US3579261A

US3579261A - Making of rivet head bimetallic electrical contacts

Info

Publication number: US3579261A
Application number: US767321A
Authority: US
Inventors: Hans Wacker
Original assignee: RENZ WACKER AND CO
Current assignee: RENZ WACKER AND CO
Priority date: 1967-10-12
Filing date: 1968-10-14
Publication date: 1971-05-18
Anticipated expiration: 1988-05-18
Also published as: CH482479A; DE1627696A1; DE1627696B2; FR1589272A

Abstract

A rivet head is formed on a bimetallic electrical contact wire by striking one end of the wire with flat surfaced cam means while retarding the advance of the wire by spring-loaded cam means.

Description

United States Patent Inventor Hans wacker 501 Field of Search 219/154, Heidelberg, Germany 149, 150, 15 1; 72/354, 452, 407, 358; 10/1 1, 15, [21] Appi. No. 767,321 24, 26 221 Filed Oct. 14, 1968 [45] Patented May 18, 1971 [56] References Cited [73] Assignee Renz Wacker & C0., Maschinen-u UNITED STATES PATENTS Y Kettenfabrik 4 1 309 523 7/1919 Hosford 219/150 [32] Pnonty Oct. 12, 1967 [33] a any 1,462,775 7/1923 Tr1ve1lon1 219/150 [31] P 16 27 696,3 Primary Examiner.i. V. Truhe Assistant Examiner-Lawrence A. Rouse Attorneys-Francis D. Stephens and Hugo Huettig, Jr. [54] MAKING OF RIVET HEAD BIMETALLIC 4 ELECTRICAL CONTACTS 7 Clam 8 mm ABSTRACT: A rivet head is formed on a bimetallic electrical [52] US. Cl 219/154 contact wire by striking one end of the wire with flat surfaced [51] Int. Cl B21j 5/06, cam means while retarding the advance of the wire by spring- H05b 1/00 loaded cam means.

TRA NSFORMA TOE Pgtgnted May 18;

2 Sheets-Sheet 2 INVENTOR Hans Wacker MAKING OF RIVET HEAD BIMETALLIC ELECTRICAL CONTACTS This invention relates to a method and apparatus for the production of resistance welded-shaped parts and especially to bimetallic welded electrical contacts made of wire in which the contact head is larger than the diameter of the original wire.

It is the object of this invention to make a more economical production than heretofore available and to improve the quality of the finished product with regard to the welding, final shape, technical and electrical characteristics.

Welded-shaped products, such as bimetallic-welded wire contacts of different metals, are produced either by cold-press welding or electrical resistance welding, that is, hot welding.

In the cold-press welding of bimetallic contacts, high pressures are used to enlarge the surfaces of the two metal components such as copper and silver which bear against each other. Since only a limited volume of both metals is available for the upsetting, more material is needed than is actually necessary for the formation of a large head. Thus, in coldpress welding, approximately the same volume of copper and silver is needed. Also, the length of the metal pieces must be such that they do not become bent during the upsetting process. Also, the rule for cold-press welding is that the quality of the cold weld increasesas the thickness of the welding layers decreases. In order to form the head, however, more material is needed as, forexarnple, copper. When the copper is fed in making a head, an upsetting fold or crease occurs during the-pressing-which can extend to the stem of a bimetallic contact. Cold-press welding of a bimetallic contact without an upsettingfold is only possible with small heads which are practically never used, that is, up to about 0.6 mm. of the rivet head height.

Bimetallic contacts produced by heat welding can be made without an upsetting fold in a limited manner, that is, with a relatively low head thickness of about I mm.

Upsetting folds made during the formation of the contact cause trouble in the finishedcontact. The electrical resistance at the fold becomes greater and that spot heats up. Since the electrical contacts strike each other constantly in the center of the contact surface, the layers which have the upsetting folds separate from one another in the course of time. Above all, this disadvantage occurs in high voltage switches.

Contacts have been produced from strip-plated bands or ribbons which are made by welding a layer of precious metal, such as fine silver and its alloys, on a layer of base metal, such as iron or monei, or by soldering under pressure inwhich a flux is used between the two combined metals. Thereafter discs are stamped out of the fine metallic bands. These discs are fed into presses or stamping tools in which they are upset to form the finished head and/or welded contact.

