[0001] This invention relates to laminations for electromagnetic cores particularly for
shell-type transformers.
[0002] In such transformers, the core comprises three I 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.
[0003] 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 is 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.
[0004] 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.
[0005] An advantage of this form of lamination is that it is available with resiliently
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.
[0006] Laminations made up of two F-shaped parts have previously been proposed in US Patent
No. 581,873 (Thomson), 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.
[0007] 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 edges 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 5%.
[0008] 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.
[0009] 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.
[0010] 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.
[0011] 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.
[0012] 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. In 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.
[0013] 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.
[0014] 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 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.
[0015] 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.
[0016] 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.
[0017] 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 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 9 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
16b is not essential since flux does not have to cross any gap between these edges.
[0018] 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 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 32b and 32a at the inside corner between the limbs 4b,
8b and 4a, 8a.
[0019] 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.
[0020] 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 I 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.
[0021] 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.
[0022] 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.
[0023] 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.
[0024] 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 tnat the cutting tool may wear. The apertures
64, however, form the recesses 42a and 42b and therefore are appropriately shaped.
[0025] 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.
[0026] 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. ,
[0027] 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.
[0028] 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.
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 F's 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 strip 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 pair of each adjacent pair of
the nested pairs of Fs commences before detachmen 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 F's 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 by 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 first 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.