The extensive cost savings and associated design flexibility made possible by precision machining have propelled diamond turning into corporate management discussions and plans. In this paper the existing and planned manufacturing technology programs of the DoD are discussed, and their coordinated relationships through the Precision Machine Tool Technology Program are explained. Due to these recent accomplishments, new applications are extending the horizon of interest in diamond turning and precision engineering. These applications include an Army night vision goggle, flight simulator optics, aircraft windscreens, coupled cavity traveling wave tube components and shaped charge liners. These developments are being stimulated both by the expanding horizon of applications and by more demanding shape/finish requirements. In addition to current diamond turning machine advanced developments, a project to diamond turn glass is discussed.
A submicroinch spindle accuracy is a requirement in achieving the capability to machine large-diameter optics to better than a 125-nm (5-μin) contour accuracy. A 100-mm (4-in)-radius air-bearing spindle with the capacity to carry a load of 880 N (200 lbf), centered at a distance of 305 mm (12 in) from the spindle faceplate, has been assembled and tested. Performance of the upgraded spindle has been evaluated. A 152-mm (6-in)-radius air-bearing spindle, capable of carrying a 2640-N (600-lbf) load centered 152 mm (6 in) from the spindle faceplate, has been fabricated and is now being assembled. Diamond machining of journal-bearing surfaces to better than a 125-nm (5-μtin) roundness error was used to achieve the desired spindle accuracy. A disc-type eddy-current motor has been designed, fabricated, and tested in efforts to improve the spindle drive system.
We are prepared to discuss special machines constructed for finishing regular geometric surfaces to optical figures and finishes, with demonstrated results on cylinders, spheres, flats, prisms, and other surfaces of revolution. Simple modifications to a spherical generator for producing standard conics and aspherics is described. Experience with machine design, inprocess measurement and control, diamond tooling, fixturing, and coolants is discussed. In general, the trend has been to beef-up standard machines for improved accuracy. Funslamentally, a massive machine is made more rigid, at t e expense of lower natural frequencies in the structure. Lighter materials like granite and concrete, modular components based on air bearings and optics, and custom configurations inside-out in nature, pro-vide excellent rigidity and accuracy and are much easier to control. On smaller parts, surface preparation is so fast that notions of a controlled environment become short term. Much of the machine design and development work has been done in West Germany with partial support from the government. Closest to productization have been the fly-cutting machines and lathes for facing and turning. Spherical generators have been in use primarily for in-house production of air bearing components, in Germany and the United States.
Precision machine tools are designed and fabricated with a great deal of consideration given to maintaining as smooth and precise a motion as possible between the cutting tool and workpiece. Air bearing slides and spindles along with pneumatic isolation systems are used to eliminate many of the mechanical disturbances associated with other machine tools. Unfortunately, the slide drive mechanism used in most cases is the ball nut/lead screw which introduces vibration and slide positioning errors due to the mechanical gearing. To avoid these problems a linear-induction-motor slide drive system has been developed which has no mechanical coupling between the motor's stationary and moving members. When interfaced with a laser interferometer position transducer, this drive system is capable of producing slide position accuracies of better than 3 microinches when driving a 1,000 lb. mass between 0 and 4 ipm. The paper describes this and other efforts that are continuing to extend the system capabilities to drive masses up to 10,000 lbs.
A new machine tool now in the final stages of development at Battelle, Pacific Northwest Laboratories uses a unique tool motion to produce diamond-turned surfaces of exceptionally high quality. Copper surfaces of revolution have been produced with a 12.3-A rms surface finish and a contour accuracy of 75 nm. The cutting tool is programmed to move in 4 nm increments along two axes: one linear (X) axis and one circular (Omega) axis. Exceptionally stiff and accurate control of the tool is possible with this "Omega-X" system. In conjuction with a unique thermally stabilized air bearing spindle and machine calibration equipment, the Omega-X system permits a significant advance in the fabrication of optical-quality surfaces.
The manufacture of aspheric optical surfaces presents both technical difficulties and unique opportunities. Military systems will see increasing use of the aspheric optical surface due to improved function and reduced system cost. This paper first summarizes the strengths and weaknesses of present diamond turning technology. The requirements of manufacturing precision aspherics in sufficient volume to be cost effective are shown in terms of the turning, polishing and gaging machines necessary for production. The remainder of the paper discloses how machine control features using programmed micro-electronics allows a completely new approach to surfacing precision aspherics.
This paper will trace the evolution and development of single point diamond tool precision machining equipment from a simple single axis machine to a two axis CNC/Interferometer controlled lathe for machining of contoured optical surfaces. The design criteria basic to such machines to control machine rigidity, friction, geometrical accuracy, vibration, temperature, and positioning accuracy will be discussed. Various surfaces and the machine configurations suitable for producing them are listed.
