RU2211133C1 - Head to grind elliptical surfaces of shafts - Google Patents

Abstract

FIELD: machining of metals, grinding of parts with outer elliptical surfaces. SUBSTANCE: head includes hollow mandrel mounted for rotation in body. The latter is hinged to base to execute cutting-in feed. Grinding wheel is composed of individual abrasive blocks forming peripheral inner cutting surface. During dressing it is divided into parts equal in height and placed at angle α with rotation axis of grinding wheel. Abrasive blocks are anchored on spring-loaded barrels mounted for radial movement to adjust inner diameter of wheel. EFFECT: expanded technological potential, increased precision and quality of machining. 1 cl, 3 dwg

Description

 The invention relates to mechanical engineering, to the field of machine-tool industry and can be used in metal working by grinding for the manufacture of parts with external elliptical surfaces.

 Known head for covering grinding screws, containing a grinding wheel, a base and a pivotally connected housing in which a hollow mandrel with a basic tapered bore hole, a metal band, an annular disk and screws are mounted [1].

 The known head in principle allows the processing of shafts with an elliptical surface, but due to the fact that the design of the enclosing circle does not have the ability to restore the original inner diameter of the circle, which must be kept constant, the design of the head requires a fundamental change.

 Known special tool holder for turning an elliptical surface on a lathe mounted in a spindle [2]. The work of a special tool holder is based on the fact that the projection of a circle on an inclined plane gives an ellipse.

 A disadvantage of the known tool holder is the inability to obtain a high class of roughness and accuracy of the machined elliptical surface, which are inherent only in abrasive-diamond processing. In addition, the hardened surfaces of the parts are difficult to turn, only grinding allows you to effectively remove the defective surface layer left as an allowance.

 The objective of the invention is the expansion of technological capabilities, improving the accuracy and quality of processing of the outer elliptical surface, reducing the roughness, increasing the accuracy of processing and solving the issue of the implementation of the infeed for repeated passes, as well as ensuring the independence of the profile of the processed product from the diameter of the grinding wheel.

 The task is achieved by the proposed head for grinding elliptical surfaces of the shafts, comprising a grinding wheel, a base and a body articulated to it, in which a hollow mandrel is rotatably mounted, wherein the grinding wheel is a composite of individual abrasive bars, the peripheral inner cutting surface of the wheel being editing is divided into two parts of equal height, located at an angle α to the axis of rotation of the tool. In addition, the hollow mandrel has radially spaced openings in which abrasive bars and screw plugs, spring-loaded with springs, spring-loaded on springs, are located with the possibility of radial movement.

 In Fig 1 shows the proposed head for grinding elliptical surfaces of the shafts and the setup scheme with the installation of the part - the shaft in the collet chuck and in the rear center, Fig 2 - section along A - A in figure 1.

 The work of the proposed head on grinding elliptical surfaces of the shafts is based on the fact that the projection of the circumference of the inner cutting surface of the enclosing circle on an inclined plane gives an ellipse.

The processing of the outer elliptical surfaces of the shafts 1 includes a message to the grinding wheel 2, set at an angle α to the longitudinal axis of the part, rotation V _and and translational longitudinal motion S _CR with the stationary part As a circle, the assembly grinding wheel 2 covering the part is used, the rotation center of which is installed on the axis of the workpiece 1, and the transverse cutting feed S _{α is} carried out by increasing the angle α for each double stroke of the longitudinal feed S _CR , while the circle is set at an angle
α = arccos (b / a),
where - a and b are, respectively, the larger and smaller semi-axes of the processed elliptical outer surface.

 In addition, use a prefabricated grinding wheel 2, composed of individual abrasive blocks 3, with the possibility of radial movement during adjustment, carried out as the bars wear and restoration of the inner diameter D = 2A of the wheel.

 When editing, the peripheral inner cutting surface of the circle 2 is divided into two parts of equal height, located at an angle α to the axis of rotation of the tool. The left part of the plane of symmetry of the circle passing through t. O, according to FIG. 1 works when the bars are at the top, relative to the longitudinal axis of the part, the right-hand side of t. O works when the bars are at the bottom.

 The adjustment of the bars 3 to the diameter D is carried out when the process is stopped by screwing in the threaded plugs 4, which move the metal cups 6, spring-loaded with springs 5, on which the abrasive bars 3 are fixed by known methods. The glasses 6 with the abrasive bars 3 are located in the radial grooves of the rotary movable hollow mandrel 7, which is installed in the housing 8 by means of bearings 9. The mandrel 7 has a pulley 10, which is connected by a belt 11 to a drive (not shown).

 The housing 8 is pivotally connected to the base 12 and can change the installation angle α of the axis of rotation of the circle 2 when changing the dimensions of the production object, as well as when transversely feeding the plunge, turning relative to point 0. The base 12 can be fixed, for example, on a support of a lathe (not shown).

 The grinding head for elliptical shaft surfaces can be used both for roughing and fine grinding.

