Press brake and press brake control method

A press brake comprising:

• an upper table on which a punch is mounted;
• a lower table on which a die is mounted;
• a table lifting mechanism configured to raise and lower the upper table or the lower table;
• an angle sensor configured to measure an angle of a sheet metal, when the table lifting mechanism raises and lowers the upper table or the lower table and bends the sheet metal, while the sheet metal is interposed between the punch and the die;
• and
• a control device configured to calculate a bending angle of the sheet metal based on an angle of the sheet metal measured by the angle sensor and configured to control the table lifting mechanism to lower the upper table or to raise the lower table, wherein
• when the control device performs control to bend a first sheet metal of a plurality of sheet metals that are made of the same material and that have the same thickness,
• the control device performs control to lower the upper table by a first depth value or to raise the lower table by the first depth value such that the first sheet metal is bent to have a temporary bending angle wider than a target bending angle,
• while the upper table is lowered by the first depth value or the lower table is raised by the first depth value, the control device calculates a first bending angle of the first sheet metal based on an angle of the first sheet metal measured by the angle sensor and holds the first bending angle,
• the control device removes a load applied to the first sheet metal, while keeping a state in which the punch is in contact with the first sheet metal, and calculates a second bending angle of the first sheet metal of which the load is removed, based on the angle of the first sheet metal measured by the angle sensor,
• using the first bending angle or a bending angle when the first sheet metal is bent to have a bending angle narrower than the first bending angle before the load applied to the first sheet metal is removed as a reference angle for calculating a spring back amount, the control device calculates a first spring back amount of the first sheet metal based on a difference between the second bending angle and the reference angle,
• while the upper table is lowered or the lower table is raised, the control device calculates a third bending angle of the first sheet metal based on the angle of the first sheet metal measured by the angle sensor such that the first sheet metal of which the load is removed is bent to have a bending angle wider than the target bending angle, based on the target bending angle and the first spring back amount,
• the control device calculates a second depth value for bending the first sheet metal, that has been bent to have the third bending angle, to have the target bending angle, based on the target bending angle, the first spring back amount, and the third bending angle and holds the second depth value,
• the control device performs control to lower the upper table by the second depth value or to raise the lower table by the second depth value, and after the first sheet metal is bent to have the target bending angle, the control device raises the upper table or lowers the lower table and ends bending of the first sheet metal,
• when the control device performs control to bend a second sheet metal that is a second sheet metal and thereafter of the plurality of sheet metals,
• the control device performs control to lower the upper table by the first depth value or to raise the lower table by the first depth value such that the second sheet metal is bent to have the temporary bending angle,
• while the upper table is lowered by the first depth value or the lower table is raised by the first depth value, the control device calculates a fourth bending angle of the second sheet metal based on an angle of the second sheet metal measured by the angle sensor,
• the control device determines whether a difference between the fourth bending angle and the first bending angle is within a predetermined angle, and
• if the difference between the fourth bending angle and the first bending angle is within the predetermined angle, the control device does not calculate a spring back amount of the second sheet metal, but performs control to lower the upper table by the second depth value or by a corrected depth value obtained by correcting the second depth value according to the difference between the fourth bending angle and the first bending angle, or performs control to raise the lower table by the second depth value or by the corrected depth value, and after the second sheet metal, that has been bent to have the temporary bending angle, is bent to have the target bending angle, the control device raises the upper table or lowers the lower table and ends bending of the second sheet metal.