Method for joining workpiece layers and connecting element and joining device

Abstract

A method for joining at least two workpiece layers ( 1, 2 ) by introducing a connecting element ( 10 ) with a coating ( 15 ) applied externally to the connecting element ( 10 ), where the connecting element ( 10 ) is guided, in particular punched, through the first workpiece layer ( 1 ) by a ram ( 26 ), forming a cut surface ( 1 ), and penetrates at least partially into the second workpiece layer and is deformed by a die ( 21 ) such that it connects the at least two workpiece layers ( 1, 2 ) together in a form-fitting manner. The connecting element ( 10 ) is heated such that the coating ( 15 ) applied externally to the connecting element ( 10 ) melts and wets, in particular completely closes, the cut surface in the first workpiece layer ( 1 ); after a cooling process, the re-solidified coating ( 15 ) adheres to the cut surface of the first workpiece layer ( 1 ).

1 . A method for joining at least two workpiece layers, the method comprising:
 providing a connecting element having a coating which is applied to the outside of the connecting element, wherein the connecting element is introduced into the workpiece layers by means of a joining device at a joint;   by means of a stamp, guiding the connecting element, from a direction of a first workpiece layer and under exertion of a stamping force, and while forming a cutting face in the first workpiece layer or passing beside a cutting face of the first workpiece layer, through at least the first workpiece layer and the connecting element penetrating, at least in part, the second workpiece layer, wherein the connecting element, by means of a die plate bearing on the second workpiece layer, is deformed under exertion of the stamping force onto the connecting element, such that said connecting element, in a form-fitting manner, interconnects the at least two workpiece layers;   heating the connecting element, during the process, to such an extent that the coating melts and wets the cutting face in the first workpiece layer, wherein the coating re-solidifies after a cooling process to form a re-solidified coating, said re-solidified coating adhering to the cutting face of the first workpiece layer.   
     
     
         2 . A method as claimed in  claim 1 , wherein the connecting element is heated to such an extent that the coating melts and completely seals the cutting face in the first workpiece layer. 
     
     
         3 . A method as claimed in  claim 1 , wherein, prior to commencing the method, at least one of the at least two workpiece layers, in a region of the joint, has a continuously closed surface without a prepunch. 
     
     
         4 . A method as claimed in  claim 1 , wherein the connecting element is a through-punching connecting element, said connecting element being punched through at least the first workpiece layer. 
     
     
         5 . A method as claimed in  claim 4 , wherein the through-punching connecting element is a punch rivet. 
     
     
         6 . A method as claimed in  claim 5 , wherein the through-punching connecting element is a semi-hollow punch rivet or a solid punch rivet. 
     
     
         7 . A method as claimed in  claim 1 , wherein the connecting element has a through hole or a tapped hole. 
     
     
         8 . A method as claimed in  claim 1 , wherein at least one of the at least two workpiece layers is composed of fiber-reinforced plastic. 
     
     
         9 . A method as claimed in  claim 1 , wherein at least one of the at least two workpiece layers is composed of a metallic material. 
     
     
         10 . A method as claimed in  claim 1 , wherein the coating comprises an adhesive or a plastic. 
     
     
         11 . A method as claimed in  claim 10 , wherein the coating is composed of a thermoplastic. 
     
     
         12 . A connecting element comprising a coating for use in a method as claimed in  claim 1 . 
     
     
         13 . A joining device for use in a method as claimed in  claim 1 , the joining device comprising:
 a die plate;   a hold-down device; and   a stamp, said die plate, said hold-down device and said stamp defining tool elements, at least one of said tool elements being heatable.   
     
     
         14 . A joining device as claimed in  claim 13 , wherein the stamp is heatable. 
     
     
         15 . A joining device as claimed in  claim 13 , wherein the joining device comprises a temperature-control device by means of which a temperature of the at least one of said tool elements can be adjusted and maintained at a constant level. 
     
     
         16 . A method as claimed in  claim 1 , wherein at least one of the at least two workpiece layers is composed of a ferrous alloy, an aluminum alloy, or a magnesium alloy. 
     
     
         17 . A method as claimed in  claim 1 , wherein the coating comprises a polymer material.