Method and apparatus for judging fracture of metal stamped product, program and computer-readable recording medium

1. A method of judging fracture in a metal stamped product which judges fracture in a metal stamped product formed using a punch and a die,

using a strain measuring unit which measures strain of at least either of the punch and the die selected as a target die to be measured, and

a storage unit which stores, as reference data, strain of the target die to be measured over the entire period or a partial period from the start time of stamping to the finishing time of stamping, and production conditions including at least sliding speed, with respect to a plurality of stamped product having no crack produced therein,

the method comprising:

an acquisition step which acquires, in a target stamping for fracture judgment, and as target data for fracture judgment, strain of the target die to be measured by the strain measuring unit over the entire period or a partial period from the start time of stamping to the finishing time of stamping, and acquires production conditions including at least sliding speed;

an extraction step which extracts, from the reference data, the one satisfying a predetermined condition as comparative data, based on the production conditions of the reference data extracted from the storage unit, and also based on the production conditions of the target data for fracture judgment, and

a judgment step which compares strain in the comparative data and strain in the target data for fracture judgment, and judges occurrence of a crack in a stamped product, if a predetermined condition is satisfied.

2. The method of judging fracture in a metal stamped product according to claim 1 , wherein the production conditions further includes, in addition to the sliding speed, at least one of production time, ambient temperature, humidity, blank holding force, lot number of work, blank process position information traceable from material lot, tensile strength of work, yield strength of work, amount of uniform elongation of work, and thickness of work.

3. The method of judging fracture in a metal stamped product according to claim 1 , wherein, the extraction step extracts the reference data, which gives the minimum total of differences between the production conditions of the reference data extracted from the storage unit and the production conditions of the target data for fracture judgment, as the comparative data.

4. The method of judging fracture in a metal stamped product according to claim 3 , wherein the extraction step extracts the reference data, which gives the minimum total of differences between the production conditions of the reference data extracted from the storage unit and the production conditions of the target data for fracture judgment, over the duration from the start time of stamping up to the time when the stamping proceeds by at least 30% or more of the stroke of stamping, as the comparative data.

5. The method of judging fracture in a metal stamped product according to claim 4 , further comprising a step of comparing maximum values of strain of the comparative data over the duration from the start time of stamping up to the time when the stamping proceeds by at least 30% or more of the stroke of stamping, with a maximum value of strain of the target data for fracture judgment; assuming a maximum value of strain of the target data for fracture judgment as a result of blankless stamping if the value is smaller than 20% of a maximum value of strain of the comparative data, and excepting the value from the fracture judgment; and subjecting only a maximum value of strain of the target data for fracture judgment not smaller than 20% of the maximum value of strain of the comparative data, to the judgment step.

6. The method of judging fracture in a metal stamped product according to claim 4 , further comprising a step of comparing strain waveforms of the comparative data over the duration from the start time of stamping up to the time when the stamping proceeds by at least 30% or more of the stroke of stamping, with a strain waveform of the target data for fracture judgment; assuming a strain waveform of the target data for fracture judgment as a result of abnormal measurement if the waveform shows a correlation coefficient with respect to the strain waveform of the comparative data of smaller than 0.6, and excepting the strain waveform from the fracture judgment; and subjecting only a strain waveform of the target data for fracture judgment showing a correlation coefficient with respect to the strain waveform of the comparative data of not smaller than 0.6, to the judgment step.

7. The method of judging fracture in a metal stamped product according to claim 3 , wherein the extraction step extracts the reference data, which gives the minimum total of differences between the production conditions of the reference data extracted from the storage unit and the production conditions of the target data for fracture judgment, over the duration from the time when the stamping proceeds by at least 60% of the stroke of stamping from the start time of stamping, up to the time when a reverse operation of a slide of a stamping press, after reaching the bottom dead position of stamping and turning into the reverse operation, proceeds by at least 20% or more of the stroke of stamping from the bottom dead position, as the comparative data.

