METHOD FOR FORMING LAMINATIONS FOR TRANSFORMER CORES

Abstract: F-shaped lamination parts (2a,b) for forming electromagnetic cores are cut from a strip of material, the lines of cut being such that pairs of Fs have their parallel cross members (4a,b,6a,b) interfitted with each other and each pair of Fs is nested with the adjacent pair of Fs. The Fs are arranged in two or more rows with the stems (8a,b) of the Fs in each row at an angle to the longitudinal edge of the strip so that substantially the only material wasted is a saw-tooth shaped portion along each edge. The Fs have resiliently interengageable projections (18a,b) and recesses (22a,b) for holding the parts together in an electromagnetic core.

Description: LAMINATIONS FOR ELECTROMAGNETIC CORES This invention relates to laminations for electromagnetic cores particularly for shell-type transformers. In such transformers, the core comprises three spaced apart parallel limbs, around the centre one of which the coil or coils is or are located, and a further pair of parallel limbs magnetically interconnecting the ends of the three parallel limbs. The core is made up of a stack of laminations, and each lamination is in two or more parts thus enabling the laminations to be assembled with the coil or coils. A variety of different shapes are known for the parts of the laminations. For example, each lamination may be made up of an E-shaped part and an I-shaped part which, in the assembled lamination, interconnects the free ends of the three parallel limbs of the E-shaped part. The laminations are generally made from sheet or strip material and an advantage of the aforementioned laminations made of E-shaped and I-shaped parts is that they can be stamped out with substantially no waste of material. The avoidance of waste material ts important in view of the high cost of the material employed. Various ways in which the E- and I-shaped lamination parts may be formed are illustrated in UK Patent Nos. 1,466,880 and 1,466,878. A further proposal for a two part lamination is illustrated in British Patent Specification No. 1,118,546 (Waasner). This lamination is made up of two parts of identical shape which is such that the line of division between the two parts in the assembled lamination includes a line extending diagonally across the centre one of the three parallel limbs, each part of the lamination comprising first and second limbs which are of generally rectangular shape and are arranged at right angles to each other in the general form of a L and a further limb, of generally triangular shape, which cooperates with the similarly shaped third limb of the other part to form the centre limb in the finished lamination. An advantage of this form of lamination is that it is available with resilently interengageable projections and recesses on the two parts for attaching the two parts together simply by sliding them towards one another in a plane. Thus, in assembling the core, two stacks of lamination parts are formed and are attached to each other in a single operation with the coil assembled around the centre limb, by means of the resiliently interengageable projections and recesses. However, a disadvantage of this shape of lamination is that it is not possible to manufacture it without substantial waste of material. In practice, 24% to 26% of the material is wasted. Laminations made up of two F-shaped parts have previously been proposed in US Patent No. 581,873 LThomson), issued in 1897, but Thomson failed to disclose any interengageable means for attaching the lamination parts together and to disclose any method of forming the laminations with a minimum of waste. One aspect of this invention concerns the problem of minimising waste in the formation of laminations from F-shaped parts, and provides a method of forming F-shaped laminations from a strip of material having parallel eages in which the lines along which the material is cut are such as to form a pattern in which Fs are arranged in pairs, the Fs of each pair being inverted relative to each other with the two parallel limbs of each F embracing the lower one of the two parallel limbs of the other F of that pair, the pairs are arranged in a row extending along the length of the strip with each pair nested with the next pair and the Fs are arranged at an angle to the edges of the material. Two or more rows of Fs may be provided from the same strip. Substantially the only material wasted is at the edges of the strip and thus, the more rows of pairs of Fs which are provided the lower the overall waste. By way of example, if two rows of Fs are provided, the waste may be 8% to 10% whereas if four rows are provided the waste may be 4% to 58. Additionally, the invention provides apparatus for forming F-shaped laminations from a strip of material having parallel edges, comprising first cutting means arranged to cut lines in the strip forming a first F, second cutting means arranged to cut lines in the strip forming a second F which is inverted relative to the first and whose two parallel limbs embrace the lower one of the two parallel limbs of the first F, and means for advancing the strip relative to the first and second cutting means such that these cutting means can cut lines forming a row of pairs of Fs in which each pair is nested with the next pair. Another aspect of the invention concerns the problem of providing a multipart lamination which has interengageable means for attaching the parts together and which may be assembled in a simple manner when the parts have orthogonal, parallel sided limbs. This aspect of the invention features a two part lamination in which each part comprises a pair of parallel limbs,each said parallel limb having parallel edges, and a further limb at right angles to said parallel with one of the parallel limbs at the end of the further limb and the other intermediate the ends thereof so that each part thereby resembles the letter "F", said lamination parts being provided with interengageable means for attaching them together. The interengageable means may comprise projections and recesses arranged to be resiliently interengageable by movement of the parts towards one another in a direction parallel to each of the pairs of parallel limbs. The resilient interengagement of the projections and recesses may be achieved by making the projections resiliently flexible and/or by making limbs of the lamination parts resiliently flexible. rn a preferred formof the invention, the projections and recesses are interlockable. However, the projections could, alternatively, be a friction fit within the recesses to attach the lamination parts together. 