SU1076474A1 - Method for relieving residual stress in parts - Google Patents

Abstract

METHOD OF REMOVING RESIDUAL VOLTAGES IN DETAILS, including preliminary static loading of a part and vibration at resonant frequencies of its individual parts, characterized in that, in order to intensify the process, to increase the geometric and dimensional accuracy of their operation, they carry out preliminary static loading of parts of parts with maximum residues stresses up to a total stress of 1.05-1.3 times the large yield strength of the material of the parts.

Description

 4 1 J

The invention relates to mechanical engineering, in particular to methods of: relieving stresses by applying to parts of loads, resulting in total stresses exceeding the yield strength of the material of the parts.

A known method for reducing the level of residual stresses in parts involves vibrating loading with the application of torsional oscillations around an axis perpendicular to the main component of residual stresses 1J.

The disadvantages of the method are that the resulting rate of relaxation of residual stresses in the parts is small and the decrease in the level of residual stresses results in a small, so the parts are deformed during operation and have little dimensional stability, especially in those parts where high level of residual stresses.

The closest in technical essence and the achieved result to the proposed one is a method of relieving internal stresses in metal parts, which accelerates the process of reducing stress levels, including preloading of parts with a concentrated mass, the value of which is machined. and the subsequent vibration of the part at the resonant frequency 2.

The disadvantage of this method is that the static loading of parts is carried out without taking into account the design features of the parts, the magnitude of the residual stresses in the parts and the magnitudes of the total stresses in some of the most loaded parts of the parts.

Loading with a concentrated mass leads to a decrease in the amplitude of oscillations of a part of the casting that has entered into resonance. The loading of a part of the part that entered into resonance comes from bending oscillations and depends on the magnitude of the bending amplitude. Since the magnitude of the bend for each cycle of oscillations has a positive and negative value relative to the neutral axis, over the cross section of the part of the part that entered into resonance, compressive and tensile stresses of a certain magnitude appear. The larger the magnitude of the concentrated mass that loads the workpiece, the lower the bending rate per cycle at resonant frequencies and the smaller the magnitude of the resulting cyclic compressive and tensile stresses. Thus, the application

This method does not allow stably, in the entire loading limit of the concentrated mass, to obtain an increase in the rate of relaxation of the residual stresses and to improve the geometrical and dimensional accuracy of the parts during their operation.

The purpose of the invention is intensification. process, increasing the geometric and dimensional accuracy of parts during their operation.

This goal is achieved by the fact that according to the method of removing residual stresses in parts, including preliminary static loading of the part and vibration at the resonant frequencies of its individual parts, the parts of the parts with maximum residual stresses are pre-static to the total stresses 1.05-1.3 times greater than the yield strength of the material of the parts.

5 The essence of the invention is that the main elements most loaded with tensile stresses are preloaded with static loads, and then vibrate at the resonant frequencies of these elements of the parts, loading with dynamic loads of such magnitude that the total stresses in these elements of the parts were 1.05-1.3 times larger than

5 yield strength of the part material. Typically, the magnitude of the residual tensile stresses in the basic elements of the castings is 40-80% of the yield strength of the material. In order to obtain the required values of the total stresses that increase the speed and completeness of the relaxation process of residual stresses, the magnitude of the applied static stresses should be 20-50% of the yield strength of the material, as the magnitude of the dynamic stresses arising from the vibration of the elements details at their resonant frequencies,

non-cracks 15-.40% of the yield strength of the material.

If the total stresses applied to the most loaded casting elements reach values

5 is 1.05-1.3 times the large yield strength of the material, plastic deformation occurs in these parts of the parts, accompanied by a decrease in the level of residual stresses and a significant redistribution of stresses in the whole structure.

When the total stresses are less than 1.05 times the yield strength of the material, the deformation rate of the most loaded elements of the parts is insufficient and in order to optimally reduce the level of residual stresses, the process of applying vibratory loads should be long.

When the total stress exceeds the yield stress by more than 1, the deformation rate of the elements of the parts is large and uneven in different parts of the parts, and as a result the parts are boxed and cracks are formed in the most loaded elements.

Short-term cyclic loading, which is obtained by vibratory loading of parts of castings at a resonant frequency, allows for the half-cycle of loading to obtain the necessary magnitude of stresses equal to 1.05-1.3 of the yield strength of the material, and at the same time the level of residual stresses decreases and redistribution of stresses in castings does not cause cracks in them.

