Mirror-Finish Electrical Discharge Machining (EDM) generally refers to EDM processes that achieve a surface roughness value below Ra < 0.2 μm, producing a surface with a mirror-like reflective effect. The resulting altered surface layer has uniform thickness, minimal micro-cracks, high wear and corrosion resistance, and requires no additional polishing.

Mirror-Finish Electrical Discharge Machining

Mirror-finish EDM is primarily used for machining complex mold cavities, especially intricate curved surfaces that are difficult to polish manually. It eliminates the need for hand polishing, improves component performance, reduces labor intensity, shortens mold manufacturing cycles, and holds significant practical value.

The effectiveness of mirror-finish machining depends on the workpiece material. For cavity molds requiring a mirror finish, materials that are conducive to such processing should be selected. Commonly used mirror-finish materials include imported steels such as SKD61, NAK80, and STAVAX, which exhibit excellent electrical erosion properties.

The electrical parameters for mirror-finish EDM have very low erosion capability, resulting in long processing times. Since dimensional changes during mirror-finish machining are minimal and the process primarily serves as a finishing operation, machining can be concluded once the required surface roughness is achieved. Therefore, the timed machining function of CNC EDM machines can be utilized, with the duration determined based on experience.

If the mirror-finished cavity has a regular rotational shape and the machine is equipped with a C-axis, using a fixture that aligns the tool electrode concentrically with the C-axis and rotating the C-axis during machining can achieve highly stable processing and improve surface roughness. However, during mirror-finish machining, the C-axis rotation speed should not be too high, as excessive speed can destabilize the process, increase arcing, and result in higher surface roughness.

The handling of the dielectric fluid during mirror-finish machining is also crucial. Generally, based on immersion machining, side flushing with appropriate pressure can be applied to maintain a slight circulation of the dielectric in the machining area. Intense flushing should be avoided, as strong flow can disrupt the normal formation of micro-discharges. Experience shows that if all aspects of the machining process are properly managed, carbon buildup is generally not an issue in mirror-finish EDM. Therefore, machining should be paused as little as possible, and the powder layer remaining on the workpiece surface should not be cleaned off, as it helps reduce parasitic and stray capacitance between the tool electrode and the workpiece, ensuring even distribution of discharge energy.

With the advancement of the mold manufacturing industry, market demands for mirror-finish EDM processes have increased. Today, mirror-finish EDM has become an essential technology in the manufacturing of precision cavity molds.