The Study Of Key Technologies Of Gear Laser Surface Treatment

This thesis is directed to key problems of laser quenching hardened depth and laser cladding layer crack control based on gear laser quenching and laser cladding.Hardened depth is a Laser quenching characteristic and quality parameter. For processing parameters optimization and hardened depth prediction, 45 steel laser quenching temperature field was simulated by ANSYS, which can predict its hardened depth. Surface absorption coefficient change and phase change latent heat was considered. Moving thermal flow load and convection heat exchange boundary term were close to practice. The rule of the transform coefficient of laser energy and technique parameters (P, v) was fetched by contrast research about prediction of hardened depth and test measured data by phase change temterature. Test measured data examinated the prediction precision. The research affords a thought of precision prediction of hardened depth. The ends hardened layer distribution rule is gotten by trial research of endwise hardened depth, which is that enter-end depth is less than that of middle-area, and exit-end depth is more than that of middle-area. The enter-end and exit-end maximum temperatures can be made close to that of middle-area by variable scanning spee ANSYS simulation. And test measured result proved that hardened layer uniformity has been improved.The test researches of fatigue life of laser heat-treated gears were done for the first time. The fatigue test of laser hardening gear showed that the fatigue life of laser hardened gears is higher than that of conventional quenching gears in ISO6336 and GB/T3480 standard. The mechanism rested with suitable hardened layer distribution of teeth surface, high and stable residual compressive stress on gear teeth surface. This means the maximum shear stress will apparently descend. Because teeth roots of laser-heated gear can obtain stable residual compressive stress, combined tensile stress in the place of pulled side of root will descend apparently. Hardness along hardened layer depth direction evenly distribution and without apparently descending gradient made the life long before pitting corrosion. Because of super comprehensive mechanical properties, peeling phenomena of "hardened then brittle" has not been found, so laser-hardened gears have high peeling resistance. About gear overlap scanning process, though hardness of overlap temper belts of laser scanning in gear teeth surface decreased about HRC7, tests show that this can not bring about " fatigue sources" of influence fatigue strength. This offers feasibility bases for big module gears using overlap scanning.There are no standards about the available hardened depth of laser quenching gears. According to mostly theories about gear quenching hardened depth, contraststudy of available hardened depth about gears carburizing treatment and laser quenching is carried through. The available hardened depth range of gears is brought forward based on domestic and overseas research results of laser quenching. It is commended that small modulus gears hardened depth range is O.3~O.8mm,and that of large modulus gears is 0.5 ~ 1.2mm.Based on contrast research results, equivalent hardened depth and its experience formulate are given for the first time. The hardened depth of laser quenching gears should be considered as the equivalent hardened depth which equals to practice hardened depth multiply equivalent coefficient. The commended equivalent coefficient value is about 1.5~2.75, and large modulus gears should choose larger. The results of calculation with different rules and application results showed the feasibility.About laser cladding, experiments performed on laser cladding crack control. Results proved cladding layer hardness was improved by growing ingredient of C > C^ W in cladding alloy powder. Gradient material laser cladding can be used to gain high quality cladding layer and avoid cladding crack, which is useful to parts repair. With nickel-based and 316L stainless steel alloy powder as cladding material, metallic parts with dense microstructure were formed, which is helpful for thicker cladding repair of parts.Laser cladding experiments under ultrasonic vibration were carried out, and the experimental results show that vibration-assisted cladding method significantly improves microstructure and hardness of cladding, which affects to crack control.The stress field of laser cladding was simulated and mechanism of cladding crack was analysed. It showed that 316L cladding layer is with remain pulling stress that scanning direction pulling stress is the largest, those of other two direction are very small. There is stress concentrate in the dividing line edges of cladding layer and substrate which may made cladding crack spread.Experiments were performed on gear laser cladding with ways of preplaced and lateral supply of alloy powder by axial scanning technics which gained fine cladding layer on gear surface. The result show the possibility of laser cladding on gear surface strength and repair. Repeat scanning without powder supply is useful to control cladding crack. Becase of cladding diffculity and cost, gear laser cladding repair technics is suitable to large and middle modulus gears...