GB2221354A

GB2221354A - Clamping laminated cores by deformable parts

Info

Publication number: GB2221354A
Application number: GB8817875A
Authority: GB
Inventors: George William Marriott; Trevor Hirst
Original assignee: Linton and Hirst Ltd
Current assignee: Linton and Hirst Ltd
Priority date: 1988-07-27
Filing date: 1988-07-27
Publication date: 1990-01-31
Anticipated expiration: 2008-07-27
Also published as: HK11296A; GB8830408D0; GB8817875D0; GB2221354B; KR900002362A

Abstract

A core, e.g. for a transformer or motor, comprises first and second packs of laminations 12, 14 that fit relatively freely together and have a complementary formations e.g. dovetail formations 16 and projections 18. The first and second packs of laminations 12, 14 are held positively together in mechanical contact e.g. in a jig (30). The formations 18 on one or both of the laminations are then deformed to engage the formations 16 of the other lamination to clamp the first and second packs of laminations 12, 14 together. <IMAGE>

Description

IMPROVEMENTS IN LAMINATIONS This invention relates to improved laminations for electromagnetic devices for making up magnetic cores thereof, to packs of said laminations and to methods of assembling said packs to form magnetic cores.

Electromagnetic devices e.g. transformers and electric motors commonly have cores made up of individual laminations which may take the form of a butted stack an interleaved stack or a so-called "Unilam" stack (see Patent No's GB-A-1466878, 1466879 and 1466880).

A variety of ways have been used to hold the laminations together to make a core for the device.

They have been bolted together. They have been welded together. They have been adhered together. They have been enclosed within a retaining frame. But all these methods are costly because they involve additional components and/or add to the time and number of operations needed to assemble the core.

It has been proposed in Patent Specification No.

US-A-4594295 to provide cut sheet metal laminations that may be force fitted together to avoid transformer noise at high load/temperature working conditions.

Thus one of the laminations has small narrow projections that are a force or interference fit into corresponding recesses of a complementary lamination.

But is is inherent in the force fit method of assembly that the complementary parts resist assembly, and any resulting incompleteness in the mechanical contact between the assembled parts increases the magnetic reluctance of the device, and corresponding loss of efficiency. Furthermore the said US Patent does not rely on force fitting as sole means for holding the laminations together but also fastens the laminations by welding as is conventional in the art. Force fitting is also described in Specification No's DE-A-2744711, 3008598 and 3008599. Our Patent Specification No. EP-A-0028494 describes and claims F-lamination parts for use in the magnetic cores of transformers having projections and recesses that are subject to an interference fit.

It is an object of the invention to provide a novel structure for laminations of electromagnetic devices that enable them to be assembled together simply and inexpensively in few operations and with minimal loss in performance.

In one aspect the invention provides a lamination assembly for an electromagnetic device comprising first and second packs of complementary laminations that fit relatively freely together and have interfitting formations, said formations on one or both of the lamination packs being deformable to engage the formations of the other lamination pack to fasten the first and second packs of laminations together.

The facility to assemble the laminations freely together enables them to be offered together and held in good mechanical contact by an external clamping force until the deformable portions are mechanically deformed to hold the packs together.

In a further aspect, the invention provides a method of assembling laminations of an electromagnetic device, which comprises: providing first and second packs of complementary laminations that fit relatively freely together and have interfitting formations; holding the first and second packs of laminations positively together in mechanical contact; and deforming said formations on one or both of the laminations to engage the interfitting formations of the other lamination to clamp the first and second packs of laminations together.

The interfitting formations of the first and second packs of laminations may simply give rise to a frictional clamping force when deformable ones of them are deformed onto non-deforming others of them but preferably they are profiled so that deformation of said formations mechanically fastens the first and second packs together. In the latter case, the interfitting formations of the first and second packs of laminations advantageously have a dovetail or other profile such that deformation of said formations positively urges the first and second packs of laminations together. The dovetail is advantageously formed on the non-deforming seat formation but it may also be formed on a deformable ear formation.

Preferably the free interfitting is provided by a clearance fit but it may also be provided by a transition fit, line contact between the male and female parts offering little resistance to assembly.

Any force needed to assemble the stacks of laminations together should be relatively small compared to the available clamping force.

Again, if the male and female parts are a tight transition fit, the properties of the product may be acceptable if the resistance reduces during the last part of the travel of the first and second packs of laminations towards the fully abutted position.

In a more specific aspect, the invention provides a lamination assembly for an electromagnetic device formed by fastening together first and second packs of complementary laminations, wherein: a) the laminations of each pack have spaced convergent faces; and b) the laminations of each pack have spaced clamping projections for fitting onto the convergent faces and that when inelastically deformed or crimped onto said faces mechanically lock the first and second packs together.

