Fluid jet and bonnet polishing of optical moulds for application from visible to x-ray

Abstract

Electroless Nickel (ENi) and binderless Tungsten Carbide (WC) are materials widely used in industry to make replication moulds for precision optics, with applications ranging from consumer camera lenses to high accuracy X-ray mirrors. The aspheric shape generation is generally performed by diamond turning in the case of Nickel, and microgrinding in the case of Tungsten Carbide. However, both machining methods fall short from meeting the ultra-precision criteria required by an increasing number of applications, because of insufficient form accuracy and the frequency content of the machining marks they leave on the surface. It is thus commonly observed in industry that moulds need to be subsequently polished by hand, a usually slow and human resource intensive operation. The Zeeko 7-axis CNC machine, equipped with sub-aperture fluid jet and precessed bonnet polishing technology, has been used to develop deterministic finishing processes on both Electroless Nickel and Tungsten Carbide. Corrective polishing to less than λ/20 (<31nm PV) form error can be achieved, as well as the ability to smooth surface texture down to 1nm Ra or less, in a time efficient manner.

Automated Finishing of Diamond Turned Dies for Hard X-Ray and EUV Optics Replication

“…The fluid jet polishing process consists of pressurized water and abrasive particles mixed and delivered through a nozzle [9]. Typical operating pressures range from 4 to 20bar, while typical abrasives range from 0.1 to 100um.…”

Analysis of infrared optical polishing effluents and reduction of COD and TSS levels by ultrafiltration and coagulation/flocculation

“…Consequently, these "worn" slurries are disposed and a "fresh" batch is prepared. Due to the industry growth [3] and diversification [4,5], effluent volume from optical polishing increases and it needs to be disposed responsibly.…”

Electrochemical magnetorheological finishing for hard-to-machine functional materials with nanometer-scaled surface roughness

“…In general, the shaping of WC molds is achieved through the utilization of the grinding process. To further improve the surface quality of the WC mold further, numerous optical surface polishing techniques have been developed, including diamond abrasive polishing [8], vibration assisted polishing [9,10], bonnet polishing [11]. These techniques have been the subject of extensive research, encompassing investigations into the polishing mechanisms, material removal models, and in uential factors, and the root mean square roughness can be reduced to nanoscale precision.…”