RU1808878C - Method of manufacture of parts with holes - Google Patents

Abstract

Usage: the invention relates to the field of pressure treatment of structural elements having openings. Essence: two concentric imprints of different depth and cross-sectional shape, located at certain distances from each other with the choice of the order of pressing these punches, by certain efforts, with the removal of prints, their depth and the force of indentation of the punches is related to the claims of the inventors. 4 ill.

Description

The invention relates to the field of pressure treatment of structural elements having openings.

The aim of the invention is to increase the resource of power structural elements by increasing the time before the occurrence of a fatigue crack and its development to critical dimensions.

Figure 1 shows the relative position and geometric parameters of the prints in the structural element; Fig. 2 shows a stress-strain state in the area of a reinforced hole; Fig. 3 is a flowchart for strengthening the area of the hole; figure 4 - the final view of the hardened hole.

The relative arrangement of the prints indicated in FIG. 1 leads to the fact that the residual compressive stresses obst,

created by plastic deformation, covering the zone of probable nucleation and the development of a fatigue crack, reduce the level of acting tensile operational stresses; the interaction of the external deformation-limiting imprint with the internal reinforcing imprint leads to an increase in the zone with residual compressive stresses.

The stress redistribution mechanism is illustrated in Fig. 2, which shows the stress field around an unstressed hole, the residual compressive stresses after imprinting, and the total stress diagram in the area of the strengthened hole to form an effective stress section below the level of rated stresses. The presence of such a site

00

about

00

00

VI

00

leads to a slowdown in the growth rate of cracks in this area.

The fingerprint sequence shown in FIG. 3 using rigid force fixation of the limiting punch pos. 1 having an annular protrusion embedded in the reinforcing material pos. 2 ensures its volumetric deformation in and around the hole when the reinforcing punch pos. 3 is introduced. The induction of residual compressive stresses under conditions of a volumetric-deformed state of the material increases the actual yield stress of the material and makes it possible to increase the level of residual compressive stresses up to the yield strength (ov) over the entire area bounded by an external ring imprint. This eliminates the possibility of occurrence of technological cracks when making an internal hardening print.

Fig. 4 shows a view of a hardened hole after its final manufacture.

The method is carried out as follows.

Holes are determined by a design or experimental method in the area of which it is advisable to reinforce in order to increase the resource. Hole markings are carried out on the structural elements and, by known methods, the first punch is pressed in, with its rigid force fixation in the final position, and then the reinforcing punch, the axis of the intended hole must coincide with the axis of the punches.

The process of releasing the hardened part is performed in the reverse order.

In determining fingerprint removal, the following factors are taken into account: achieving a maximum level of residual compressive stresses in the peak area of the operational stresses caused by the presence of a stress concentrator; propagation of a high level of residual compressive stresses in the zone of slow development of a fatigue crack.

The level of operational voltages operating in the immediate vicinity of the voltage concentrator is characterized by a theoretical concentration coefficient (s) determined by the ratio:

aa onom

where ohiax, OHOM are the maximum and rated voltages, respectively.

Essential to the durability of the structural element has

also a stress gradient characterizing the rate of decrease in the effective stresses with distance from the concentrator. An analysis of the magnitude and zone of action of the increased stresses caused by the hub in the form of an aperture shows that the magnitude of the maximum stresses is (2.5-3) On, and the zone of their action is determined by a value of 1.5 / mm.

A statistical analysis of the kinetic fracture diagram with a linear piecewise approximation of the crack growth rate function shows that the following ranges can be taken:

to

t "ZpriO, 35

25

t "4.5 0.356 Ј 0.5 1 0,, 0

where t and s are the characteristics of the material;

m is a parameter characterizing the intensity of the increase in the rate of development of cracks with change;

K is the stress intensity factor;

35

where I is the half-length of the crack;

o acting voltage. Taking into account that the period of development of cracks in the range- | t- 0-015 is 80-90%

total crack growth duration (CRT), it makes no sense to form a zone of residual compressive stresses that goes beyond this condition, i.e. the removal of prints (I) from each other is determined under the condition K 0.5 Ks.

To simplify calculations, the operational spectrum usually leads to voltage levels.

cr 0.5or

where (P is the calculated stress determined by taking into account the coefficient of sensitivity of the material to the notch (a).

g- ° P33P s

0.8-1.0

Analysis of fatigue curves shows that the same durability is unstrengthened and hardened by modern methods of plastic deformation, provided

 (0.75-0.85)

Thus, the average effective level of stresses acting in the hardened zone is 0.75-0.85 times the level of nominal stresses.

