SU1764953A1 - Grinding process - Google Patents

Abstract

Usage: when grinding parts on circular and surface grinding machines with reciprocating desktop and variable continuous transverse grinding wheel (HQ). SUBSTANCE: at a depth of cut, the RPE is continuously reduced at a constant RPE speed by an increase in the RPV speed of the part. In addition, the speed of rotation of the CC is reduced to a value commensurate with the speed of the RPM of the part. 1 hp f-ly, 3 ill.

Description

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The invention relates to mechanical engineering and can be used in planar mortise and round grinding.

A known method of grinding flat surfaces with the periphery of a circle, carried out on machines with a rectangular table, in which a product is given a reciprocating movement, and the direction of rotation of the grinding wheel is reversed with each successive pass in order to carry out counter grinding

However, the implementation of this method is difficult because of the large dynamic loads when reversing high-speed spindles of grinding machines, the occurrence of vibrations and the deterioration of the quality of the surface layer of parts.

There is a known method of flat mortise grinding, in which parts provide reciprocating motion at a constant speed and with an overrun relative to the circle at the end of the longitudinal stroke, and a rotating wheel with a constant speed to the circle - a periodic vertical feed to the depth of cut.

The disadvantage of this method is that the process system is prone to vibrations caused by periodic signals. turning on the drive vertical feed, reducing the quality of machining parts.

There is a method of round grinding, in which the parts communicate a reciprocating motion at a constant speed relative to the grinding wheel, and a grinding wheel rotating at a constant speed, a continuous transverse feed.

The known method has disadvantages: a decrease in the quality of the surface layer due to the large depth of the defective layer after each pass, significant

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deformations due to residual stresses, limited ability to control the process of forming the physicomechanical and geometric characteristics of the quality of the surface layer of parts.

The aim of the invention is to improve the quality of processing by controlling the process of removing the stock and forming the physicomechanical and geometric characteristics of the quality of the surface layer of parts.

This is achieved by allowing the grinding wheel to be rotated and continuously transversely fed at a constant speed, while the parts are reciprocated, the speed of which is continuously increased to a value at which the grinding depth corresponds to a given surface roughness value.

In order to reduce the vibration of the technological system caused by high dynamic loads when reversing the reciprocating movement of the machine at high speed, the speed of rotation of the grinding wheel is reduced to a value commensurate with the speed of the reciprocating movement of the part. In addition, such a reduction in the speed of rotation of the circle provides for the formation on the surface of the workpiece of a mesh of abrasive grain trajectories corresponding to honing, and the work hardening and compressive residual stresses occur in the surface layer.

With continuous transverse feeding of the wheel and reduction of its rotational speed, the thickness of the layer being cut off with a single abrasive grain remains unchanged, and the removal of the allowance is redistributed to two or more grain faces, which contributes to a significant reduction in the specific cutting forces, reduction in the magnitude and area of residual stresses time, the depth and thermal effect of the grinding wheel on the surface layer, the depth of the defective layer from passage to passage.

An additional advantage of the grinding method proposed is the increased fatigue strength and corrosion resistance of the parts.

FIG. 1 shows a grinding pattern for external cylindrical surfaces; in fig. 2 is a diagram for removal of an allowance: in FIG. 3 - geometry of the microrelief of a polished surface.

Parts 1 rotating at a speed Vfl (Fig. 1). reported reciprocating motion at speed / forward. relative to the grinding wheel 2, rotating at a cutting speed VK.

Grinding wheel 2 is reported to continuously transversely feed to the depth of cut at a constant speed, gradually decreasing it due to a continuous increase in speed / Cont. reciprocating movement of the part.

The removal of the allowance t is carried out on conic surfaces (Fig. 2), the angle of inclination of which form decreases with each successive pass, and the maximum amount of the removed allowance is equal to g max 51 / product, where S is continuous transverse feed to the depth of cut, mm / min ; L-length of the forming part, mm: Up. - speed of the longitudinal reciprocating movement of the part, mm / min.

Each pass begins with a minimum thickness of the cutting layer equal to zero in the absence of overshoots of the grinding wheel, and ends with a maximum equal to the feed per double stroke.

In addition, the speed of rotation of the grinding wheel VK is reduced to a value commensurate with the speed / Prod of the reciprocating movement of the part. In this case, a mesh of trajectories corresponding to honing is formed on parts, which improves the quality and operational properties of the surface.

This method of grinding allows you to control the process of forming the quality of the surface layer of the part, taking into account its operational requirements.

The machine is configured for processing as follows.

