Method and apparatus for tube expansion

An apparatus for expanding a tube having an inner surface, said apparatus comprising:

• a punch having a plurality of circumferentially spaced segments, said segments having a radially inner surface and being movable in a radial direction with respect to a longitudinal axis of said punch;
• a first workpiece contacting surface disposed on a radially outer portion of each of said segments of the punch;
• a second workpiece contacting surface disposed on a radially outer portion of each of said segments of the punch, said second workpiece contacting surface being circumferentially offset and longitudinally spaced with respect to said first workpiece contacting surface;
• first means for moving said segments outwardly in said radial direction, said means having a mandrel, said mandrel being coaxially disposed with respect to the longitudinal axis of said punch and having a frustoconical portion at a distal end and a connecting portion at a proximal end of said mandrel, said frustoconical portion being positioned radially inwardly of said radial inner surface of the segments, and second means for moving the mandrel along said longitudinal axis, said second means being connected to said connecting portion of the mandrel;
• third means for moving said punch and said first means simultaneously in a direction parallel with the longitudinal axis of said punch;
• and
• fourth means for controlling the first and third means;
• said third means maintaining a variable pressure on said first means to cause said first means to maintain a substantially constant force of the first and second workpiece contact surfaces against the inner surface of the tube being expanded in the opening.

A tube expander comprising:

• an elongate member having a longitudinal axis and a plurality of circumferentially spaced segments at its distal end, each segment having an inner surface and being cantilevered from a point spaced longitudinally from said distal end, the distal end of each segment being movable in a radial direction with respect to the longitudinal axis from a first at-rest position outwardly to a second position, each segment having first and second arcuate outer surfaces at the distal end for contacting the inside of a tube, the arcuate surfaces being longitudinally spaced and circumferentially offset with respect to each other, each segment having longitudinal radially-extending sides each of which is parallel to the side of the adjacent segment in the at-rest position, and the sides being closely adjacent each other;
• a mandrel coaxial with the longitudinal axis, the mandrel having a frustoconical portion at its distal end for contacting said inner surfaces of the segments;
• and
• means for moving the mandrel along said longitudinal axis toward the distal end of the segments to move them outwardly in said radial direction from the first at-rest position to the second position, said means being movable away from the distal end of the segments to allow them to return to the at-rest position.

A method of joining a tube to a bore surface defining an opening, including the steps of:

• positioning an end of said tube into one end of the opening;
• inserting an expandable punch having a plurality of circumferentially spaced workpiece contacting surfaces into the end of said tube positioned in said opening, from an end of the opening opposite said one end;
• moving said circumferentially spaced workpiece contacting surfaces radially outwardly and contacting an inner surface of said tube with a controlled force sufficient to form an outer surface of the tube to a predetermined shape with respect to a surface defining the opening;
• longitudinally moving said punch toward said opposite end of the opening initially contacting the inner surface of said tube with a first plurality of circumferentially spaced workpiece contacting surfaces on said punch and forming a plurality of radially inwardly extending ridges on the inner surface of the tube between adjacent workpiece contacting surfaces, said inwardly extending ridges being formed simultaneously with the forming of the outer surface of the tube to said predetermined shape, subsequently contacting the inner surface of said tube with a second plurality of workpiece contacting surfaces on said punch to flatten the inwardly extending ridges and form a smooth wall on the inner surface of said tube, and simultaneously maintaining a substantially constant contact force on the inner surface of said tube;
• moving said circumferentially spaced workpiece contacting surfaces radially inwardly;
• and,
• withdrawing said expandable punch from the opening in said wall member.