Numerical Simulation Of Temperature Field During The Entire Process Of Vacuum Brazing Furnace And Optimization Of Tooling And Process

The research group has established a numerical model of the temperature field of a product in the process of heating up and brazing in the vacuum brazing furnace,but the model has a large error in the cooling stage,which is not suitable for the full process process simulation simulation of brazing production.On the basis of analyzing the reasons for the significant errors in the cooling stage of the model,this article optimizes the model as follows: considering the changes in the cooling water temperature during the cooling process,and setting the heating carbon rod to vary with the ambient temperature during the cooling process.In the actual temperature measurement process,extend the actual temperature measurement time in the cooling stage,fully collect the temperature field data in the cooling stage,and optimize the finite element model,so as to obtain a more accurate temperature field change model of the whole process in the Vacuum furnace,and use this model to calculate the workpiece with the fastest and slowest temperature rise,and then optimize the production tooling and brazing process,and predict the whole process cycle according to this model.Finally,a temperature field simulation was conducted for the actual situation where the workpiece was not fully loaded in the furnace during production,and the brazing process was designed based on the simulation results.A reasonable brazing production process was designed.The research results indicate that:(1)The temperature field of a three-dimensional vacuum brazing furnace under no-load conditions was simulated and measured,and the temperature numerical error between the simulation results and the measured results was within ±1℃,proving the feasibility of using the new model for temperature field simulation;(2)The new model simulates the full load Vacuum furnace production process,and the simulation results are in good agreement with the measured values,especially in the cooling stage,which indicates that the model has a good simulation effect on the whole process flow;(3)The simulation results of the fully loaded model show that the heating speed of the upper and lower layers of the workpiece is faster,while the temperature rise and fall of the middle layer workpiece has a significant lag,and the speed is the slowest.The fastest heating workpiece(workpiece A)is located at the upper corner,while the slowest heating workpiece(workpiece B)is located near the center of the middle layer.During the process,the maximum temperature difference between the two can reach over 200℃;(4)Under the existing process conditions,the maximum brazing temperature of workpiece A in the fully loaded model is 822℃,and the duration of temperature from 800℃to 830℃ is 42 minutes.The maximum brazing temperature of workpiece B is 807℃,and the duration of temperature from 800℃ to 830℃ is 22 minutes;(5)After optimizing the tooling of the fully loaded model,the overall temperature in the furnace is more uniform,and the optimization effect is excellent.Therefore,subsequent process optimization is based on this optimized tooling;(6)After process optimization of the fully loaded model,the optimal process is as follows: the heating rate is consistent with the original process,with a holding time of 115 minutes at 770℃ and 20 minutes at 830℃.At this time,the highest brazing temperature of workpiece A in the model is 819℃,and the temperature duration from 800℃ to 830℃ is32.8 minutes;The maximum brazing temperature of workpiece B is 806℃,and the temperature duration from 800℃ to 830℃ is 22.3 minutes;(7)Simulate the temperature field of the fully loaded model during the cooling stage,and ultimately obtain that when the fully loaded model uses the original process,the time to cool to 140℃(outlet temperature)is the 1502 nd minute of the entire process cycle.The measured data is 1498 minutes,with an error of only 4 minutes.After improving the tooling of the fully loaded model and adopting the optimal process,the entire process cycle time was 1463 minutes,which means that the optimized production process saved 35 minutes of cycle time;(8)The process optimization was conducted on the model that only assembled two layers of workpieces,and the optimal process was ultimately selected as follows: 9.375℃/min heating to 770℃ for 95 minutes,3.75℃/min heating to 830℃ for 20 minutes,and cooling with the furnace.Under this process,the highest brazing temperature of workpiece A with the fastest heating rate is 820℃,and the duration of the temperature range from800℃ to 830℃ is 28 minutes;The maximum brazing temperature of workpiece B is 809℃,and the temperature duration from 800℃ to 830℃ is 23.5 minutes.