Sandwich structure

Abstract

A sandwich structure employs a core sheet including alternating peaks and valleys therein. In another aspect, a sandwich structure includes at least one metallic core and at least one adhesively bonded outer face sheet. Yet another aspect of a sandwich structure has raised ridges bridging between adjacent peaks in a core sheet in one direction but not in a perpendicular direction, thereby achieving different properties in the different sheet directions.

The invention claimed is: 
     
         1 . A method of making a vehicular trailer sandwich structure, the method comprising:
 (a) applying tension to a metallic core sheet;   (b) forming alternating peaks and valleys in the core sheet during step (a);   (c) forming raised ridges bridging between at least some of the peaks along a first direction but not along a perpendicular second direction during step (b);   (d) the forming steps being done at ambient room temperature with embossing rollers which have rotational axes set at a fixed distance from each other during the forming steps;   (e) applying an adhesive to substantially flat ends of the peaks after the forming steps;   (f) pre-heating a metallic outer sheet and the core sheet after the application of the adhesive;   (g) laminating the vehicular trailer sandwich structure under greater heat than in the pre-heating step, in an oven containing heaters to create at least an initial green curing of the bonded sandwich structure in 30 seconds or less;   (h) cooling the laminated vehicular trailer sandwich structure in a cooling unit;   (i) wherein out-of-plane shear strength of the core sheet is at least 1.05 times greater in a cross-feeding direction as compared to a manufacturing feed direction; and   (j) wherein a length shrinkage factor of the core sheet, where a ratio of initial versus end formed length, is at least 1.08 along the manufacturing feed direction, which is greater than a shrinkage factor along the cross-feeding direction.   
     
     
         2 . A method of making a sandwich structure, the method comprising:
 (a) applying tension to a core sheet while forming alternating peaks and valleys into the core sheet at ambient room temperature with embossing rollers;   (b) applying an adhesive to outermost lands of the opposed peak and valley surfaces after forming the peaks and valleys in the core sheet between the embossing rollers;   (c) pre-heating the outer sheets and core sheet after the application of the adhesive; and   (d) laminating the assembled sheets under greater heat than in step (c) and under substantially uniform pressure.   
     
     
         3 . The method of  claim 2 , wherein the laminating comprises laminating the outer facing sheets onto the lands of the core sheet at a pressure of at least 5 and less than 20 pounds per square foot. 
     
     
         4 . The method of  claim 2 , further comprising cooling the laminated sheets with a cooling unit after the lamination. 
     
     
         5 . The method of  claim 2 , further comprising:
 (a) creating an offset stepped peripheral flange between the outer face sheets without the core sheet located therebetween; and   (b) hemming together the outer face sheets at the peripheral flange.   
     
     
         6 . The method of  claim 2 , wherein the tension applied to the core sheet during the peak and valley forming is done with at least one pinch roller contacting the core sheet. 
     
     
         7 . The method of  claim 2 , wherein the tension applied to the core sheet during the peak and valley forming is done with at least one biased pressure arm contacting the core sheet to create tension in only the feeding direction while the core sheet is being formed. 
     
     
         8 . The method of  claim 2 , further comprising feeding individually cut blanks of the core sheet between the forming rollers which have rotational axes that are parallel and at a fixed positional spacing during the entire formation of the peaks and valleys within the core sheet. 
     
     
         9 . The method of  claim 2 , wherein each embossing roller has a set of forming pins projecting at a free-standing height relative to a substantially cylindrical roller drum surface, the lateral diameter of each pin being no less than the free-standing height of the associated pin, and a radius located from the sidewall of each pin to the roller drum surface, and the forming of the peaks and valleys is free of a lubricant between the core sheet and the embossing rollers. 
     
     
         10 . The method of  claim 2 , wherein the sheets are all aluminum, without foam therebetween. 
     
     
         11 . The method of  claim 2 , wherein the sheets are all steel, without foam therebetween. 
     
     
         12 . A method of making a sandwich structure, the method comprising applying tension to a core sheet while forming alternating peaks and valleys into the core sheet at ambient room temperature with forming rollers, and free of a lubricant between the core sheet and the forming rollers. 
     
     
         13 . The method of  claim 12 , further comprising:
 (a) applying an adhesive to outermost lands of the opposed peak and valley surfaces after forming the peaks and valleys in the core sheet between the forming rollers; and   (b) laminating outer facing sheets onto the lands of the core sheet at a pressure of less than 20 pounds per square foot.   
     
     
         14 . The method of  claim 13 , further comprising:
 (a) pre-heating the stacked outer sheets and core sheet after the application of the adhesive; and   (b) laminating the assembly under greater heat than in step (a) and under substantially uniform pressure; and   (c) cooling the laminated sheets with a cooling unit after the lamination.   
     
