Research On Melt Pool Temperature Field Detection Method In Laser Cladding Based On Color CCD

Laser cladding technology uses high-energy laser beam to rapidly melt,solidify and stack the cladding materials,and finally realize the direct forming of solid parts.In the process,there are complex physical and chemical changes inside the melt pool,and the temperature of the melt pool directly affects the forming accuracy and quality of the final solid part.The actual size of the melt pool is small,and the temperature field inside changes drastically,which brings certain difficulties to the detection of the temperature field of the melt pool.Currently,radiation thermometry is the mainsteam method for temperature measurement of melt pool,and the temperature is obtained with the help of two-color pyrometer,thermal imager,CCD camera and other equipment.There are many problems,such as low precision of temperature measurement results,unclear melt pool images and difficulty in obtaining melt pool characteristics.This subject takes the melt pool temperature field as the research object,carries out the research on the in-situ detection method of temperature field of melt pool based on color CCD,constructs the detection model of melt pool temperature field based on color CCD,studies the influence of the forming process parameters on the melt pool temperature,and constructs the model of the relationships between melt pool temperature and main process parameters,provides theoretical guidance for guiding the optimization of process parameters,seeking the best combination of process parameters,and improving forming accuracy and forming quality.The specific research contents are as follows:(1)The establishment of melt pool temperature field detection model and error correction method are studied.Considering the thermal radiation characteristics of high temperature and high brightness of melt pool,a temperature field detection model of melt pool based on the principle of color CCD colorimetric temperature measurement is constructed.The main error sources of the temperature field detection model are discussed in detail,and the errors caused by the change of the surface emissivity of the high temperature melt pool,the non-ideal operation of the color CCD and the improper use of the color CCD are analyzed and studied.For reducing the error caused by non ideal impulse response of color CCD,a melt pool temperature detection model with correction coefficient is proposed.(2)The high-temperature melt pool image processing algorithm under complex working conditions is studied.For reducing the effects of noise interference caused by the radiation interference sources such as dust in the laser cladding forming process,the high-temperature melt pool image processing method under complex working conditions is mainly studied.A segmentation method based on mathematical morphology and Chan-Vese active contour model is proposed,realizing the rapid segmentation of the melt pool area.The melt pool temperature field detection software based on color CCD is designed,which integrates the functions of image acquisition,image processing and result display,realizes the visualization of melt pool temperature field information,and basically meets the requirements of monitoring and analysis of melt pool temperature under complex working conditions.(3)The influence of key process parameters on melt pool temperature is studied.Using the method of controlling variables,single-track and single-layer laser cladding forming experiments under different process parameters were carried out.The melt pool temperature field detection system was used to track and detect the temperature change of the melt pool in real time.The relationships between melt pool temperature and key process parameters are analyzed.The results show that the peak temperature and average temperature of melt pool increase with the increase of laser power,and decrease with the increase of laser scanning speed and powder feeding rate.Furthermore,the model of the relationships between melt pool temperature and main process parameters is constructed based on the differential equation of heat conduction.The maximum relative error of the model is 5.236%,and the prediction results are basically consistent with the experimental results,which provides a theoretical basis for the follow-up melt pool temperature feedback control,seeking the optimal regulation strategy and improving the forming quality.