Method of forming a panel from a metal alloy sheet

Abstract

A method is provided for forming a panel from a metal alloy sheet having known stress-strain forming properties including a forming strain limit that is exceeded when a single forming operation is used to form the panel. The method comprises determining a stress relieving treatment and an incremental forming treatment for forming the panel. The total incremental forming strain comprises a first strain increment. The stress relieving treatment results in the total incremental forming strain remaining within the forming strain limit. A first preform shape is determined in which the geometry of the shape does not exceed the first strain increment. The sheet is formed into the first preform shape. The first preform shape is then stress relieved. The first preform shape is then formed into a panel shape having a geometry that is within the total incremental forming strain.

1 . A method of forming a panel from a metal alloy sheet having a grain microstructure and known stress-strain forming properties including a monotonic ultimate elongation and a forming strain limit, where the forming strain limit of the sheet is exceeded at a location in the panel when a single forming operation is used to shape the sheet into the panel, the sheet being strain hardenable and being initially in a tempered condition for forming, the method comprising:
 determining a stress relieving treatment for forming the panel such that the stress relieving treatment does not generate substantial grain growth of the grain microstructure;   determining an incremental forming treatment including a total incremental forming strain comprising a first strain increment, wherein the stress relieving treatment enables the total incremental forming strain to be within the forming strain limit of the sheet;   determining a first preform shape as a forming precursor of the panel, wherein the geometry of the first preform shape does not exceed the first strain increment;   forming the sheet into the first preform shape;   stress relieving at least a portion of the first preform shape by the stress relieving treatment; and   forming the stress relieved first preform shape into the panel by the incremental forming treatment, wherein the geometry of the panel does not exceed the total incremental forming strain and is within the forming strain limit of the sheet.   
   
   
       2 . The method according to  claim 1  wherein the total incremental forming strain exceeds the monotonic ultimate elongation. 
   
   
       3 . The method according to  claim 1  wherein forming includes stamping. 
   
   
       4 . The method according to  claim 1  wherein forming includes hydroforming. 
   
   
       5 . The method according to  claim 1  wherein the total incremental forming strain further comprises a second strain increment and the method further comprising:
 determining a second preform shape as a forming precursor of the panel, wherein the geometry of the second preform shape does not exceed the sum of the first and the second strain increment; and   the step of forming the stress relieved first preform shape includes:
 forming the stress relieved first preform shape into a second preform shape; 
 stress relieving at least a portion of the second preform shape by the stress relieving treatment; and 
 forming the stress relieved second preform shape into the panel by the incremental forming treatment. 
   
   
   
       6 . The method according to  claim 1  wherein the stress relieving treatment includes a temperature-time treatment, wherein the time for the temperature treatment is in the range of approximately 1 to 30 seconds. 
   
   
       7 . The method according to  claim 6  wherein the temperature treatment includes contact heating. 
   
   
       8 . The method according to  claim 6  wherein the temperature treatment includes induction heating. 
   
   
       9 . The method according to  claim 6  wherein the metal alloy sheet is aluminum alloy of the AA6xxx family and the temperature treatment does not heat the grain microstructure to a temperature in excess of 345C. 
   
   
       10 . The method according to  claim 9  wherein the time for temperature treatment is in the range of approximately 4 to 8 seconds and the temperature treatment heats the grain microstructure to a temperature in the range of approximately 145 C to 165 C. 
   
   
       11 . The method according to  claim 9  wherein the first strain increment is in the range of approximately 10% to 17%. 
   
   
       12 . The method according to  claim 6  wherein the metal alloy sheet is aluminum alloy of the AA5xxx family and the temperature treatment heats the grain microstructure to a temperature in the range of approximately 375 C to 465 C. 
   
   
       13 . The method according to  claim 12  wherein the time for temperature treatment is in the range of approximately 4 to 12 seconds and the first strain increment is in the range of approximately 10% to 17%. 
   
   
       14 . A method of forming a panel from a metal alloy sheet having a grain microstructure and known stress-strain forming properties including a monotonic ultimate elongation and a forming strain limit, where the forming strain limit of the sheet is exceeded at a location in the panel when a single forming operation is used to shape the sheet into the panel, the sheet being strain hardenable and being initially in a tempered condition for forming, the method comprising:
 forming the sheet into a first preform shape by an incremental forming treatment, wherein the incremental forming treatment includes a total incremental forming strain which exceeds the monotonic ultimate elongation and comprises a first strain increment, wherein the first preform shape is a forming precursor of the panel and the geometry of the first preform shape does not exceed the first strain increment;   stress relieving at least a portion of the first preform shape by a stress relieving treatment, wherein the stress relieving treatment does not substantially recrystalize the grain microstructure and enables the total incremental forming strain to be within the forming strain limit of the sheet; and   forming the stress relieved first preform shape into the panel by the incremental forming treatment, wherein the geometry of the panel does not exceed the total incremental forming strain and is within the forming strain limit of the sheet.   
   
   
       15 . The method according to  claim 14  wherein the total incremental forming strain further comprises a second strain incremental and the step of forming the stress relieved first preform shape includes:
 forming the stress relieved first preform shape into a second preform shape, wherein the second preform shape is a forming precursor of the panel and the geometry of the second preform shape does not exceed the sum of the first and the second strain increment;   stress relieving at least a portion of the second preform shape by the stress relieving treatment; and   forming the stress relieved second preform shape into the panel by the incremental forming treatment.   
   
   
       16 . The method according to  claim 14  wherein the total incremental forming strain comprises a plurality of strain increments within the range of approximately 4% to 17%. 
   
   
       17 . The method according to  claim 14  wherein the stress relieving treatment includes a temperature-time treatment, wherein the time for the temperature treatment is in the range of approximately 1 to 12 seconds. 
   
   
       18 . The method according to  claim 17  wherein the metal alloy sheet is aluminum alloy of the AA6xxx family and the temperature treatment heats the grain microstructure to a temperature in the range of approximately 145 C to 165 C. 
   
   
       19 . The method according to  claim 17  wherein the metal alloy sheet is aluminum alloy of the AA5xxx family and the temperature treatment heats the grain microstructure to a temperature in the range of approximately 375 C to 465 C. 
   
   
       20 . The method according to  claim 17  wherein the step of forming the panel includes stamping.