GB2024667A

GB2024667A - Manufacture of commutators

Info

Publication number: GB2024667A
Application number: GB7921334A
Authority: GB
Original assignee: QUALTEX IND Ltd
Current assignee: QUALTEX IND Ltd
Priority date: 1978-07-07
Filing date: 1979-06-19
Publication date: 1980-01-16

Abstract

A method of making a commutator for electric motors and generators comprises extruding a strip of metal, coining recesses and ridges 5, cutting slots 8 to form tongues 9, shining ridges 5 and leading up the ends, forming the strip into a cylinder, Figure 5, moulding insulating material inside the cylinder, leading over tongues 9 to form connecting points, and cutting slots in the cylinder to form commutator segments. <IMAGE>

Description

SPECIFICATION.

Improvements in or relating to methods of manufacturing commutators: This invention relates to methods of manufacturing commutators for electric motors and generators.

A commutator consists of a plurality of segments of electrically conductive material and electrically insulating material arranged alternately around the surface of a cylinder. At one time it was normal practice to manufacture a commutator from separate segments of copper and mica. However, it is now more usual, at least in the case of relatively small motors and generators, to produce a ring of electrically conductive material, to embed the ring in insulating material by a moulding process, and thereafter to cut the ring into the required number of segments.

Usually the ring is produced from a strip of copper, or similar electrically conductive material, which is then broached form a plurality of channels extending parallel to the axis of the ring and facing radially inwards. It is to be understood that, after the ring has been embedded in the electrically insulating material, the bases of the channels are cut away so that the commutator segments are formed by the ridges which remain between the channels.

In order to improve the adhesion of the copper to the insulating material, it is usual to skive the ends of the ridges before the moulding process in order to form projecting tangs which lock the copper to the insulating material. Further, it is common practice to make a plurality of cuts in the copper at one end of the ring in order to form tabs which will be used for making connections to the armature winding in the finished motor or generator.

The broaching operation referred to above involves the removal of a considerable amount of copper from the ring and, accordingly, it is an object of the present invention to provide a modified process in which this removal of copper is avoided.

Accordingly, from one aspect the invention consists in a method of manufacturing a commutator for an electric motor or generator from a strip of electrically conductive material having a longitudinally extending marginal portion thinner than the remainder of the strip, including the following steps: 1) a plurality of parallel channels separated by ridges are formed extending transversely across the thicker portion of said strip; 2) a plurality of parallel slots are formed in said marginal portion, each slot being aligned with a respective one of said channels.

3) the ends of each of said ridges are deformed to make them project from the strip;and 4) the strip is formed into a ring with said ridges facing inwardly.

It will be understood from the above that a method in accordance with the invention differs from known methods of manufacturing commutators primarily in that the broaching operation carried out on the copper ring is replaced by an operation carried out on the copper while it is stiil in the form of a flat strip.

Accordingly, from another aspect the invention consists in a method of manufacturing a commutator for an electric motor or generator, including the step of forming a plurality of parallel transverse channels separated by ridges in a flat strip of electrically conductive material.

Preferably the channels and ridges are formed by a-coining operation. In other words, the strip of electrically conductive material is placed in a press provided with a tool having a plurality of parallel ridges separated by channels. During the pressing operation, the tool causes material in the strip to flow from the regions in contact with the ridges of the tool into the intervening channels of the tool, thus forming said series of parallel channels separated by ridges in the strip. It will be understood that an operation of this kind produces a result similar to that produced by the broaching operation of the known manufacturing method, but does not involve the removal of any of the electrically conductive material.

Preferably the slots in the marginal portion of the strip are produced by a piercing operation, and the deformation of the ends of the ridges is carried out by a skiving operation.

Preferably the three steps of coining, piercing and skiving are carried out successively in a multiple press.

Methods of performing the invention will now be described with reference to the accompanying diagrammatic drawings, in which : Figure 1 is a perspective view of a blank cut from a continuous strip; Figure 2 shows the blank illustrated in Figure 1 after it has been subjected to a coining operating; Figure 3 shows the blank illustrated in Figure 2 after it has been trimmed and pierced; Figure 4 shows the blank illustrated in Figure 3 after it has been subjected to a skiving operation.

Figure 4a is an end view of the blank illustrated in Figure 4; Figure 4b is an end view of a blank generally similar to that illustrated in Figure 4 after it has been subjected to a modified skiving operation; Figure 5 is a perspective view of the blank illustrated in Figure 4 after it has been formed into a ring; Figure 6 shows the blank illustrated in Figure 5 after a moulding operation; Figure 7 shows the blank illustrated in Figure 6 after the tabs on the end of the blank have been turned over; and Figure 8 shows the finished commutator.

The blank illustrated in Figure 1 includes a main portion 1, a relatively thin marginal portion 2, and an intermediate portion 3 having a thickness between that of the portions 1 and 2. The blank is cut from a continuous strip of copper which is extruded to the shape shown in Figure 1.

The blank illustrated in Figure 1 is subjected to a coining operation in a press provided with a tool having a plurality of parallel ridges separated by channels. During the pressing operation, the tool causes material in the strip to flow from the regions in contact with the ridges of the tool into the intervening channels of the tool, thus forming a series of parallel channels 4, as shown in Figure 2, separated by upstanding ridges 5.

