After preliminary grinding, many workpieces look bright to the naked eye, but microscopic inspection still finds residual fine abrasive marks, polishing lines and local halo defects. Ordinary polishing mainly brightens the surface through friction of consumables, which only covers up flaws rather than completely eliminating microscopic unevenness. Unstable polishing pressure causes local over-polishing and edge collapse while concave areas cannot be fully polished, resulting in poor batch consistency of finished products. It easily leads to peeling, spots and other defects in subsequent electroplating and coating processes, which is the core reason why conventional polishing fails to produce qualified flawless mirror surfaces.