Efficiency of a new tool for machining hard materials 1. Cutting natural diamonds

Abstract

galvanic cutting disks (GCDs) in which the diamond grains are secured to the metallic matrix by galvanic nickel or iron binders [2]. This technology makes it possible to obtain a coating with a concentration of diamond powder of 5-55% [3] and a uniform distribution of the powder over the surface (Fig. 1). The galvanic method of coating application is simple, has low energy and material costs, does not require nickel-plating or iron-plating electrolytes, and is safer and more environmentally sound than (for example) technologies that employ chromium-plating and copper-plating electrolytes. It follows from the production and lab test results shown in Table 1 that disk life and grinding speed are both greater for the operation of "pregrinding" when the galvanic disks are used instead of conventional disks obtained by spray-coating and rolling. Use of the galvanic disks is particularly effective for grinding diamonds with knot defects: the disks last ten times longer than conventional disks. The new cutting disks are especially suited for grinding "fine" diamonds (d = 1.3-1.8 mm); in this case, diamond is removed five times faster than with the use of the traditional equipment. The life of the GCD is greater than conventional disks for top-cutting, although the rate of diamond removal is somewhat lower (by 5%). The latter is explained by the fact that during build-up some of the ASM 10/7 powder -- which is finer than ASM 20/14 powder -- enters discontinuities on the surface of the disk (which are larger than the grains of the powder) and thus does not participate in the cutting process. Making the disk with the use of a smoother steel base solved this problem, increasing grinding speed from 0.0079 to 0.0083 caratJmin. The use of galvanic cutting disks has made it possible to reduce the composition of diamond powder for the operation of "pregrinding" by 20%, while the amount used in "top-cutting" has been decreased 15%. Use of the new tool also improves working conditions thanks ~o a fivefold reduction in the use of toxic organic binder BF-2, which is normally used in the deposition of diamond powder on cutting disks. Calculations performed by the Gomel' factory "Kristall" showed that the galvanic disks last 4.67 times longer than conventional disks. (Similar results were obtained at the "Kristall" plant in Vinitsa). This has made it possible to reduce annual disk consumption by 444 and the annual consumption of cover plates by 15526. Corresponding reductions were realized in the consumption of diamond powder and toxic binder BF-2. In the machining of natural diamonds, grinding and polishing occur not only due to the action of the diamond grains secured in the metallic matrix of the disk, but also as a result of self-charging of the tool, i.e., the introduction of small fragments of diamond formed during machining into the working surface [4]. During the machining of diamond on cast-iron disks, self-charging occurs mainly as a result of fragmentary inclusions in the graphite of the cast iron. In the galvanic disks, the binder is hard and dense and has a high coefficient of friction with diamond. All of these factors make self-charging more difficult.