Research On Quality Monitoring Method And Systam For Spot Welding Process Based On Ethernet

Because of its high production efficiency and easy realization of automation,the resistance spot welding is the main sheet-metal joining method for body in whiteassembly. Many factors that influence welding quality stability exist in weldingprocess, and some abnormal phenomena often occur in body in white assembly,which case multiple quality problems. At present, it is lack of monitoringtechnology at automobile assembly field, the manufacture information can not beanalyzed, and the abnormal phenomena are not processed timely, so the productionefficiency and quality improvement are restricted at some degree. This dissertationtakes resistance spot welding in automobile assembly process as the leadinginvestigated subjects, and the monitoring technology and process monitoring systembased on Ethernet are researched.The overall architecture of monitoring technology based on Ethernet isestablished, according to different functions, the Ethernet-based monitoring systemis divided into four parts: enterprise information management layer, fieldinformation management layer, process monitoring layer and production equipmentlayer. The mode of distribute monitoring is adopted in process monitoring layer, theseveral monitoring systems are used to monitor welding process of different workstations dispersedly, and all the sampling data are sent to computer informationmanagement system via Ethernet. The structure of information management systemis proposed, which includes four parts: real time information management,equipment information management, process information management and systeminformation management. The key technologies of utilizing eight bit microcontrollerunit to realize Ethernet data communication and information management methodsare solved in monitoring system realization process.In order to obtain real time information in welding process, the Ethernet-basedresistance spot welding monitoring system is designed and developed, which usesdouble MCUs as the core, dual-port RAM as the data shared cell, and dedicatednetwork chip as the Ethernet controller, the monitoring system can independentlyfulfill the functions of signal conditioning, A/D conversion, data local temporarystorage, Ethernet communication and so on. Digital display model displays numberof workpiece and joint, welding current, welding time and electrical conductivity, sothe assembly field executives can easily adjust production schedule and improveproduction quality. The alarm system with eight independent voice segments isdesigned, according to the voice prompt, the operators can deal with such abnormalphenomena as electrode invalidation and lack of joints timely. At the same time, on the precondition of unchanging the current production equipments, the methods ofvehicle classification and joint counting are utilized to design the welding craftautomatic adjustment model, the problem of utilizing the same welding process tofinish different thickness panels is solved. The software of system is programmed byC language, under the control of unified logical signal and time signal, the abovemonitoring functions are accomplished.The splash metal cases amplitude sudden change of dynamic resistance whenspatter occurs, so the amplitude sudden change is the characteristic quantity toreflect spatter. The relationship between electrode life and dynamic resistance isresearched, and the whole amplitude sudden change of dynamic resistance isproposed as the characteristic quantity to reflect electrode life, which provides withtheoretical foundations for on-line electrode life monitoring. In order to identifyaccuracy of welding process conversion, the relationship between thickness anddynamic resistance is researched, and the dynamic resistance amplitude differencecan be utilized as the indirect mean for thickness measurement. The support vectormachine basic principles are introduced, the problem that quadratic programmingproblem consumes excessive resources in calculation process is fully considered,Sequential Minimal Optimization(SMO) is proposed as information classificationmethod. The basic principles, program flow and the concrete realization methods ofSMO are discussed in detail. It is showed experimentally that criterions built in thisdissertation can recognize weld defects and reflect the status of machine operationby applying a large amount of data sample.Based on the fully understanding of production flows and process features atbody in white assembly field, information management system is built, which canaccurately record and feedback of static equipment information, spot inspection, andfault information, process information of workpiece, welding process and operatorsare orderly managed, and real time information of welding process are accuratelyrecorded and orderly managed. Based on analysis of the information styles and basicinformation flow, the process information models are built, modularization andobject-oriented knowledge representation are used to describe each research objects,constraint conditions between information are defined through correlation betweeninvestigated subjects. The development environment LabView is utilized to establishinformation management system, the database technology is utilized to store andmanage process information. The ODBC technology is adopted as the data access ofdifferent databases, the functions of real time information displaying, storage andquerying of process and equipment information are realized.The classification results are using to on-line monitor the status of electrode,when the abnormal status occurred, the alarm is generated to suggest the operatordeal with the abnormal in real time, and the results indicate that electrode status identification accurate rate is high. Aiming at fulfill the functions of weldingprocess auto conversion and welding process evaluation, two concurrent weldingcrafts with two impulses are set, and the functions of craft conversion and real timeevaluation are obtained, it is proved that craft conversion accuracy ratio is about98.8%, which is fit for industrial production application.The research of monitoring technology based on Ethernet for body in whiteassembly not only improves the informatization level of workshop, the functions ofprocess information visualization and related information accurately record andmanagement are realized, which provides resources for future technologyimprovement, and also guarantees the stability and continuity of production process,the phenomenon of welding lack is reduced, the welding process for differentthickness are improved, and the function of on-line monitoring of electrode life isimplemented.