Study On Molten Pool Monitoring System Based On Accurate Remanufacturing Of Key Components Of Shield Machine By Laser Cladding

Shield machine is the pillar of a great power with independent intellectual property rights,which has been gradually formed in China in the past decade,and has been playing an irreplaceable role in the underground tunnel construction,coal mining and the newly launched "Sichuan-Tibet line construction" in China.The reliable operation of its key components(shield cutter and main drive)is an important guarantee for the healthy,rapid and sustainable development of the shield construction industry.Laser cladding remanufacturing,based on the principle of laser deposition technology,is an important method of size recovery and performance improvement of damaged parts.At present,laser cladding technology is used to shape products with high precision requirements,which has applied to experimental optimization of process parameters and path planning system.However,it is difficult to control the heat input caused by thermal deposition in the process of laser cladding deposition,which makes it hard to meet the expected forming precision.This uncontrollability is particularly obvious in the process of multilayer surface remanufacturing.Therefore,the key to achieve accurate remanufacturing is monitoring the temperature and shape of the molten pool in the process of laser cladding deposition,which will also guarantees the development of “Cross-generation” laser cladding remanufacturing technology.In view of above problems,this thesis focuses on the problem of accurate remanufacturing of key components of shield machine by laser cladding.Molten pool real-time monitoring system platform based on color CCD camera has been constructed,and experiments were conducted with Circular spot fiber laser,during which the FeCr-B spherical alloy powder was used.The correlation between the laser cladding process parameters and the temperature and shape of molten pool was established through the obtained temperature and size data of molten pool.The main research work is as follows:(1)The image processing algorithm of high temperature radiator was studied.The actual size of the molten pool image was calibrated by correcting lens distortion and image distortion.The image preprocessing method combined with median filtering and Wiener filtering was put in use to reduce the noise and interference during the cladding process,and the speed of image segmentation was further improved by the temperature threshold pool segmentation method.Finally,the morphological processing method based on the first closed operation and the second open operation was used to reduce the interference of free points and holes in the segmented image.(2)The color CCD temperature measurement technology was studied.A colorimetric measurement of temperature in sections,based on the calibration of black body furnace,was proposed through analysing of color CCD colorimetric temperature measurement method.The temperature calculation model of different temperature segments,determined by the obtained temperature calculation models of the corrected response bandwidth coefficient and the polynomial fitting,has ensured that the absolute error of temperature measurement in the whole temperature range is lower than 3.5?.(3)The laser cladding molten pool monitoring system of key components of shield machine was developed.The hardware platform of the molten pool monitoring system consists of the color CCD camera,the related optical system and experimental equipments,and the software platform of the system is constructed by the LabVIEW programming software and the Opencv visual library.The shape and temperature signal of the molten pool were acquired by the image processing algorithm of high temperature radiator and color CCD temperature measurement technology.(4)The effects of laser cladding process parameters on the shape and temperature of the molten pool were studied,and a method to characterize the temperature and shape of the laser cladding molten pool was established.The results show that it is more appropriate to select the width of the molten pool as the prior input quantity in the development of accurate remanufacturing system for key parts of shield machine by laser cladding.