Tool vibration effect on surface roughness of polymethylmethacrylate in diamond turning

The surface roughness required for the optical application and lenses is in the range of nanometers possible to achieve in single-point diamond turning (SPDT). The machining parameters like feed, spindle speed, tool nose radius, and depth of cut influence the surface roughness. These parameters, along with tool-workpiece interaction, develop vibration, and this vibration deteriorates the surface roughness. Three different vibrations as feed, cutting, and infeed act on the tool in three directions: X, Y, and Z. In this study, the impact of these three-direction vibrations is studied on the polymethylmethacrylate (PMMA). The infeed vibration is creating a 'tool jump,' leaving the material left uncut below it. This uncut material is responsible for the variation in surface roughness. The Taguchi's L-18 orthogonal array is used for experimentation, and the three-axis accelerometer is used to measure the tool vibrations during machining. Grey relational analysis is applied to find out the optimum parameters for lower surface finish and low vibration responses. A mathematical regression model has been developed, followed by a confirmation test to verify the experimental responses. The surface roughness (S-a) 25.9 nm is formed by utilizing optimized parameters. This study is beneficial for optical industries manufacturing, e.g., Intra-ocular lenses, Spectacle lenses, ophthalmic lenses, by providing optimum processing conditions.

Automated summary

The study found that feed, cutting, and infeed vibrations affect the tool in three directions, with the infeed vibration causing a "tool jump" that leaves material uncut below it. By experimentation and analysis, optimal machining parameters for reducing surface roughness and minimizing vibration responses were determined.