A process for extruding an axle tube for use in an automotive vehicle and the like, comprising the steps of:
- positioning a tubular blank, in coaxial relationship, within an open ended, substantially circular die cavity having an inlet end through which the blank is inserted and an opposite extrusion end formed by an annular, inwardly extending, continuous shoulder providing a die extrusion throat through which the blank is extruded, and with the diameter of the throat being larger than the inner diameter of the tubular blank;
- inserting a punch into the inlet end of the die, and with the punch having an annular shoulder positioned against the trailing end of the blank, that is, the end remote from the throat, and with the punch having a first punch extension closely fitted within the interior wall of the blank, and with the punch having a second extension of a smaller diameter than the blank interior extending through part of the blank and die throat, and having a third punch extension, which is coaxial with and extends from the first and second punch extensions, but is of a smaller diameter than the second punch extension, with the punch shoulder and punch extensions being coaxial with each other and with the blank and die throat, and with the first punch extension being elliptical in cross-section while the second and third extensions are substantially circular in cross-section;
- moving the punch towards the die throat so that the punch shoulder pushes against the blank trailing end to force the blank leading end through the die throat, and simultaneously aligning the second punch extension within the die throat for extruding the lead end of the blank through the annular space located between said second punch extension and the die throat to form a forward, thickened end of a metal tube;
- continuing moving the punch towards the die throat while aligning the first punch extension with the die throat to provide an annular space between the die throat and the first punch extension which space is substantially circular on its exterior and elliptical on its interior, and thereby extruding the blank through the space to form a relatively thin wall metal tube middle portion whose exterior wall surface is substantially circular and whose interior wall surface is substantially elliptical in cross-section;
- removing the punch from the die before completely extruding the tubular blank through the throat, and inserting a second tubular blank within the die in end-to-end contact with the trailing end of the partially extruded blank;
- reinserting the punch in the die with its punch shoulder engaging the trailing end of the second blank and engaging the lead end of the second blank against the trailing end of the first blank;
- moving the punch towards the die throat, with the third punch extension positioned within the die throat to extrude a portion of the first, partially extruded blank, through the annular space between the die throat and third punch extension for forming a relatively thick wall, rear section adjacent the trailing end of the partially extruded first blank;
- moving the punch further while moving the second punch extension within the die throat and the second blank pushes the remainder of the first, partially extruded, blank through the annular space between the second punch extension and the die throat to form an inwardly thickened end portion on the trailing end of the first blank and to also simultaneously extrude an inwardly thickened end portion on the leading end of the second blank;
- removing the extruded first blank and continuing and repeating the foregoing steps on the second and successive blanks;
- thereby forming a tube having a circular exterior wall and a thicker wall section at its forward, lead end, and a thicker wall section near, but spaced from, its trailing end and with the wall section between the two thicker wall sections being substantially elliptical in interior cross-section and substantially circular in exterior cross-section to form diametrically opposing thicker wall portions and 90.degree. offset diametrically opposing thinner wall sections.