Research Of Optimizing Laser Microtexturing Parameters On The Cam Based On Hydrodynamic Lubrication Theory

The frictional pairs of cam-tappet are the main drive mechanisms in the valve mechanism and fuel supply system,its friction and wear will lead to the worsening of the contact conditions and the change of surface morphology from this may increase the probability of surface fatigue and can have a destabilizing effect on the parts. especially with the development of engine to the high-speed and heavy-power direction in recent years,the contact stress between cam and tappet will be increased inevitably,lubrication conditions become more stringent and this can lead to the initial failure of cam and tappet.To satisfy the requirements of stability,reliability and durability of the internal combustion engine,many scholars have done a vast amount of effective work.As one of the effective ways to improve tribological properties(Non-contact processing,fast processing speed,no pollution to the environment,accurate controlling of shapes and sizes),the technology of laser surface micro-texturing has become the first choice of achieving precise surface micro-texturing to abtain good lubrication condition.Based on the analysis of the interaction mechanism between laser and surface materials of cam,a new idea of cam surface complex treatment by taking the technology of laser surface micro-texturing into cam surface come out.Based on elastic hydrodynamic lubrication theory,a mathematical model of cam with regular microstructure has been built and analyzed,a simulation experimental study has been carried out by using UMT-2 friction-wear tester.Firstly,taking one pore in the axis direction of LST cam as the study object,a mathematical model is established for the cam surface with regular microstructure in the form of paraboloid, making use of the multi-grid method to solve the mathematical model with Reynolds cavitation boundary conditions.Dimensionless minimal fluid film between the two sliding surface is taken as the criterion to estimate the LST cam's hydrodynamic lubrication performance,the impact of micro-pores'area density and ratio of depth to diameter on EHL performance of cam surface,then gained the optimized parameters of micro-pores.Secondly,making use of the "single pulse at the same point interval more times" LST processing technics,a laser processing test has been carried out.A variety of factors which effect the machining quality of cam's surface microstucrure such as laser wavelength,scanning speed,pumped current,Q-switching repetition frequency have been analyzed and the reasonable processing parameters have been chosen.Finally,the friction-wear test is carried out with an UMT-2 friction-wear tester under the cam Simulation conditions.The results show that the samples with micro-structures not only reduce the friction but also improve lubrication performance obviously.The results are similar to the one obtained by numerical calculation...