The invention further provides a pack of laminations for use in an electromagnetic device, said laminations having spaced convergent faces for receiving projections of laminations of a complementary pack that when deformed onto said faces lock the packs of laminations together.

The invention yet further provides a pack of laminations for use in an electromagnetic device, said laminations having spaced clamping projections for fitting onto convergent faces of laminations of a complementary pack and that when deformed onto said faces mechanically lock the laminations together.

The above method of assembly can be used for loose laminations and stacked laminations. Thus a rigid pack of E-laminations may be assembled to a pack of Ilaminations which is flexible e.g. because the undivided laminations are held together by a single peg. With this flexibility the I-laminations easily accomodate any irregularities in the E-laminations and good mechanical and magnetic contact is obtained.

However, the use of two or more pegs for both E-laminations and I-laminations is within the invention.

In a further aspect the invention provides a lamination for use in an electromagnetic device having spaced convergent faces for receiving projections of a complementary lamination that when deformed onto said faces lock the laminations together.

In another aspect, the invention provides a lamination for use in an electromagnetic device having spaced clamping projections for fitting onto convergent faces of a complementary lamination and that when deformed onto said faces mechanically lock the laminations together.

Various forms of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figures la is a front view of components of an electrical transformer prior to assembly, and Figures lb, lc and ld are respectively a central transverse section of a pack of I-laminations, a transverse section of a core and an end view of a pack of E-laminations all being components that appear in Figure 1; Figure 2a is a front view of a transformer assembled from the components shown in Figure 1, Figure 2b is an enlarged detail of one side of the transformer core at an interface between the I- and E-laminations prior to attachment of them together and Figure 2c and 2d are end views of the transformer showing alternative core structures; Figure 3 is a front view of the transformer during assembly.

Figures 4a, 4b and 4c are enlarged details of one side of the transformer core at an interface between I- and E-laminations after attachment together and showing alternative notch profiles; Figures 5a, 5b and Sc are enlarged details of one side of the transformer core at an interface between an Iand an E-lamination showing the use of different notch angles and crimp blade profiles; Figures 6a to 6e are front views of typical laminate assemblies for a variety of transformers and chokes assembled according to the invention; Figure 7 is a diagrammatic front view of a core of a shaded pole motor assembled according to the invention;; Figures 8a and 8b are front and side views of an interleaved stack of I- and E-laminations according to the invention and Figure 8c is a view of the I- and E-laminations from which the interleaved stack is formed; Figures 9 and 10 are front views of transformer laminations showing an alternative form of attachment; Figures 11, ila and 12, 12a are detail views showing alternative notch and projection profiles for use in the laminations of Figures 9 and 10; and Figures 13 and 13a are detail views showing a yet further notch and projection profile.

In Figure la and Figures lb, lc and Id a transformer 10 has windings 11 and a core assembled from an E-lamination pack 12 and an I-lamination pack 14. The laminations of the E-lamination pack 10 are held together by a pair of stamped-in spigot and socket fasteners. The upper extremities of the E-laminations of the pack 12 are formed on the outer edges thereof with dovetail formations 16 and the I-laminations of the pack 14 are formed with deformable projections or ears 18. The dovetail formations 16 and the ears 18 are desirably formed on the respective laminations during stamping or pressing thereof. The size or length and width of the lugs and the size and profile of the dovetail groove vary depending on the size, weight and stack length of the intended transformer assembly.For assembly of the transformer the E-lamination pack 12 is placed in a jig, the windings 11 is placed on the centre limb of the E-laminations and the I-lamination pack is placed onto the E-lamination pack and is a loose fit thereon. Clamping force F is applied to urge the packs 12,14 into good mechanical contact, which is assisted if the I-pack 18 is torsionally flexible. Good mechanical contact avoids interruption of the magnetic flux path in the assembled core and hence loss of efficiency.

An inwards deformation D (Figure 2b) is then caused by impact e.g. of appropriately profiled crimping fingers onto the ears 18 to seat them onto the dovetail formations and to fasten the E- and I-lamination packs 12, 14 together mechanically. Because of the dovetail formations, the act of deformation also pulls the I-stack 14 firmly against the E-stack 12. The resulting attachment between the lamination packs 12, 14 is sufficiently strong and permanent that no additional method of attachment is needed, through adhesive or other conventional means of holding the packs together may be employed if desired. The assembled transformer has the appearance shown in Figures 2a and 2c.

In a variation (Figure 2d) the E-laminations 25 are loose rather than adhered to one another in a pack and are held together by locator formations 26 of the bobbin 11. The laminations 25 are attached to a pack of I-laminations 27 as described above. The Elaminations can also be stacked laminations held together by one or more impingent pegs.

Figure 3 shows diagrammatically the transformer winding 11 and laminations 12, 14 in a jig 30 during assembly thereof, crimping blades 32 having angled end faces 34 impinging on the projections or ears 18 to bring about the required inward deformation thereof.

