| Spot welding electrode takes three functions of conducting current, dissipating heat and applying pressure. During the process of spot welding, the temperature of electrode rises rapidly. Under high-temperature and pressure, spot welding electrode will quickly be wear and broken down. This failure process of electrode will not only reduce the reliability and robusty of weld quality, but also directly influences the cost and production efficiency of automobile welding and assembly. Heat convection is the main process of heat dissipation in electrode. Bad cooling condition on electrode will cause the premature wear and the increase of production cost. Furthermore, the production efficiency and quality of welding assembly will be influenced greatly. The existing researches of spot welding electrode are all focused on improving and replacing of electrode material without thinking about the result of heat convection in electrode. Also, there is absent of mathematic model on performance evaluation to electrode heat convection. It is incapable to make full use of the heat exchange potency of electrode cooling. Therefore, study on modeling and optimizing of heat convection for spot welding electrode based on heat and flow coupling analysis are performed detailedly and systematically. The aim is to improving the performance and effection of heat convection, reducing the speed of electrode wear and decreasing the production cost.Aiming at the problem of electrode heat convection, analysis about the process and characteristic of electrode heat convection are executed in details firstly. The flow pattern of cooling water is calculated out and the mechanism of heat dissipating is determined. By using finite element method and heat and flow coupling method, the relationship between the influencing factors and the heat convection performance is confirmed. According to the concept of cooling rate and heat removal rate which are the evaluating indicators for electrode heat convection, response surface model is built to evaluate the performance of electrode heat convection. Based on the above, improving design of electrode structure is implemented for better performance of heat convection and GA is utilized to study the multiple-object optimal method and result for electrode heat convection. Finally, the validity of the method and the conclusions is done by the case and experiment analysis of heat convection for spot welding electrode under actual technological conditions. To fulfill the above research objectives, the following five aspects of efforts are performed:1. Heat convection analysis of spot welding electrodeBased on the introduction of spot welding process and the composition of cooling system, the problem of electrode heat convection is separated into two procedures of heat and flow for analysis. Flow pattern and performance of cooling water are determined and the heat exchange of cooling water in each phase of spot welding is dissected. Based on the description of heat source and heat contact, the path and process of heat conducting, dissipating is analyzed and the emphasis is on the mechanism and composition of electrode heat inputting. In succession, heat balance equation is established for electrode. For convenience, the conceptions of heat cooling rate and heat removal rate are lead in to evaluate the performance and effection of electrode heat convection. At last, analysis on the influence factors of electrode heat convection is done as a base for the continued works.2. Simulation of the process of electrode heat convectionAccording to the analysis of influencing factors, one-time solution for the simulation of electrode heat convection is implemented by using direct coupling calculation of heat and flow fields. Based on the code Gambit and Fluent and its parametric language, numeric simulation mode for electrode heat convection in FE analysis environment is established. By numerous calculations, analysis of the characteristic of cooling flow and heat convection is done and the emphasis is on the relationship between the influencing factors and heat convection effect. This is the tool for the coming testing and modeling.3. Performance evaluating and modeling on electrode heat convectionBased on the front analysis and the reference research, flow velocity, pipe diameter and pipe height are selected to be defined as the design parameters and performance evaluating indicators of electrode heat convection are defined as the design object. At the same time, test design scheme with 8 two level factors test points, 6 axial test points and 1 center test point is carried out. According to the basic rules of response surface method and center utilized design method, response surface model for performance evaluating of electrode heat convection is built. Leading in the variance analysis and F test, validation of model significance is done. By analysis on the surface drawing and contour drawing of response surface model, the relationship between the design parameters and the performance of heat convection is distinct.4. Structure improving and parameters optimizing of electrode heat convectionThe type of pipe end and cooling cavity structure can influence the distribution of flow velocity which causes different thickness of boundary layer near cooling wall. Furthermore, the heat exchange efficiency between the flow and the electrode can be affected. By using the coupling analysis method of heat and flow fields, study on the relationship between the structure type and the heat convection is made to determine the improving scheme of electrode structure for heat convection. According to the actual request, the multiple-object optimal model is built with the cooling rate, the production efficiency and the energy consumption as the indexes. In the help of GA with the good features of parallel search and probability search, the parallel global searches for optimal match variables under different weighs are implemented. The optimized solutions are gained.5. Case analysis of spot welding electrode and experiment validationThe heat inputted into the electrode is changed with the time in practice. According to the mechanism and composition of heat inputting, the heat and electric contact parameters are gained by theory calculation and based on the exist spot welding model, the magnitude and rule of heat inputting are distinct. Applied the coupling method of heat and flow fields, study on the performance of electrode temperature and heat convection under actual spot welding conditions are carried out. Also, the schemes of structure improvement and optimal design are analyzed under the spot welding technical process. According to the analysis of the relationship between electrode wear and electrode heat convection, the experiment scheme is determined and the validation of the structure improvement and parameters optimization scheme by test data is accomplished.In this study, by absorbing and referring the exist achievements, the coupling method of heat and flow fields and the performance of heat convection for spot welding electrode are researched and analyzed. Furthermore, the study results are applied to the actual electrode cooling case. The works are not only benefit to the life research of electrode, but also to the design and application of welding machine practically.
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