Original Date: 11/03/1996
Revision Date: 01/18/2007
Best Practice : Ion Milling
The Optical Manufacturing Operational Development and Integration Laboratory (MODIL) within the Y-12 plant site at Oak Ridge has four cells for machining material to high quality optical surfaces. One machine is an ion milling cell which uses the impact of ionized argon on the surface of a material to dislodge surface atoms. With characterized process parameters, surface material is selectively removed by controlling the position and dwell time of the ionized argon beam, thus improving the figure of optical components. In the Y-12 cell, two systems utilize a beam of ionized atoms fired in a vacuum on a work surface, dislodging work surface atoms.
A part with a target four inches in diameter is mounted vertically in a vacuum chamber in the larger system. Peaks of 3,000 to 5,000 angstroms are identified for error mapping. The map is convoluted with a beam profile to create a map of dwell time for peak reduction. The inert gas (argon) ion beam is rastered across the workface and the depth of cut is controlled by the dwell time. Location of the beam is X-Y coordinate controlled. A neutralizer is utilized to eliminate charged particles on the workface to eliminate any beam rejection. The peaks are reduced by two thirds. The smaller tungsten filament-actuated system is used for research on smaller parts. Materials such as aluminum, beryllium, or electroless nickel roughen rather than improve smoother surfaces. This problem is overcome by coating the surfaces of these materials with gold or copper.
This process accomplishes in a few hours that which conventional polishing and inspection techniques require 20 to 30 days to complete. This process is also independent of thermal and mechanical isolation. Integration of the coating with milling has been demonstrated to improve the turnaround time and is very application specific.
For more information see the
Point of Contact for this survey.