| Resistance spot welding(RSW)technology is widely used in automobile and other machinery manufacturing industry due to its simple process,easy to realize mechanization and automatic welding,high production efficiency,good working conditions and other advantages.In the past two decades,RSW has been widely used in new stainless steel subway buses,which has greatly improved the manufacturing technology level.As stainless steel subway body contains tens of thousands of ASW joints,the high quality requirements are not only reflected in internal connection,but also reflected in surface aesthetics.Therefore,this has put forward higher requirements for RSW quality control,and also make the research of efficient RSW quality control technology has great significance.Due to the complex factors affecting the quality of RSW,the existing quality monitoring methods include RSW current method,electrode voltage method,thermal expansion method,dynamic resistance method and ultrasonic method,etc.The main feature of these methods is to monitor and evaluate RSW quality based on single parameter.However,due to the complexity and diversity of influencing factors of RSW quality,the single parameter monitoring method has great limitations both in terms of monitoring principle and practicability,which affects the accuracy and stability of spot welding quality monitoring results.In order to meet the constantly increasing requirements of RSW quality monitoring,this paper presents a composite monitoring method of electrical-acoustic signal for stainless steel RSW joints.This is a multi-parameter monitoring method which combines welding current,voltage and other electrical parameters during RSW welding process with the ultrasonic monitoring singals embedded in the electrode.The actual welding heat input of RSW process is evaluated by monitoring the electrical parameters during welding process,so as to evaluate the stability of spot welding process and equipment.Meanwhile,the formation of RSW joints can be directly monitored by ultrasonic detection during welding process.Therefore,the monitoring and evaluation of RSW joint quality is more effective and reliable.In addition,as the contact status of workpieces during preloading stage has greatly influenced RSW joint quality,this contact state can be detected and evaluated by ultrasonic detection method,which cannot be achieved by other RSW quality monitoring methods,so it is of great significance to the actual RSW products.In this paper,the RSW quality monitoring system based on electro-acoustic composite signal is developed,which realizes online data acquisition and processing of welding current,voltage,pressure and other electrical parameters during RSW process.The dynamic ultrasonic signal acquisition and analysis are realized,as well as the synchronous and cooperative acquisition and processing of electrical and acoustic signals.The acquisition and monitoring software based on electrical-acoustic composite signal is developed to realize data acquisition and analysis of various monitoring signals as well as the digital,curve and graphic output of the results.The algorithm model based on electrical-acoustic signal composite monitoring was studied.By analyzing the monitoring results of electrical and acoustic signals,the welding heat input information which has great influence on spot welding quality was effectively integrated with the ultrasonic characteristic information which reflects the dimensions of RSW joint,which greatly improved the effectiveness and reliability of spot welding quality monitoring.The test results show that the RSW quality monitoring system based on electricalacoustic signals is stable and reliable.The results of quality monitoring and evaluation are in good agreement with those of metallographic test and strength performance test.It shows that the quality monitoring method and technology of spot welding have a good prospect of engineering application. |
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