A technique to improve the adherence of multilayer dielectric coatings to diamond-turned copper mirror surfaces was developed. The method employs carefully controlled ion polishing, vacuum annealing, and "in situ" coating of the mirror substrates. It was found that ion polishing the substrates, with as little as 100 A removed, prior to coating improved the film adhesion significantly. All of the samples prepared in this manner passed all of the standard MIL SPEC mechanical tests while control samples produced by conventional methods failed the tests. Additional coating evaluation such as reflectivity and laser damage threshold measurements at 10.6 pm, Auger analysis for contaminants in the films and at interfaces, SEM characterization, and x-ray energy dispersive analysis are also discussed.
The potential for large DOD cost savings by fabricating optical parts using state-of-the-art precision turning techniques has resulted in an Air Force Materials Laboratory program to commercialize the technology, now largely within DOE contractor laboratories and production facilities. Machining process is becoming an extension of optical process requiring a melding of optical and machining disciplines, including cost trade off for part complexity and production volume. Differences in terminology and specification conventions are being resolved. The goal of the three-year commercialization program is to accelerate a technology diffusion process faster than is likely to be realized by market forces so as to capture potential fabrication savings for presently identified needs. The program will sponsor seminars and workshops, aid in procurement specification writing, provide shop floor assistance in tool performance testing and supply documentation of the technology for individual reference. Program plans call for a partnership with selected industrial companies in commercializing state-of-the-art precision turning technology.
The application of diamond turning technology has made it possible for Honeywell, who possesses limited conventional optical fabrication capability, to rapidly become its own supplier of lower-cost infrared optics for in-house production programs. The achievement was originally instigated by an AFML MM&T program and is part of a two-phase plan outlined as this symposium in 1976. Phase I of the plan called for Honeywell, entirely on its own funds, to acquire a diamond flycutter to initially become familiar with the process and finally to produce usable infrared flat mirrors. Although the cycle required ten months of learning and some machine improvements, significant cost savings are now being accrued from the production of scanning and flat mirrors for thermal imaging systems. Phase II of the plan was commenced in 1977 by AFML sponsorship of a program to transfer diamond contouring machine technology from government laboratories initially to Honeywell so that broader industrial usage of infrared aspheric optics could result. Also, an NV&EOL contract is reinforcing the plan by utilizing Air Force program results to build and test aspheric diamond turned lenses and mirrors for Army infrared applications. Contract results are being publicized -through reports and briefings. Within the plan, Honeywell is committing funds to obtain a 2-axis CNC contouring machine, the required optical metrology, and the temperature-controlled facilities. Because continued cost-saving success is expected from the aspheric capability, as has been demonstrated with the flycutter on flat infrared mirrors, Honeywell hopes to become a production optics supplier to the DoD/DoE community by contributing its systems, computer science, and optical testing expertise.
The development of precision machines for generating aspheric optical surfaces at Bell & Howell Company, which were the ancestors of many of today's diamond turning machines, is outlined together with present machine capability. A practical procedure for compensating for repeatable machine position errors based upon measurement of a "best-fit" sphere is described. Applications of diamond turning to reflective and transmissive (germanium and silicon) infrared optical elements are illustrated.
The ability to successfully fabricate an optical element has as its bounds on contour accuracy and functional system performance the level to which these features can be charact erized via test methods. In addition, product saleability and satisfaction, of specification must also be provided in a production-compatible optical evaluation program. These restric tions are even more severe in the case of a diamond-turned sample, particularly aspherics. The impact of slope-errors, finish and subsurface micro structure on the imaging properties of an element as a result of the diamond-turning process is to this point illdefined and must become an important part of an overall characterization scheme. While a measure of the element Optical Transfer Function (OTF) would provide proof of suitability in its wavelength of use, the costly, non-universal nature of this test precludes its use in a production. environment. This paper addresses an overall characterization program for diamond-turned elements for infrared-systems use which will provide specification verification, systems performance parameters and production. buy off potential while remaining compatible with needs of production-level operation.
A fabrication process is now available that can manufacture focusing mirrors for the 10-kJ laser fusion experiment being conducted by the Los Alamos Scientific Laboratory. Techniques have been developed for satisfactory metal preparation, copper electroplating, single-crystal diamond turning, and optical inspection. Fabrication of these mirrors by these techniques, and a post diamond-turning polish, resulted in diffraction-limited optics at a wavelength of 10.6 µm.
An explanation of the electroless nickel plating process is given and important metallurgical and mechanical properties of the plating are discussed. Optical applications of electroless nickel are described. Machinability tests were conducted with variations in types of plating, thickness of plating, types of substrates, and heat treatment of the plating; results of the testing program are presented.