Measurement And Analysis Of 316LVM Stainless Steel Resistance Spot Welding Information And Research Of Real-time Quality Control

Resistance spot welding is a highly non-linear, multi-parameter coupling, instantaneous, and unobservable process, whose characteristic information are difficulty to acquire due to complicated uncertain factors, and the problem of real-time control of welding quality has puzzled people for a long time. In this paper, in order to put forward a more applicable quality control method of spot welding of implanted 316 LVM stainless steel based on electrode displacement, the dynamic process information influenced by different factors were measured and analyzed.The electrode displacement is mainly influenced by heating factor and mechanical factor, and the mechanical factor contains applied welding pressure and constraint condition of workpiece. Traditional electrode displacement control method is restricted in practical application due to its ignorance of mechanical factor. In order to overcome this disadvantage, a servo pressure system for spot welding based on servo motor and DSP controller was designed. Fast down and flexible touch process of electrode and stable output pressure were realized by mechanism analysis and optimization, system parameter analysis and modeling, and reasonable control mode.A multi-information acquisition platform was designed to collect the process information, such as welding current, electrode voltage, welding pressure, and electrode displacement. The process information obtained under different constraint conditions were analyzed systematically, and an identification method of mechanical constraint conditions by dynamic information and its feasibility were discussed. Results show that the comprehensive information of electrode voltage, dynamic resistance, and electrode displacement, influencing by small edge distance, workpiece warping, and other mechanical factor, are distinguishable characteristic. According to these characteristics, an identification method of small edge distance and workpiece warping was proposed. Furthermore, the characteristic information and its change rule under small edge distance were achieved.Then, a novel real-time quality control method of resistance spot welding based on electrode voltage and displacement was proposed. According to this method, the workpiece constraint conditions could be identified real-time by the characteristics of electrode voltage and displacement, and corresponding electrode displacement obtained from the fitting equation was considered as new reference criterion. During the quality control process, the output displacement was controlled to trace this new reference criterion. To verify the validity of this control method, a numerical model was built based on S-function and NARX neural network in Simulink. The simulation results indicate that the output displacement could well trace the desire reference criterion and its control effect takes precedence over the traditional method for both heat factors and mechanical factors.