this maximum efficiency and value of a corresponding to it vary with final radius x f and the efficiency increases as the cut off radius is reduced it is apparent from the foregoing that efficiency can be maximized and thus the size of the bank necessary to accelerate a given work piece to the impact welding velocity can be minimized by matching the characteristics of the work piece to those of the capacitor bank or power source through the choice of a max for a given x f the work piece 10 in fig1 and 2 includes a chamfered section above which the driving coil and associated equipment are disposed so that upon implosion the ballistic work piece welds the pipe 12 and fills in the chamfered portions thereof flexible electrical insulators 16 are connected to the ballistic work piece 12 and an electrical insulator 17 prevents short circuiting of the driving coil 18 referring to fig4 and 5 this depicts the situation of a ring shaped driving coil driving a ring shaped work piece this applies to the situation which would occur in connection with impact welding of pipe and other cylindrical pieces the arrangement comprises a work piece 20 in the form of a pipe such as that employed in connection with oil pipelines the work piece 20 includes chamfers 21 that are of the conventional 60 90 degree type employed in conventional fusion welding arrayed.