Deciphering the ultra-precision machining technology of ultra-precision diamond tools

Ultra-precision diamond is one of the key elements to achieve ultra-precision machining of molds. This article introduces the performance of UPC (UltraPrecisionCuttingTool) ultra-precision diamond tools produced by Japan AlliedDiamond Co., Ltd., the wear status of the tool when super-precision cutting different workpiece materials, and processing examples.

1. The performance of UPC ultra-precision diamond tools

Single crystal diamond has a cubic crystal structure in which carbon atoms are firmly bonded by covalent bonds. 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 that other materials do not have. UPC ultra-precision diamond tools are prepared by ultra-precision grinding technology, which can maximize the material characteristics and obtain a cutting edge with smooth sharpness and wear resistance. It can be matched with ultra-finishing machine tools to achieve high-precision aspheric and fine shapes. The 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 cutting tools are: ①The radius of the arc of the tool tip reaches a sharpness of tens of nanometers; ②The smoothness of the cutting edge ridge reaches the nanometer level. When processing with the same depth of cut as the radius of the tool nose, it is not easy to damage the working surface of the workpiece, the processing is stable, the chip evacuation is smooth, and the cutting thickness change caused by the elastic deformation of the workpiece is also very small, which can realize super-finishing.

2. The difference in wear status 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 face turning of oxygen-free copper and pure aluminum with a straight cutting edge super-precision diamond turning tool with a nose angle of 130° on an ultra-precision lathe, the wear state of the tool tip indicates that the rake face of the tool for cutting oxygen-free copper has produced The crescent crater wears, but the cutting edge ridge line remains sharp; the cutting edge ridgeline wear of the tool for cutting pure aluminum becomes a circular arc edge, but no crescent crater wear is found on the rake face. From the differences in these wear states, different wear mechanisms can be seen: when cutting copper, the crater wear on the rake face of the tool is caused by the oxidation of the diamond by the catalytic action of copper, and the ridgeline of the cutting edge of the tool is due to the workpiece Complete contact without gaps without oxidative wear; when cutting aluminum, aluminum carbide is generated due to the direct contact between the working surface and the tool surface, and the workpiece material is removed by the cutting edge and the cutting edge is worn. However, the direction of wear spreads and when cutting copper On the contrary (expanding from the cutting edge to the flank face), the crescent wear of the rake face will not occur.

Because of the different thermochemical phenomena of different workpiece materials, the wear state of the tool is also different, so the reasonable front and back angles of the tool should be designed according to different types of workpiece materials.

3. Examples of UPC-R ultra-precision diamond tool processing

UPC-R is a UPC ultra-precision diamond tool with a circular cutting edge. Its typical use is for the ultra-finishing of aspheric mirror molds such as DVDs. The contour accuracy of the arc cutting edge of UPC-R tool is less than 50nm, which is the highest accuracy in the world; the arc R is only 5μm, which is also the smallest in the world. The main points of processing aspheric mirror molds on CNC two-axis ultra-precision machine tools with UPC-R ultra-precision diamond tools include: ①How to continuously form thin and stable chips and discharge them smoothly; ②The workpiece should have a high level of dynamic balance performance when rotating. ③The workpiece can be accurately centered; ④The stable supply of cutting fluid, etc. Because the thermochemical reaction during steel processing will graphitize the diamond and diffuse it to the workpiece, UPC diamond tools are not suitable for super-finishing steel molds. However, if the surface of the steel mold is electrolessly plated with a nickel coating of tens of microns to hundreds of microns in thickness, UPC diamond tools can be used for ultra-finishing. Regarding coating quality, choose an amorphous coating that does not produce crystalline structural defects such as porosity and segregation.

4. Examples of UPC-T ultra-precision diamond tool processing

UPC-T is a UPC ultra-precision diamond tool with triangular cutting edges, which is mainly used for ultra-finishing of diffraction grating molds such as Fresnel lens molds and liquid crystal light guide plates.

In recent years, the high-precision, miniaturization and integration of optical components have developed rapidly. From aspheric lenses to Fresnel lenses that can be thin, lightweight, and integrated, the requirements for ultra-finishing technology are increasing. high. This processing mode is an example of using a UPC-T ultra-precision diamond tool to super-finish the fine grating part and aspherical shape. Therefore, the cutting edge of the turning tool is required to have a cutting edge R<100nm and excellent cutting performance. The cutting edge of UPC-T's tip is a small cutting edge of 50nm, which can realize super finishing.

Machining molds with ultra-precision diamond tools has developed into an indispensable processing method in lens mold processing. In the future, with the improvement of mold quality and the ever-increasing market demand for high-precision and multi-functional molded parts, as well as the increase in demand for mold processing in the medical and biological fields, the development of new tools will continue to be promoted.