PERCUSSIVE WELDING 895 



mined ])y the mass of the gun and the stillness of the statio!iarv part to 

 he welded. 



The effeets on weld (niality of that hammer blow jjioduced by the 

 gun are not well understood but there is some evidence that this l)i()w 

 may be advantageous in producing intimate mixing. 



SUMMARY 



The basic processes of percussive welding haxe been discussed. Large 

 variations in arc duration are caused by the spread in the initiation 

 separation, l^ridging phenomena, and the amplifjdng effect of evapora- 

 tion. 



The relative spread of initiation separation is minimized by working 

 at high \oltages, in excess of 1,000 volts. Bridging, which causes pre- 

 mature extinguishing of the arc, is minimized by maintaining the ratio 

 of current to separation at a minimum. 



A welding circuit offering independence from arc duration variations 

 has been developed on the basis of one-dimensional heat flow. The analy- 

 sis presented suggests a capacitative transmission line, which can how- 

 ever be approximated by two or more r-c sections. Greatly improved 

 process control has been effected with this circuit. 



ACKXOAVLEDGMENT 



The author gratefully acknowledges the assistance of J. J. Madden 

 in all phases of experimentation connected with this project. Miss L. 

 Mitchell performed the study of breakdown voltage. S. P. Morgan sug- 

 gested the model of bridging time. 



