Intelligent Control Strategies And Performance Evaluation Of Aluminum Alloy Sheet Pulsed MIG Welding Power Source

Aluminum alloys as light materials have been becoming more and more popular in themanufacture industry and taking place of traditional steel materials, besides, welding is anindispensable procedure in industrial production process. In order to promote benefits andimprove quality of products synchronously, high strength aluminum plates with thicknessbelow3.0mm are commonly used currently, especially in the automotive industry. Theapplication of these sheets, making the sheet-processing and corresponding weldingtechnology become hot spots of research. During welding process, sheets made of aluminumalloys are highly sensitive to the controlling of current signal input, if inappropriate currentinput is loaded, it will probably result in welding instability, weld defects or other problems.Therefore, the precise control of current during welding process is the key point of its weldingtechnology research. This paper is aiming at investigating how to improve the quality andproperty of welding joint of thin aluminum alloy plate and corresponding intelligencetechnology.Specially, research on pulsed MIG welding power source and its key technologies ofcontrol system is our target. Based on software and hardware design of DSP+ARM dual-corecontrolled welding power source, system model was established based on Simulink andsimulation analysis was conducted, which lay the foundation for improvement of powersupply performance and subsequent research.Regarding interference during welding, digital filter study is needed. Firstly,experimental results are deduced from the design of wavelet soft threshold and wavelet packetfilter, which illustrates that wavelet filtering is productive when applied to filtering outinterference within the current signal. Secondly, one of anti-interference methods of weightedKalman filter was explored, and the global rough precision study (via genetic algorithm) onBP neural network’s initial weights and threshold was also conducted. Besides above, neuralnetwork was used to do on-line real-time setting of self-adjusting Kalman filter’s weightedfactor. In this way, filtering effects are guaranteed and corresponding simulation tests are given, which provide guidance to the design of digital welding power source filter.In order to ensure the accuracy of welding current output regulation, thus make up fordeficiency introduced from multilevel control of discretized welding power source, and torealize the accurate regulation of welding current, then further promote intelligent level ofaluminum alloy sheet pulse MIG welding power source, we studied the parameters unifiedadjustment which based on least squares and the parameters self-learning algorithm whichbased on long-step calibration, to achieve the aim of “continuous adjustment” via generatingmatching welding parameters automatically through intelligent algorithm. Additionally,changing the "read only" property of welding power expert database to flexible "self learning"by utilizing local Newton interpolation algorithm to realize parameters’ self-learning.The arc length changes under external interference. For the sake of real-time controllingarc length and then ensure the stability of aluminium alloy plate MIG welding and weldingquality, mathematical model of electric arc length was built up to analyze the adjustmentmechanism and characteristics of weld wire arc. Besides, we proposed that arc length controlmethod can be used to adjusting electric arc.It is complex to control aluminum alloy thin plate welding process and match theparameters of wire feeding and welding process, so developing a strategy of predicting andcontrolling wire feeding speed intelligently is necessary, a wire feeding speed predictionmodel based on multidimensional regression analysis and neural network was built up andused to do simulation. The results showed that neural network is more effective when it comesto prediction of wire feeding speed, which provides some reference for improvement ofintelligent level of welding power source.To ensure a more elaborate and accurate control of current during welding process, wedesigned a control algorithm based on Fuzzy self-tuning PID parameters and anotherimproved control algorithm that based on variable universe Fuzzy self-tuning PID parameters,therewith achieved on-line self-tuning of PID parameters, which contributes to obtainingbetter effects on control of aluminum alloy plate pulsed MIG welding process comparing withtraditional PID methods. From the electrical signal perspective, quantitative evaluation of welding performancewas studied as well. Using probability density distribution function statistically, toquantificationally assess the stability of welding quality, and develop methods of evaluatingthe stability of welding process based on periodic repetition rate of working points in U-Ifigure. Meanwhile, in order to avoid the subjective randomness of assessment on weldsquality, we utilized fuzzy mathematics to evaluate welds quality which adopts the FuzzyComprehensive Evaluation Model. Moreover, quantitative evaluation of welds quality alsoneeds fusion of multi-information to set up a comprehensive and quantitative assessmentmodel for evaluating welding performance based on neural network.Performance tests, single and double pulsed MIG welding process performance tests onwelding power source (self-developed) of aluminum alloy plate pulsed MIG welding wereconducted on welding tests platform that is self-designed, in addition, the contentions andarguments proposed in every chapter were verified.