Method for piercing two aligned holes in a hydroformed tube

A method for concurrently punching first and second aligned holes through opposed walls of a tube while hydroforming said tube to a predetermined diameter by internally pressurizing said tube between a pair of dies, comprising the steps of;

• providing said dies with a cross passage generally perpendicular to said tube through which a punch can be pushed,
• providing one side of said cross passage with a female die button having an inner diameter equal to the second hole desired and having a predetermined axial thickness,
• providing the end of a male punch having an outer diameter equal to said female die button inner edge with a central bore sufficiently large to leave a surrounding annular cutting edge that is sufficiently radially thin and sharp both to cleanly cut a slug of material equal in diameter to said cutting edge as well as allowing said slug to be deformed by the internal pressure within said tube up into said punch central bore and clear of said cutting edge,
• forming a pressure feed orifice through the side of said punch and into said punch central bore that is axially spaced from said punch end by approximately said tube diameter plus a portion of said die button predetermined thickness,
• clamping said tube between said dies and internally pressurizing it to said predetermined diameter,
• pushing said punch through said cross passage and into said tube interior, thereby cutting a first slug equal in diameter to said cutting edge allowing said first slug to be deformed by said tube internal pressure into said punch cross bore sufficiently to cause said first slug to be wedged into said cross bore while leaving said punch cutting edge substantially clear,
• pushing said punch end partially into said die button, thereby shearing a second slug equal in diameter to said die button which stacks closely against said first slug and is forced into said die button, and,
• continuing to push said punch and stacked first and second slugs through said die button until said pressure feed orifice enters said tube interior, thereby allowing pressurized fluid from said tube interior to hit the back side of said first slug and thereby blow both slugs away out of and away from said punch end.

A method for concurrently punching first and second aligned holes through opposed walls of a tube while hydroforming said tube to a predetermined diameter by internally pressurizing said tube between a pair of dies, comprising the steps of;

• providing said dies with a cross passage generally perpendicular to said tube through which a punch can be pushed,
• providing one side of said cross passage with a female die button having an inner diameter equal to the second hole desired and having a predetermined axial thickness,
• providing the end of a male punch having an outer diameter equal to said female die button inner edge with a central bore sufficiently large to leave a surrounding annular cutting edge that is sufficiently radially thin and sharp both to cleanly cut a slug of material equal in diameter to said cutting edge as well as allowing said slug to be deformed by the internal pressure within said tube up into said punch central bore and clear of said cutting edge,
• forming a pressure feed orifice through the side of said punch and into said punch central bore that is axially spaced from said punch end by approximately said tube diameter plus a portion of said die button predetermined thickness,
• providing said punch with a widened shoulder located midway between said punch end and said pressure feed orifice,
• clamping said tube between said dies and internally pressurizing it to said predetermined diameter,
• pushing said punch through said cross passage and into said tube interior, thereby cutting a first slug equal in diameter to said cutting edge allowing said first slug to be deformed by said tube internal pressure into said punch cross bore sufficiently to cause said first slug to be wedged into said cross bore while leaving said punch cutting edge substantially clear,
• continuing to push said punch through said tube interior to push said shoulder through said first hole, thereby widening it and extruding a short sleeve surrounding said first hole,
• pushing said punch end partially into said die button, thereby shearing a second slug equal in diameter to said die button which stacks closely against said first slug and is forced into said die button, and,
• continuing to push said punch and stacked first and second slugs through said die button until said pressure feed orifice enters said tube interior, thereby allowing pressurized fluid from said tube interior to hit the back side of said first slug and thereby blow both slugs away out of and away from said punch end.