CONTACT WELDING IN WIKE ttl'KlNC KELAYS 899 



mot on the location of the pnM-ious metal. For example, Fiji;. 5, the upper 

 contact surfaces had to be located with a precision of 0.004 inch. The con- 

 tact itself had to he centered lateially with respect to the straight portion 

 of the wire within 0.004 inch. X'ariahles in the \vir(^ materials, such as 

 elasticit}', make such limits difficult to meet. The wires in the twin 

 combs are oriented in pairs to pro^'ide bifurcated contacts, i.e., the con- 

 tacts on both wires of any pair mate with one stationary contact of the 

 single wire comb to furnish two current paths. Any number of pairs 

 up to a maximum of twelve may be required })j^ a code of relays. To 

 conser^'e precious metal, contacts are welded only to those wires needed 

 for a particular comb. The wires not required are clipped from the comb 

 l)y a hydraulic press operated die in the automatic welding and wire 

 forming line. 



The 24-circuit capacitor discharge resistance welders, one of which is 

 shown in Fig. 3, were designed and constructed for welding twin wire 

 contacts. As stated before, this welder is one of the units in a welding 

 and wire forming line. Combs from the molding operation are delivered 

 to the beginning of the line in magazines. By fully automatic means 

 they are removed from the magazine, carried by a reciprocating conveyor 

 through each machine luiit in the line and, when fully processed, placed 

 in another magazine. The line of machine units, Fig. 4, forms the con- 

 tact end of the ^^■ires, degreases the wires, welds the contacts to the 

 \nres, coins the contacts to the specified dimensions, forms the termi- 

 nals, clips the ends to length, tension bends the wres, removes unneces- 

 sary ^Wres and tins the terminal ends. 



REASONS FOR SELECTION OF PROJECTION TYPE RESISTANCE WELDING 



A capacitor discharge resistance projection welder was chosen for 

 this job for the following reasons: 



1. It is capable of welding automatically in a line of other machines. 



2. It can pro\'ide the fast rate of temperature build-up required to 

 prevent excessive heating of the small nickel silver wire ends. 



3. A capacitor, charged to a fixed voltage, offers a good means of con- 

 trolling weld energy within narrow limits. 



4. Resistance projection welding can concentrate heat at the point 

 required. The use of a projection at the welding interface lowers the 

 electrical current needed to a value which can be handled by electrodes 

 without excessive heating. By plachig a projection on the metal with the 

 lower electrical resistance, in this instance the palladium, the temperature 

 of the palladium can be increased in the weld zone as compared to that 

 of the nickel silver wire, thus securing a better heat balance at the joint 



