Achieving the Best Possible Surface Finish for Sinker EDM Machining

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Q: Does high-qualify surface finish (HQSF) technology produce the best possible surface finish on Makino EDMs, and what is added to the machine for this option?

A: For over 20 years, Makino has offered HQSF technology as an option on sinker EDM products. The benefits of this technology are still a valuable and important function for fine-finish applications. When initially released, HQSF was designed with a focus on the improvement of surface finish and finish consistency to eliminate post-machine polishing, but the technology also yields additional benefits.

HQSF technology uses a special proprietary powder (µSc) designed to be neutrally buoyant so that it remains suspended when added to the dielectric oil fluid. During machining, the powder additive evenly distributes the discharge spark energy over the entire electrode contour. This design provides a more controlled and stable EDM process by minimizing any local concentrations of power that can create shortages resulting in “hot spot,” or pin-hole, discharge.

HQSF does not necessarily improve the “best possible surface finish” capability of a machine, as seen with the use of copper electrodes. However, the use of HQSF with copper electrodes does dramatically improve the total cycle time.

When using graphite electrodes, HQSF dramatically impacts and improves the best achievable surface finish. Performing standard EDM processing using graphite electrodes yields a best surface finish of 0.7µRa (27µinRa). Using HQSF with graphite electrode can produce a best surface finish of 0.4µRa (16µinRa), which is a significant improvement of almost 50 percent. Additional cycle time, however, is required to achieve this finer finish with the HQSF special generator settings.

During HQSF machining, the machine filters are bypassed, and the machine tracks the machining hours of the HQSF powder. Once the powder is depleted, the filters are reactivated to collect the material debris from the fluid. Early machines with HQSF technology are equipped with magnetic separators used to filter large metal contaminants from fluids. The magnetic separator system is still an available option, but this system is recommended only for large EDM applications that use 120-amp or higher power settings.

The Makino EDAF-Series machines offer HQSF technology as a retrofit option (except for machines equipped with the fine-hole EDM drilling options), but the larger EDNC-Series machines offer HQSF only as a factory-ordered option.

HQSF Technology Benefits:

  • Faster roughing speeds
  • Faster total cycle time to fine surface finishes using copper electrodes
  • Faster total cycle time to standard surface finishes using graphite electrodes
  • Up to 50 percent finer surface finish with additional cycle time using graphite electrodes
  • Improved metallurgical quality (less recast, HAZ and micro-cracking) that can extend the service life of the part/tooling component
  • Reduction or elimination of polishing time

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