RU2215642C2 - Method to control process of abrasive-flow machining - Google Patents

Abstract

FIELD: mechanical engineering. SUBSTANCE: invention can be used in production of precision friction pairs, mainly, parts of fuel devices of diesel engines. Oil micropockets are formed on surface of part to be machined, said pockets being arranged at preset uniform pitch. For this purpose concentration of abrasive material in two-phase jet approaching the part is controlled by adjusting initial swirling of jet in working nozzle. Design formula is given in description of invention making it possible to determine pitch between pockets depending on air flow rate through axial and tangential branch pipes of working nozzle and grain size of abrasive. EFFECT: increased service life of machine parts. 1 ex, 3 dwg

Description

 The invention relates to methods for controlling the process of jet-abrasive processing (SOA) and can be used to create double roughness with an equal pitch between oil micro pockets on the surfaces of parts.

 As the closest analogue, the method of monitoring and controlling the process of abrasive blasting of the surface of the parts by adjusting the working speeds of the abrasive is selected, where operating speeds are selected as the control parameter and the control is carried out by comparing the working and critical speeds depending on the cleanliness of the processed surface, and the control is carried out regulation of the operating speeds of the abrasive. For this, the technological parameters of the process are determined in accordance with the fractional composition of the abrasive (see AS USSR 852517, class B 24 C 1/00, 08/07/1981).

 The disadvantage of this method is the inability to obtain a double roughness with an equal pitch between the oil micropockets and the regulation of the relative area occupied by the oil micropockets, which is advisable to change depending on the operating conditions of the part. GOST 24773-81 on a partially-regular microrelief (CRMR) of a surface indicates that the area occupied by the CRMR can vary within 5-90% of the nominal area depending on the operating conditions of the part.

 The technical result of the invention is to obtain a double roughness with an equal pitch between the oil micro-pockets.

This result is achieved by the fact that in a two-phase jet create surfaces using an adjustable initial twist of a two-phase jet z ₀ , which is defined as the ratio of the tangential Q _τ and axial Q _{about the} air flow in the working nozzle (z ₀ = Q _τ / Q _o ), while step S - the distance between the oil micro-pockets is determined by the formula
S / d = k • z ₀ ,
where S is the step between the oil micro-pockets;
z ₀ - the initial twist of a two-phase jet (z ₀ = Q _τ / Q _o );
d is the granularity of the abrasive (μm);
Q _τ - air flow through the tangential pipe, (m ³ / s), (control action);
Q _about - air flow through the axial pipe, (m ³ / s);
k is the coefficient of proportionality; k - varies from 2 to 10 with a change in the grain size of the abrasive from 5 to 120 microns and a distance from the nozzle x = 40 mm

 In FIG. 1 shows a processing unit for implementing the proposed method.

The technological installation consists of a nozzle 1, nozzles 2 - for axial air supply, 3 - for supplying abrasive, 4 - for tangential air supply (control action), 5 - containers with an abrasive with a hole 6. Number 7 denotes abrasive particles, 8 - processed surface, x is the distance between the nozzle exit 1 and the surface 8, Q _о is the air flow through the axial pipe 2, Q _A is the air flow (not taken into account), Q _τ is the air flow through the tangential pipe 4 (control action), s - concentration of abrasive.

Figure 2 shows a graph of the change in the relative step S / d of oil micro-pockets from the change in the initial twist of a two-phase jet z ₀ , for abrasives: 1-12 (grain size d = 100-120 μm), 2 - M40 (d = 28- 40 μm), 3 - M5 (d = 3-5 μm).

Figure 3 shows a graph of the change in the relative pitch S / d of the oil micropockets from the processing time t, M40, x = 40 mm, z ₀ = 0.6.

 Principle of operation.

When a two-phase jet moves without a control action (Q _τ = 0), the abrasive is grouped in its axial zone according to a law close to the law of the normal Gaussian distribution (Fig. 1, plot B). When applying the control action Q _τ , the velocity vector of the two-phase jet changes and the abrasive under the action of centrifugal forces moves to the periphery of the two-phase jet, as a result of which its concentration over the cross section becomes uniform (Fig. 1, plot D), which leads to a uniform step S between the oil micro-pockets on the treated surface 8 (figure 1, callout I).

 Example.

When compressed air is supplied from the nozzle 2 to the nozzle 1 in the nozzle 3, a vacuum is created, while the air from the atmosphere passes through the hole 6 and creates a flow in the tank 5 and the pipe 3, due to which the abrasive from the tank 5 enters the nozzle 1. Compressed air, supplied through the pipe 4 (control action), gives the two-phase jet located in the nozzle 1, the rotational movement around its axis, the intensity of which depends on the value z ₀ = Q _τ / Q _o . By changing the value of z ₀ , it is possible to obtain a concentration of the abrasive that is uniform over the cross section of the jet with a given distance between the abrasive particles as they approach the surface to be treated, on which a given step S will be obtained between the oil micro-pockets.

The experiment was carried out with the following values of variables: nozzle with inlet nozzle diameter 2 = 3 mm, nozzle exit diameter 6 mm, abrasives 12, M40, M5, abrasive consumption 2 g / s (abrasive consumption was taken into account experimentally by counting the number of grains per 1 mm ² ), the distance from the nozzle exit to the workpiece x = 40 mm, processing time t = 4 s, constant total air flow Q _Σ = 16 • 10 ^-4 m ³ / s, tangential flow Q _τ varied from 0 to 6 • 10 ^-4 m ³ / s. The experimental results are shown in figure 2.

 With a constant consumption of abrasive and a certain initial twist of a two-phase jet, the distance between the oil micro-pockets can be changed, as well as the processing time, Fig.3.

Claims (1)

A method for controlling the process of jet-abrasive machining of parts, including monitoring and controlling at least one of the parameters of the processing mode, characterized in that the concentration of the abrasive in the two-phase jet is selected as the parameter mentioned when it approaches the surface to be formed, on which oil micropockets are formed with a given step, while controlling the concentration of abrasive is carried out by adjusting the initial twist of the two-phase jet in the working nozzle, and the step between the oil micro-pockets is determined condition
S / d = k • z ₀ ,
where S is the step between the oil micro-pockets;
d is the granularity of the abrasive, microns;
k is the proportionality coefficient, changing from 2 to 10 when changing the grain size of the abrasive from 5 to 120 microns and when the distance between the slice of the working nozzle and the treated surface is 40 mm;
z ₀ - the initial twist of the two-phase jet in the working nozzle, equal to Q _τ / Q _o ;
Q _τ - air flow through the tangential nozzle of the working nozzle - control action, m ³ / s;
Q _o - air flow through the axial pipe of the working nozzle, m ³ / s

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