Ultra-precision machining of optoelectronic parts moulds with superfine diamond tools

Superfinishing with super-fine diamond tools is a processing technology that achieves nanometer dimensional accuracy and surface roughness. Recently, superfinishing technology has been applied in the processing of precision molds in the field of optoelectronics and biology. Ultra-precision diamond tools are one of the key elements to achieve super-finishing of molds. This paper introduces the performance of UPC (Ultra Precision Cutting Tool) super-precision diamond tool produced by Allied Diamond Co., Ltd. in Japan, the wear state of the tool when super-finishing different workpiece materials and the processing examples.
1. Performance of UPC super-precision diamond cutter Single crystal diamond has a cubic crystal structure in which carbon atoms are strongly bonded by covalent bonds, and its lattice constant is 3.567 angstroms, and the distance between bonded atoms is 1.544 angstroms. Due to the characteristics of the atomic structure of single crystal diamond, it can be used as a tool material to obtain excellent hardness and smooth, sharp cutting edges which are not possessed by other materials. UPC super-fine diamond tools are prepared by super-fine grinding technology, which can maximize the material properties and obtain a cutting edge with smooth sharpness and wear resistance. It can match the ultra-precision machine tool to achieve high-precision aspheric shape and fine shape. Super finishing.
In order to meet the requirements of mold super finishing, the cutting depth should be set in the nanometer range. For this reason, the requirements for the cutting tool are: 1 the sharpness of the radius R of the cutting edge reaches tens of nanometers; 2 the smoothness of the cutting edge ridge line reaches the nanometer level. When machining with the same depth of cut with the radius of the tool nose arc, it is not easy to damage the working surface of the workpiece, the processing is smooth, the chip removal is smooth, and the cutting thickness variation caused by the elastic deformation of the workpiece is also extremely small, and super finishing can be realized.
2. Differences in wear state of different workpiece materials processed by UPC tools The thermochemical wear state of diamond tools varies greatly depending on the type of material being processed. After the end face turning of oxygen-free copper and pure aluminum using a straight-cut cutting edge ultra-precision diamond turning tool with a tip angle of 130° on an ultra-precision lathe, the wear state of the tool tip indicates that the tool rake face for cutting oxygen-free copper is produced. The crater wears, but the edge of the cutting edge remains sharp; the cutting edge of the cutting edge of the pure aluminum cutter becomes a circular arc, but the flank wear is not found on the rake face. From the difference of these wear states, different wear mechanisms can be seen: when cutting copper, the crater wear of the tool rake face is caused by the oxidation of the diamond by the catalytic action of copper, and the cutting edge of the tool is caused by the workpiece. Complete contact without gaps without oxidative wear; when aluminum is cut, aluminum carbide is formed by direct contact between the working surface and the tool surface, and the workpiece material is cut by the cutting edge to cause wear of the cutting edge, but the direction of wear is extended and copper is cut. Conversely (expanding from the cutting edge to the flank), there is no crater wear on the rake face.
Due to the different thermochemical phenomena of different workpiece materials, the wear state of the tool is also different. Therefore, reasonable tool rake angle and back angle should be designed according to different kinds of workpiece materials.
3. UPC-R super-fine diamond tool processing example UPC-R is a UPC super-precision diamond tool with a circular cutting edge. Its typical use is for super finishing of aspherical mirror molds such as DVD. The contour accuracy of the arc cutting edge of the UPC-R tool is less than 50nm, which is the highest precision in the world; the arc R is only 5μm, which is also the smallest in the world. The processing points of machining aspherical mirror molds on CNC two-coordinate super-precision machine tools using UPC-R super-precision diamond tools include: 1 how to continuously form thin and stable chips and smooth discharge; 2 the workpiece should have a high level of dynamic balance when rotating 3 workpiece can be accurately centered; 4 stable supply of cutting fluid.
Since the thermochemical reaction during processing of steel causes graphitization of diamond and diffusion to the workpiece, UPC diamond tools are not suitable for superfinishing of steel molds. However, if a nickel plating layer of several tens of micrometers to several hundreds of micrometers is plated by electroless plating on the surface of the steel mold, superfinishing can be performed using a UPC diamond cutter. Regarding the plating quality, an amorphous plating layer which does not cause crystal structure defects such as pores and segregation should be selected.
4. UPC-T super-fine diamond tool processing example UPC-T is a UPC super-precision diamond tool with triangular cutting edge, which is mainly used for super-finishing of diffraction grating molds such as Fresnel lens mold and liquid crystal light guide plate. In recent years, high precision, miniaturization, and integration of optical components have progressed rapidly. From aspherical lenses to Fresnel lenses that can achieve thin, lightweight, and integrated, the requirements for superfinishing technology are increasing. This machining mode is an example of superfinishing the fine grating portion and the aspherical shape with one UPC-T ultra-precision diamond tool. Therefore, the cutting edge of the turning tool edge is required to be R<100 nm and has excellent cutting performance. The cutting edge of the UPC-T is a 50nm cutting edge that enables super finishing.
Machining molds with superfine diamond tools has evolved into an indispensable processing method for lens mold processing. In the future, with the improvement of mold grades and the increasing market demand for high-precision and multi-functional parts, as well as the growing demand for mold processing in medical and biological fields, the development of new tools will continue.
("Tool Outlook" Liao Xianfu translation)