Digital online measurement method for improving measurement accuracy of hole expansion ratio

Abstract

The invention relates to a digital online measurement method for improving the measurement accuracy of a hole expansion ratio. The method comprises the following steps: an image captured through a camera in real time is transmitted to a computer control system in real time; the computer analyzes and processes the edge state of an expanded hole in the image through the image processing method, andautomatically judges whether the expanded hole reaches a limit state or not through setting of a certain threshold value; and meanwhile the computer analyzes the determined limit moment correspondingto the hole edge on a picture to obtain a real-time aperture of the expanded hole. By use of the method, the automation of crack judgment is implemented, the influence of human factors is avoided, andthe result is relatively stable; meanwhile the measured aperture is based on a boundary recognition algorithm of image processing, thereby avoiding the human measurement error; and the aperture is measured online but is not obtained by taking down a sample and rebounding, thus the measurement precision is improved.

Description

technical field [0001] The invention belongs to the field of sheet metal forming, and in particular relates to a digital on-line measurement method for improving the measurement accuracy of the hole expansion rate. Background technique [0002] The hole expansion rate is an important index reflecting the forming ability of the metal sheet, and the level of the hole expansion rate directly affects the ultimate deformation capacity of the metal sheet in the hole expansion forming method. The national standard GB / T24524:2009 gives the conventional test method for the measurement of the hole expansion rate, that is, firstly punch a round hole on the sample, and then push the conical hole expansion punch of the specified shape and size into the punching of the metal sheet sample. Carry out the hole reaming test on the circular hole until a crack penetrating the thickness of the sample appears on the edge of the circular hole, stop the test, and measure the ratio of the expansion ...

AI Technical Summary

Problems solved by technology

[0007] (1) When the test is stopped when the crack “penetrates” through the thickness section of the test, it is often found that the crack has undergone a large brittle expansion, which leads to a large deviation in the measurement of the hole expansion rate;

[0008] (2) When the crack is observed to penetrate and the sample is removed, due to the elastic recovery of the material, the actual measured value is not the corresponding hole diameter at the time of rupture, which also affects the measurement accuracy of the hole expansion rate

[0012] (1) The punch displacement and hole height used for calculation are not at the same time, and there is a deviation;

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