| Both welding quality and cost are the focus of attention in Friction stir welding(FSW)technology.On the one hand,the working life of the tool has an impact on the welding cost and quality;on the other hand,the temperature field inside the weld will affect the final welding quality.Therefore,it is very important to measure the life of the tool and the internal temperature of the weld.A lot of research work shows that the heat in FSW welding process mainly comes from the friction between the tool and the workpiece,so the temperature measurement of the contact interface between the tool and the workpiece is particularly important.Based on the above,this paper designed a high life temperature measurement tool for FSW,and conducted a simulation study on the temperature field in the welding process,mainly including the study of the high life tool,the design and preparation of the thin film sensor and the design of the temperature data acquisition and wireless transmission system.FSW heat flux coupling simulation model was established to study the temperature distribution of workpiece and agitator during welding process.First of all,the design and preparation of the long life tool and the thin film sensor are carried out.Based on the two main failure modes of tool,severe wear and fatigue fracture,the wear and fatigue tests of uncoated and coated tool were carried out.The results show that the wear quantity of uncoated and coated tool is very small,and the failure mode of tool is fatigue fracture,and the coating technology should improve the working life of tool.The reasonable process parameters of specific thin films prepared by DC magnetron sputtering were determined.SEM observation and EDS analysis showed that the thin films were smooth,continuous and compact,without obvious defects,and the composition difference between the thin films and corresponding target material was small,indicating that the sputtering process can meet the requirements.The high temperature conductive silver paint used to connect wire and film electrode can fully meet the requirements.In order to ensure the reliability of wire and film electrode connection,a scheme of secondary fixed compensation wire is proposed.Secondly,a temperature data acquisition and wireless transmission system is designed for high-speed rotation.Temperature data acquisition and wireless transmission module is composed of power supply module,signal acquisition,amplification and conversion module and wireless transmission module.All modules and their peripheral circuits are integrated on the circular PCB board,and fixed on the bracket that rotates synchronously with the stirring head.In order to realize the real-time monitoring of temperature data,the real-time monitoring software of temperature is developed based on VS platform.And the changes of cold end temperature and hot end temperature of thinfilm thermocouple sensor can be observed in real time.Finally,the FSW heat flux coupling simulation model was established to study the temperature field distribution of welder and agitator.Based on CFD(Computational fluid dynamics),a numerical model for the coupling of temperature field and flow field in FSW transient and steady state welding process is established.The results show that the temperature field of the transient model reaches a stable state after a period of time,which is almost the same as the temperature field of the steady state model.In this paper,the steady-state model is used to simulate various parameters,which saves a lot of time.By mapping the steady-state model temperature field results to the friction surface of the corresponding tool and setting reasonable boundary conditions,the temperature field distribution of the tool in the steady-state welding process was obtained.Based on this as a reference and combined with the structure characteristics of the designed tool,the installation position of the film sensor and the location of the temperature measurement point were determined. |
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