the part 2a but identified in the drawing with the same reference numbers but the letter b added instead of the letter a.
The part 2b is inverted relative to the part 2a and assembled therewith with the edges 16a and 16b of the limbs 6a and 6b lying along and in abutment with each other. The two parts are held together by resilient engagement of the projections 18a and 186 in the recesses 22b and 22a respectively.
In this instance, the projections and recesses are generally rectangular in form and are arranged such that by slight flexing of the arms 4a, 4b of the two parts, the projections are insertable into the recesses. The limbs 4a, 4b are resiliently flexible both to permit such insertion to be effected and, after insertion of the projections into the recesses, to bias the projections into firm frictional engagement with respective edges of the recesses.
A transformer is assembled using laminations as shown in Figure 1 by forming a stack of lamination parts 2a and a further stack of lamination parts 2b, then assembling these two stacks with the coil surrounding the limb of the core formed by the limbs 6a and 6b, the two stacks of laminations simply being held in engagement with each other by the resilient engagement of the projections 18a and 18b with the recesses 22b and 22a. The provision of the radiussed corners 20a and 20b on the limbs 6a and 6b facilitates the guidance of the leading edge of each of these limbs along the side of the opposite limb when the two parts of the core are assembled with each other. An advantage of this lamination is that tight engagement between the edges 16a and 1 6b is not essential since flux does not have to cross any gap between these edges.
Referring to Figure 2, the laminations of Figure 1 are formed from a strip of material 24 which is cut along the lines shown to form two rows 26 and 28 of F-shaped lamination parts, each two comprising a succession of pairs of F lamination shapes 2a and 2b with the limb 6a of the lamination 2a arranged between the limbs 4b and 6b of the lamination 2b, it thus being seen that the projections 18a and 18b of the laminations 2a and 2b leave recesses 30b and 30a respectively in the limbs 8b and 8a of the laminations 2b and 2a. Similarly, the provision of the radiussed corners 20a and 20b on the limbs 6a and 6b leaves radiusses 32b and 32a at the inside corner between the limbs 4b, 8b and 4a, 8a.
The lines along which the strip 24 is cut are also such that each lamination pair 2a, 2b is nested with the adjacent pair in the row and the lamination pairs are arranged at an angle to the edge 34 of the strip 24 such that the corners 36a of the laminations 2a lie on a straight line parallel to the edge 34. The rows 26 and 28 are both arranged in this way and are interfitted with each other so that the only material wasted is a narrow margin 38 of saw-tooth shape from each edge of the strip 24.
With reference to Figure 3, laminations 2a and 2b are basically similar to the laminations shown in Figure 1. However, this embodiment differs from the embodiment of Figure 1 in the form and location of the interengageable projections and recesses for attaching the two parts together. In the Figure 3 embodiment the projections, 40a and 40b, are located at the lower ends of the limbs 8a and 8b instead of on the lower corners of the limbs 4a and 4b. The recesses, 42a and 42b, are, therefore, provided at the upper corners of the limbs 4a and 4b whereas in the Figure 1 embodiment the recesses 22a and 22b are formed in the limbs 8a and 8b. Further, the projections 40a and 40b are somewhat of hook shape so as to interlock with the recesses which are of similar shape. Thus, the projections 40a, 40b are each formed with a nose 44a, 44b which is engageable behind a nose 46b, 46a of the limb 4b, 4a for holding the two lamination parts 2a and 2b together. The limbs 4a, 4b and/or the projections 40a, 40b are resiliently flexible to enable the noses 44a, 44b to pass the noses 46b, 46a respectively on bringing the two parts together in a direction parallel to the limbs 4a, 4b for assembling a core. In addition, the tips of all the noses are rounded to facilitate entry of the projections into the recesses.
It is not essential for the projections 40a, 40b to be located on the limbs 8a, 8b of the two lamination parts in Figure 3 embodiment and, instead, they may be located on the limbs 4a, 4b for example in the same situation as the projections 18a, 18b of the Figure 1 embodiment. If this is the case, of course, the recesses 42a, 42b must be slightly enlarged relative to the projections 40a, 40b so that there is room for the noses 44a, 44b to pass the noses 46b, 46a as the projections enter the recesses during the assembly of a core.
Turning to Figure 6, this shows an alternative shape of projection which may be used in the lamination illustrated in Figure 3 in place of the projections 40a, 40b. This projection, 50, has a nose 52 with a rounded tip, as before, but in this instance the tip of the nose does not coincide with the outermost end of the projection, which results in the hook shape of the projection in the Figure 3 embodiment, but is disposed half way between the foot of the projection and its outermost end. This strengthens the projection and, at the same time, facilitates assembly of the two lamination parts together.
As shown in Figure 4, the strip 24 is cut in a manner similar to that shown in Figure 2 for producing the laminations of Figure 3 with a minimum of waste. It will be noted that the recesses 50a and 50b in the limbs 8a and 8b of the laminations of Figure 3 arise from the formation of the projections 40a and 406 and have no functional significance.
The recesses 52a, 52b and 54a, 54b arise from the sequence of cutting operations carried out on the strip 24 by a progression tool (not shown), whose operations are illustrated in Figure 5. In Figure 5, the strip 24 is advanced step wise from right to left by a distance x so that each successive portion of the strip is moved intermittently to each of ten successive zones or stations A to J of the tool. At zone A holes 60 are punched at the edges of the strip for registration purposes as the strip moves through the zones. It will be noted that the holes 60 are staggered relative to each other at the two edges of the strip and this is because of the angle arrangement of the Fs to be cut. No cutting takes place at zone B. At zone C two apertures 62 and two apertures 64 are punched at spaced positions on a line at a slight angle to a line transverse to the strip. The apertures 62 will form recesses 52a and 52b and are simply to ensure proper severance of the Fs from the strip at the corners of the laminations despite the possibility that the cutting tool may wear. The apertures 64, however, form the recesses 42a and 42b and therefore are appropriately shaped.
At zone D the shaded area 66 is blanked from the strip thus forming one F-shaped lamination part. No cutting takes place at zone E. At zone F the shaded portion 68 is blanked from the strip thus forming a further lamination part.
No cutting takes place at zone G or zone I, but at zones H and J the shaded parts 70, 72, forming two further laminations, are blanked from the strip.
It should be understood that once the cutting process is operating, the punching or blanking operations taking place at zones A, C, D, F, H and J all take place simultaneously.
A progression tool for carrying out the operations described with reference to Figure 5 can be constructed by conventional techniques, and therefore need not be described in detail. It is, however, to be understood that the invention also resides in a tool, or other apparatus for carrying out the method described with reference to Figure 5.