Various notch and ear profiles are shown in Figures 4a-4c. In Figure 4a the notch 16 is a plain dovetail and the ear 18a extends part way e.g. slightly over half way along it. In Figure 4b the dovetail surface of the notch 16b is doubly curved. In Figure 4c the notch 16c is again angular, but its lower face is inclined away from rather than parallel to the end face of the E-lamination 12 and the ear 18c extends substantially the whole way along the dovetail notch.

In Figure 5a the blade 32 has a plain inclined surface 34. The impact of blade 32 on the ear 18 both deforms the ear inwardly and causes a slight extensiion thereof as indicated by arrow 36. The angle between the working face of the dovetail notch 16 and a normal 38 to the end surface of the E-laminations 12 is advantageously above about 50 and may have whatever value is needed to bring about secure attachment of the lamination packs 12, 14. Angles above and below 0 50 may be used, the angle being selected in any individual case depending on the size and weight of the intended core structure. The arrangement of Figure 5b is similar except that the end face 34a of the blade 32a is ribbed as shown.In Figure Sc the blade 32b has an angled line of action to increase the component along the notch 16 and has a convexly curved end face 36b to maximise crimp and extrusion pressure on the ear 18.

In Figure 6 there are shown various possible core configurations. In Figure 6a there is shown a choke core having a pair of E-laminations 40 with an airgap 42 between the central limbs 44. Figure 6b shows another choke core formed by a U-lamination 46 and a T-lamination 48. In Figure 6c a third choke core is formed by E-lamination 50 and I-lamination 52. Figure 6d shows a transformer core formed by a pair of F-laminations 54. In this structure it will be noted that one of the laminations 54 has the notches or recesses 56 and the other has the clamping ears 58.

Figure 6e shows a further transformer core formed by a U-lamination 60 and a T-lamination 62. In this structure, inclined surfaces 64 on the T-lamination 62 receive clamping ears 66 on the U-lamination 60.

In Figure 7 a structure is shown for a shaded pole electric motor having a rotor 70 that rotates in a stator defined by U-laminations 72. A pole bobbin 74 on lamination pack 76 is attached to by clamping ears and recesses as previously described.

In Figures 8a-8c there is shown an arrangement for an interleaved stack of E and I laminations 80,81. As seen in Figure 8c which shows the cut-lines on blank steel sheets the I-laminations 81 nest within the E-laminations 80 and can be cut from sheet by a progressive forming tool substantially without waste.

The sides of the E-laminations 80 are formed with recesses 82 typically of semi-circular shape which, as seen in Figure 8b, alternate with the ears and recesses 16,18 in the assembled interleaved stack.

The ends 18a of the ears 18 are convexly curved to produce correspondingly curved recesses in the E-member 18. The curvature is selected to minimise disturbance to the flux path in the assembled transformer core. The I-laminations 81 have a single spigot and socket formation 83 for assembly into a torsionally flexible pack and the E-laminations 80 may have more than one spigot and socket connector 85 whose number and location is selected depending upon the size and other characteristics of the core being made.

In Figure 9 an I-lamination 90 fits to an E-lamination 92 to form a transformer core. The I-lamination 90 has depending projections or ears 94 offset sligthly inwards from its ends 96 that fit into notches 98 in the end faces of the E-laminations 92. Assembly is by crimping inwards the thin material of the outer faces of the notches 98 as shown by arrows 100 using crimping blades, of the kind previously described. In Figure 10 a "Unilam" type core is formed in which an E-lamination 102 having an extended side limb 104 receives an abbreviated I-lamination 106. The E-lamination 102 has a slot 103 in the inner side face of its extended side limb 104 and a slot 108 in the end face of its other side limb that receive corresponding projections or ears on the I-laminations 106.It will be noted that the slots 103, 108 and the corresponding lines of action of the necessary crimping blades are directed generally at right angles to one another as shown by arrows 110, 112.

Details of the possible slot and ear formations of the I- and E-laminations are shown in Figures 11, lla and 12,12a which are respectively before and after deformation. In Figure 11a the dovetail surface 111 is formed on the deformable outer portion of the slot 98 and in Figure 12a it is formed at 114 on the outer surface of ear 94.

It will be appreciated that the fastening system described above has a number of advantages. It enables a core from an electromagnetic device to be assembled rapidly and inexpensively. The laminations can be made nearly without waste. The method can be used for assembly of loose lamination transformers and stacked lamination transformers or transformers having laminations which are partly stacked and partly loose or inter-leaved lamination transformers. Tests have shown that the efficiency of an assembled core according to the invention is substantially the same as or only slightly less than that of a conventionally assembled core.

