Grinding simulation and process optimization method of tungsten carbide alloy

  Objective  Precision glass molding technology is the primary technology for the mass production of high-precision glass-based optical components. The ultra-precision machining of mold plays an essential role in the performance and quality of glass molding products. Tungsten carbide alloy has become the first choice of precision glass molding materials because of its advantages of high hardness, high wear resistance, and high chemical stability. In order to improve the surface quality of tungsten carbide mold core during ultra-precision grinding, the influence of critical process parameters on surface roughness was studied.

  Methods  The influence of process parameters on surface roughness was studied by combining simulation and experiment, and process optimization was carried out. First, based on the physical characteristics of WC-6%Co tungsten carbide alloy, a grinding process simulation model was established by using Abaqus to simulate the effects of grinding depth, feed speed, wheel speed, workpiece speed and other process parameters on the surface roughness of WC-6%Co tungsten carbide grinding. The reasonable process parameters of grinding tungsten carbide alloy were determined by simulation. Then, the Taguchi method was used to optimize the grinding process of tungsten carbide alloy. Finally, under the guidance of the optimal process, the experiment of tungsten carbide aspheric mold core ultra-precision grinding was completed.

  Results and Discussions  The simulation results show that the roughness increases relatively slowly when the grinding depth increases in the range of 1-1.8 μm; When the grinding depth increases in the range of 1.8-2.6 μm, the corresponding roughness growth rate is relatively large, and the reasonable grinding depth range is 1-1.8 μm (Fig.5); With the increase of the feed speed, the surface roughness decreases first and then increases. The reasonable selection range of the feed speed is 0.5 mm/min-1.5 mm/min (Fig.6); There is a nonlinear inverse relationship between surface roughness and grinding wheel speed, so a larger grinding wheel speed should be selected as far as possible (Fig.7); the surface roughness decreases first and then increases with the increase of workpiece rotation speed. The reasonable selection range of workpiece rotation speed is 100 rpm/min-300 rpm/min (Fig.8). The process optimization experiments were carried out according to the process parameter range selected by the simulation results. The experimental results show that the surface roughness increases with the grinding depth (Fig.10); The surface roughness decreases first and then increases with the increase of feed speed and workpiece speed. It is proved that the simulation results have the same variation trend as the experimental results.

  Conclusions  Aiming at the ultra-precision grinding process of WC-6%Co tungsten carbide alloy, the finite element simulation analysis and process optimization experiment were carried out, in order to improve the surface quality of tungsten carbide mold core ultra-precision grinding. Abaqus was used to simulate the effects of grinding depth, feed speed, wheel speed, and workpiece speed on the surface roughness during grinding. The optimization experiments were carried out according to the process parameter range selected by the simulation results. The simulation results demonstrate that the surface roughness increases with the increase of grinding depth, decreases first and then increases with the increase of feed speed and workpiece speed, and decreases with the increase of grinding wheel speed. The analysis and comparison of simulation and experimental results show that reducing grinding depth, increasing grinding wheel speed, and selecting appropriate workpiece speed and feed speed are beneficial to control the surface roughness of tungsten carbide alloy after ultra-precision grinding. The optimum process parameters are as follows: grinding depth 1 μm, feed speed 1 mm/min, grinding wheel speed 40000 rpm/min, and workpiece speed 200 rpm/min. An aspheric core with an average surface roughness of 3.379 nm was obtained by ultra-precision grinding of an 11.8 mm diameter tungsten carbide alloy core with the optimum process parameters obtained by the optimization experiment.