Research On Temperature Control Based On Hollow Laser Light Internal Powder Deposition

Laser deposition manufacturing technology is an advanced manufacturing technology combining rapid prototyping technology and laser cladding technology.In the deposition process,due to the change of working conditions,the temperature of the molten pool will be unstable,which may lead to over burning or under melting of the molten pool,which will seriously affect the melting performance and morphology of the molten pool.Therefore,it is very important to monitor and control the temperature of molten pool in the deposition process.However,it is difficult to measure the temperature of the moving molten pool stably and accurately due to the violent thermal reaction.The direct measurement,mechanism model and closed-loop control algorithm of the temperature of the molten pool are complex.At present,most of the methods used by scholars at home and abroad for measuring and controlling the temperature of the molten pool are complex in system,high in cost and poor in reliability.In this paper,the infrared thermometer is used to measure and obtain the temperature change data in the trailing area behind the molten pool instead of the molten pool,and PID control algorithm is designed to realize the closed-loop control of the molten pool temperature in the deposition process,so as to obtain the stable molten pool temperature.Through the actual measurement and using Ansys software to simulate the temperature field of the titanium alloy deposition process,the temperature characteristics of the trailing area behind the molten pool were analyzed.The results show that the temperature of the molten pool and the temperature of the trailing area behind the molten pool have a certain linear relationship.The temperature of the molten pool can be controlled by controlling the temperature in the area behind the molten pool.In addition,the 2.5mm area behind the molten pool has a large temperature fluctuation during the deposition process,which is conducive to the effect of temperature control,and the initial temperature here is within the measurement range of the thermometer,so it is determined that it is made by laser deposition.Temperature monitoring point.In order to verify the accuracy of the temperature field simulation,the experiment of stacking thin-walled parts under the same process conditions was carried out.The measured temperature data and the simulated data are in good agreement.The design and research of the closed-loop control system of the molten pool temperature was carried out.The temperature signal communication software is designed to realize the real-time transmission of temperature signals in the control system,and then a comprehensive analysis of the degree of the influence of the process parameters(scanning speed,laser power,defocusing amount,powder feeding speed)of the melt pool temperature and the deposit layer morphology The laser power was determined as the main control parameter of the single-factor feedback experiment of the molten pool temperature,and then based on the PID control algorithm,a PI temperature controller was designed to adjust the input laser power according to the average temperature of the deposited layer.In view of the strong thermal sensitivity of titanium alloys,this study used TC4 titanium alloy powder for bulk deposition experiments to verify the effect of the PI molten pool temperature control system,and studied the temperature control of the deposition process on the shape quality,The influence of macrostructure and microhardness.The results show that the temperature closed-loop control system can effectively alleviate the heat accumulation phenomenon,significantly reduce the oxidation of titanium alloy caused by excessive temperature,and at the same time make the macrostructure and microhardness of the block more uniform,and to achieve an open environment The continuous deposition of the lower titanium alloy provides technical support.