Figures 13 and 13a show a yet further profile for a slot and ear which can be used when high retaining force is required. One pack of laminations has an ear 120 having a convex blind face 122 which is deformable into contact with a concavity 124 in the other pack of laminations 126. The convex blind face 122 initially passes face 125 of lamination 126 with clearance but after deformation mechanically interlocks therewith.

Claims

CLAIMS:

1. A lamination assembly for an electromagnetic device comprising first and second packs of complementary laminations that fit relatively freely together and have portions that are deformable to clamp the first and second packs of laminations together.

2. A lamination assembly according to claim 1 which is an E-lamination, a U-lamination an I-lamination, a F-lamination or a motor lamination.

3. A lamination assembly according to claim 1 or 2, wherein the deformable portions are formed to opposed sides of one of the packs and adjacent an end plane that defines an abutment for the laminations of the other pack.

4. A lamination assembly according to claim 1 or 2, wherein the deformable portions occur on faces of the laminations that are non-parallel.

5. A lamination assembly according to claim 4, wherein the deformable portions occur on faces of the laminations that are directed at right angles to one another.

6. A lamination assembly according to any preceding claim, wherein the interfitting formations of the first and second packs of laminations are profiled so that deformation of said formations mechanically fastens the first and second packs together.

7. A lamination assembly according to claim 6, wherein the interfitting formations of the first and second packs of laminations are profiled so that deformation of said formations positively urges the first and second packs of laminations together.

8. A lamination assembly according to claim 6 or 7, wherein the first lamination has spaced convergent faces for receiving deformable projections on the second lamination.

9. A lamination assembly according to claim 8, wherein the convergent faces of the first lamination are directed inwardly at an angle of at least 5 the sides of said lamination.

10. A lamination assembly according to any preceding claim, wherein the laminae have been punched or stamped from sheet, and wherein the convergent faces have been formed during the punching or stamping operation.

11. A lamination assembly according to any preceding claim wherein at least one of the packs of laminations is torsionally flexible.

12. A lamination assembly according to claim 11, wherein each lamination of the or each torsionally flexible pack is connected to an adjacent lamination by a single connection.

13. A pack of laminations according to claim 12, wherein each lamination of the or each torsionally flexible pack comprises, on a common axis perpendicular to the lamination, a single depression on one side thereof and a single projection on the other side thereof, each lamination being coupled to an adjacent lamination only by the single projection projecting into the single depression of the adjacent lamination.

14. A lamination assembly for an electromagnetic device formed by fastening together first and second packs of complementary laminations, wherein: a) the laminations of the first pack have spaced convergent faces; and b) the laminations of the second pack have spaced clamping projections for fitting onto the convergent faces of the laminations of the first pack and that when crimped onto said faces mechanically lock the first and second packs together.

15. An assembly according to claim 14, wherein the first and second laminations meet at an abutment plane, and are held together by a single pair of clamping projections and convergent faces adjacent the abutment plane.

16. A method of assembling packs of laminations of an electromagnetic device, which comprises: providing first and second packs of complementary laminations that fit freely together and have interfitting formations; holding the first and second packs of laminations positively together in mechanical contact; and deforming said formations on one or both of the laminations to engage the formations of the other lamination to clamp the first and second packs of laminations together.

17. A method according to claim 16, wherein the interfitting formations of the first and second packs of laminations are profiled so that deformation of said formations mechanically fastens the first and second packs together.

18. A method according to claim 17, wherein the interfitting formations of the first and second packs of laminations are profiled so that deformation of said formations positively urges the first and second packs of laminations together.

19. A method according to any of claims 16 to 18, wherein the first and second laminations of each pack are stamped from sheet nest within one another so that they can be stamped from sheet substantially without waste.

20. A pack of laminations for use in an electromagnetic device, said laminations having spaced convergent faces for receiving deformable projections of laminations of a complementary pack that when deformed onto said faces lock the packs of laminations together.

21. A pack of laminations for use in an electromagnetic device, said laminations having spaced clamping projections for fitting onto convergent faces of a lamination of a complementary pack and that when deformed onto said faces mechanically lock the laminations together.

22. A lamination for use in an electromagnetic device having spaced convergent faces for receiving deformable projections of a complementary lamination that when deformed onto said faces lock the laminations together.

23. A lamination for use in an electromagnetic device having spaced clamping projections for fitting onto convergent faces of a complementary lamination and that when deformed onto said faces mechanically lock the laminations together.

24. A transformer having a lamination assembly as claimed in any of claims 1-15 or made by the method of any of claims 16-19.

25. A choke having a lamination assembly as claimed in any of claims 1-15 or made by the method of any of claims 16-19.

26. An electric motor having a lamination assembly as claimed in any of claims 1-15 or made by the method of any of claims 16-19.

27. First and second laminations for an electromagnetic device having fastening formations sudbbstantially as hereinbefore described with reference to and as illustrated in any of the accompanying drawings.