Method and tool for folding a metal strip

Abstract

A method for folding a metal strip is proposed, the method comprising the steps of providing a metal strip having a first surface and a second surface; providing the metal strip with a groove in the first surface; folding the metal strip into a corner wherein the first surface forms a concave side of the corner and the second surface forms a convex side of the corner and the groove extends along the concave side of the corner; the metal strip being folded by means of at least one set of rollers. According to an important aspect of the invention, one of the rollers comprises a bead pressing the groove into said metal strip, the bead having a substantially rounded profile. The invention further concerns a folded tube having a groove with substantially rounded profile and a forming tool having a bead with substantially rounded profile.

1 . A method for folding a metal strip comprising the steps of: 
 providing a metal strip having a first surface and a second surface;    providing said metal strip with a groove in said first surface;    folding said metal strip into a corner wherein said first surface forms a concave side of said corner and said second surface forms a convex side of said corner and said groove extends along said concave side of said corner;    characterized in that 
 said groove is pressed into said metal strip by means of a bead having a substantially rounded profile.  
   
     
     
         2 . Method according to  claim 1 , wherein said bead has a circular arc profile.  
     
     
         3 . Method according to  claim 1 , wherein said bead has an elliptical arc profile.  
     
     
         4 . Method according to  claim 1 , wherein the substantially rounded profile of the bead is formed by polygonal surfaces.  
     
     
         5 . Method according to any of the previous claims, wherein said metal strip has a thickness between 0.15 mm and 0.40 mm, preferably 0.25 mm.  
     
     
         6 . Method according to any of the previous claims, wherein said bead has a radius between about 0.8 and about 1.0, preferably about 1.0 times the thickness of said metal strip.  
     
     
         7 . Method according to any of the previous claims, wherein said bead has a protruding height between about 0.5 and about 1.1, preferably about 0.66 times the thickness of said metal strip.  
     
     
         8 . Method according to any of the previous claims, wherein said groove is located so as to delimit a marginal region of said metal strip from a central region of said metal strip, said marginal region forming on said concave side of said corner an obtuse angle with respect to said central region.  
     
     
         9 . Method according to  claim 8 , wherein said obtuse angle is between about 135 and about 150 degrees, preferably about 135 degrees.  
     
     
         10 . Method according to any of the previous claims, wherein said central region of said metal strip is bow shaped.  
     
     
         11 . Method according to any of the previous claims, wherein said metal strip passes through a second set of rollers, wherein said marginal region is folded so that said marginal region forms on said concave side of said corner a substantially right angle with respect to said central region.  
     
     
         12 . Method according to any of the previous claims, wherein said metal strip is provided with two grooves in said first surface, a first groove delimiting a first marginal region from said central region and a second groove delimiting a second marginal region from said central region, said first and second marginal regions being on opposite ends of said metal strip.  
     
     
         13 . Method according to  claim 12 , wherein said central region of said metal strip is folded such that the first and second marginal regions meet and that the free ends of the marginal regions come into contact with the first surface of the central region, so as to form a folded tube.  
     
     
         14 . Method according to any of the previous claims, wherein said metal strip is made from aluminium or aluminium alloy.  
     
     
         15 . Method according to any of the previous claims, wherein said metal strip comprises cladding material on at least said second surface.  
     
     
         16 . Method according to any of the previous claims, wherein said metal strip comprises cladding material on said first and said second surfaces.  
     
     
         17 . Method according to claims  13  or  14 , wherein said folded tube is brazed so as to secure said first and second marginal regions to one another and to said first surface of said central region.  
     
     
         18 . Folded tube comprising: 
 a first side wall having a first and a second portion;    a second side wall extending substantially parallel to said first side wall;    a first and a second end wall for connecting said first side wall to a second side wall;    wherein said folded tube is formed in one piece from a metal strip;    wherein said first and second portions of said first side wall each have a marginal region on their respective free ends, said marginal regions being folded into a corner so as to extend inwardly from said first side wall towards said second side wall;    wherein a groove is arranged on the concave side of said corner    characterized in that 
 said groove has substantially rounded profile.  
   
     
     
         19 . Folded tube according to  claim 18 , wherein said groove has a circular arc profile.  
     
     
         20 . Folded tube according to  claim 18 , wherein said groove has a elliptical arc profile.  
     
     
         21 . Folded tube according to  claim 18 , wherein the substantially rounded profile of the groove is formed by polygonal surfaces.  
     
     
         22 . Folded tube according to any of  claims 18  to  21 , wherein said groove has a depth between about 0.1 and about 0.4, preferably about 0.2 times the thickness of said metal strip.  
     
     
         23 . Folded tube according to any of  claims 18  to  22 , wherein said folded tube is folded according to any of  claims 1  to  17 .  
     
     
         24 . Forming tool for forming a metal strip, wherein said forming tool comprises a bead for pushing a groove into said metal strip at the desired location of bend 
 characterized in that 
 said bead has substantially rounded profile.  
   
     
     
         25 . Forming tool according to  claim 24 , wherein said bead has a circular arc profile.  
     
     
         26 . Forming tool according to  claim 24 , wherein said bead has a elliptical arc profile.  
     
     
         27 . Forming tool according to  claim 24 , wherein the substantially rounded profile of the bead is formed by polygonal surfaces.  
     
     
         28 . Forming tool according to any of  claims 24  to  27 , wherein said forming tool is a roller assembly comprising a first and second roller, said first roller comprising said bead.  
     
     
         29 . Forming tool according to  claim 27 , wherein said second roller comprises a cut-out for receiving some of the metal displaced by said bead of said first roller.  
     
     
         30 . Forming tool according to any of  claims 24  to  29 , wherein said bead has a protruding height between about 0.5 and about 1.1, preferably about 0.66 times the thickness of said metal strip.  
     
     
         31 . Forming tool according to  claim 29  or  30 , wherein said cut-out has a depth between about 0 and about 0.5, preferably about 0.3 times the thickness of said metal strip.