8. The method of judging fracture in a metal stamped product according to claim 7 , further comprising a step of comparing strain waveforms of the comparative data over the duration from the time when the stamping proceeds by at least 60% of the stroke of stamping from the start time of stamping, up to the time when a reverse operation of a slide of a stamping press, after reaching the bottom dead position of stamping and turning into the reverse operation, proceeds by at least 20% or more of the stroke of stamping from the bottom dead position, with a strain waveform of the target data for fracture judgment; assuming a strain waveform of the target data for fracture judgment as a result of abnormal measurement if the waveform shows a correlation coefficient with respect to the strain waveform of the comparative data of smaller than 0.6, and excepting the strain waveform from the fracture judgment; and subjecting only a strain waveform of the target data for fracture judgment showing a correlation coefficient with respect to the strain waveform of the comparative data of not smaller than 0.6, to the judgment step, over the duration from the time when the stamping proceeds by at least 60% of the stroke of stamping from the start time of stamping, up to the time when a reverse operation of a slide of a stamping press, after reaching the bottom dead position of stamping and turning into the reverse operation, proceeds by at least 20% or more of a stroke of stamping from the bottom dead position.

9. The method of judging fracture in a metal stamped product according to claim 1 , wherein the judgment step judges occurrence of a crack in a stamped product, if a maximum value of difference between strain of the comparative data and strain of the target data for fracture judgment exceeds a predetermined value.

10. The method of judging fracture in a metal stamped product according to claim 1 , wherein, further by using a blank holding die, at least one of the punch, the die and the blank holding die is selected as the target die to be measured.

11. The method of judging fracture in a metal stamped product according to claim 1 , wherein the extraction step extracts the reference data based on production conditions of the reference data extracted from the storage unit, and production conditions of the target data for fracture judgment, over the duration from the start time of stamping up to the time when the stamping proceeds beyond a predetermined range of the stroke of stamping, as the comparative data.

12. A fracture judgment apparatus for judging fracture in a metal stamped product which judges fracture in a metal stamped product formed using a punch and a die, comprising:

a strain measuring unit which measures strain of at least either of the punch and the die selected as a target die to be measured; and

a storage unit which stores, as reference data, strain of the target die to be measured over the entire period or a partial period from the start time of stamping to the finishing time of stamping, and production conditions including at least sliding speed, with respect to a plurality of stamped product having no crack produced therein;

an acquisition unit which acquires, in a target stamping for fracture judgment, and as target data for fracture judgment, strain of the target die to be measured by the strain measuring unit over the entire period or a partial period from the start time of stamping to the finishing time of stamping, and acquires production conditions including at least sliding speed;

an extraction unit which extracts, from the reference data, the one satisfying a predetermined condition as comparative data, based on the production conditions of the reference data extracted from the storage unit, and also based on the production conditions of the target data for fracture judgment; and

a judgment unit which compares strain in the comparative data and strain in the target data for fracture judgment, and judges occurrence of a crack in a stamped product, if a predetermined condition is satisfied.

13. A non-transitory computer-readable medium having a program stored thereon, the program having instructions to be executed by a processor, the instructions which, when executed, cause the processor to execute fracture judgment of a metal stamped product, which judges fracture in a metal stamped product formed using a punch and a die,

using a strain measuring unit which measures strain of at least either of the punch and the die selected as a target die to be measured, and

a storage unit which stores, as reference data, strain of the target die to be measured over the entire period or a partial period from the start time of stamping to the finishing time of stamping, and production conditions including at least sliding speed, with respect to a plurality of stamped product having no crack produced therein,

the program comprising:

an acquisition process which acquires, in a target stamping for fracture judgment, and as target data for fracture judgment, strain of the target die to be measured by the strain measuring unit over the entire period or a partial period from the start time of stamping to the finishing time of stamping, and acquires production conditions including at least sliding speed;

an extraction process which extracts, from the reference data, the one satisfying a predetermined condition as comparative data, based on the production conditions of the reference data extracted from the storage unit, and also based on the production conditions of the target data for fracture judgment; and

a judgment process which compares strain in the comparative data and strain in the target data for fracture judgment, and judges occurrence of a crack in a stamped product, if a predetermined condition is satisfied.