Research On Drill-grinding Silicon Nitride Ceramics With Diamond Thin-wall Drill

In the modern industrial fields of petroleum, chemical, aerospace and nuclear power generation, complicated working conditions such as high temperature, high pressure and strong corrosion gradually increase. More strict requirements are put forward on the performance of ball valve. Due to superior performance such as high hardness, high temperature resistance and corrosion resistance, ceramic ball valve can meet the requirements of complicated working conditions and is widely used. However, for its high hardness and high strength, ceramic ball valve is very difficult to be machined, especially the hole. Which seriously hinder its promotion and application. Therefore, silicon nitride ceramics was selected as workpiece material, and was drill-grinded with brazed diamond thin-wall drill. The main research and conclusions are as follows.First, according to constant pressure feed, pneumatic constant pressure feeding device was designed and manufactured specially. Axial force was calibrated using tension-compression sensor MCL-S1, by which the relationship curve between the pressure and axial force was gotten.Second, by single-factor test, the effects of diamond size, wall thickness of drill, spindle speed and drilling pressure on machining efficiency were studied. The results demonstrate that machining efficiency remains basically unchanged with the increase of diamond size, increases slowly first and then decreases rapidly with the rise of wall thickness, and increases quickly first and then grow slowly with the increments of spindle speed and drilling pressure. By orthogonal experiment, the influence degree of the four parameters on machining efficiency was further studied, and the collocation of optimal factors level was obtained. According to the influence degree on machining efficiency, the order of four parameters in descending order is that wall thickness, drilling pressure, spindle speed, diamond size. And the collocation of optimal factors level is that 35/40 of diamond size,1.5mm of wall thickness, 900r/min of spindle speed,819N of drilling pressure. Finally, based on genetic algorithm BP neural network, prediction model of machining efficiency was established.Then, the removal mechanism and the effects of various parameters on the removal mechanism of silicon nitride ceramics were studied by analyzing the surface microscopic morphology under different parameters. The results show that the removal mechanism includes brittle removal and plastic removal, and the brittle removal is the main removal mechanism. The proportion of plastic removal increases with the growth of wall thickness, and decreases with the increase of spindle speed and drilling pressure. The relationship between brittle removal and machining efficiency was further studied by comparing the variation of the proportion of brittle removal and machining efficiency with various parameters. The results show that with the increase of the proportion of brittle removal, machining efficiency increases, but not keeping increasing.Finally, the effects of diamond size, wall thickness of drill, spindle speed and drilling pressure on drill life were studied. The results demonstrate that drill life decreases with the rise of diamond size and wall thickness, increases first and then decreases with the growth of spindle speed and drilling pressure. The wear forms were further studied by observing micro morphology of drill end face. The results demonstrate that the wear of drill includes diamond grit wear and bond wear. Diamond grit wear forms include wearing flat, fragmentation and dislodgment, and grit wearing flat is the main wear form, grit dislodgment is very less. Bond wear forms mainly include bond fracture and shifting sand form.