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Method of bending workpiece to target bending angle accurately and press brake for use in the same method

  • US 5,857,366 A
  • Filed: 01/08/1997
  • Issued: 01/12/1999
  • Est. Priority Date: 07/08/1994
  • Status: Expired due to Fees
First Claim
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1. A method of bending a sheet-shaped workpiece using a press brake in which said workpiece is pinched between an upper tool and a lower die while an engagement positional relationship between said upper tool and said lower die is controlled, said press brake further including an upper apron having said upper tool installed thereon, a lower apron having said lower die installed thereon and drive means for driving either one of said upper and lower aprons close to or apart from the other of said upper and lower aprons, and method comprising:

  • (a) calculating a theoretical D value indicating a theoretical engagement positional relationship between said upper tool and said lower die that corresponds to a target bending angle, according to workpiece information, die information and bending information;

    (b) bending said workpiece while controlling said engagement positional relationship between said upper tool and said lower die, according to said theoretical D value;

    (c) measuring bending angles of said workpiece at a plurality of positions after said bending and calculating a mean value of said bending angles;

    (d) calculating a theoretical load value for bending said workpiece according to said mean value of said bending angles and calculating a theoretical mechanical deflection value based on said theoretical load value;

    (e) detecting actual pressure applied on said drive means during said bending of said workpiece;

    (f) calculating an actual mechanical deflection value based on said actual pressure;

    (g) calculating a correction value for said D value according to a difference between said theoretical mechanical deflection value and said actual mechanical deflection value;

    (h) correcting said engagement positional relationship between said upper tool and said lower die by adding said correction value to said D value and performing said bending of said workpiece again;

    (i) repeating the above steps (c)-(h) until said mean bending angle of said workpiece reaches a value within a predetermined tolerance of said target bending angle;

    (j) controlling said engagement positional relationship between said upper tool and said lower die such that said engagement positional relationship remains constant after said bending angle of said workpiece reaches said value constant after said bending angle of said workpiece reaches said value and repeating said bending a predetermined number of times in accordance with a quality of workpieces.

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