B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
B21C—MANUFACTURE OF METAL SHEETS, WIRE, RODS, TUBES, PROFILES OR LIKE SEMI-MANUFACTURED PRODUCTS OTHERWISE THAN BY ROLLING; AUXILIARY OPERATIONS USED IN CONNECTION WITH METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL
B21C23/00—Extruding metal; Impact extrusion
B21C23/02—Making uncoated products
B21C23/03—Making uncoated products by both direct and backward extrusion
Procédé de fabrication d'une douille cylindrique munie de rainures intérieures fermées à l'une au moins de leurs extrémités et douille ainsi obtenue