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 fragmentry 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 tFt, 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 lOa, 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 18b 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 t limbs 4a, 4b are resiliently flexible both to permit such insertion to be effected and, after insertion of the projections into the recesses, to bas 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 6S, 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 225 and 22a. The provision of the radiussed corners 2Qa 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 165 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--------------7 F-shaped lamination parts, each row 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 t 32b and 32a at the inside corner between the limbs 4b, 8b and 4a, Ba. 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 tiie 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 interenaaaeable 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 engagable 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, lSb 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 40b 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 tie two edges of the strip and this ts 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 5b and are simply to ensure proper severance of the Fs from the strip at the corners of the laminations despite the possibility trat 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: CLAIMS: 1. A method of forming F-shaped laminations from a strip of material having parallel edges, charaterised by cutting the material along lines which form a pattern wherein the F's are arranged in pairs, the F's of each pair being inverted relative to each other with the two parallel limbs of each F embracing the lower one of the two parallel limbs of the other F 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 such that the stems of the Fs are inclined relative to the edges of the strip. 2. A method as claimed in claim 1, characterised in that lines along which the material is cut are arranged to form a plurality of rows of nested pairs of Fs, wherein adjacent rows are fitted together so as to leave substantially no spare material therebetween. 3. A method as claimed in claim 1 or 2,characterised by forming the F's with projections and recesses which are arranged such that the Fs, when detached from the strip, may be assembled into a core by interengagement of the projections and recesses. 4. A method as claimed in claim 3, characterised in that projections are formed by the cutting of the strip. 5. A method as claimed in claim 3 or 4, characterised in that the recesses are formed from apertures made in the strip in advance of the cutting thereof. 6. A method as claimed in any preceding claim; characterised in that the lines along which the material is cut are arranged to produce a radiussed corner on the lower limb of each F. 7. A method as claimed in any preceding claim, characterised by making severance apertures in the strip, which severance apertures are arranged to lie at corners of the Fs, whereby to facilitate detachment of the Fbs from the strip after cutting. 8. A method as claimed in any preceding claim, characterised in that the two Fs in each pair are identical. 9. A method as claimed in any preceding claim, characterisedin that the cutting of the strip is effected such that the two Fs in each pair are detached successively from the strip. 10. 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 Fs from the strop is completed successively. 11. A method as claimed in claim 10, characterised in that cutting of the strip is effected such that detachment from the strip of one par of each adjacent pair of the nested pairs of Fs commences before detachment of the other pair is completed. 12. A method as claimed in claim 2, characterised in that cutting of the strip is effected such that detachment from the strip of the Fts in one row of Fs occurs in advance of detachment from the strip of the Fs in an adjacent row of Fs. 13. A method as claimed in any preceding claim, characterised by advancing the strip intermittently and effecting the cutting during period between the advances. 14. A method as claimed in claim l,characterised by advancing the strip intermittently through a first cutting station at which the strip is cut to form one of the Fs in each pair which is thereupon removed from the strip, and a second cutting station at which the strip is cut to form the other of the Fs in each pair which is thereupon removed from the strip 15. A method as claimed in claim 2, characterised b advancing the strip intermittently through a first cutting station at which the strip is cut to form one of the Fs of each pair in a tirst one of the rows, which one F in the first row is thereupon removed from the strip, a second cutting station at which the strip is cut to form the other of the Fs in each pair of the first row, which other F in the first row is thereupon removed from the strip, a third cutting station at which the strip is cut to form one of the Fs of each pair in a second one of the rows, which one F in the second row is thereupon removed from the strip, and a fourth cutting station at which the strip is cut to form the other of the Fs of each pair in the second row, which other F in the second row is thereupon removed from the strip. 16. A method as claimed in claim 14 or 15, further characterised by advancing the strip intermittently through a punching station upstream of the cutting stations, at which punching station registration holes are produced at the edges of the strip such that the registration holes at one edge are staggered relative to the registration holes at the other edge. 17. A lamination when produced by the method of any preceding claim. 18. Apparatus for forming F-shaped laminations from a strip of material having parallel edges, characterised by first cutting means arranged to cut lines in the strip forming a first F, second cutting means arranged to cut lines in the strip forming a second F which is inverted relative to the first and whose two parallel limbs embrace the lower one of the two parallel limbs of the first F, and means for advancing the strip relative to the first and second cutting means such that these cutting means can cut lines forming a row of pairs of Fs in which each pair is nested with the next pair. 19. A two part lamination in which each part comprises a pair of parallel limbs, each such parallel limb having parallel edges, and a further limb at right angles to said parallel limbs with one of said parallel limbs at the end of the further limb and the other intermediate the ends thereof so that each part thereby resembles the letter F, characterised in that said lamination parts are provided with interengageable means for attaching them together.

Inventors: FRENCH, WILLIAM GEORGE, HIRST, SIDNEY, ROSSMAN, CHRISTOPH
Applicants: LINTON AND HIRST LIMITED
Application year: 1980
Main classification: H01F41
IPC codes: H01F27, H01F41