In the next operation, which is preferably carried out in the same press as the coining operation, end portions 6 and 7(Figure 3) are trimmed from the blank and slots 8 are formed by a piercing operation in the marginal and intermediate portions 2 and 3 of the blank. This piercing operation forms a plurality of tabs 9, each of which is aligned with a respective one of the ridges 5.

In the next operation, the ends of the ridges 5 are deformed by means of a skiving operation. This operation may be a single skiving operation to produce a blank as illustrated in Figures 4 and 4a in which the ends of the ridges are shown bent upwardly at 10 and 11. Alternatively the operation may be a double skiving operation to produce not onlythe upturned ends 10 and 11, butalsotwo further curved portions 12 and 13 as shown in Figure 4b.

In the next operation, the blank illustrated in Figure 4 is bent by means of a suitable tool to form a ring as shown in Figure 5. It will be seen that the trimmed ends of the blank meet along a line 19. The trimming operation referred to is carried out in such a way that, after the ring has been formed, the spacing between adjacent tabs 9 on each side of the line 19 is idential with the spacing between the remaining tabs 9. The ring is then transferred to a mould in which synthetic resin insulating material is introduced into the interior of the ring as shown at 14 in Figure 6. It will be seen that the ridges 5 and, in particular, the upturned ends 10 and 11 are embedded in the insulating material. Thus these parts form a key to lock the ring to the insulating material 14.

After the insulating material has set, the ring is placed in a lathe or similar tool and, if necessary, skimmed to ensure that the outer surface of the ring 16 is coaxial with the axis of rotation which is indicated at 15.

In the next operation, the tabs 9 are bent over as shown in Figure 7 to provide terminals for connection of the armature winding when the commutator has been mounted on the armature.

Finally, slots 17 are cut through the ring between the ridges 5 which are now embedded in the insulating material 14. It will be understood that the slots 17 extend right through the base of the channels 4 so that separate commutator segments 18 are formed by the ridges 5 and the remaining material of the portion 1 below each ridge. It will also be understood that each one of these segments will be integral with a respective one of the tabs 9.

Finally, it will be understood that one of the slots 17 will embrace the line 19 between the ends of the trimmed blank.

The process described is suitable for production of commutators for relatively small electric motors and generators. However, a modified form of this pro cess can also be applied to larger commutators. In this case, it is preferable to form the ring from two separate semi-circular portions each produced from a blank similar to that shown in Figure 1. In even larger machines, the commutator could be formed from three or more portions.

Claims

1. A method of manufacturing a commutator for an electric motor or generator, including the step of forming a plurality of parallel transverse channels separated by ridges in a flat strip of electrically conductive material.

2. A method as claimed in Claim 1, wherein the channels and ridges are formed by a coining operation.

3. A method of manufacturing a commutator for an electric motor or generator from a strip of electrically conductive material having a longitudinally extending marginal portion thinnerthan the remainder of the strip, including the following steps: a) a plurality of parallel channels separated by ridges are formed extending transversely across the thicker portion of said strip; b. a plurality of parallel slots are formed in said marginal portion, each slot being aligned with a respective one of said channels; c) the ends of each of said ridges are deformed to make them project from the strip; and d) the strip is formed into a ring with solid ridges facing inwardly.

4. A method as claimed in Claim 3, wherein the channels and ridges are formed by a coining operation.

5. A method as claimed in Claim 3 or 4, wherein the slots in the marginal portion ofthe strip are produced by a piercing operation.

6. A method as claimed in any of Claims 3 to 5, wherein the deformation of the ends of the ridges is carried out by a skiving operation.

7. A method as claimed in Claims 4,5, and 6 in which the three steps of coining, piercing and skiving are carried out successively in a multiple press.

8. A method as claimed in any of Claims 3 to 7, wherein insulating material is introduced into the interior of the ring so that the said ridges are embedded in the insulating material.

9. A method as claimed in Claim 8, wherein a plurality of parallel slots are cut through the material of the ring not embedded in the insulating material, each of said slots being aligned with one of said parallel slots formed in said marginal portion.

10. A method of manufacturing a commutator for an electric motor or generator from a strip of electrically conductive material having a longitudinally extending marginal portion thinner than the remainder of the strip including the following steps a) said strip is cut into a plurality of lengths; b) a plurality of parallel channels separated by ridges are formed extending transversely across the thicker portion of each of said lengths; c) a plurality of parallel slots are formed in the marginal portion of each of said lengths, each slot being aligned with a respective one of said channels; d) the ends of each of said ridges in each of said lengths are deformed to make them project from the respective length; e) each length is formed into a segment of a circle with said ridges facing inwardly; ; f) a plurality of said lengths forming a complete ring are inserted in a mould and insulating material is introduced into the interior of said ring, and g) slots are cut in each of said lengths to form a plurality of commutator segments, each aligned with a respective one of said ridges embedded in said insulating material.

11. A method of manufacturing a commutator for an electric motor or generator substantially as hereinbefore described with reference to the accompanying diagrammatic drawings.

12. Acommutatorforan electric motor or generator manufactured by a method as claimed in any of the preceding Claims.

13. Any features of novelty, taken singly or in combination, of the embodiments of invention as hereinbefore described with reference to the accompanying diagrammatic drawings.