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Mornitoring Method and Mechanism of Resistance Spot Weld Quality Based on Electrode Vibartion

Author: WangXianFeng
Tutor: MengGuoXiang；LiYongBing
School: Shanghai Jiaotong University
Course: Mechanical and Electronic Engineering
Keywords: Resistance spot welding Electrode displacement Electrode vibration Accelerometer Quality monitoring Mechanism
CLC: TG453.9
Type: PhD thesis
Year: 2011
Downloads: 121
Quote: 0
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Abstract

Resistance spot welding technology for its high-efficiency, low-cost, high degree of automation, etc., have a wide range of applications in the metal plate in the connection process. In the automobile manufacturing industry, a typical car body probably thin pieces of from 300 to 400 by 4000 to 6000 solder joints assembled in 2010, China's automobile production and sales volume of over 18 million. Therefore, to ensure that the pass rate of resistance spot welding quality automotive safety and reduce production costs has an important social and economic significance. However, the quality of resistance spot welding nugget formation process observability and instantaneous difficult to directly monitor. For this reason, only by monitoring the welding quality is closely related to a variety of electrical and physical parameters to indirectly monitor the quality of welding, wherein the electrode displacement is considered to be the ideal one of the monitored parameters of the quality of resistance spot welding. However, the electrode displacement monitoring methods can not be industrialized application interference and economic problems due to the installation of the displacement sensor. In the study of the resistance spot welding, electrode oscillation has been most researchers as interference or useless information received little attention, and monitoring electrodes to the displacement signal filtering or cross-cycle sampling to eliminate the effect of these vibrations . However, few researchers noted that the mechanical vibrations of the welding machine and the monitoring electrode displacement curve to fluctuations caused by the AC welding current, and the nugget formation process, but there is no systematic research. In this paper, from the direction of the electrode vibration study, accelerometer resistance spot welding quality monitoring, aims to develop new resistance spot welding quality monitoring methods, while addressing the lack of traditional thermal expansion displacement monitoring method. The Firstly developed electrodes vibration monitoring system, simultaneous acquisition of the resistance spot welding process, the welding voltage, welding current, the electrode displacement and the acceleration signal; Secondly, starting from the fluctuation phenomenon of the electrode displacement, analyze the fluctuations in the mechanism of the electrode displacement and extraction electrodes displacement fluctuation characteristics, study the changes in the mechanism; then start from the direction of the electrode vibration, displacement sensors and dual-accelerometer monitoring resistance spot welding process electrode amplitude signal, and its resistance spot welding quality monitoring ; Finally, the amplitude of the lower electrode to monitor the quality of resistance spot welding electrode amplitude, HMM is used to carry out the assessment of the quality of the classification of the resistance spot welding. The main research work are as follows: (1) resistance spot welding electrode vibration signal monitoring system including monitoring parameters for sensing and measuring technology for resistance spot welding, the hardware configuration of the monitoring system and using LabVIEW software development based on the resistance of the IPC. spot welding monitoring and open-loop control system procedures and tests. The test results show that the development of resistance spot welding monitoring system with high accuracy, reliable performance, operability. (2) the resistance spot welding process mechanism analysis and experimental study of the electrode displacement fluctuation characteristics through the acquisition of the welding process, welding current and electrode displacement curve analysis of the mechanism of the electrode displacement fluctuation, and the pulse expansion incremental extraction electrode displacement, displacement fluctuations peak. Binding the primary dynamic change in resistance in the welding process and in each cycle when a photomicrograph of the nugget, the analysis of resistance spot welding process, the relationship between the displacement fluctuations peak and the nugget grow. According to the variation of the displacement fluctuations peak can be used five feature points displacement fluctuations peak curve is divided into four stages, and different welding current and electrode force under the conditions of displacement fluctuations peak curve changes its feature points, the results show the displacement fluctuation characteristics can be used to effectively monitor the welding quality. Although the resistance spot welding quality monitoring method (3) using a dual accelerometer displacement sensor is able to monitor the fluctuations in the electrode displacement, but because of its installation interference and expensive and can not be industrialized application. This paper dual accelerometer measures the acceleration signal of the upper and lower electrodes, electrode oscillation amplitude curve obtained by the data processing, and monitoring the displacement sensor electrode vibration amplitude curve for comparison, the results show that the two are consistent. Secondly, the study using dual accelerometer monitoring the change of the electrode amplitude curve in the different welding current conditions, the results show that electrode oscillation can be used to monitor the quality of welding, such as \qualified solder joints \Finally, the study of abnormal welding conditions, such as shunt, edge welding, oil surface and with the poor quality of resistance spot welding electrode vibration signal monitoring. (4) use of a single accelerometer and HMM online classified assessment of the quality of resistance spot welding process, the upper and lower electrodes are vibrated, and the amplitude of the lower electrode is more obvious. Accordingly, by improving the acceleration signal of the band-pass filtering parameters, related to the amplitude of the lower electrode and the amplitude of the total electrode linear to monitor the quality of resistance spot welding. Under the condition of different welding current is obtained by experimentation using a single accelerometer monitoring the amplitude curve of the lower electrode, and its value is increased as the welding current increases, and sequentially without welds, adhesion pads \qualified solder joints \When the spatter generation nowadays electrode amplitude larger hopping occurs, and therefore by setting a threshold to monitor the occurrence of spatter. \diameter of the state values ??respectively HMM modeling, and then using HMMs to treat the test sample to perform pattern recognition to verify that the classification method, the test is valid and reliable. The fully absorb and learn from the results of previous studies based on the mechanism of the electrode displacement fluctuation and extract the displacement fluctuations peak displacement fluctuations peak changes in the the nugget growth process in the mechanism by experiment. On this basis, in order to overcome the deficiencies of the displacement sensor, the angle of the electrode vibrations from the start, using an acceleration sensor monitoring the electrode amplitude and to study the method of application in the monitoring of the quality of resistance spot. The study provides an important reference for resistance spot welding electrode vibration-based quality monitoring methods.

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