Method of and apparatus for fabricating spiral wrapped cartridge cases

A method of fabricating spiral wrapped cartridge cases or the like each of which includes a base and a hollow body made of spirally wrapped sheet metal with the margins of the sheet metal at least partially overlapped, one end of said body being securable to the base and the other end of the body being open and constituting a mouth for the cartridge case, said method comprising:

• placing a base and a body in a cavity in a die, the cavity being shaped to form the body into the desired shape for the cartridge casing or the like by expansion of the body, said die being part of an assembly comprising an expandable bladder in the cavity and a hydraulic pressure generator adapted to deliver hydraulic fluid under pressure to the bladder for expanding it on compression of said assembly;
• the body being positioned for expansion of the bladder therein;
• positioning said assembly with the base and body in the die in a press between platens of the press;
• closing the platens to effect compression of said assembly for delivery of hydraulic fluid under pressure to the bladder to expand it for forming the body in the die;
• during an initial portion of the closing motion of the platens, delivering hydraulic fluid from the hydraulic pressure generator at a relatively low hydraulic pressure level and at a relatively high flow rate to said bladder to expand said bladder into engagement with the body, in response to the closing of the platens;
• during a subsequent portion of the closing motion of the platens, delivering hydraulic fluid from the hydraulic pressure generator at a relatively high hydraulic pressure level and at a relatively low flow rate to said bladder to expand said bladder to form the body in the die cavity, in response to the closing of the platens;
• and including moving the platens through said initial and subsequent portions of their closing motion at a substantially constant speed.