Method for Bending Metal Sheet to Achieve High Angle Accuracy

Abstract

A method for controlling the bending of a metal sheet includes the steps of: establishing a relational database on a relationship among material parameters, forming angles, amounts of springback, and amounts of press of an upper die; blanking and reverse-engineering a material parameter of a metal sheet to be processed; comparing the material parameters in the relational database with the material parameter of the metal sheet to be processed which is obtained by the reverse-engineering; and performing an bending operation.

What is claimed is: 
     
         1 . A method for controlling bending of a metal sheet comprising the steps of:
 (1) establishing a relational database on a relationship among material parameters, forming angles, amounts of springback, and amounts of press of an upper die,   the establishing including
 establishing a finite element simulation model for forming based on a structure parameter of a die used for a bending process, obtaining a simulated amount of springback corresponding to a forming angle by inputting a material parameter of a metal sheet for a simulation into the finite element simulation model for the forming and thus simulating the bending process of the metal sheet for the simulation, and using the simulated amount of springback as an amount of springback to be added to the relational database, and 
 after measuring material parameters of different metal sheets, simulating the bending process of each different metal sheet based on the obtained finite element simulation model for the forming, and for each of the different metal sheets, establishing a relational database on a relationship among a material parameter, a forming angle, an amount of springback, and an amount of press of the upper die; 
   (2) blanking and reverse-engineering a material parameter of a metal sheet to be processed,   the blanking and reverse-engineering including
 blanking the metal sheet to be processed, and thereby obtaining a blank, and 
 obtaining an experimental load-stroke curve of the metal sheet to be processed during a blanking experiment by measurement, establishing a finite element simulation model using a method for reverse-engineering an actual physical parameter of the metal sheet, simulating the blanking, and repeatedly reverse-engineering the material parameter of the metal sheet to be processed, 
   (3) comparing the material parameters in the relational database with the material parameter of the metal sheet to be processed which is obtained by the reverse-engineering,
 if a reference material parameter, between which and the material parameter of the metal sheet to be processed an error is less than a second threshold value, exists in the relational database, performing a bending operation, and 
 if a reference material parameter, between which and the material parameter of the metal sheet to be processed an error is less than a second threshold value, does not exist in the relational database, like in the establishing the relational database, simulating the bending process using the material parameter of the metal sheet to be processed which is obtained by the reverse-engineering, adding a relationship which is obtained by the simulation among the material parameter of the metal sheet to be processed, a forming angle, an amount of springback, and an amount of press of the upper die to the relational database, making the material parameter of the metal sheet to be processed which is obtained by the reverse-engineering become the reference material parameter of the metal sheet to be processed in the relational database, and subsequently performing the bending operation; and 
   (4) performing the bending operation,   the performing including
 inputting a bending angle, and 
 calculating a needed amount of press of the upper die based on a formula representing a relation between the forming angle corresponding to the reference material parameter and the amount of press of the upper die of the die of a bending machine for performing the bending operation, sending the needed amount of press of the upper die to the bending machine, and controlling the bending machine in a way that the bending machine bends the blank. 
   
     
     
         2 . The method for controlling bending of a metal sheet according to  claim 1 , wherein the structure parameter of the die used for the bending process includes a draw radius of the upper die and an opening of a lower die in the die. 
     
     
         3 . The method for controlling bending of a metal sheet according to  claim 1 , wherein
 in order to establish the finite element simulation model for the forming, an actual amount of springback of the metal sheet for the simulation is obtained by performing a bending test, and a difference between the actual amount of springback and the simulated amount of springback is calculated, and   if the difference is greater than a first threshold value, the simulation is repeatedly performed by refining a grid size of the finite element simulation model for the forming until the difference becomes less than the first threshold value.   
     
     
         4 . The method for controlling bending of a metal sheet according to  claim 1 , wherein each material parameter used to establish the relational database on the relationship among the material parameters, the forming angles, the amounts of springback, and the amounts of press of an upper die includes a performance parameter and a flow stress curve of a material measured by a tensile test for detecting the material. 
     
     
         5 . The method for controlling bending of a metal sheet according to  claim 1 , wherein the first threshold value is 2%. 
     
     
         6 . The method for controlling bending of a metal sheet according to  claim 1 , wherein
 the bending process is simulated, and a relationship between a different bending angle θ′ and an amount ΔH of press is recorded,   subsequently, an amount Δθ of springback corresponding to the different bending angle θ′ is predicted using the finite element simulation model, and a relationship between the different bending angle θ′ and the amount Δθ of springback is obtained, and   based on θ=θ′+Δθ representing a relationship among a forming angle θ, the bending angle θ′ and the amount Δθ of springback, a relationship between the forming angle θ and the amount ΔH of press is obtained   
     
     
         7 . The method for controlling bending of a metal sheet according to  claim 1 , wherein the second threshold value is 1%. 
     
     
         8 . The method for controlling bending of a metal sheet according to  claim 7 , wherein
 if the reference material parameter, between which and the material parameter of the metal sheet to be processed an error is less than the second threshold value, does not exist in the relational database,   the bending process is simulated by inputting the material parameter of the metal sheet to be processed, which is obtained by the reverse-engineering, into the finite element simulation model,   thereby, a relationship between a forming angle θ of the metal sheet to be processed and an amount ΔH of press is obtained, and   the relationship between the forming angle θ of the metal sheet to be processed and the amount ΔH of press is sent to the relational database.