A Study on Tangential Ultrasonic-Assisted Mirror Grinding of Zirconia Ceramic Curved Surfaces

Zirconia ceramics have been used in the field of smartphone manufacturing, especially for the phone shells. To improve the machining efficiency and simultaneously obtain a mirror-surface quality on the curved surface made by zirconia ceramics, the tangential ultrasonic-assisted grinding (TUAG) was proposed, in which the ultrasonic vibrations of the grinding wheel are always in the direction tangential to the work surface at the grinding point. To reveal the fundamental grinding characteristics of the TUAG on the zirconia ceramic curved surface, the processing principle and according experimental setups were given out at first. The effects of the proposed method on the surface morphology and surface roughness were investigated experimentally and analyzed numerically under different process parameters for plane workpieces. Finally, a curved surface was successfully processed by the novel method with the optimized experimental conditions. The obtained results demonstrated that (1) typical sinusoidal cutting traces appeared on the work surface, which implied that the surface morphology was affected significantly by the ultrasonic vibrations; (2) the surface roughness was distinctly affected by the amplitude of the grinding wheel, and a higher efficiency was attained on the surface quality enhancement when the larger amplitude was applied, e.g., R a was reduced by 58.3% when an amplitude of A p–p = 4.66 μm was imposed; and (3) the R a value in the direction vertical to the wheel feed direction on the curved surface decreased to 39.5 nm, implying that a mirror curved surface can be obtained by TUAG with the appropriate process conditions.