WELDING OF LAMP LEADS TO STRANDED WIRES

Abstract: A method for attaching stranded wires (50, 52) to lamp pins (24, 26), and the resulting lamp assembly, includes plasma welding the lamp pin to the stranded wire in an atmosphere of argon and hydrogen.

Description: WELDING OF LAMP LEADS TO STRANDED WIRES BACKGROUND OF THE INVENTION Field of the Invention This invention relates to the lamp arts, more particularly, this invention relates to a method of connecting a stranded lead wire to a lamp base pin and will be described with particular reference thereto. It should be appreciated, however, that the technique is also suited to the formation of electrical connections between stranded wires and other electrical components. Discussion of the Art Stranded wires, that is, wires formed from multiple strands of thin wire, generally shielded by an electrical insulator, are used in a number of applications for connecting lamps and other electrical appliances to a source of electricity. Resistance welding is generally used for forming a connection between the stranded wire and the lamp base pin . Prior to welding, a strip of the insulation is removed at the end of the stranded wire and a metal welding strap or collar is placed around the loose, exposed strands to form a bundle. An electric current is then passed across the stranded wire and the lamp base pin to resistance heat the two components. Such stranded wire connections are used, for example, in aircraft runway markers where it is important to have a long, effective life. However, this technique tends to result in poor weld reliability. First, the welding strap is compressed during welding and the seam, where ends of the straps meet, tends to open, allowing some of the wire strands to escape. As a result, the connection is not as electrically efficient as it could be if all the strands were included. Second, the weld does not melt the entire bundle of strands, sometimes leading to poor mechanical strength of the weld, and poor passage of the current. This is because, during heating, the current takes the path of least resistance and it is at this point where the weld is formed. Therefore, the extent and position of the weld is often undefined. These problems result m a number of welded connections being rejected. The present invention provides a new and improved method of connecting stranded wires to lamp wires and which overcomes the above referenced problems and others. BRIEF SUMMARY OF THE INVENTION This application is directed to a method for connecting a lamp base pin to a stranded wire which includes plasma welding the stranded wire One advantage of the present invention is the provision of a new and improved method of attaching stranded lead wires to lamp pins which is reliable and reproducible. Another advantage of the present invention is the provision of a weld with higher mechanical strength and an improved electrical path. BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is an exploded front view of a lamp assembly, FIGURE 2 is an alternative embodiment of lamp base pins attached to stranded wires, according to the present invention; FIGURE 3 is another alternative embodiment of lamp base pins attached to stranded wires, according to the present invention, and FIGURE 4 is a schematic view of a system for welding stranded wires to lamp base pins . DETAILED DESCRIPTION OF THE INVENTION With reference to FIGURE 1, a lamp or light source A includes an envelope 12, optically aligned and cemented in reflector base 14 A light emitting filament 16 is enclosed within the envelope Filament leads 18, 20 hermetically sealed in a seal region 22 of the envelope, electrically connect the filament 16 with lamp base pins 24, 26, here shown in the form of hollow nickel sleeves. The lamp base pins extend externally of the base 14 and/or seal region 22 for connecting the filament with a source of electrical power. With reference also to FIGURES 2, and 3, and the lamp base pins may be formed m a variety of different geometries. FIGURE 2 shows a pair of solid lamp base pms 30, 32, while FIGURE 3 shows lamp pins 34, 36, m which external ends of solid, connecting leads 38, 40 are each capped at their free ends with a hollow sleeve or ferrule 42, 44 The lamp pms can be formed from a variety of materials, such as nickel, molybdenum, nickel plated copper, or silver plated copper. For example, the lamp pms 24, 26 of FIGURE 1 may be nickel, the base pms 30, 32 of FIGURE 2, molybdenum, and the composite pins 34, 36 of FIGURE 3, molybdenum for the connecting pins and nickel for the ferrules 42, 44. With particular reference to FIGURES 2 and 3, a pair of stranded lead wires 50, 52 are attached to the lamp pins The stranded lead wires can be formed form a variety of materials. The wire includes a core 54 of multiple strands of conductive metal, such as copper, nickel plated with copper, or a high nickel composition, such as a 90% nickel composition The strands are preferably twisted together to form a compact wire The core 54 is surrounded by a layer of insulation 56 With reference now to FIGURE 4, the weld is created by plasma welding using a plasma beam The stranded wire 50, 52 and the corresponding lamp pin 24, 26, 30, 32, 34, 36 are overlapped by a distance sufficient for forming a weld. This distance is preferably about 0 5 to 5 millimeters, more preferably, an overhang of about 1 millimeter is used A