Given the above, we have:

0.5KS 0.5-0.8-0.850L

where from

 0.64 Since the ratio of modern alloys is in the range of 3.0-4.5, size I is in the range of 6-14 mm.

The calculated data are confirmed by experimental ones, where a flat section of the fatigue zone of a fracture characterized by a slow crack development, a specimen of the type of strip with an aperture of 36 mm wide and a POTV of 6 mm is 3-5 mm to each side of the aperture, i.e. The total size of 2P, taking into account 0tv, is 12-16 mm. Thus, the final removal of prints from each other is recommended in the range I (0.8-1.5) 00tv.

The depth of the bounding imprint (h) is selected based on the requirement of sufficient tightness of the material in the radial direction while maintaining sufficient strength characteristics of the cross section weakened by this imprint and is taken in the range (0.05-0.15) 5, and the shape of the cross section should create the lowest possible concentration voltages, for example, in the form of conjugation of radii.

The depth and shape of the hardening print is selected from the condition of maximum uniform displacement of the material in the radial direction, and a depth in the range of (0.3-0.5) 5 is accepted, the shape is cylindrical with a spherical end.

The condition that determines the force acting on the limiting punch is to load the inner contact area of this punch, limited by an annular protrusion, by stresses exceeding the yield strength (ov) of the hardened material by 20–25% to ensure that the dimensions of the formed hardening joint are preserved. , when the material is displaced by a reinforcing punch, which, in turn, must create stresses exceeding the aforementioned ones by a similar value, for its guaranteed penetration to a predetermined depth. Based on this, the efforts to limit and strengthen the punches are determined by the formulas:

Ro (1.2-1.5) No. (12 - 0.25 Ootv2)

Ru (0.35-0.6) n From Ootv2, where I is the distance between the centers of the prints; . DOTB hole diameter.

As an example, consider the option of hardening a 10 mm hole in a VT20 panel of 4 mm thickness.

For material VT20, the characteristic is Or 85-100 kg / mm2. The correlation between the print parameters and the efforts was determined using the recommended formulas using the following coefficients: 1.3r0tv 1.3-10 13mm The coefficient 1.3 was chosen for the following reasons: since the free edge of the part is removed from the hardened hole, this eliminates the cracking of the part jumper and allows to increase the zone of residual compressive stresses, taking a large value of the coefficient, for materials with

high ffj it is not recommended to use the maximum allowable values of the coefficients, since this requires great efforts to act on the limiting punch d 0.1 5 0.1 4 0.4 mm

in a first approximation, it is recommended to take the average value of the coefficient 0.1, which can be adjusted according to the results of laboratory tests

N (0.4-0.5) S (0.4-0.5) 4 1.6-2.0 mm.

For plastic materials, it is recommended that large coefficient values be adopted.

Po and Py are determined using the average values of the coefficient, which

can be adjusted according to laboratory tests

Po 1.35 L From (h - 0.250otv2) 1.35 -l-100 (132- 0.25 -102) “60t Ru 0.5p -Ot- Otv2 0.5 -l: - 100

The effectiveness of plastic deformation to increase the service life of parts is confirmed by the results of block tests of specimens of the type strip with an aperture of 1440 alloy plates with dimensions of 10 60 250 mm; DOTB 8 mm. The block was a set of loads of seven different levels of C0taxHeTT ° 32.3 kg / mm2.

Claims (1)

The longevity before the destruction of samples with prints is 1.5 times greater than the durability of samples without prints. SUMMARY OF THE INVENTION A method of manufacturing parts with holes, comprising pre-cold plate-like deformation of the hole forming zone with punches and subsequent hole making, characterized in that, in order to increase the service life of the parts, before plastic deformation, additional cold plastic deformation is carried out using limiting punches with the application of force P0 (1.21, 5) CFr (l2 - 0.25 Dota2) and obtaining ring prints with a depth of h (0.05-0.15) 5 per distance 1 (0.8-1.5) 0 from the axis of the hole, and plastic deformation of the zone of the hole is carried out without removing the force P0 with application efforts Ru (0.35-0, b) l: OgOvtv2 on the reinforcing punch, to obtain an imprint of depth H (0.3-0.5) 5, where S is the thickness of the part; sgt is the yield strength of the material of the part; DOTB - hole diameter.