Processes for welding composite materails and articles therefrom

Abstract

The invention is directed at a method for welding a composite material and to welded structures thus prepared. The method includes a step of contacting a substrate material with a composite material, wherein the composite material includes a pair of spaced apart steel sheets and a core layer between the sheets; the volume of the core layer is about 25 volume % or more, based on the total volume of the composite material; the core layer includes a plurality of steel fibers arranged in one or more masses of fibers that extend the thickness of the core layer so that the core layer is in electrical communication with the steel sheets; and the steel fibers have a cross sectional area perpendicular to the length of the fibers from about 1×10 −5 mm 2 to about 2.5×10 −2 mm 2 .

What is claimed is: 
     
         1 - 18 . (canceled) 
     
     
         19 . A weld joint prepared according to the method of  claim 22 . 
     
     
         20 . (canceled) 
     
     
         21 . A method of measuring the weldability of a light weight composite material comprising the steps of:
 i) applying an electric current, I, to a weld stack consisting of a layer of a composite material and a layer of a monolithic steel sheet using a pair of electrodes having a diameter, D e ;   ii) measuring the diameter of the weld button (D b ), if any, formed in step i)   iii) repeating steps i) and ii) with increasing electric current until the ratio of the diameter of the weld button to the diameter of the electrodes (D b /D e ) is at least 0.95; and the electric current at the last iteration is the minimum weld current, I min ;   iv) repeating steps i) and ii) with further increases in the electric current until metal expulsion, sticking of a sheet to an electrode, or weld popping noise is encountered at a final weld current, I final , and the maximum weld electrical current, I max  is the electrical current during the iteration immediately prior to the last iteration;   v) calculating a weld current range for the composite material by subtracting the minimum weld current from the maximum weld current,
     I   range   =I   max   −I   min ; 
   vi) repeating steps i) through v) except the light weight composite material is replaced by a second monolithic steel sheet having the same thickness as the light weight composite material for measuring the weld current range of the steel sheet; and   vii) calculating the weld current ratio as the ratio of the weld current range of the light weight composite material divided by the weld current range of the steel sheet;   
       wherein a weld current ratio greater than 1 indicates a larger processing window than the steel sheet 
       wherein the light weight composite is a sandwich composite including a core layer interposed between spaced apart steel layers, the core layer including metallic fibers distributed in a polymer matrix. 
     
     
         22 . A process of forming a weld joint comprising the steps of:
 forming a weld stack including at least a substrate material and a light weight composite material, wherein the substrate material is a metallic material, wherein the weld stack has a total thickness from about 1 to about 8 mm and the light weight composite material has a weld current range ratio of about 1.1 or more; and   welding the weld stack including welding the light weight composite material directly to the substrate material to form a weld joint;   wherein the step of welding includes a step of applying a weld current to the substrate material and the light weight composite material using electrodes of a resistance welding apparatus to weld the substrate material with the light weight composite material;   wherein the light weight composite material includes a pair of spaced apart steel sheets and a core layer including a filled polymeric material between the steel sheets, wherein the core layer has a thickness;   the filled polymeric material is present at a concentration from about 30 volume % to about 75 volume %, based on the total volume of the light weight composite material;   the core layer includes a polymeric matrix and a plurality of steel fibers arranged in one or more masses of fibers that extend the thickness of the core layer so that the core layer is in electrical communication with the steel sheets,   the polymer matrix includes one or more polymers and the polymer and fibers are present at a volume ratio of polymer to fiber of about 19:1 to about 2.2:1;   the steel fibers have a length of less than 10 mm; and   wherein the step of applying a weld current includes applying a weld current from about 2.5 kA to about 25 kA to the substrate and the light weight composite material in a welding zone to weld the substrate with the light weight composite material; and the weld joint has a weld button having an area of more than 1 mm 2 ;   wherein the step of welding includes melting some or all of the polymer in the welding zone, and removing some or all of the polymer from the weld joint.   
     
     
         23 . The process of  claim 22 , wherein the process includes flowing a fluid through the electrodes, wherein the fluid has a temperature less than a melting temperature of the polymer. 
     
     
         24 . The process of  claim 22 , wherein the process includes melting some or all of the steel fibers in the welding zone. 
     
     
         25 . The process of  claim 24 , wherein some or all of the steel fibers in the welding zone melt before the melting of one of the spaced apart steel sheets. 
     