plasma weldmg torch 60 is positioned about one to two centimeters from the overlapping wire and a generator 62 generates an argon plasma 64. The plasma gas is fed to the torch at a flow rate of about 0.1 to 0.3 1/mιn. It is ionized and fired at the overlap as a beam 66 of plasma ions from a nozzle 68 of the torch. An inert forming gas, such as a mixture of argon and hydrogen, preferably a 80:20 mix, surrounds the plasma beam 66 The nozzle 68 aids in focusing the beam to a cross section of desired width for forming the weld A potential is applied across the stranded wire 50, 52 and corresponding pm 24, 26, 30, 32, 34, 36 wire while the weld is formed. The overlap section melts and forms a homogeneous weld 70, as shown in FIGURES 2 and 3. The plasma weldmg creates a solid nugget 70 at the end of the stranded lead wire while it is melting. This ensures capturing all the wire strands creating a greatly improved electrical path and a higher strength mechamcal junction. The resulting weld has high mechanical strength, few unincorporated stranded wires, and a resulting high electrical conductivity. The method allows the nickel ferrule 42, 44 as shown in FIGURE 3 to be optionally eliminated Traditionally, the ferrule is added to improve formation of the weld during resistance welding The exemplary embodiment of the invention as described is particularly useful in environments where a constant current or high current on the order of greater than 6.0 amps, or more particularly about 6.6 amps, is encountered. In addition, environments where extreme vibrahons or G forces are encountered is another important consideration in using the plasma weld. The prior resistance welded arrangement was simply unacceptable and unreliable since the contacts in a porcelain socket added resistance and heat to the assembly. The plasma welded assembly of the present invention, on the other hand, provides a more reliable connection between the external pms of the lamp and the fixture The invention has been described with references to the preferred embodiment Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims: WHAT IS CLAIMED IS: 1. A lamp assembly for use in constant current and high current environments, the lamp assembly comprising: a light source (A) having a light transmissive envelope (12); first and second pins (24, 26) associated with the light source and having first ends disposed in sealed relation with the envelope and second ends extending therefrom; and first and second stranded wires (50, 52) for electrically interconnecting the first and second pins, respectively, to an associated fixture, the first and second stranded wires being plasma welded (70) to the pins to enhance the electrical path through the lamp assembly. 2. The lamp assembly of claim 1 wherein the stranded wires (50, 52) are one of copper, nickel plated with copper, and high nickel composition. 3. The lamp assembly of claim 1 wherein the light source (A) includes first and second lead wires (18, 20) extending from the first and second pins, respectively, the lead wires secured to opposite ends of a filament (16). 4. The lamp assembly of claim 1 wherein the first and second pins (24, 26) are molybdenum lamp leads extending from sealed relation with the envelope. 5. The lamp assembly of claim 4 further comprising first and second nickel sleeves (42, 44) received over the molybdenum lamp leads and the lamp leads, nickel sleeves and stranded wires being welded to form a homogenous nugget of all three components. 6. The lamp assembly of claim 1 wherein the first and second pins (24, 26) are nickel lamp leads (30, 32) extending from sealed relationship with the envelope and welded to the stranded wires. 7. A method of forming a lamp assembly having a light source (A) that includes a light transmissive envelope (12), first and second pins (24, 26) extending from sealed relation with the envelope, and first and second stranded wires (50, 52) for electrically interconnecting the first and second pins, respectively, to an associated fixture, the method comprising the steps of: overlapping the first and second pins with the first and second stranded wires, respectively; positioning a plasma torch closely adjacent the overlapped wires and pins: and welding the wires and pins together to form a homogenous nugget of material. 8. The method of claim 7 wherein the overlapping step includes positioning the pins and wires with an overlap of about 0.5 to 5 millimeters. 9. The method of claim 8 wherein the overlapping step includes positioning the pins and wires with an overlap of about 1.0 millimeter. 10. The method of claim 7 comprising the further step of applying an electrical potential across the stranded wires during the welding step. 11. The method of claim 7 wherein the welding step includes surrounding the pins and wires with an inert gas during the welding step.

Inventors: GREENWOOD RANDAL, KELLNER ROBERT JOSEPH, LAGERMASINI JOSEPH PAUL III, RACHEL BERNARD WHITE, GREENWOOD, RANDAL, KELLNER, ROBERT, JOSEPH, LAGERMASINI, JOSEPH, PAUL, III, RACHEL, BERNARD, WHITE
Applicants: GEN ELECTRIC, GREENWOOD RANDAL, KELLNER ROBERT JOSEPH, LAGERMASINI JOSEPH PAUL III, RACHEL BERNARD WHITE, GENERAL ELECTRIC COMPANY, GREENWOOD, RANDAL, KELLNER, ROBERT, JOSEPH, LAGERMASINI, JOSEPH, PAUL, III, RACHEL, BERNARD, WHITE
Application year: 2000
Main classification: B23K10
IPC codes: B23K10, H01J5, H01J61, H01K1, H01K3, H01R4