| Laser cladding uses high-energy laser to melt metal powders on the surface of the substrate to form metallurgical bonding layer with special properties,so as to improve the surface properties of metal parts.Laser cladding process is a complex physical and chemical reaction process,in which the melt pool is the smallest forming unit.The melt pool is produced by the interaction of high-energy laser beam,metal powder and substrate.The quality of the cladding layer is directly determined by the quality of the melt pool.The number of cracks,compactness and roughness of the solidified melt pool are directly related to the temperature of the melt pool.At present,some scholars have studied the relationship between the melt pool temperature and the quality of laser cladding,but they have not designed and analyzed the whole control system.In addition,there is little research on the melt pool temperature control based on embedded system in the field of laser cladding in China,and most of the embedded control systems used in factories still rely on foreign imports.Therefore,it is of great significance to design and study the detection and feedback control system of molten pool temperature for laser cladding technology.The main contents of this paper are as follows:(1)The effects of laser power,scanning speed and scanning path on the melt pool temperature were studied.The influence of process parameters on the melt pool temperature was studied by measuring the melt pool temperature under different laser power,scanning speed,scanning path and filling strategy.The experimental results show that,when the laser power was within the range of 1200 W to 1800 W,the laser power was within 10 mm/s to 15 mm/s,the melt pool temperature changes linearly with the laser power and scanning speed.The melt pool temperature increases with the increase of laser power and decreases with the increase of scanning speed.Different scanning paths will affect the temperature fluctuation of melt pool.The more complex the scanning path shape is,the greater the temperature fluctuation of melt pool will be.The filling strategy will affect the heat distribution of the part and melt pool.(2)The three-dimensional simulation model of the melt pool in the laser cladding process was established,and the two-dimensional and three-dimensional models of the temperature distribution of the melt pool were obtained.By using Gauss moving heat source model and heat conduction differential equation,the temperature of melt pool is simulated by finite element method,and the moving heat source is loaded by ANSYS software.The experimental results show that the temperature distribution of the melt pool is comet like,and the temperature changes sharply in the first half of the laser spot,but slowly in the second half.(3)The circuit diagram of each function module of the melt pool temperature control board based on embedded system is designed and analyzed.This paper analyzed and compared the commonly used temperature measurement and industrial communication methods,described the characteristics and functions of the main control chip based on ARM Cortex-A7 architecture,and on this basis,designed and analyzed the circuit schematic diagram of each function module of the control board,and completed the design of signal acquisition circuit,communication circuit,control circuit and power management circuit.The acquisition error of 4?20m A current is less than 0.6%,and the output voltage linearity error of 0?10V control signal is less than0.5%.(4)The influence of laser scanning path on the temperature distribution of the part was studied,and a preprocessing method of G code file based on laser scanning path was proposed to optimize the temperature control of melt pool.By analyzing the G code file containing laser power,scanning speed,scanning path and other information in laser cladding,the temperature distribution of the part can be dynamically analyzed through program algorithm,and the laser power will be adjusted according to the local temperature and saved in the form of G code command,so as to optimize the control of the melt pool temperature.In the conventional process,the proportion of time required by the algorithm is less than 1.5% of the total processing time.The results show that this method can effectively optimize the temperature fluctuation of melt pool,and the microstructure of the samples with this method is better than that without this method.(5)The software program of the control system was developed,and the data monitoring software based on Windows system is designed and developed.The UBOOT of the control board,the kernel of the embedded Linux system and the file system of the embedded Linux are compiled in the Linux environment.GCC tools were used to compile the control program and GDB tool was used to debug the control program.In addition,by using Python 3.7 and the GUI graphics library wx Python the data monitoring software based on Windows system was developed.The software can monitor the data information in the actual application process of the control board in real time,and can be also used to complete the initial configuration of the control board.(6)The construction and debugging of the whole measurement and control system were completed,and the effectiveness of the control system was verified through comparative experiments.The schematic diagram and PCB diagram of the control board were drawn by using the circuit design software tools,and the completed PCB circuit board was soldered and debugged to verify the correctness of the hardware design.After setting up the complete control system,the melt pool temperature control system was verified by contrast experiment.The experiment results show that the melt pool temperature data detected by the control system was accurate and reliable,the samples also showed a good metallurgical combination,and the cracks were significantly reduced.In conclusion,the temperature measurement and optimal control system designed in this paper can control the temperature of melt pool in real time and obtain high quality laser cladding layer. |
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