Patent GB-667278-A (GB)
Title: Improved manufacture of commutators for dynamo electric machines
IPC: H01R43/06
Filed: 1948-11-16
Abstract: 667,278. Making dynamo &c. commutators; dies; jointing by stamping. GENERAL MOTORS CORPORATION. Nov. 16, 1948 [Nov. 29, 1947], No. 29750/48. Classes 83 (ii) and 83 (iv). Forging; flanging; jointing by stamping.-A commutator, comprising an annulus of metal bars 20 and insulator segments 21 retained on a tubular rivet 22 by means of clamping rings 23 separated from the bars by insulation rings 24, is made by forming a tightly-compacted annulus A of the bars and segments, forming V-grooves 28 to produce a dovetail shape on a tang 27 provided on each bar while the annulus is tightly compacted, assembling the annulus, rings 23 and insulation 24 on the rivet, and deforming the rivet to force the clamping rings into the V-grooves while the annulus is still tightly compacted. The annulus A, Fig. 1, is assembled in a ring 30 from which it is pressed by a plunger 36, Fig. 7, into a building ring 31 against the action of a spring- pressed plunger 35, the ring 31 being of a lesser diameter than the ring 30 so as to tightly compact the annulus. A press, Fig. 9, adapted to upset the edges of the tangs 27 and form the V- grooves 28 therein, has a topplate 48 and base B to support upsetting dies 42, 49 and a holder 52, 55 which carries the building ring 31 and annulus A. The holder 52, 55 is suspended by bolts 53 from the top plate 48 and guided on posts 46 which are secured to the base B and received at their upper ends in sleeves 47 so as to guide the annulus A on to a spring-pressed mandrel 41 when the plate 48 is fed downwardly on a ram of the press. This movement causes the annulus to engage the die 42 and the bolts 53 to slide in slots 54a in the top plate 48 until the die 49 engages the upper edges of the tangs 27; the dies then upset the edges and form the V-grooves. Bolts 40a, on which the holder slides, are secured to a part 40 of the base B. The insulating rings 24 each comprise preferably four washers of glass cloth impregnated with a substance that creates heat on compression and are pressed into the V-grooves by dies 64, 68 in a press, Fig. 11, which support the building ring 31 and annulus A on a resilient platform 63. The generation of heat by the rings 24 as they are compressed allows them to be deformed permanently. The rivet 22, Fig. 13, on which the annulus and insulating rings 24 are secured by the clamping rings 23, is reduced in thickness intermediate its ends by a groove 26 and formed with a flange 25 at one end. This end is located on a die 73 of similar shape carried by a tube 71 which is located on a base 70 supported on a press. A spring-urged block 75, also located on the base 70, carries the building ring 31 and annulus A which are assembled with the clamping rings 23 on the rivet. A second die 80, formed with a conical end, is secured to a holder 81 attached to the ram of the press and advanced by the ram to engage the rivet 22 and expand it outwardly around the upper ring 23 as the block 75 engages the base 70 against the influence of springs 76. When the die 80 is withdrawn, the building ring 31 and rivet 22 are stripped from the die 73 by expansion of the springs 76. A second flaring operation is effected by a tool of similar construction, in which the flaring edges of the dies are so shaped as to curl the ends of the rivet around the clamping rings 23. The annulus, complete with clamping rings, is then forced out of the building ring 31 and through a C-ring by a plunger. The rivet is finally compressed between heating electrodes, Fig. 17, to effect a hot upsetting of the material at the groove 26 and cooled under compression by compressed air passing through ducts 91, 94 in the electrodes so as to further grip the rings 23 as it contracts on cooling.