RU2111843C1 - Method of intermittent grinding - Google Patents

Abstract

FIELD: deep peripheral grinding of materials liable to defects, such as burns and microcracks. SUBSTANCE: grinding wheel includes fixed and movable parts at different graininess; grinding wheel is set in rotation at longitudinal feed relative to work. Fixed and movable parts of wheel are engageable by end surfaces due to the segmental grooves and projections; they are mounted for relative longitudinal motion on the condition of automatic change of height of wheel from B_min to B_max at change of direction of longitudinal feed. Amount of change of wheel height is selected to be multiple of distance between projections of microirregularities formed by abrasive grains and is determined by the following formula: B_max-B_min= n•l_cp/2, where h is any integral number; l_cp is mean distance between grains of fixed part of wheel determined by known methods. EFFECT: enhanced efficiency. 6 dwg

Description

 The invention relates to deep peripheral grinding of materials predisposed to defect formation in the form of burns and microcracks.

 A known method of intermittent grinding, in which a grinding wheel with a circumferentially varying grain with sections limited by curves of variable radius is informed of rotation and movement relative to the workpiece, in addition, a circle is taken, each section of which is bounded by a convex curve, while the direction of rotation of the wheel is periodically reverse [1]. The method allows processing using the entire peripheral working part of the tool while maintaining the advantages of the intermittent grinding process, increasing its dimensional and overall durability, and in combination with the combination of roughing and finishing passes, productivity and quality of processing.

 The disadvantage of this method is: the constant presence of vibrations introduced by the curved sections of the periphery of the circle, which worsen the roughness of the surface layer, the difficulty of dressing, the complexity of the kinematics of the machine and control due to the need for reverse, which leads to an increase in the cost of the grinding method.

 As a prototype, a method of intermittent grinding with a circle consisting of at least two interconnected parts with different grit, changing in the axial direction of the circle [2].

 The disadvantage of this method is the difficulty of manufacturing an abrasive tool, obtaining a machined surface of various roughness due to the interaction of the workpiece and parts of the wheel with different grain sizes.

 The claimed invention solves the problem of increasing tool life, accuracy and processing performance while maintaining the advantages of the intermittent grinding process.

This is achieved by the fact that with the method of intermittent grinding, in which the grinding wheel, consisting of two parts with different grain sizes, is informed of the rotation and the longitudinal feed relative to the workpiece being machined, while the wheel is taken with the fixed and moving parts mating with the end surfaces by means of the grooves made on the latter and projections of a segment shape and installed with the possibility of relative longitudinal movement from the condition of automatically changing the height of the circle from B _min to B _max when changing the pitch of the longitudinal feed, while the magnitude of the change in the height of the circle is selected as a multiple of the distance between the protrusions of the microroughness formed by abrasive grains, and is determined by the formula:
B _max - B _min = n • l _sr / 2,
Where
n is any integer;
l _cf - the average distance between the grains of the stationary abrasive part of the circle, determined by known methods.

 In FIG. 1 schematically depicts a tool for implementing the proposed grinding method and its position outside the cutting zone, where the height B is maximum; in FIG. 2 - the moment of cutting, the rapprochement of the parts of the circle when the height of the circle B is minimal; in FIG. 3 - grinding process with a minimum wheel height with longitudinal feed from right to left; in FIG. 4 - the left part of the circle leaves the cutting zone when the height of the circle B is maximum; in FIG. 5 - grinding process with a maximum wheel height in the direction of longitudinal feed from left to right; in FIG. 6 - the right side of the circle leaves the cutting zone when the height of the circle B is minimal.

 The proposed method of intermittent grinding is as follows.

The abrasive parts of different grit in the inoperative position are divorced and the grinding wheel has a maximum height B _max (Fig. 1). When cutting into the blank 1 of the left, movable part of the circle 2, due to the special design of the tool, it approaches the right, stationary part 3, changing the height of the circle to B _min (Fig. 2). Processing with longitudinal feed from right to left is carried out by a tool with B _min (Fig. 3).

As soon as the left side of the circle 2 leaves the treatment zone and the cutting forces cease to act on it, the right side of the circle 3, thanks to the effective cutting forces, rotates and moves the left side to the left, increasing the height of the circle to B _max (Fig. 4). During further processing, when changing the direction of the longitudinal feed of the tool from left to right, the circle will retain its maximum height B _max (Fig. 5). When the right-hand side leaves the treatment zone, the cutting forces acting on the left-hand side bring both parts of the circle 2 closer to the value of B _min (Fig. 6).

Thus, the proposed method of intermittent grinding allows you to implement the principle of non-repeating marks by selecting the heights B _max and B _{min of the} circle, taking into account the average distance between the protrusions of microroughness formed by abrasive grains, determined by the formula:
B _max - B _min = n • l _sr / 2,
Where
n is any integer;
l _cf - the average distance between the grains of the stationary abrasive part of the circle, determined by known methods.

 This makes it possible to increase the cutting ability of the abrasive parts of the wheel and significantly improve the surface roughness.

Example. On the internal grinding machine mod. 3K228V polished a through hole with a diameter of D ₃ = 60 H7 (+ 0.03) and a length l = 60 mm. The surface roughness parameter R _a = 0.63 μm. Side allowance h = 0.2 mm. The workpiece material is steel 45, hardened, hardness HRC _e = 45. The machine is equipped with a device for the active control of workpieces. We used a grinding wheel made of two parts (see Fig. 2, 4) with abrasive layers recommended for this steel (the full characteristics of the fixed part are 24A25PS25K8A, the movable 24A16PS25K8A). For internal grinding, it is recommended that D _k / D _z = 0.8 ... 0.9. Therefore, a circle was made with a diameter of D _k = 50 mm, a minimum height B _min = 50 mm, and a maximum height B _max = 55 mm. Processing was carried out under the following cutting conditions. The rotational speed of the circle was taken n _k = 13000 min ^-1 ; the rotation speed of the workpiece was taken n _s = 200 min ^-1 . The longitudinal feed according to the recommendations was set S _m = 5390 mm / min. Cross feed for normal circles recommended S _{t dv.kh} = _0,004 mm / dv. move. For this special circle, S _{t dv.x} = 0.006 mm / dv.hod was taken. Although the treatment was carried out with increased metal removal performance, the appearance of burns on the treated surfaces was not recorded.

 The use of this method of intermittent grinding with an automatic change in height increases the processing productivity by 1.8 ... 2 times, eliminates the operation of semi-grinding due to the improvement of surface roughness by 1 - 2 classes. At the same time, the consumption of an abrasive tool is reduced by 25%.

Claims (1)

The method of intermittent grinding, in which the grinding wheel, consisting of two parts with different grit, is informed of the rotation and longitudinal feed relative to the workpiece, characterized in that they take a circle with a fixed and moving parts, mating end surfaces by means of segment shapes made on the last depressions and protrusions and installed with the possibility of relative longitudinal movement from the condition of automatically changing the height of the circle from B _min to B _max when changing the direction of the longitudinal feed, while the magnitude of the change in the height of the circle is selected as a multiple of the distance between the protrusions of the microroughness formed by abrasive grains, and is determined by the formula
B _max - B _min = n • l _sr / 2,
where n is any integer;
l _cf - the average distance between the grains of the stationary abrasive part of the circle, determined by known methods.

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