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DETECTION METHOD OF SPOT WELDING BASED ON MULTI-INFORMATION FUSION AND FRACTAL

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Chinese Journal of Mechanical Engineering 2008年第6期21卷 76-81页

作者： LIU Pengfei SHAN Ping LUO Zhen SHEN Junqi QIN Hede Luoyang Ship Material Research Institute Luoyang 471039 China School of Material Science and Engineering Tianjin University Tianjin 300072 China School of Xinxiang Etectromechanical Engineering Xinxiang 453000 China

A novel detection method of support vector machine （SVM） based on fractal dimension of signals is presented. And models of SVM are made based on nugget size defects of spot welding. Classification using these trained SVM models is done to signals of spot welding. It is shown from effect of different SVM models that these models with different inputs. In detection of defects, these models with inputs including sound signal have a high percentage of accuracy, the detection accuracy of these models with inputs including voltage signal will reduce. So the SVM models based on fractal dimensions of sound are some optimal nondestructive detection ones. At last a comparison between SVM detection model and ANNS detection model is researched which indicates that SVM is a more effective measure than Artificial neural networks in detection of nugget size defects during spot welding.

关键词： Multi-information fusion Support vector machine box counting dimension Detection Spot welding

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Identification of acoustic emission signal in aluminum alloys spot welding based on fractal theory

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China Welding 2007年第3期16卷 51-55页

作者：罗震罗保发单平邹帆高战蛟 School of Materials Science and Engineering Tianjin University

The acoustic emission signal of aluminum alloys spot welding includes the information of forming nugget and is one of the important parameters in the quality control. Due to the nonlinearity of the signals, classic Euclidean geometry can not be applied to depict exactly. The fractal theory is implemented to quantitatively describe the characteristics of the acoustic emission signals. The experiment and calculation results show that the box counting dimension of acoustic emission signal, between 1 and 2, are distinctive from different nugget areas in AC spot welding. It is proved that box counting dimension is an effective characteristic parameter to evaluate spot welding quality. In addition, fractal theory can also be applied in other spot welding parameters, such as voltage, current, electrode force and so on, for the purpose of recognizing the spot welding quality.

关键词： acoustic emission signal spot welding box counting dimension aluminum alloy

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Analysis of Acoustic Emission Signal by Fractal Theory in Aluminum Alloy Spot Welding

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Transactions of Tianjin University 2007年第3期13卷 186-190页

作者：罗震董安单平邢志东 School of Material Science and Engineering Tianjin University Daqing Oil Field Design and Research Institute

The relation between acoustic emission signal and nugget during aluminum alloy spot welding was investigated in order to evaluate spot welding quality. Due to the nonlinearity of the signals, fractal theory was utilized to quantitatively describe the characteristics of the signals instead of classical Euclidean geometry which cannot describe the acoustic emission signal accurately. Through experiments and computing, the box counting dimension is found distinct from other acoustic emission signals and is a better approach to discriminating weld nugget stages. Results show that fractal dimensions increase from 1.51 to 1.78,and they are related to nugget areas added from non-fusion to over-heated nugget. And the box counting dimension can effectively evaluate the quality of the nugget in the spot welding and can be aoolied with current, displace, and other soot welding parameters.

关键词： aluminum alloy spot welding box counting dimension welding quality LabVIEW

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Sensor Fault Diagnosis Method Based on Fractal dimension

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Sensor Fault Diagnosis Method Based on Fractal Dimension