Surface Roughness Simulation And Parameters Optimization On High Hardness Spherical Precision Grinding

The ball valve, which can resist high (>500℃) temperature, high (>30MPa) pressure, corrosion and wear, is the core components of fluid and gascontrol device in natural gas transmission, petroleum chemical engineering,steel smelting, coal liquefaction and nuclear power plant. In order to meet thestringent requirements of harsh working environment, the ball of the valve istypically made of the304stainless steel base material with thick thermalspray coated tungsten carbide (WC) in Co matrix surface layer to achieve thehigh hardness and wear resistance. The spherical surface of the ball needs tobe precise. Surface roughness has an important influence on the wear, thefatigue, the corrosion, the installation and fit of valve core, it directly affectsthe quality of valve core. Therefore, in the paper, the technology of predictionand control of surface roughness on high hardness and high precisionspherical grinding are studied based on self-developed spherical grindingmachine. Specific research contents are as follows: Firstly, Base on the undeformed chip thickness model, study therelationship between surface roughness Ra and four process parameters (cupwheel speed ns, workpiece speed nw, feed rate apand wheel block number Ns),a new analytical surface roughness model is developed based on the effect ofoverlapping of multiple abrasive grains. The process parameters which effecton the spherical surface roughness have been theoretically analyzed andexperimentally studied, four process parameters (cup wheel speed ns,workpiece speed nw, feed rate apand wheel block number Ns) are the biggestinfluences on surface roughness. The presented model has been validated bythe experimental results of spherical grinding. The theoretical roughnessvalues are agreed quantitatively well with the experimental results.Secondly, Surface texture model of spherical grinding is built by usingcoordinate transformation. The time varying grain trajectory form is alsopresented. The effect of grinding parameters to The surface roughnessdistribution and process parameter optimization are discussed by theoreticalanalysis and experimental research, and the modeling and simulation resultsare tested through surface roughness experiment. The simulation andexperimental results showed the trajectory density on the middle area arelower than that on the both sides. With spherical workpiece size increasing,the differences between the middle and two sides are greater. Propose the trajectory density concept, Difine the grinding speed ratio k (k=ns/nw) and thegreater the k is, the greater the surface trajectory density is, the greater thesurface roughness is. When the grinding speed ratio k is not an integer, thegrinding trajectory do not overlap each other, so it is conducive to increasethe trajectory density and decrease the surface roughness.Finally, The spherical grinding process parameters are optimized bySPEA2genetic algorithm for the target of maximum material removal rateand minimum surface roughness Ra, with cup wheel speed ns, workpiecespeed nw, feed rate ap and wheel block number Ns as variables. Theexperimental results showed SPEA2genetic algorithm can make the materialremoval rate increases to121mm3/min, and the surface roughness decreasesto0.03μm. It is better than orthogonal experiment. SPEA2genetic algorithmcan quickly and efficiently obtain high quality and inspiring optimized results.It can effectively solve the optimization of the hard sphere grinding.