     
         26 . The process of  claim 25 , wherein the steel fibers have a generally rectangular cross-section perpendicular to the length of the fibers. 
     
     
         27 . The process of  claim 26 , wherein a power density of at least about 15 W/cm 2  is applied in the welding zone. 
     
     
         28 . The process of  claim 27 , wherein the one or more polymers includes a low density polyethylene or a linear low density polyethylene, wherein the linear low density polyethylene is a copolymer having a density of about 0.915 to about 0.930 g/cm 3 . 
     
     
         29 : The process of  claim 28 , wherein the light weight composite material having a stamped configuration, a roll formed configuration, a bent configuration, or a punched configuration. 
     
     
         30 : The process of  claim 22 , wherein the light weight composite material has a stamped configuration, a roll formed configuration, a bent configuration, or a punched configuration. 
     
     
         31 : A welded article prepared according to the method of  claim 22 , comprising
 i) the light weight composite material;   ii) the steel substrate; and   iii) a weld joint characterized by at least one of the following:
 a) a weld button size of about 2 mm 2  or more; 
 b) a tensile strength of about 1 kN or more; and 
 c) a weld free of metal expulsion. 
   
     
     
         32 : A welded article prepared according to  claim 29 , comprising
 i) the light weight composite material;   ii) the steel substrate; and   iii) a weld joint characterized by at least one of the following:
 a) a weld button size of about 2 mm 2  or more; 
 b) a tensile strength of about 1 kN or more; and 
 c) a weld free of metal expulsion. 
   
     
     
         33 : A light weight composite material, wherein
 the light weight composite material has a weld current range ratio of about 1.1 or more;   the light weight composite material includes a pair of spaced apart steel sheets and a core layer including a filled polymeric material between the steel sheets, wherein the core layer has a thickness;   the filled polymeric material is present at a concentration from about 30 volume % to about 75 volume %, based on the total volume of the light weight composite material;   the core layer includes a polymeric matrix and a plurality of steel fibers arranged in one or more masses of fibers that extend the thickness of the core layer so that the core layer is in electrical communication with the steel sheets,   the polymer matrix includes one or more polymers and the polymer and fibers are present at a volume ratio of polymer to fiber of about 19:1 to about 2.2:1,   the steel fibers have a length of less than 10 mm.   
     
     
         34 : The light weight composite material of  claim 33 , wherein
 the concentration of metallic fibers is from about 10 percent by volume to about 30 percent by volume, based on the total volume of the core layer of the light weight composite material; and   the polymeric matrix includes at least one polymer selected from the group consisting of a polyolefin, a polyamide, a polyester, a polyether, a polystyrene, a polymer including an acrylonitrile, a polymer including an acrylic acid, a polymer including an acrylate, a polyimide, a polycarbonate, an ionomer, and a copolymer including one or more of the above polymers.   
     
     
         35 : The light weight composite material of  claim 33 , wherein from about 0% to 40% of the steel fibers individually span the thickness of the core layer. 
     
     
         36 . A welded article comprising
 i) the light weight composite material of  claim 34 ;   ii) a steel substrate; and   iii) a weld joint characterized by at least one of the following:
 a) a weld button size of about 2 mm 2  or more; 
 b) a tensile strength of about 1 kN or more; and 
 c) a weld free of metal expulsion; 
   
       wherein the thickness of the light weight composite material is from about 0.4 to about 4 mm; and the polymeric matrix includes a polyethylene including about 70 wt. % or more ethylene. 
     
     
         37 : The article of  claim 36 , wherein the combined thickness of the pair of metallic sheets of the light weight composite material is about 1.5 mm or less and is less than about 75% of the total thickness of the light weight composite material. 
     
     
         38 : The article of  claim 37 , wherein the core layer includes from about 10 volume percent to about 30 volume percent metallic fibers, wherein the metallic fibers have a cross-section in the direction perpendicular to the length of the fibers having a cross-sectional area of about 8×10 −5  mm 2  or more, wherein the static resistance of the light weight composite material is about 1.5 mOhm or less, as measured between two electrodes each having a face diameter of about 3.8 mm using a load of about 2200 kN and a sample coupon width of about 25 mm and length of about 25 mm. 
     
     
         39 : The article of  claim 36 , wherein from about 0% to 40% of the steel fibers individually span the thickness of the core layer.