Research On Pulsed Laser Cleaning Technology And Mechanism Of Automobile Gearbox Parts

The proportion of parts imported in China’s automobile industry is relatively high.Among the scrapped automobile parts,automatic transmission,steering gear,turbocharger and other parts have high residual value.Remanufacturing can realize the efficient recycling of high-value solid waste resources,greatly reduce pollution emissions and reduce the dependence of the remanufacturing industry on imported parts,which has great economic and social benefits.cleaning is an important link of the remanufacturing industry.As an emerging cleaning method,laser cleaning is more widely used in industrial production because of its advantages of micro-damage,green environmental protection and high efficiency,which are different from traditional cleaning.In this study,the torque converter and oil pump in the gearbox parts are selected as the experimental objects,and the laser cleaning experimental platform is built.The experimental and simulation methods are used to study the influence of laser process parameters on the removal effect of the coating on the torque converter shell and the oxide layer on the oil pump shell,and the removal mechanism of the surface material.The main work of this paper is as follows:(1)The layered characteristics,structural feature and elemental composition of the surface of gearbox parts were analyzed by means of metallographic microscope,infrared spectrometer and scanning electron microscope.There is a light yellow rust remover layer with a thickness of 3.2-7.3μm on the surface of the torque converter shell,and there are spherical particles with a diameter of 2-5μm on the surface.There is an oxide layer with a thickness of 6.2-18.7μm on the surface of the oil pump shell.The lamellar oxides are stacked with each other,and the spherical impurities are dispersed.(2)Orthogonal experiments were designed to study the influence of process parameters such as average power,repetition frequency,scanning speed and cleaning times on the cleaning effect.The degree of influence on the cleaning effect of the torque converter shell is average power>repetition frequency.The optimal process combination is average power 45 W and repetition frequency 30 k Hz.The degree of influence on the cleaning effect of the oil pump shell is average power>cleaning times>scanning speed.The optimal process combination is average power 30 W,cleaning times 10 times and scanning speed 1500 mm/s.After the parts of the gearbox were cleaned by the optimal process parameters,the silver white matrix was exposed on the surface,the surface coating and the oxide layer were cleaned,and the cleaning effect was good.(3)Single pulse cleaning experiments with different energy densities were conducted and the surface morphology changes were observed after laser cleaning.The cleaning threshold and damage threshold of the torque converter and the oil pump shell were 5.10J/cm~2,40.56 J/cm~2 and 10.19 J/cm~2,45.76 J/cm~2 respectively by element determination and image binarization.At the same time,the ablation threshold of the two parts was10.34 J/cm~2 and 19.90 J/cm~2 respectively by area extrapolation method.The plasma behavior in the cleaning process was investigated by high-speed camera,and the plasma began to appear when the energy density reached 25.50 J/cm~2.With the increase of energy density,the surface gradually undergoes non-flat melting,melting and gasification caused by slip and interference.(4)Taking the torque converter shell as the research object,the heat flow coupling model of single pulse laser cleaning process was established by COMSOL Multiphysics software.The influence of different energy densities on the temperature field distribution and cleaning depth of the material was studied,and the flow behavior of the molten body on the surface of the torque converter shell was explored when the energy density was50.95 J/cm~2.It is proved that the surface temperature and ablation depth of the parts are positively correlated with the energy density.When the energy density is 15.29 J/cm~2,the maximum surface temperature reaches 1377 K,which is below the melting temperature.When the energy density is 25.48 J/cm~2,the maximum surface temperature reaches 2114K,the surface of the material undergoes a melting phase transition.When the energy density is 50.95 J/cm~2,the maximum surface temperature reaches 5008 K,which is reaching the critical temperature,exceeding the boiling point of the material,causing phase explosion.When the energy density is 50.95 J/cm~2,the melt moves obliquely upward along the solid-liquid interface to form the edge of the ablation crater,and the velocity reaches a maximum of 0.15 m/s at 0.2μs.As the temperature decreases,the melt changes along the velocity direction of the solid-liquid interface at 0.7μs,and the velocity value gradually decreases with time.