918 THE BELL SYSTEM TECHNICAL JOURNAL, JULY 1954 



WELDING GUNS 



The welding gun is a light reciprocating member that carries two 

 opposing steel fingers or jaws to receive the contact block from the 

 transfer finger mentioned above. The jaw opening is a few thousandths 

 of an inch less than the nominal height of the contact, however, the edges 

 are beveled so that when a contact is pressed against them they spring 

 open, the contact enters and is held securely in place. After welding the 

 jaws are pulled off the contact. At the extreme return travel of the gini 

 any contact which might remain in the jaws because it was not properlj^ 

 welded is removed by an ejector blade. When in the loading position, a 

 portion of the blade stops the travel of the contact through the jaw 

 opening so it is held in a uniform position and A\ill be located on the Anre 

 with precision. 



GUN MASS CONSIDERATION 



During welding the comb must be supported accurately to meet the 

 close contact location requirements. It must be supported securely to 

 ^\^thstand the impact of the guns, or weak welds may result. The mass of 

 the gun is important. Evidence indicates that more uniform and higher 

 weld strengths are obtained with lightweight guns. A magnesium gun 

 weighing about 60 grams produced better welds than did the original 

 steel gun weighing about 130 grams. A newly installed steel gun weighing 

 about 30 grams appears to be even more satisfactory. Other guns are 

 being designed and tested to further check various features. A striking 

 force of approximately 75 pounds tends to loosen the ^^dres in the plastic 

 and to produce weak welds. The 60 and 30 gram guns propelled at about 

 40 inches per second at impact produce less than half this force. The 

 velocity during the arcing period is important to control the amount of 

 heating. One-half cycle of vibration of jaw and ^^dre after impact is the 

 time available for the weld to freeze before a tension strain is placed on 

 it. This time has been measured in the laboratory by the use of a trans- 

 ducer. Weak welds resulted when the time was less than 1 millisecond. 



ELECTRICAL FUNCTIONS 



Fundamentally, each weld circuit includes a capacitor which is 

 charged during a small portion of each cycle and subsequently discharged 

 through a resistance in series with the weld. During the charging period, 

 which is controlled by a cam and microswitch, the contact and the 

 wire end of the comb are separated electrically at the weld point. A mul- 