     
         15 . The method of  claim 12 , further comprising:
 (a) creating a peripheral flange between the outer face sheets without the core sheet located therebetween; and   (b) hemming together the outer face sheets at the peripheral flange.   
     
     
         16 . The method of  claim 12 , wherein the tension applied to the core sheet during the peak and valley forming is done with at least one pinch roller contacting the core sheet. 
     
     
         17 . The method of  claim 12 , wherein the tension applied to the core sheet during the peak and valley forming is done with at least one biased pressure arm contacting the core sheet to create tension in only a feeding direction while the core sheet is being formed. 
     
     
         18 . The method of  claim 12 , further comprising feeding individually cut blanks of the core sheet between the forming rollers which have rotational axes that are parallel and at a fixed positional spacing during the entire formation of the peaks and valleys within the core sheet. 
     
     
         19 . The method of  claim 12 , wherein each of the forming rollers has a set of forming pins projecting at a free-standing height relative to a substantially cylindrical roller drum surface, the lateral diameter of each pin being no less than the free-standing height of the associated pin, and a radius located from the sidewall of each pin to the roller drum surface. 
     
     
         20 . The method of  claim 12 , wherein out-of-plane shear stiffness of the core sheet is at least 1.3 times greater in a cross-feeding direction as compared to a manufacturing feed direction. 
     
     
         21 . The method of  claim 12 , wherein out-of-plane shear strength of the core sheet is at least 1.05 times greater in a cross-feeding direction as compared to a manufacturing feed direction. 
     
     
         22 . The method of  claim 12 , wherein a length shrinkage factor of the core sheet, where a ratio of initial versus end formed length, is at least 1.08 along a manufacturing feed direction, which is greater than a shrinkage factor along a cross-feeding direction. 
     
     
         23 . The method of  claim 12 , further comprising configuring the sandwich for attachment to a vehicle trailer. 
     
     
         24 . A method of making a sandwich structure, the method comprising:
 (a) forming alternating peaks and valleys into a metallic core sheet at ambient room temperature with forming rollers which have axes stationarily set at a fixed distance from each other during the complete forming operation;   (b) applying an adhesive to the peaks after the forming of the peaks and valleys;   (c) pre-heating a metallic outer sheet and the core sheet after the application of the adhesive; and   (d) laminating the assembly under greater heat than in step (c), in an oven containing heaters to create at least an initial green curing of the bonded sandwich structure in 30 seconds or less.   
     
     
         25 . The method of  claim 24 , wherein the laminating includes using at least one elongated belt to compress against at least one of the sheets at a pressure of at least 5 and less than 20 pounds per square foot. 
     
     
         26 . The method of  claim 24 , further comprising:
 (a) bonding a second outer face sheet to the core sheet;   (b) creating a bent peripheral flange between the outer face sheets without the core sheet located therebetween; and   (c) securing together the outer face sheets at the peripheral flange.   
     
     
         27 . The method of  claim 24 , further comprising:
 (a) continuously feeding the core sheet to the forming rollers from a coil of sheet metal; and   (b) cooling the laminated sheets with a chiller or refrigerator.   
     
     
         28 . The method of  claim 24 , further comprising:
 (a) feeding individually cut blanks of the core sheet between the forming rollers; and   (b) cooling the laminated sheets with a chiller or refrigerator.   
     
     
         29 . The method of  claim 24 , further comprising applying tension to the core sheet during the peak and valley forming with at least one pinch roller contacting the core sheet. 
     
     
         30 . The method of  claim 24 , further comprising applying tension to the core sheet during the peak and valley forming with at least one biased pressure arm contacting the core sheet to create tension in only the feeding direction while the core sheet is being formed. 
     
     
         31 . The method of  claim 24 , wherein each of the forming rollers has a set of forming pins projecting at a free-standing height relative to a substantially cylindrical roller drum surface, the lateral diameter of each pin being no less than the free-standing height of the associated pin, and a radius located from the sidewall of each pin to the roller drum surface. 
     
     
         32 . The method of  claim 24 , wherein out-of-plane shear strength of the core sheet is at least 1.05 times greater in a cross-feeding direction as compared to a manufacturing feed direction. 
     
     
         33 . The method of  claim 24 , wherein a length shrinkage factor of the core sheet, where a ratio of initial versus end formed length, is at least 1.08 along a manufacturing feed direction, which is greater than a shrinkage factor along a cross-feeding direction. 
     
     
         34 . The method of  claim 24 , wherein out-of-plane shear stiffness of the core sheet is at least 1.3 times greater in a cross-feeding direction as compared to a manufacturing feed direction. 
     
     
         35 . The method of  claim 24 , further comprising folding the sandwich along a crease elongated in a direction substantially parallel to a cross-feeding direction. 
     
     
         36 . The method of  claim 24 , further comprising configuring the sandwich for attachment to a vehicle trailer.