Parts 1, rotating at a speed of Od (Fig. 1), communicate reciprocatingly at a speed of Conn. with respect to the grinding wheel 2 rotating at the cutting speed VK. The grinding wheel 2 is provided with a continuous transverse feed S to the cutting depth at a constant speed, and the speed of the reciprocating movement VnpoA. parts 1 continuously increase.

The method is implemented on software controlled machines. On universal circular grinding machines, the method can be implemented after a corresponding modernization of the cross feed mechanism and the speed control mechanism for the reciprocating movement of the table.

The adjustment of the machine for processing with a decrease in the speed of rotation of the grinding wheel is carried out as follows.

Parts 1 rotating at a speed VA (Fig. 1) are reciprocated at a speed of Uprod. with respect to the grinding wheel 2 rotating at the cutting speed VK. The grinding wheel 2 is reported to have a continuous transverse feed S at the depth of cut, the speed of the reciprocating movement Uprod. the parts are continuously increased, and then on finishing, final passes, the rotation speed of the grinding wheel. The VK circle is reduced to a value that is comparable with the speed / cont. reciprocating movement of the part.

The method is implemented on CNC machines with an adjustable number of revolutions of the grinding wheel or after a corresponding modernization of the grinding wheel drive, for example, installation of a direct current motor.

The proposed grinding method is also applicable for flat milling grinding and for grinding conic surfaces and holes.

Example. The part with a diameter of 20 mm and a length of 500 mm is grinded from an HNSE 50 ... 55 hardened to hardness steel 40X with an abrasive circle PP of 300x127x40 24A40SM17K5 on a circular grinding machine model Z130.

To perform a continuous cross feed to the depth of cut, the cross feed mechanism of the machine is equipped with a special device, which consists of a housing, an electric motor and a gear unit. It allows you to set the speed of continuous cross feed both in magnitude and in the direction from 0.005 to 0.8 mm / stroke. The block diagram of the device is a flat four-dialer. (On the ZM151 machine, the grinding headstock has a continuous feed drive from the hydraulic motor. To implement a continuous feed, it is necessary to simultaneously disconnect the longitudinal stroke from the cross feed. At the same time, the gear ratio of the kinematic chain of the continuous feed from the hydraulic motor to the cross feed screw of the grinding head is equal to 1/1000.With a screw pitch of mm, the speed of continuous cross feed is regulated steplessly within 0.4 ... 8 mm / min. The speed of the longitudinal movement of the table changes continuously within 0.05 ... 5 m / min. For the indicated ratios, the minimum feed per table stroke (500 mm) is 0.04 mm / stroke, and the maximum - 0.8 mm / stroke, and with an optional device from 0.005 to 0.8 mm / stroke).

Processing mode:

cutting speed 30 m / s

part rotation speed 18.8 m / min

reciprocating speed 0.1 ... 6 mm / min

the grinding depth at the end of the part continuously varies from 0.025 to 0.005 mm.

After processing a batch of workpieces of 30 pieces under specified conditions, the surface roughness decreased from 0.63 to 0.16 microns relative to the base, the error in the longitudinal section profile from 0.0129 to 0.003 mm, and the residual tensile stresses reaching +350 MPa With the basic method of processing, they were transformed into compressive stresses of the order of 210 MPa, the total depth of the tension layer decreased from 0.360 to 0.250 mm.

Grinding with a decrease in the speed of rotation of the grinding wheel to a value commensurate with the speed of the reciprocating movement of the part is produced on a machine model Z130, parts made of hardened steel 40X, HRC3 50 ... 55 with dimensions of 20x500 mm with a grinding wheel of a 260x127x40 ПП brand 24А16МЗК7 with a small upgrade grinding headstock to reduce the spindle speed. By reducing the transmission ratio of the V-belt transmission to 2 and reducing the engine speed to 940 minutes, the speed of the grinding wheel with a diameter of 260 mm will be 375 m / min. At a rotational speed of 400, the speed of the part is 250 m / min, with a concomitant rotation of the part, the resultant cutting speed is 125 m / min. The maximum speed of the longitudinal course of the table is 6 m / min.

Claims (2)

1. Grinding method, in which parts provide reciprocating movement, and grinding wheel - rotation and continuous transverse feed at a constant speed, which is different from the fact that, in order to improve the quality of processing, the speed of reciprocating movement of the part continuously increase to the value at which the grinding depth corresponds to the specified roughness. 2. A method according to claim 1, characterized in that the speed of rotation of the grinding wheel is reduced to a value commensurate with the speed of the reciprocating movement of the part. J Vnpod Fig. / FIG. 2 V / r / W