Parameters Optimization And Surface Quality Analysis On High-Precision Spherical Grinding

As the crucial component on media-flow process, metal sealing ball valve is widely applied in industrial areas such as electric power, water conservation, chemical engineering, oil gas, metallurgy, etc. It has the advantages of less fluid resistance, convenient operation, quickly opening and closing, good sealing and high reliability. In order to meet the strict requirements in working condition, the surface strengthening is obliged to ball valve core, always using HVOF hard alloy, nitriding process (HRC≥65). However, it also brings some difficulties to the subsequent grinding. For different sizes of valve core sphere, two methods spherical grinding with cup wheel are usual: the first is cup-wheel spherical grinding without swing (CSGNS) for the large-scale workpiece, and the second is cup-wheel spherical grinding with swing (CSGS) for the medium and smaller one. This work presents the relationship between surface quality and parameters selection with diamond abrasvie wheel for two methods of spherical grinding.Indexes of grinding surface quality include the surface roughness, surface exture on trajectores, surface hardness, and surface residual stress and cracks. According to the four aspects, this paper launched some researches:Firstly, two trajectories equations for CSGNS and CSGS were derived based on the spherical surface forming grinding principle and coordinate transformation theory. Some analyses and two experiments were carried out based on its texture formed by trajectories of a single grinding block in two conditions. It reveals how relationship between some key parameters (i.e., cup-wheel rotation speed, spindle speed, and swing speed, etc.) is to affect the trajectories texture.Secondly, due to the multi-block superposition of grinding trajectories, density of trajectories points (DTP) was defined and quantized in subsection. Relationship between distribution of DTP and distribution of surface roughness was studied among different grinding wheel radiuses. Conclusions show that the appropriate area for cup wheel radius is [0.6L, 0.8L] under the consideration of roughness distribution and machining time. In addition, the "lack-phase" problem of trajectories caused by the initial error was researched, and the initial error control and the maximum value requirements were proposed. Finally, grinding surface micro-characteristics on WC-Co coating were watched out via scanning electron microscopy (SEM) aiming at spindle speed, cup-wheel rotation speed, swing speed and feed amount. It comes out a conclusion that the amount of feeding is above the other three priorities in the respect of grinding surface quality. The defect in the form of granular or flaky fall-off material is shown in spherical grinding on the WC-Co coating, and WC is vulnerable to decarburization and carbonaceous nodes are generated. Furthermore, the residual stress of surface was analysed through X-ray diffraction (XRD) method based on four ways to feed having an influence on it. It shows that the appropriate feed amount is ap = (1~1.5)μm.