 With small differences between the major and minor semiaxes “a” and “b” of the elliptical surface, the latter is formed by the proposed method, dividing the entire operation into draft, semi-finished, finishing and finishing transitions. In this case, preliminary, for example turning, turning of the shaft neck is carried out in a cylindrical shape.

 With large sizes of the major and minor axes “a” and “b” of the elliptical surface, the formation of the latter is carried out in two operations: preliminary, for example turning, turning the neck of the shaft of an elliptical shape [2] with leaving an allowance for grinding and final finishing with the proposed head.

The work of the head on grinding elliptical surfaces of the shafts is as follows. Before processing, the combined grinding wheel 2 is corrected, maintaining the inner diameter D and dividing its peripheral inner surface by two parts of equal height, positioning the cutting surfaces of these parts at an angle α to the axis of rotation of the tool. Instrument balancing is carried out by known methods without fail. The rotational movement of the mandrel 7 with the tool 2 is turned on at a speed V _and determined by the cutting properties of the abrasive, and when the inclination angle α = 0 of the housing 8, the workpiece is introduced into it, if necessary, it is pressed by the rear center, and the part 1 is stationary during processing. Giving a longitudinal feed S _CR , the value of which is determined in the traditional way, for each double stroke it feeds the cut-in S _α by increasing the angle α. The treatment is completed by nursing, which is carried out without feeding plunge S _α , only with a longitudinal feed S _pr

 As the working surfaces of the abrasive bars wear, the inner circle diameter D increases, which is restored by screwing in the screw plugs 4. The angle α of inclination of the cutting surfaces of the bars due to self-sharpening will remain for a long time, however, as the cutting surfaces deviate significantly from the nominal value of the angle α, the bars are corrected by known methods and tools, such as diamond pencil, as the most common and cheapest.

 As can be seen in figure 1, the processing of the proposed head can improve the accuracy of the product and the vibration resistance of the process, since the enclosing circle is in contact with the workpiece in two diametrically opposite places and the resulting radial components of the cutting forces are mutually balanced without causing bending of the part.

An elliptical shaft neck with a length of 20 mm was processed, having the dimensions of the cross section: 2a = 27 ^-0.05 mm, 2b = 23.38 ^-0.05 mm. The installation angle of the tool was determined by the formula α = arccos (b / a) = arccos (11.69 / 13.5) = 30 ^o . A cylindrical billet that underwent preliminary turning with a diameter of ⌀ 27 mm, i.e. the larger diameter of the ellipse is machined. The inner diameter of the grinding wheel was corrected and adjusted to D = 27 mm. The roughness of the treated surface should be Ra = 0.4 μm, material - steel 18HGT GOST 4543-74, hardness HB 207. ..228. The processing was carried out on a mod screw-cutting machine. 16K20, instrumental female head with an abrasive female circle assembled from rectangular bars of the type SP 45x55x80 24A16C25K GOST 2464-82, head speed V _i = 7.85 m / s, n _i = 3000 min ^-1 , S _pr = 900 mm / min, S _α = 2'2,4 '' / dv.hod, or in terms of mm on a diameter of 27 mm S _α = 0,008 mm / dv. move. The required roughness and accuracy of the elliptical surface of the neck of the shaft was achieved through T _m = (45 + 20) • 1.81 • 1.4 / 900 • 0.008 = 22.9 min, where (45 + 20) is the caliper travel length when the wheel runs over on each side equal to 0.5 bar width, (13.5-11.69) = 1.81 mm - the maximum allowance taken in the area of the small axis of the ellipse, 1.4 - coefficient taking into account the time spent on nursing.

 Thanks to the use of the proposed head, it became possible to finish abrasive the external elliptical surfaces of the shafts, i.e. technological capabilities have expanded, quality has improved, roughness has decreased and productivity has increased due to the use of the enclosing circle and the increase in the length of the arc of contact between the wheel and the workpiece, and issues have been resolved on how to feed the plunge during repeated passes, as well as ensuring the independence of the profile of the processed product from the diameter of the grinding wheel.

Sources of information
1. RF patent 2169644, MKI B 23 G 1/36. The method of finishing the screws. Stepanov Yu.S., Afanasyev B.I. and other Application 99121764/02, application. 12.10.99, publ. 05/27/2001. Bull. fifteen.

 2. Karelin N.M. Ball-free machining of cylindrical parts with curved cross sections. - M.: Mechanical Engineering, 1966, p. 11-13, fig. 11-12.

Claims (2)

 1. The head for grinding elliptical surfaces of the shafts, comprising a base, a housing and a grinding wheel, characterized in that it is equipped with a hollow mandrel mounted for rotation in the housing, pivotally connected to the base, and the grinding wheel is made of individual abrasive blocks forming a peripheral the inner cutting surface, divided during editing into two parts of equal height, located at an angle α to the axis of rotation of the grinding wheel.  2. The head according to claim 1, characterized in that it is equipped with threaded plugs and spring-loaded metal cups for securing the abrasive bars, located with the possibility of radial movement in the radial holes made in the hollow mandrel.

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