Surface quality study of longitudinal torsional ultrasonic micro-milling of borosilicate glass based on morphological modeling

Borosilicate glass has good light transmittance and stable chemical property, which is an ideal material for microfluidic chip matrix, However, brittle fracture is easy to occur during processing, which is a typical material difficult to process. This limits the surface accuracy. In recent years, longitudinal torsional ultrasonic vibration–assisted milling (LTUVAM) has been proposed as an effective way to machine hard and brittle materials. To elucidate the mechanism of material removal methods and elaborate the material removal mechanism during longitudinal torsional ultrasonic vibration–assisted milling process, this paper established a 3D morphology prediction model to investigate the material removal method. Firstly, the three-dimensional surface morphology model was created by describing the intricate tool path and the workpiece surface morphology reconstruction process under ultrasonic conditions while also considering the tool run-out effect. The model exhibited a certain degree of scalability, enabling the acquisition of various process morphology prediction models by altering the tool coordinates via matrix manipulation. Secondly, the accuracy of the model was verified by longitudinal torsional ultrasonic processing experiments. Thirdly, longitudinal torsional ultrasonic vibration–assisted milling experiments and longitudinal ultrasonic vibration–assisted milling experiments were conducted, and the surface roughness of the machined workpieces was measured. The experimental results show that LTUVAM further reduces the roughness compared with LUVAM, indicating that the reduction ratio reaches a maximum value of 61.06% at the spindle speed of 16,000 RPM, and then, the reduction ratio decreases to 42.88% with the increase of spindle speed. Combining modeling and experimental results, we concluded that LTUVAM was more advantageous in achieving plastic material removal and enhancing the surface quality of the machined surface compared to LUVAM. And under the same process conditions, as the spindle speed increases, the surface roughness of the workpiece increases first and then decreases.