Claims

1. A method of forming a plurality of identical lamination parts for use in the magnetic cores of transformers, each part comprising a first limb (8a, 8b), a second limb (4a, 4b) extending at right angles to the first limb (8a, 8b) at one end thereof and a third limb (6a, 6b) extending substantially parallel to the second limb (4a, 4b), and located intermediate the ends of the first limb (8a, 8b) so that said lamination parts are generally in the form of a letter "F", said lamination parts being adapted to be formed into stacks from which each transformer magnetic core may be formed by assembling two of the stacks with the "F"s of one stack inverted relative to the "F"s of the other stack and with said third limbs (6a) of said one stack lying alongside and in edge-to-edge engagement with said third limbs (6b) of said other stack, said third limbs (6a, 6b) thus forming a centre core portion of said magnetic core, said lamination parts being provided with projections and recesses (18a: 40a, 40b: 42a, 42b) which interlock with each other to hold the two stacks together when the core is assembled, characterised in that said lamination parts are cut from a strip of material (24) having parallel edges in such a way that:

a) said second (4a, 4b) and third (6a, 6b) limbs are of equal length;

b) the longitudinal edges of said third limbs (6a, 6b) are parallel to each other so that the width of the third limb (6a, 6b) is substantially uniform along its length and is equal to that of the first and second limbs (8a, 8b; 4a, 4b);

c) the lines along which the strip (24) is cut define pairs of lamination parts with the parts of each pair being inverted relative to each other such that the second and third limbs (4a, 6a) of one part embrace the third limb (6b) of the other part of that pair, the pairs being arranged in a row extending along the length of the strip with each pair nested with the next pair and the first limbs (8a, 8b) inclined relative to the edges of the strip.

2. A method according to claim 1, characterised in that said projections and recesses (40a, 40b, 42a, 42b) are located at the outer corner of the free end of the second limb (4a, 4b) and the inner corner of the free end of the first limb (8a, 8b).

3. A method according to claim 1 or 2, characterised in that the corner (20a, 20b) of the third limb (6a, 6b) at the free end thereof and at the edge remote from the second limb (4a, 4b) is relieved to form guide surfaces which assist in assembling the two stacks.

4. A method as claimed in any preceding claim, characterised in that lines along which the material is cut are arranged to form a plurality of said rows of nested pairs of "F"s, wherein adjacent rows are fitted together so as to leave substantially no waste material therebetween.

5. A method as claimed in any preceding claim, characterised in that the cutting of the strip is effected such that the two "F"s in each pair are detached successively from the strip.

6. A method as claimed in any preceding claim, characterised in that the cutting of the strip is effected such that the detachment from the strip of adjacent pairs of the nested pairs of "F"s is completed successively.

7. A method as claimed in claim 6, characterised in that cutting of the strip is effected such that detachment from the strip of one pair of each of the adjacent pairs of the nested pairs of "F"s commences before detachment of the other pair is completed.

8. A method as claimed in claim 4, characterised in that cutting of the strip is effected such that detachment from the strip of the "F"s in one row of "F"s occurs in advance of detachment from the strip of the "F"s in an adjacent row of "F"s.

9. A method as claimed in any preceding claim, characterised by advancing the strip intermittently and effecting the cutting during periods between the advances.