Importance

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Abstract

A bending method and bending apparatus directed to avoiding the risk of die breakage and damage to ram coupling parts due to an abnormal condition of a ram drive shaft and directed to achieving high-accuracy bending in which a uniform bend angle can be produced throughout the entire length of a workpiece without forming a boat-formed belly. In a press brake having three or more drive shafts, the deformation amounts of the ram and the table at each shaft-load imposed point are calculated based on input bending process data. A target closest distance between the punch and the die at each shaft-load imposed point is calculated from its corresponding deformation amounts. The difference between the actual bend angle of the workpiece after bending and a target bend angle is obtained at at least three positions, that are, the ends and center of the workpiece. From these differences, a correction amount for the moving amount of the ram at each shaft-load imposed point is obtained. Further, an adequate limit for the pressing force to be generated by each drive shaft is calculated based on the bending process data and the ram is driven by independently controlling each drive shaft so as not to generate a pressing force exceeding the set limit. To detect an abnormal situation due to abnormal movement of a drive shaft, a line connecting the positions of the drive shafts disposed at the points corresponding to the ends of the workpiece is obtained and the respective deviations of other drive shafts from the connecting line are obtained. If one of the deviations exceeds a preset allowable value, an abnormal situation is detected.

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First Claim