Finishing with abrasive tools

Methods of machining parts without chip removal and finishing work are increasingly used in various branches of engineering. Especially they are necessary for equipment and machines operating under harsh operating conditions and at the same time providing a high resource, stability, accuracy of operation, etc. These methods are quite different in physical essence. They are united only by the fact that they make it possible to form a surface layer of a part with predetermined stable properties (a decrease in roughness, an increase in dimensional accuracy) and give it a marketable appearance. Such treatment is subjected to pre-prepared surfaces.

For finishing processing: diamond turning and boring, fine grinding, polishing, lapping, finishing (superfinishing).

The methods of processing without chip removal include: vibro-rolling, rolling of the relief pattern on the surface of the part, shot blasting, etc.

Finishing abrasive processing is divided into processes:

• dimensional debugging with a decrease in the shape deviation and the surface roughness parameter: fine grinding, abrasive brushing, honing and debugging;

• dimensionless debugging, which is used only to reduce the roughness parameter: superfinishing, polishing.

Fine grinding. Fine grinding is characterized by removal of small allowances of 0.04-0.08 mm per diameter. It is not isolated in a separate operation, but is performed at the final stage of the final processing for one part of the part.

Processing with abrasive brushes. The introduction of high-speed automated processing methods in modern production causes the need for better finishing processes, including the removal of sharp edges and deburring. One of the methods that can effectively solve these problems is the treatment of complex surfaces with brushes made of nylon fibers filled with abrasive.

Abrasive brushes are used at low speeds so that they can strike and rip off the treated surfaces. Their appearance is shown in Fig. 14.1, the settings are in Fig. 14.2.

Abrasive brush

Fig. 14.1. Abrasive brush

Setting for blunting edges and deburring

Fig. 14.2. Setting for edge blunting and deburring:

1 - the table; 2 - to fly; 3 - abrasive brushes

Abrasive fibers vary in fiber diameter, type of abrasive grains, their size and content. For example, an enlarged fragment of a fiber is shown in Fig. 14.3.

Brushed fibers with embedded abrasive (enlarged)

Fig. 14.3. Brushed fibers with embedded abrasive (increased)

Most often, silicon carbide and aluminum oxide are used for the abrasive. There are other, more exotic abrasives, for example, diamond. The diameter of the fibers varies 0.3-1.5 mm. This ratio is necessary for effective bonding of abrasive. By weight, the abrasive content in the fibers is 20-40%.

Abrasive action takes place both at the ends of the fibers, and on the side surfaces. As the fibers wear out, new grains appear on their surface. Essentially, the fibers are self-sharpening & quot ;. They act as a kind of flexible files. This property makes them ideal for machining irregularly shaped surfaces. Removing material, they mainly affect the burrs and sharp edges. It is recommended to use fibers in cases where it is necessary to remove burrs and/or to give radii to the edges without adversely affecting the geometric tolerances of the parts.

Advantages of the abrasive brush method:

• Improves the cleanliness of the surface: in fact, the torn and bent metal is removed from the treated surfaces, the roughness is reduced without removing the base metal and changing the dimensions of the part;

• limited cutting ability: metal is removed only but the edge with the formation of a small radius in a short time;

• does not damage the surface layer of the part;

• Provides consistent results.

Disadvantages of brushes: limited cutting action (does not remove large burrs from high-strength materials) and low temperature in the processing area (with its increase, melting of polymeric material and adherence to the surface of the part, therefore, additional processing is necessary to remove this adherent layer) .

thematic pictures

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