The strip-plated bands are also made by the cold-press welding of the metal components. This method is principally currently used in the United States. Again, discs are stamped out of the bands, which discs are then formed into the rivet contacts.

The strip-plated bands can also be produced on middle and/or high frequency automats into which a precious metal and a base metal band are fed. and followed by a welding process. After the welding, the bands are soft. The final The aforesaid method of producing strip-plated bands has numerous disadvantages. The forming of the initial stripplated starting material is very expensive. Because the discs have to be stamped out of the striplike plated material, there is a relatively high waste since it is expensive to separate the precious metal from the base metal in the waste or scrap. F urthermore, the volume rate of production in these methods is relatively low. Also, the reduction burning welding machine with electronic control is very costly.

Up to now it was, therefore, possible to produce bimetallic contacts from wires of different metals by cold-pressing or heat welding wherein the precious metal layer for the most part was composed of silver and its alloys and the base metal was copper. These are combinations of metals whose electrical conductivity differs very little from one another. It has been impossible up to now to produce the so-called head and/or welded contacts of wires of different metals, on the one hand, because the great difference in their electrical conductivity between the base metal, such as iron or monel, and the coating layer, such as silver and its alloys, and, on the other hand, because of the difficulty in shaping the welding contacts.

In the method and apparatus of this invention, it is now possible to produce bimetallic contacts as well as head and/or welded contacts from wires of differentmetals in the required size and with the desired and necessary characteristics in one and the same machine, which has not heretofore been possible. In this invention, the precious metal wire in a resistance welding process using alternating current is supplied with a diameter which is somewhat smaller than that of the base product is therefor subsequently cold-formed on profile cylinders to obtain the desired mechanical stability. Following this, again, is the stamping out of the discs and the shaping of the same.

Also, another method is used for the production of the head and/or welded contacts in that the discs are stamped from the base metal. These discs are fed into reduction welding machines which weld an exactly measured coating or layer of precious metal onto the disc from a roll of wire controlled by an electronically programmedmachine. Following this is the pressing process to obtain the finished head and/or welded contact. This method is principally used in the U.S.A. and in England and is known under the term paddling".

metal wire, and in a direct current condenser discharge surge welding process with the diameter that is the same as that of the base metal wire, as well as with various lengths of wire components in relation and depending upon the difference in the conductivity of the wire ends which are welded together. The wires are fed toward each other until the two end abutting surfacesmeet and then are butt welded together in a flat seam. A welded piece of any desired length is then cut off and introduced into a press for shaping the contact head. Thus for the hot welding of the two wires in this invention, the length of the metal conductors as well as the diameter of the wires is changed in order to equalize the difference in the electrical conductivity values.

In a further feature of this invention, the head is shaped by means of a continuous movement of the upsetting die in an assembly line pressing process with a simultaneous continuous forward feeding of the initial wire from the support. Following 'the preshaping of the head by means of this continuous pressing operation, it is possible to finish the head by means of one single upsetting hammer stroke.

The apparatus for performing the method of this invention has a die for holding the wire which is to be upset in which is a rod driven by a cam having several cam surfaces following one another, the wire being driven against a counter springloaded die which is retarded in movement by a cam having a continuous surface. In the cam having several surfaces, the first three surfaces form a rising straight line and the following two surfaces intersect in an-obtuse angle Y.

The means by which the objects of the invention are obtained are described more fully with reference to the accompanying drawings in which:

FIG. 1 is a crossasectional view through the welding apparatus;

FIG. 2 is a cross-sectional view through the upsetting rivet head tool;

FIG. 3 is a'view similar to FIG. 2 showing a further step in the upsetting operation;

FIG. 4 is a detailed view of a part of FIG. 3 showing the final form of the rivet head;

FIG. 5 is an enlarged cross-sectional view through a partially formed bimetallic contact;

FIG. 6 is a view similar to FIG. 5 showing the finished contact-head;

