COXTACT WELDING IX WIKE 81'1{1N(J I{ELAYS 1)03 



The projection also confines the location of the weld to a central area 

 of the wire end. When the weld nugget is confined to a central area, cold 

 surrounding metal helps prevent flashing out of hot metal and results 

 in stronger welds. To further centralize the weld nugget and to limit 

 the projection area in contact with the nickel silver wii-e, the wire siu*- 

 face is preformed to a large radius at right angles to the weld bead. 



WELDER HEAD OPERATION 



Welding is done in two stages. Head No. 1 welds the odd numbered 

 \\ires of each pair, after which the comb is advanced and head No. 2 

 welds the even number wires. This is necessary because of the small 

 distance between the wire centers. The electrodes in each head are spaced 

 to match the interval between odd or even numbered ^^^re centers. Fig. 5 

 shows an isometric sketch of a welding head. The sequence of operations 

 for either head is as follows: 



1. The tAnn A\'ire comb is advanced to a locating nest and lowered into 

 position with the reference holes in the plastic engaged on pilot pins. 



2. As the comb is lowered, the contact wires enter guide slots of a rake 

 at a point adjacent to the plastic. 



3. This rake is moved toward the ends of the wires, thereby spacing 

 and positioning them as shown in Fig. 5. A plastic spacing member is 

 incorporated in the relay for aligning the contacts in the relay assembly. 



4. The palladium contact metal, in tape form, is advanced the proper 

 distance to pro\'ide a contact of the specified length. These tapes, parallel 

 \Wth the \Aires, extend from guide slots for a distance slightly greater 

 than a contact length and project over the \\are ends. The tape guide 

 slots, incorporated in a split holder, consist of steel inserts embedded in 

 phenol fibre so designed that when the upper section is shifted laterally 

 with respect to the lower section, the steel inserts clamp or release the 

 tapes. Since the rake is located A\ith reference to the tape guide, accurate 

 spacing of contacts in the relay assembly is secured regardless of minor 

 deviations of position of the wire ends at the welding machine. The 

 phenol fibre mounting electrically insulates the tapes from one another 

 to prevent part of the weld current from passing through adjacent tapes. 



5. The upper electrodes, on the end of cantilever arms, are brought 

 do^vn on the palladium-nickel silver wire assembly. 



6. The capacitors are discharged and the welds are made. 



7. The upper electrodes are pivoted upward out of the way. 



8. The ^^^re guide rake is returned to a position near the plastic. 



9. The upper shear blade is lowered onto the contact ends clamping 

 them against the loAver electrode. 



