| The heavy launch vehicle is the basic vehicle for manned lunar landing and deep space exploration in China.Its fuel tank is made of2219 aluminum alloy and friction stir welding process is adopted.Due to the increase of the size of the heavy launch vehicle fuel tank,the thickness of the weld is increased from 6mm to 18～30mm,and the length of a single circumferential weld is increased from 15 m to 30 m.The ultra long and large thickness friction stir welding welds bring a series of problems: long welding time,wear of the mixing head Large changes in heat transfer and contact thermal resistance of tooling lead to large temperature difference between long and thick welding of welds,which makes it difficult to achieve stable welding process,and ultimately leads to a significant decline in weld strength and performance.In this paper,the temperature signal in the core area of friction stir welding process is studied,a real-time temperature detection system for friction stir welding is established,and the regression model between welding temperature and process parameters is further studied,which lays a foundation for the temperature control of friction stir welding and the improvement of welding stability.The main contents of this paper are as follows:(1)In order to realize the real-time temperature measurement of the welding core area,firstly,the optimal temperature measurement points in the welding temperature field are analyzed,the finite element temperature field simulation model of the whole process of 2219 aluminum alloy friction stir welding is established,and the distribution and fluctuation of the temperature field are analyzed.The results show that the peak temperature of the whole welding process is always at the intersection of the shaft shoulder and the stirring needle;During the whole welding process,the temperature at the characteristic point of the shoulder of the stirring welding head near the root circle of the stirring needle is the highest and relatively stable.Through simulation analysis,the best temperature measurement point is determined to be 1mm near the shaft shoulder and the bottom circle of the stirring needle.The temperature curves of nine characteristic points of friction stir welding head are analyzed,and the temperature relationship between each characteristic point is constructed.(2)A real-time on-line temperature detection system for friction stir welding is established to meet the engineering application.A thermocouple is set in the welding head,and a signal processing and transmission system is set in the chuck of the welding head.The system includes AD conversion,wireless transmission and power supply modules.The temperature measurement range of the friction stir welding temperature measurement system is 0～800 ℃.The full state real-time temperature monitoring experiment shows that the system meets the engineering application requirements,and the measurement accuracy is± 1.5 ℃,which provides a key support for constant temperature friction stir welding.(3)In order to determine the relationship between welding temperature and process parameters,a three factor and three level experimental scheme is designed by using response surface method.Based on the experimental results,a regression model between process parameters and welding temperature is established.Variance analysis shows that the established welding temperature model r2=0.99943,P ≤ 0.0001,which confirms that the model has good fitting.The regression model of welding temperature is verified by temperature measurement experiment.The results show that the predicted temperature of the model is 521 ℃,the measured temperature is 513～525 ℃,and the relative error is 2.3%,which confirms the accuracy of the model.There are 52 figures,12 tables and 67 references... |
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