Research On On-Line Detection And Control System Of Laser Cladding Molten Pool Width

As a new surface modification technology,laser cladding has been widely used in the fields of complex parts forming,product surface repairing and surface modification due to its unique properties,and it has been widely concerned by scholars and industry.Laser cladding process is affected by laser,powder,substrate,processing environment and other factors,and there is a complex coupling relationship between the process parameters,so there are still some limitations in the actual processing and production process,mainly reflected in the poor repeatability of the laser cladding process,and processing quality is difficult to guarantee.Aiming at the above problems,this paper introduces detection and closed-loop control technology in the process of laser cladding.In this paper,the molten pool in the laser cladding process is used as the detection object,The coaxial detection system of laser cladding molten pool is set up,without affecting the laser beam transmission and changing the beam quality,the CMOS camera is integrated into the laser head,the different process parameters are used for cladding,and the best camera parameters(such as exposure time,gain,etc.)range of the capture pool are debugged.The integrated image processing of the melting pool image is carried out by filtering,threshold segmentation,morphological processing and edge detection,and the program is written by LabVIEW Vision module to generate the molten pool image detection system,and the length,width and area information of the molten pool are extracted by the system.Through the analysis of the test results,the width of molten pool is an important parameter to determine the cladding quality,under the constant process parameters,the processing is not stable,this article selects the electric moving stage's velocity,the scanning speed as the input of system,under the condition of open loop,randomly stimulate system,the molten pool width information is collected through the molten pool image detection system,and it is used as the output of the system,according to the system input and output data,through LabVIEW system identification module to determine continuous transfer function model of the system.The model is simulated and a continuous transfer function model with the best data fitting is selected.The continuous transfer function is discretized,and the Z transfer function directly determines three parameters of the PID controller through the CD Design PID for Discrete Systems.vi of the LabVIEW control and simulation module.Through visual detection results,comparing the molten pool width information obtained after image processing algorithm with practical molten pool width of the preset value to calculate the difference,and PID controller converts difference to electric moving stage's movement speed,the speed signal real-time transmits to the motion control card of the electric moving stage,by controlling the frequency of the pulse sent by the controller of the electric moving stage and driving the motor to change the speed,realizes the real-time control of the laser scanning speed in the laser cladding process.The feasibility and practicability of the CMOS camera real-time detection system are verified by comparing the errors between the actual molten pool width and the detection width.The single-track cladding experiment is carried out under the condition of open loop and closed loop respectively,Comparing the stability of melting pool width with the morphological accuracy of cladding layer under the two conditions,both of them are improved when the PID controller is added,and then the feasibility of PID controller for the width control of laser cladding melting pool is verified.