The History And Present Situation Of Ultra-precision CNC Machine Tools In The United States

In the late 1950s, the United States began to carry out ultra-precision processing machine tools research, when the development of laser nuclear fusion experimental devices and infrared experimental devices need large metal reflectors, the urgent need for ultra-precision processing technology and ultra-precision processing machine tools. By using precision machine tools with high precision at that time, a single-point diamond cart knife was used for mirror cutting of aluminum alloy and copper oxide-free, so as a starting point, ultra-precision processing as a new machining process has been developed rapidly.

In 1962, UnionCarbide first developed an ultra-precision hemethic crib with porous graphite air bearings, which successfully realized ultra-precision mirror turning with dimensional accuracy of : - 0. 6btm, surface roughness is Rd0. 025gm, thus taking the first step in sub-micron processing. However, diamond ultra-precision turning is more suitable for some soft metal materials, and in aerospace, astronomy, military and other applications of satellite cameras, the most commonly used are such as glass, ceramics and other brittle materials of non-metallic devices. Cutting these materials with diamond cutters can cause cracks in the self-processing surface. Ultra-precision grinding is more conducive to the processing of brittle materials.

Another representative product of UnionCarbide is its successful R-e-form as-spondial as-a-ball machine tool in 1972. This is a dual-coordinate CNC crib with position feedback, which can change the corner and radius of the knife base rail in real time only, and realize the mirror processing of as-sple. Processing diameter of 380mm, the shape accuracy of the work piece is plus or minus 0. 63um with a surface roughness of Ra0.023um.

MoorlSpecialT001 developed the Moori-type ultra-precision mirror bed with air spindle in 1968, but in order to achieve ultra-precision processing of brittle materials, the company in 1980 in the world for the first time developed three-coordinate control of the M-18AG type asperter diamond tool turning, diamond grinding machine. The machine uses an air spindle with a radial rotation accuracy of 0. 075Bm: Using the Allen-Braley 7320 CNC system, the X- and Z-axis strokes are 410mm and 230mm, respectively, and the straightness of the rails is 0. Within 5gm, the positioning accuracy of the B-axis is 0. 38um, using diamond grinding wheels to process a variety of asymthic metal mirrors with a maximum diameter of 356mm.

RankPneumo introduced a two-axis linkage MSG ultra-precision CNC lathe in 1980 that uses laser interferometers to complete positional closed-loop control. The crib can process 350mm diameter ase speral metal mirror, processing surface roughness of R to O. 05Bm. In 1988, the company also developed the successful ASG2500, ASG2500T, Nanoform300 machine tools: these machines can not only be ultra-fine close cutting, but also can be processed up to 300mm diameter as spular mirrors. Based on the above-mentioned machine tools, the company also developed the Nanoform600 in 1990, which can process asperterial mirrors with a diameter of 600mm, and the shape accuracy of the workpiece is better than O. 14, surface roughness is better than Ra0. 01um. In 1996, the company introduced the Nanoform250 ultra-precision composite machining machine, which not only enables diamond cutting, grinding and polishing, but also directly grinds out hard and brittle material optical parts that meet optical surface quality and surface accuracy.

At present, the United States engaged in ultra-precision processing and manufacturing more well-known companies, enterprises at least 30. Among the most representative and significant results were the aforementioned Lawrence Livermore National Laboratory laboratory at Union Carbide. Since the 1960s, LLNL Laboratories has developed DTM-1, DTM-2 ultra-precision machine tools, and in September 1983 successfully developed the DTM-3 horizontal large optical diamond ultra-precision crib representing the highest level of contemporary ultra-precision machine tools. The machine can process 2100rain diameter, weight 4497k2 work parts, its tool frame transmission device using friction drive, the use of laser interferometer for position measurement, the use of liquid static pressure bearings and liquid static pressure guide, position accuracy of up to 0. 013 to m: processing brass parts, surface roughness up to R to 0. 0076Bra.

In September 1984, LLNL Laboratories, in collaboration with the Wright Aviation Research Institute of the U.S. Air Force, developed the large vertical ultra-precision CNC crib of the Large Optics Diaramond Turning Machine. The bed can process 1625mm diameter work parts, the use of specially developed 7-way dual-frequency laser interferometer for a variety of position information measurement, and then through data processing, to provide accurate feedback information to the servo system, drive knife holder to ensure the position of the tool relative to the work piece, measurement resolution of 0. 635nm. In order to ensure the accuracy of position servo control, the precision digital servo control method is adopted, and the control part is an internal CNC device. In order to achieve the micro-inward of the tool, the machine uses the pedic current micro-displacement mechanism, which can realize the nano-scale micro-displacement, and the processing accuracy can reach 0. 025 to m. LODTM is recognized as one of the highest levels of ultra-precision cribs in the world today.