Improving Optical Mold Surface Roughness and Figure with MRF

Case Study Summary

QED Technologies applied Magnetorheological Finishing (MRF) to smooth mid-spatial-frequency errors, reduce micro-roughness, and correct figure on a tungsten carbide optical mold. The mold featured a steep concave spherical surface with a 55 mm radius and an 18 mm aperture, presenting a challenging geometry for conventional polishing methods.

Using a Q-flex 100 system in rotational mode with a 20 mm polishing wheel and D10 MR fluid, approximately 200 nm of material was removed in under two hours. This process achieved an order-of-magnitude improvement in surface figure, reducing peak-to-valley error from approximately λ to better than λ/12 while lowering RMS error to ~6 nm. Surface texture analysis confirmed excellent suppression of polishing rings and improved roughness consistency.

This case study demonstrates MRF’s effectiveness in finishing hard mold materials with high geometric accuracy and surface quality. The deterministic nature of the process enables optical mold manufacturers to achieve repeatable results without introducing subsurface damage or residual tool marks.