In 1977 Kollmorgen's Electra-Optical Division began investigating the application of air bearing technology to precision optics manufacturing. As a result, in 1979, a new venture group was formed known as the IntOp Division. The objective of the IntOp operating plan was to develop the diamond turning machines and related technology to produce superior optical surfaces so as to broaden the application of diamond turned optics from IR toward shorter wavelength applications. Diamond machined optics for use in the visual portion of the spectrum was clearly in mind. It was also during this period that IntOp was awarded a contract to become the U.S. Army Industrial Partner in the Precision Machining Commercialization program for the Department of Defense.
A computer controlled production system has been developed and commissioned for the production of various types of contact lenses for use in vision correction in humans. Precision diamond point turning was chosen for this application due to its flexibility and potential to cope with a wide variety of lens designs, materials and variation in production batch size. This paper reviews the choice of diamond point turning for this production problem, the results achieved and the potential for future development.
Using diamond CNC machining equipment, surface roughness specimens have been produced in moderate volume, which have a sinusoidal wave form. Arithmetic average (Ra) values of 0.3, 1.0, and 3.0 micrometers have been produced and delivered under contract to the National Bureau of Standards. The spatial wavelength for all was 100 micrometers. The sinusoidal wave form was diamond machined into the thickness of a .006 inch thick electroless nickel plating on a tool steel substrate. Any combination of Ra and wavelength is possible within the constraints of nickel plate thickness and trough radius. A major consideration was the diamond tool radius, its accuracy, and its effect on the turned profile.
Philips Research Laboratories have developed various new facilities for high-precision single-point diamond turning and precision grinding during the last few years. The COLATH machine, a high-precision NC lathe, operational since 1978 and generating contour accuracies better than 0.5 micron with an optically smooth surface finish (peak-to-valley < 20 nm), has been renovated in several aspects. Other new machines have been built. For transferring the precision machining technology in an effective way from the research section to the production departments of Philips, a second COLATH was built and installed in the Machine Factories (June 19831. A special grinding machine for manufacturing ultra-precision single-point diamond tools (ΔR <0.2 micron) was also built. The ultra-precise tools produced are available for external customers. In the last few years precision grinding in hard materials (steel, glass) for making moulds has been perfectioned; new precision measurement equipment is being developed and installed.
Recent results on the ultra-precision machining of plastics by a single crystal diamond tool with a highly precise rigid cutting apparatus are described in this paper. Using a newly developed ultra-precision air spindle and slide, detailed experiments were carried out for polymethyl methacrylate, polycarbonate and ally di-glycol carbonate among eight kinds of plastics, under different cutting speeds, depths of cut and feeding rates with several kinds of cutting tools. Chips from plastics cutting, cut surfaces and surface roughness were observed. It was clarified that these phenomena depend on characteristics of plastics. As a result, it was found that PMMA is the most suitable material for obtaining an optical grade finish by a single point diamond cutting.
An example of a physical system whose mechanical accuracy can be improved by feedback control is a simple motor-driven spindle. This system is being used as a test bed to study measurement and actuation systems as well as control algorithms. The specific apparatus reported utilizes an eddy-current probe for runout error measurement, a piezoelectric crystal to move the spindle to reduce the error, and a mini computer using a FORTRAN program for the feedback controller. The spindle runout before correction is in the 150 microinch range; the main contributors are master-ball centering error and bearing runout. With the error correction system in place, this error is reduced to less than 10 microinches--an order of magnitude improvement. While the final runout figures for the corrected spindle are still above that of a precision air spindle, the technique presents new possibilities for precision spindle performance including correction for wear, thermal deformations and unbalanced loads.
The contents describe interferometry, define its limitations on diamond machining surfaces, and will state the assumption on which this work is based. The background of the problems and difficulty of using existing test methods to acquire various fringe patterns caused by surface imperfections and the interpretation of those fringe patterns is discussed. A summary description of Phase I of the program is reviewed. In the current system, which is Phase II, a method of obtaining an interferogram of a thin radial swath of the surface has been developed. The method of rotating the part and observing the variation of the radial interferometric signature to obtain a topographic map of the part surface is discussed.
This paper deals with a basic research on an on-line monitoring of surface roughness by using laser. The relation between an intensity distribution of the reflected laser light and the surface profile is studied. A function of the processed r.m.s. roughness is used, which is taken from the spatial filtering of the surface profile measured by stylus method. An experiment was carried out by using a rolled metallic sheet and pieces finished by an electrical discharge machine. The results show that the intensity distribution is approximately proportional to the r.m.s. roughness of a certain filterd surface profile. The experimental results are proved to be reasonable by theoretical analysis.
A simple and straightforward procedure for designing an aplanatic null lens, used in the testing of certain common convex ellipsoids and concave hyperboloids on a Fizeau interferometer, is described. In a conventional design the null lens aberrations are only reduced to some finite minimum which, depending on the asphere parameters and the design itself, may turn out to be significant. Using the proposed technique, which involves solving a set of simple equations, the determination of the parameters of an aplanatic null lens is readily achieved. The resulting null lens is nominally free of aberrations since each of the null lens surfaces transfers the analyzing wavefront aplanatically. Apart from gaining a more accurate means of evaluating aspherical lens surfaces, this reduction of aberrations results in a relaxation of otherwise tight null lens fabrication tolerances. Aplanatic null lenses have been designed and fabricated and are currently being used to test single point diamond machined aspherical Germanium lenses. Interferograms showing a null lens in a stand alone mode and in an asphere test configuration are shown.