FIG. 1 is a View similar to FIG. but showing a modified are feeding slides'joined on one side to the welding trans-' former by copper bands and the other side being connected to shearing knives 5. The distance between the contacting ends of the wires 1 and 2 from the shearing knives 5 depends upon the difference in the electrical conductivity of the wires being welded and varies in this butt welding process. When the necessary welding pressure, which is dependent on the wire diameter, is obtained, the welding surges are initiated by means of a transistorized welding machine control, not shown, and this causes the welding of the abutting ends of the wires 1 and 2. The

electrodes

3 and 4 forming the forward feeding slides are moved into cutting position for the length of wire desired. The adjustable shearing knife blade 6 moves in the direction of the arrow C and shears off the length of the welded-wire in cooperation with the knives 5. The finger 7 mounted in a reciprocatable slide 8' which moves in the direction of the arrow D picks up the sheared off bimetallic wire 12 and carries it to the entrance of die 9. The springloaded initial die press 10 pushes the bimetallic wire into the opening in the die 9. which, in turn, is carried by a block 11. Bimetallic wire 12 is then pushed by an upsetting shaft 13 driven by a plunger 14 against the die 10. The plunger 14 has at its opposite ehd a cylindrical pin 15 which, in turn, is driven by a continuously rising eccentric cam 16. The spring-loaded initial die 10 which is mounted in a recess 17 attached toa roller slide 18 moves slowly back with its movement being controlled by the curved cam 19. The cam surfaceof cam 19 is such that the movement is limited to about from L5 to 2 mm. Thus, because the continuously rising cam 16 works together with the. slowly falling cam 19, the bimetallic wire, as shown in FIGS. 3 and 5, is gradually formed. The upsetting .shaft 13 for forming the contact has a recess in the end of the shaft for forming a contact with a welding boss on it, as indicated in FIG. 4. If the required finished form cannot be obtained by the continuous pressing operation alone, then the cam can be shaped to give a final upsetting stroke to finish the electrical contact. If desired, a third cam can be employed for this'purpose.

Two different types of electrical contacts are shown in FIGS. 5 to 8 In FIGS. 5 and 6, the'bimetallic contact has a stern, and in FIGS. 7 and 8 the bimetallic contact has a welding boss. FIGS. 5 and 7 show the preformed contacts, and

FIGS. 6 and 8 show the complete finished contacts. The contact in FIGS. 5 and 6 has been welded from two pieces of wire to form a bimetallic rivet contact formed with a layer of precious metal 20 on the head of base metal 21 which includes a stem 22. These rivet contacts are used mainly for the removable and exchangeable contacts with springs, for example, for switches and relays in the electricalfield. The contact shown in FIGS. 7 and 8 is also made from welded wires so that the final contact has a precious metal layer 23 on the head 24 of base metal and which includes a welding boss 25. These welded contacts are used primarily for the permanent and irreplaceable welding of contact springs and contact bands for switches and relays.

lclaim: f

l. A-method of making bimetallic electrical contacts comprising the steps of feeding the ends of two elongated wires,

' one-of the base. metal, the other of the precious metal of which the contact is to bemade, into end to end contact, the 'wires being supported by welding electrodes, the lengths of each e ual parts, passing electric current through the wires to effect a utt weld, severing a piece including the welded ends of the wires from the long lengths of wire, placing the severed piece in an upsetting press and shaping the piece to form an electric contact head.

2. The method of claim 1 in which the head is formed in the press by continuously advancing the severed piece against a surface moving in the same direction but at a lesser speed.

3. The method of claim 1 in which the wire of the precious metal wire is of less diameter than the base metal wire.

4. The method of claim 1 in which the diameters of the wires are the same.

5. The method'of claim 4 in which the electric current is the discharge of a condenser. I

6. The method of claim I in which the electric welding current is direct current.

temating current.

Claims

1. A method of making bimetallic electrical contacts comprising the steps of feeding the ends of two elongated wires, one of the base metal, the other of the precious metal of which the contact is to be made, into end to end contact, the wires being supported by welding electrodes, the lengths of each wire from its electrode to its contact with the other wire being such, depending on the electrical conductivity of the wires as to divide the electrical resistance between the electrodes into equal parts, passing electric current through the wires to effect a butt weld, severing a piece including the welded ends of the wires from the long lengths of wire, placing the severed piece in an upsetting press and shaping the piece to form an electric contact head.

4. The method of claim 1 in which the diameters of the wires are the same.

5. The method of claim 4 in which the electric current is the discharge of a condenser.

6. The method of claim 1 in which the electric welding current is direct current.

7. The method of claim 1 in which the welding current is alternating current.