Development Of NC Grinding Machine For Rail And Research On Profiling Grinding Process

During the service life of rails,the complexity,variability and external environmental factors of wheel-rail loads can cause many damages on the surface of rails,such as rail edge wear,uneven rail profile wear,rail fish scaling,poor straightness,rail surface peeling,etc.These damages have serious effects on the stability,economy,and safety of high-speed train operation.Currently,rail grinding maintenance technology is an important means to repair rail profiles,extend rail service life,and improve the safety and stability of train operation.In this paper,based on the analysis of rail grinding principles and processes,a technical solution using lithium batteries as the power source,DC motors to drive the grinding wheel for main motion,and stepper motors to drive the movement module,swing and walking mechanism to realize the contour grinding was proposed to solve the problems of low machining accuracy,high labor intensity,and low work efficiency of traditional rail grinders.The touch screen PLC was used for automatic control of the rail grinder to provide technical equipment for high-precision and high-efficiency grinding of rails.A mathematical model of the rail standard profile was established,and the grinding mechanism of the grinding wheel end face and its effect on the profile were analyzed.Based on a single abrasive grain,dynamic,grinding force,and grinding power models were established.The theoretical rail profile was approximated using a multi-segment small straight line interpolation grinding method.The design calculation of contour grinding angle was completed,and the influence of process parameters such as grinding passes,grinding depth,and walking speed on grinding quality was analyzed.A reasonable contour grinding strategy was determined.Based on the technical parameters and functional requirements of rail grinding machines,a general motion scheme was designed to develop a numerical control rail grinder with automatic feeding,automatic deflecting,automatic walking,and in-machine inspection functions.A finite element model of the entire machine was established,and static and modal simulations were performed to calculate the displacement deformation and static stiffness changes in different grinding angles in the X,Y,and Z directions.Moreover,the constrained modal characteristics of the machine under weak operating conditions were analyzed.The natural frequencies and principal modes of the machine were obtained.The overall scheme of the control system for the CNC rail grinder was designed.Based on the Mitsubishi FX-1N series touchscreen PLC,the hardware circuit design of the control system was completed.The touchscreen human-machine interface and the PLC control ladder diagram program were developed.The control system was tested by program simulation and online debugging to verify that it can achieve digital control of preset grinding wheel rotation,automatic feed,automatic deviation,and automatic walking,as well as on-machine detection of contour errors.The prototype of the CNC rail grinder was manufactured,installed,and debugged.The vibration characteristics of the entire machine,the surface roughness of the ground rail,and the changes in grinding temperature were studied under different grinding process parameters.The machine detection accuracy of the rail error was experimentally tested,and the rail grinding strategy was developed based on the detected rail error.The grinding test results showed that compared with grinding depth and deviation angle,the grinding wheel speed had the greatest impact on the vibration characteristics of the grinder.The frequency and amplitude of the vibration acceleration spectrum peak were closely related to the grinding wheel speed.Grinding depth and walking speed were positively correlated with rail surface roughness and grinding temperature,while grinding wheel speed was negatively correlated with rail surface roughness and temperature.Evaluating the entire machine vibration characteristics,rail surface roughness,and grinding temperature as evaluation indicators,and taking into account grinding efficiency and other factors,the optimized grinding process parameters were determined as n=3000r/min,ap=0.2mm,and vs=4m/min.Using these parameters for grinding rails resulted in a straightness error of 0.106mm and a surface roughness of Ra0.2～Ra0.5,fulfilling the requirements of the rail grinding technical standard.