Analysis And Performance Evaluation Of High-Speed Heavy-Load Gears With PVD Coating

In low speed and heavy load gear transmission, gear tooth relative sliding velocityis too low when engaging near the pith circle, oil film formatting is poor and poorlubrication causes larger friction while hertz stress is higher in a single tooth meshingzone, therefore, surface fatigue pitting appears at root surface near the pith circle. Inhigh speed and heavy load gear transmission, the tooth contact surface under a heavyload will sticky welded together because of high instantaneous temperature, rupturing oflubricant film between the engagement surface when large sliding velocity of the directmetal surface contact. Softer contact tooth surface will torn or wrinkled along therelative sliding direction, generating tooth surface scuffing failure. Appling solidlubrication composite coating, with low friction and anti-scuffing, to high speed andheavy load gear tooth surface in order to meet the needs, and it will improve theperformance of transmission obviously.Aiming to gear transmission of electric propulsion system final use, the paperadopts theory of gear meshing, gear scuffing failure theory, tribology, surfaceengineering, heat transfer and thermal analysis techniques and FEM to researchtransmission performance and friction and wear mechanisms of high speed and heavyload gear coating, in order to apply solid lubrication composite coating, with lowfriction and anti-scuffing, on gear surface successfully to meet the critical demandsimposed on functionality and performance of gear transmission, many theory andexperiment study have been done. The concrete research works include:1) Determine boundary conditions and related parameters for gear bodytemperature field FEA, including convective heat transfer coefficient, the tooth surfacerelative sliding velocity, tooth contact pressure, tooth surface coefficient of friction,tooth surface friction heat flows, heat distribution coefficients, gear material propertiesand lubricants characteristics et al. The first six parameters are a function of meshingposition, a MATLAB program is writhed to get the final load of the finite elementfunctions and related boundary conditions. In conditions, temperature40°C, load: FZG6stage,8stage and12stage, speed:2175r/min,6000r/min, driving wheel bodytemperature distribution has been calculated, and the characteristics of the distributionand the main factors has been analyzed. Flash temperature distribution of driving gearhas been achieved, and the distribution of the main factors has been analyzed. 2) Considering the complicated condition and actual load, using nonlinear springelement to simulate the interface, a gear coating contact mechanical calculation modelwas established. A finite element analysis on load capacity of heavy-load transmittinggears coating was carried out to investigate the influence of PVD coating type, coatingthickness and load level on stress distribution and failure mode. Based on experimentalresearch other scholars have did, the main reason for coating surface crack and the mainfactor for coating peeling is analyzed.3) According to coating preparation process and use conditions particularity,appropriate gear material, heat treatment process and surface state are selected. In orderto improve adhesion strength, reduce heat generated by residual stress in the preparationprocess, a commercially pure Ti as a buffer layer between the substrate and the coatingare processed. Reference to domestic and foreign scholars PVD coating preparationresearch has done, considering influence of different process parameters on coatingfriction coefficient, critical scratches load, nano-hardness, elastic modulus, friction andwear rate and other factors, minimizing friction and wear rate of the coating, coatingprocess parameters of unbalanced magnetron sputtering technology are selected todeposit DLC, WC/C and TiN solid lubricant, respectively, formulated detailed processsteps. Make a Preparation for friction and wear experiment and FZG gear scuffingexperiment.4) In order to apply the surface PVD coating to power transmitting gears whichunder high-speed and heavy-load, TiN WC/C, and DLC coating are deposited onbearing balls. Friction and wear tests are performed using a MRS-1J test rig andload-carrying capacity tests are performed using a MMW-1P test rig. The tribologicalperformance and load-carrying capacity of balls which coated coating or no areinvestigated. Optical microscopy and X-ray photoelectron spectrometer are used toobserve the surface of coating and wear scar, and a numerical wear contact model isproposed to analyze the wear mechanisms. The results demonstrate that WC/C and DLCcoating exhibit excellent tribological properties, running performance and load-carryingcapacity. Coating wear mechanism under heavy load are, peeling failure for TiN, fatiguepitting for WC/C and adhesive transfer for DLC.