Grinding large

The development of large diamond wheels for machining large parts.

Courtesy of All images: “ALKON”

Editor’s note: The most effective method of machining new structural and tool materials is a diamond-abrasive one, according to the concern “ALKON” of the National Academy of Sciences of Ukraine, which developed the technology of manufacturing large tools made with metallic and metallic-polymer composites. Such tools have been applied for machining large parts, including insulators, gears and cutting tools.

Figure 1: The V.N. Bakul Institute for Superhard Materials of the National Academy of Sciences of Ukraine developed a technology for fabricating large diamond wheels with (from left to right) 1A1, 6A2-SS, 1EE1 and 1A1R shapes. The 6A2-SS diamond grinding wheels, which each weigh 30 kg (66 lbs.), were developed for the first time.

Analysis of patents and scientific and technical information indicates that the development of large diamond wheels whose functional varieties and dimensions exceed existing standards requires:

• Studies on the technological basis and detection of regularities between the compositions and characteristics of metallic and metallic-polymer composites;

• Applications of the superhard materials’ powders with the uniformity coefficient equaling 1.2 to 1.3;

• Development of new designs of the tools’ cutting layers; and

• Optimization of the parameters for pressing, sintering and binding the cutting elements.

Figure 2: Truing via EDM of the 6A2-SS diamond-abrasive wheel. 1) Appartus to control electric current and voltage. 2) Diamond-abrasive wheel with the 6A2-SS shape. 3) Truing tool. 4) Current collector. 5) Rectifier. 6) Autotransformer. S_np) Reciprocal movement of the truing tool. ^V1) Rotational speed of the grinding wheel. ^V2) Rotational speed of the truing tool.

The main objective of the research was to increase the working capacity 1.5 to 2.0 times for the new tools compared with similar tools fabricated by Ukrainian companies and those in other countries.

The V.N. Bakul Institute for Superhard Materials of the National Academy of Sciences of Ukraine has developed a technology for fabricating large diamond wheels with the new 6A2-SS shape and existing 1A1R, 1EE1 and 1A1 shapes from 250mm to 600mm (10 ” to 24 “) in diameter (Figure 1). The cutting area of the diamond layer for these tools is up to 5,000 cm² (775 cu. in.).

The new technology is based on utilization of the following:

• Scientifically proven foundation for the manufacturing processes of the integrated technology for tool production;

• Definition regularities for optimal composition and characteristics of metallic (declarative patent 70825A of Ukraine) and metallic-polymer (patent for a useful design No. 41448 of Ukraine) composites and the superhard material powders;

• Advanced designs of the cutting layer; and

• Computerized control and optimization of functional parameters of pressing, sintering and binding the cutting elements made of superhard materials.

Such technology secures production of large diamond wheels whose working capacity is 1.5 to 2.0 times that of conventional wheels.

While conducting the research on the composites made of superhard materials, the following equipment was used:

• The roentgen-spectral analysis was performed on an Ultra 55 Gementi FE-SEM raster electron microscope with STEM-detector from Carl Zeiss to work in a regime of a transmissible microscope and a Kemskan-4dv raster electron microscope-analyzer having a Link-860 analysis system;

• The hardness was measured by a HRA-2 Rockwell tester (Rockwell scale A);

• Study of the structure of composites was performed on a Microtech MMO-1600 metallographic microscope with an HDCE-10A camera;

• Computerized treatment of the experimental results;

• Complex evaluation method for the rates of working capacity of the grinding wheels made of synthetic diamonds and CBN, based on their applications.

The studies of relationships between compositions and technical characteristics of the metallic (MX series) and metallic-polymer (B2-01-1 series) composites for large wheels were conducted on the following tool shapes and geometries:

• Wheels with a 1A1 shape are 400mm to 500mm (16 ” to 20 “) in diameter, and the cutting layers are 40mm to 100mm (1.6 ” to 4.0 “) wide;

• Wheels with the 6A2-SS shape are 600mm (24 “) in diameter, and the cutting layers are 250mm (10 “) wide;

• Wheels with the 1A1R shape are 400mm to 500mm (16 ” to 20 “) in diameter, and the cutting layers are 10mm (0.4 “) wide;

• Wheels with the shape 1EE1 have cutting layers 10mm (0.4 “) wide.

Surface Deviation

It was determined that deviation of the cutting surface of a diamond wheel after being EDMed did not exceed 20μm to 50μm (790 to 1,970 μin.), while the required protrusion of diamond grains from the tool binder is achievable. Flexible steel rods measuring 0.12mm (0.005 “) in diameter were used as truing tool electrodes. The truing process creates fine-dispersed relief, containing reinforced miniature posts for the diamond grains in a wheel.