Method and apparatus for making tubes

Abstract

In a method of making a tube a sheet metal blank. having opposite longitudinal flanks is placed in a die of a shaping tool. At least one of the longitudinal flanks of the sheet metal is provided with a contact projection suitable for resistance pressure welding. The blank is pressed into a U-shaped cavity of the cavity by a ram to shape the blank into a U-shaped configuration which is then shaped between an upper mold and a lower mold of a molding press into a tubular profile with the longitudinal flanks confronting one another. The upper mold has in an area of the confronting longitudinal flanks oppositely poled electrode strips which are insulated against one another. During subsequent welding operation, the contact projection on the one longitudinal flank is welded to the confronting longitudinal flank as a result of welding heat generated through introduction of an electric current via the electrode strips into the longitudinal flanks and a clamping pressure by which the upper and lower molds are held together.

1 . A method of making a tube, comprising the steps of: 
 placing in a shaping tool a sheet metal blank having opposite longitudinal flanks;    providing at least one of the longitudinal flanks of the sheet metal with contact projections suitable for resistance pressure welding;    pressing the blank into a U-shaped cavity of a lower mold of the shaping tool by a ram to shape the blank into a U-shaped configuration;    shaping the U-shaped blank between an upper mold and the lower mold into a tubular profile with the longitudinal flanks confronting one another, wherein the upper mold has in an area of the confronting longitudinal flanks oppositely poled electrode strips which are insulated against one another; and    welding the contact projections on the one longitudinal flank to the confronting longitudinal flank as a consequence of welding heat generated through introduction of electrical current by means of the electrode strips into the longitudinal flanks, and an applied clamping pressure that holds the upper and lower molds together.    
   
   
       2 . The method of  claim 1 , wherein both longitudinal flanks are formed with said contact projections.  
   
   
       3 . The method of  claim 2 , wherein the contact projections of the longitudinal flanks are disposed in offset relationship.  
   
   
       4 . The method of  claim 2 , wherein the contact projections of the longitudinal flanks oppose each other in pairs.  
   
   
       5 . Apparatus for making a tube, comprising a shaping tool having an upper mold and a lower mold for shaping a U-shaped blank into a substantially tubular profile, said upper mold having electrode strips which are disposed in an area of confronting longitudinal flanks of the tubular profile in parallel relationship to the longitudinal flanks, said electrode strips being insulated against one another and including contact surfaces facing an outer circumference of the tubular profile for introduction of a welding current into the tubular profile.  
   
   
       6 . The apparatus of  claim 5 , wherein the contact surfaces of the electrode strips have a contour which conforms to the outer circumference of the tubular profile.  
   
   
       7 . The apparatus of  claim 5 , wherein the contact surfaces of the electrode strips are part of a shaping contour of the upper mold.  
   
   
       8 . The apparatus of  claim 5 , wherein the electrode strips are configured as mirror images in relation to a longitudinal center plane between the longitudinal flanks to be welded.  
   
   
       9 . The apparatus of  claim 5 , further comprising an insulation layer, disposed in a longitudinal center plane between the longitudinal flanks to be welded, for separating the electrode strips form one another.  
   
   
       10 . The apparatus of  claim 5 , wherein the contact surfaces of the electrode strip are pieced at uniform distances at the outer circumference of the tubular profile by the upper mold which carries the electrode strips.  
   
   
       11 . The apparatus of  claim 5 , wherein each said electrode strip has a generally comb-shaped configuration, with a spine and plural spaced-apart electrode fingers extending from the spine.