This paper compares two methods of measuring the finish of precision-machined optical surfaces: the older and well-established use of a mechanical stylus gauge (Talystep) and the recently developed optical technique based on interference microscopy (Wyko NCP). Results are found to be in good quantitative agreement for both random and periodic surface features providing appropriate filtering procedures are included in the data analysis to account for the differing transfer functions and bandwidths of the two measurement techniques. These results affirm the use of these techniques for the quantitative measurement and specification of machined optical-surfaces.
Samples of precision-machined optical flats were solicited from a number of commercial suppliers, examined by visual and Nomarski microscopy, and measured using a Wyko Non-Contacting Profiling instrument. The profile data were analyzed in terms of finish statistics which are directly related to optical performance, and these are presented in a common format and compared. The results are of intrinsic interest and suggest a number of intriguing generalities regarding surface materials and the machining process.
Measurements of BRDF, reflectance, and surface roughness of precision diamond machined flat aluminum substrates are presented. Two inch diameter samples fabricated on three "brands" of machine and six feed and speed combinations on a single machine were evaluated. Visual resolution measurements of a system consisting of an f/6 diffraction limited doublet and two precision diamond machined flats at 45 degrees are discussed.
Gone are the days when virtually the sole requirement of a single point diamond cutting tool lay in its ability to generate a cosmetically pleasing surface - components used in the Electro Optics Industry and other high technology areas demand very much more than this but of all the factors involved in the manufacture of these high precision tools, the achievement of predictable and consistent cutting edge life has emerged as one of the most vital and probably the most difficult to achieve. In this paper we examine various critical stages in manufacture and look at the means which have been developed to achieve consistent tool performance with predictable life between relaps.
Successful production of diamond turned components can be extremely dependent on the fixturing used to support the workpiece during the machining operation. Typical fixturing methods include vacuum chucking, air chucking and mechanical clamping. Depending on the type of part to be machined, suggested fixturing methods can vary widely. For example, a part requiring a flycut surface is not subject to the centrifugal forces and balance requirements of a part that must be turned about an axis of rotation. Therefore, in many cases the fixturing required for flycutting may be much simpler than that required for turning. In all cases, there are general guidelines that should be followed to determine the best method of fixturing.
Diamond Point Machining is an extremely sensitive machining operation with very special facility considerations and support equipment requirements. This paper will cover the philosophy, production flow, facility configuration, and support equipment requirements for a complete Diamond Point Machining Facility. The Texas Instruments facility will be used as a model and the design specifications for that facility will be reviewed. General production processes will be covered to explain machine and equipment use as well as to describe the complexity involved in Diamond Machining.
A short programme has been carried out to examine the preparation of strengthened polycrystalline alkali halide optics by hot-forging of single crystals. Potassium chloride and caesium iodide were chosen as subjects for this study which began with the optimisation of forging conditions for preparation of 25 mm diameter plano and plano-convex specimens. The following parameters were varied; temperature, load, deformation ratio, strain rate, lubricant, and crystal orientation. The use of optically polished die platens resulted in a surface quality suitable for direct use in lower grade optics; further improvement could be made by standard optical polishing methods. Variation in grain size was investigated by etching the surfaces of forged pieces and examining the grain structure by optical microscopy. Following initial results on 25 mm forgings the work has been extended to 75 mm diameter forgings of potassium chloride. Some experiments have also been carried out with a hot isostatic pressing system using pressurised helium as an improved lubricating medium. Initial results of strength and optical quality measurements are presented.
To date, the tribology of the single-crystal diamond cutting edge and its effect on the diamond single-point machined optical surface is poorly understood. The factors that result in certain diamond tools having superior wear performance to others is equally uncertain. In addressing these issues, the present understanding of the tool-wear mechanisms involved in machining is reviewed, with particular emphasis on ultrahard tool materials. Current research at the Naval Weapons Center has attempted to extend this knowledge to the field of diamond-turned optics and identify the processes that degrade the performance of the tool.
Diamond single-point tools of the very highest quality are required for precision machining of optical surfaces. However, a great variation in edge quality and tool life is observed in practice. The differences between poor and excellent tools are subtle and not easily detectable without verification by actual machining. A companion paper concerning the tribologic aspects of tool-edge quality and life discusses the possible mechanisms of tool degradation. This paper provides a discussion of practical methods for preselecting tools for high performance without resorting to machining use. Edge quality as observed by optical microscopy is not sufficient. Scanning electron microscopy and a recently developed two-stage replication process for the cutting edge and subsequent examination in transmission electron microscopy can yield the necessary resolution (<< 100 Å). In addition to characterization by high resolution microscopy, tool crystallographic orientation and perfection are also crucial. X-ray diffraction characterization is described in detail.