Stamping of work hardenable aluminum alloy sheets

Abstract

Work hardenable aluminum alloy sheet material is progressively stamped to a final stamped shape in a succession of stamping operations. A blank sheet of annealed starting material is stamped into a least a first preform shape between heated stamping tools to form a preform shape and subsequently anneal the worked preform shape. After one or more annealed preform shapes have been progressively attained, the last preform shape is cooled, if necessary, and stamped to its final stamped shape between unheated stamping tools.

1 . A method of forming an aluminum alloy sheet into an article with a final stamped shape in a sequence of at least two stamping steps, the sheet being progressively deformed in each of the stamping steps by stretching between successive sets of a punch tool and a complementary stamping surface tool, at least one of each punch tool and complementary forming surface tool in a set being movable between an open position for receiving an aluminum alloy sheet or preform and a closed position for stamping the blank or preform, the method comprising:
 heating the punch surface and complementary stamping surface of a first stamping stage of punch tool and forming surface tool so that their respective surfaces are maintained at a temperature for annealing the aluminum alloy blank material;   placing an unheated blank of an aluminum alloy sheet between the heated first stamping stage tools and closing the tools to form the blank into a preform shape and to anneal the preform shape;   removing the annealed preform shape from the first stamping stage tools;   transferring the preform shape to a set of unheated final stage stamping tools, and   forming the preform shape to a final article stamped shape between the unheated final stage stamping tools.   
     
     
         2 . A method of forming an aluminum alloy sheet as recited in  claim 1  in which the punch tool and complementary stamping surface tool of the first stamping stage are insulated and internally heated for attaining the annealing temperatures of their respective surfaces. 
     
     
         3 . A method of forming an aluminum alloy sheet as recited in  claim 1  in which the preform shape is stamped to a second preform shape and annealed in a second set of heated stamping tools before being transferred to the unheated final stage stamping tools. 
     
     
         4 . A method of forming an aluminum alloy sheet as recited in  claim 1  in which an annealed preform shape is cooled to ambient temperature before being transferred to the unheated final stage stamping tools. 
     
     
         5 . A method of forming an aluminum alloy sheet as recited in  claim 1  in which each step is performed in about the same time period so that a continuous series of like aluminum alloy sheets are successively stamped to like final stamped shapes in a continuous flow sequence. 
     
     
         6 . A method of forming an annealed, work hardenable, aluminum alloy sheet into a formed article with a final stamped shape in a sequence of at least two stamping steps, the sheet being progressively deformed in each of the stamping steps by stretching between successive sets of a punch tool and a complementary stamping surface tool, each punch tool and stamping surface tool comprising a unitary metal block providing the punch surface or respective complementary stamping surface, at least one of each punch tool and complementary forming surface tool in a set being movable between an open position for receiving an aluminum alloy sheet blank or preform shape and a closed position for stamping the blank or preform shape, the following steps being of substantially equal duration, the method comprising:
 heating the punch surface and complementary forming surface of a first stamping stage of punch tool and forming surface tool so that their respective surfaces are maintained at a temperature for annealing the aluminum alloy blank material;   placing an unheated blank of an aluminum alloy sheet between the heated first stamping stage tools and closing the tools to stamp the sheet metal blank into a preform shape and retaining the preform shape between the hated and closed tools for a period to anneal the preform shape;   removing the annealed preform shape from the first stamping stage tools;   transferring the preform shape to a set of unheated final stage stamping tools, and   stamping the preform shape to a final stamped shape between the unheated final stage stamping tools.   
     
     
         7 . A method of forming an aluminum alloy sheet as recited in  claim 6  in which the punch tool and complementary stamping surface tool of the first stamping stage are insulated and internally heated for attaining the annealing temperatures of their respective surfaces. 
     
     
         8 . A method of forming an aluminum alloy sheet as recited in  claim 6  in which the preform shape is stamped to a second preform shape in a second set of heated stamping tools before being transferred to the unheated final stage stamping tools. 
     
     
         9 . A method of forming an aluminum alloy sheet as recited in  claim 6  in which an annealed preform shape is cooled to ambient temperature before being transferred to the unheated final stage stamping tools. 
     
     
         10 . A method of forming an aluminum alloy sheet as recited in  claim 6  in which each step is performed in about the same time period so that a continuous series of like aluminum alloy sheets are successively stamped to like final stamping shapes in a continuous flow sequence.