The machined parts according to the method proposed have a low level of residual stresses, and therefore at. operation, the geometrical and dimensional accuracy of parts is maintained.

Example. Comparative studies of the processing according to the known and proposed methods are carried out on the housing of a roller reducer for rubber made of cast iron of grade SCH 20. The overall dimensions of the casting are 11bхх8080, weight 825 kg, the prevailing wall thickness is 15 mm. Investigation of the level of residual stresses in the casting show that the highest level of tensile stresses is observed in the interface between the bearings and the side walls of the gearbox housing.

Obtained during the research data are given in the table.

From the data in the table it can be seen that modes 1-4 correspond to the known method, mode 5 has a total load less than necessary, mode 10 has a total load more than necessary, and they cut 6-9 correspond to the proposed method.

The loading of the gearbox according to the proposed method is carried out with clamps, special jacks, brackets, which can be manufactured specifically for a particular part or can be unified.

Studies show that the use of a concentrated mass for loading within 0.03–50 values of the mass of the workpiece, especially at the upper loading limit, causes in parts of the part with a maximum level of tensile stress compressive stresses. In addition, loading parts with a concentrated mass significantly increases the load on the vibrators and reduces the magnitude of the stresses that occur in different parts of the parts when they vibrate at resonant frequencies.

Measurements of the bored parts of the worm gearboxes, the test results of which are presented in the table, show that if the internal diameter of the worm wheel case is ovality when using the known method of vibro-processing of parts is 0.9-0.12 mm (modes 1-4) When using the proposed method of vibration treatment, the value of the diameter ovality decreases by 0.040.0.05 mm (modes 9-11), i.e. more than twice. For case parts that have not undergone the process of vibro-processing, the ovality of the diameter after boring is 0.15-0.18 mm.

Thus, the proposed 1 ”method compared to the known method allows to obtain parts with greater geometric and dimensional accuracy.

The obtained results show that, in comparison with the known, the proposed method of removing residual stresses in parts allows in places with the maximum tensile stresses to reduce the level of stress from 37.4-38.1 to 27.5-29.3 MP In addition In addition, it was found that the use of the proposed method makes it possible to reduce by 1.65-1.9 times the deformation of parts during operation.

The expected economic effect of the off-line method of the proposed method by reducing the level of residual stresses by 20-27%, reducing the deformation of parts by 1.65-1.9 times and increasing the geometric accuracy of parts will be 6.32-6.78 rubles. on 1 ton of suitable parts like gearbox housing.

The magnitude of the compressive stresses that occur in castings when loaded with a concentrated mass, MPa

Maximum tensile stresses due to static loading of parts, MPa

Frequency limits for vibration machining of a part, .Hz

Duration of vibration loading of parts

The magnitude of the tensile stress, arises tsikh when vibrating processing of castings, MPa

The value of the yield strength of the casting material, MPa

The value of the total stress in the casting during its processing in different modes, MPa

The maximum value of residual stresses in castings after the proposed treatment, MPa

33.4. 54.3

69.5

44-10338-10639-104

0.8

0.8

0.75

21.4

21.9

2 9, .8

142

142

142

137

4.6

26.5

34,335,7.30,4

Table continuation

Maximum tensile residual stresses in castings, MPa

37.9

37.6. 37.4

37.5 Amount of working stresses in the process of operation of casting, MPa Amount of loading in mass of the mass of casting Amount of compressive stresses that occur in castings when loaded with their concentrated mass, MPa Maximum value of tensile stresses from static loading of parts, MPa Frequency limits of vibration processing of a part, 41-103 42-10 Hz Duration of vibration loading of parts, h The magnitude of tensile stresses arising from the vibration treatment, 3 28.6 castings, MPa The magnitude of the yield point and the casting material, MPa The magnitude of the total stresses in the casting during its processing in various 149.1163.4 modes, MPa The maximum value of the residual stresses in the castings after the proposed treatment, MPa

Continuation of the table 97.2 0.70 26.1 8-46 38-4638-46 07.0 43-101 1-106 43-103 0.80, 75 0.70 8.4 72.8 5.7 Casting cracked

Claims (1)

METHOD FOR REMOVING RESIDUAL STRESSES IN DETAILS, including preliminary static loading of a part and vibration at resonant frequencies of its individual parts, characterized in that, in order to intensify the process, increase geometric and dimensional accuracy during their operation, preliminary static loading of parts of parts with maximum residual stresses to a value of total stresses of 1.05-1.3 times the yield strength of the material of the parts. 1076474 A