Edge Preparation Process For Natural Diamond Cutting Tools

Natural diamond cutting tool is an ideal tool for ultra-precision machining due to its excellent cutting performance. With the continuous development of ultra-precision machining technology, the shape and s urface quality of tool cutting edge become stringent more and more. Restricted by the-state-of-the-art, the mechanical polishing is still the preferred manufacturing method for the natural diamond cutting tools. Alt hough the mechanically prepared cutting edge is extremely sharp, many micro defects form on it, which destroys the strength of cutting edge. When such diamond cutting tool is used to machine the hard and brittle materials, the left micro defects grow up easily, which means tool wear will be accelerated. As a result, tool life is shortened. Therefore, passivation treatment is necessary for the mechanically shaped cutting edge of diamond tool. This process is specially designed to properly increase the rounded cutting edge radius and reduce the nanoscale defects on the surface of cutting edge. In such a way, the surface quality and mechanical strength of tool cutting edge can be improved, which in return increases the durability of tool cutting edge.The wear process can be regarded as the process of carbon atoms leaving from the surface of the diamond tool. In other word, the passivating cutting edge technology is the a special tool wear process which condition is in a controllable range. Firstly, This paper investigated the different wear rates when machining various workpiece materials with diamond tool, and drew a conclusion that diamond tool wore when machining brittle and hard materials such as silicon, optical glass within shorter cutting distance than conventional non-ferrous metals and polymers. Futhermore, tool wear was more intense owing to machine transition metal containing iron cobalt nickel etc. According to the different wear rates that diamond tool machined different materials, this paper used the polymer —polishing pad for cutting edge passivation. Based on that, the model of diamond tool cutting edge passivation was established, and the reasons for blade passivation by the polishing pad were explained. We not only established the system of diamond cutting edge passivation process, but also drew the conclusion that the cutting edge passivation technique was feasible according to the experiment of cutting edge passivation preliminary feasibility analysis. Significantly, the experiment paved the way for the following experiment of natural diamond tool cutting edge passivation.Secondly,natural diamond tool cutting edge passivation quality evaluation criterion was established in this paper, namely: 1) edge sharpness of 50nm; 2) there is no visible nanoscale defect on the surface of cutting edge in the AFM scanning range 2μm×2μm, and the surface roughness Ra and Rz are less than 1 nm and 15 nm, respectively. Based on the evaluation criterion of natural diamond tool cutting edge passivation quality, the optimal process parameters of R(100)F(110) natural diamond tool cutting edge passivation were selected. We discussed the influence of process parameters on the passivation quality, and optimized the process parameters of R(100)F(110) natural diamond tool cutting edge passivation, i.e. passivation time is 100~120min, machine tool spindle speed is 1800~2400rpm, depth of edge press polishing pad is 20~25μm, contact pressure of cutting edge and polishing pad is 4.9~14.7N, reciprocating stroke of polishing pad is 2~4mm, reciprocating motion frequency of polishing pad is 0.2~0.3Hz, and pitch angle of hilt is 0 degree.Moreover, a lot of process experiments on R(100)F(100) natural diamond cutting edge passivation were carried out. Based on results from the experiments, we discussed the influence of process parameters on the passivation quality, and set up the optimum parameters of R(100)F(100) natural diamond tool cutting edge passivation process, i.e. passivation time is 60~80min, machine tool spindle speed is 2100~2400rpm, depth of edge press polishing pad is 5~10μm, contact pressure of cutting edge and polishing pad is 14.7~19.6N, reciprocating stroke of polishing pad is 4mm, reciprocating motion frequency of polishing pad is 0.3~0.4Hz, and pitch angle of hilt is 0 degree.Finally, the tool life experiments for machining single crystal germanium were carried out on ultra-precision lathe, and the total cutting distance i.e. the tool life in this paper, was obtained when the surface roughness of the workpiece is less than 5 nm.. With this method, the life of diamond tool with and without passivation treatment were compared. The results of test showed that service life of diamond tool treated with the edge passivation was 1.45 times as much as the tool life without passivation.