CONTACT WELDIXC; IX AVIKK SI'UIN(; UKLAYS 



913 



freoly, controlled only by its mass and the applied s])iiiiii; loi'ce. From 

 this study the presently used spring actuated welding gun has evolved. 



To determine the operating conditions that would l)e required, an 

 investigation was made in which a group of 48 contacts was welded 

 under carefully controlled conditions following which one condition 

 was \-aried and the tests repeated. Many curves were esta])lished in this 

 way for such variable factors as voltage, capacitance, resistance, spring 

 forc(^, and distance traveled; all related to weld strength. Weld strength 

 was measured by a hook-pull gage developed at Bell Telephone Labora- 

 tories. The "burn-off" i.e., reduction in length of the wire and contact 

 as a result of the arc heat, was determined in many of these tests because 

 it usually provided a measure of weld strength uniformity. Many other 

 concUtions were investigated such as the weldability of different metals; 

 the effect of cleanliness and of contamination on the joining metals; 

 the influence of the physical form of the joining metals, such as pointed, 

 rounded, or flat surfaces on wire ends; the effect of atmospheric condi- 

 tions, of the presence of various gases, or a stream of compressed air, 

 and of shields in or near the weld zone. The nature of the weld flash 

 deposit was studied. Neither streamers of base metal which might 

 extend over the edges of the palladium caps nor loosely adhering and 

 easily dislodged metallic particles could be tolerated. Charted data from 

 some of these tests are shown in Figs. 14, 15, and 16. 



Another phase of the in^-estigation was concerned with obtaining such 



0.01 Q1 1 5 10 20 30 40 50 60 70 80 90 95 



CUMULATIVE PER CENT OF CONTACTS WITH WELD STRENGTHS; 



99 99.9 



VALUE SHOWN 



Fig. 15 — Effect of voltage variation on weld strength. 



