N.E. Sadkovskaya – Dr.Sc. (Eng.), Professor, 

Department «Innovation Management», Moscow Aviation Institute (National Technical University)

E-mail: natsadkovskaya@rambler.ru

A.E. Tsykin – Post-graduate Student, 

Department «Innovation Management», Moscow Aviation Institute (National Technical University);  PAO «NPO «ALMAZ» (Moscow)

E-mail: a.tzuikin@ya.ru

In radar stations and air traffic control systems, large-sized metal structures are load-bearing parts, and, during the manufacturing process, both temporary and residual stresses and strains appear in them, affecting dimensional stability in subsequent production processes or causing fatigue cracks and a tendency to corrosion cracking during operation.

Domestic scientists have proposed a classification of stresses into voltages of the first kind (macrostresses) and voltages of the second kind (microstresses).

Depending on the spatial arrangement and interaction, welding stresses are distinguished into linear (uniaxial), planar (biaxial) and volumetric (triaxial).

In the direction of action, the stresses are distinguished into longitudinal and transverse.

The reasons for the occurrence of residual stresses are local non-uniform heating of the metal during welding, non-uniform structural transformations in the metal, and casting shrinkage of the deposited metal. Like stresses, welding strains can be temporary and residual, and in the direction of action longitudinal and transverse.

Temporary and residual deformations are distinguished into general and local.

In modern foreign literature, the main parameters related to welding and affecting the manufacturing quality of welded metal structures are divided into metallurgical, welding process parameters and technological parameters.

At present, various methods have been developed and applied to eliminate welding deformations and reduce residual stresses.

The most effective ways are considered thermal: high tempering and thermal dressing. But, large-sized metal structures, due to their large overall dimensions, are not always able to subject to general vacation. Local tempering is used in the case when the occurrence of destruction is most dangerous, and the deformability of the structure during the machining and operation is insignificant. Taking into account that large-sized metal structures have a large length and uneven distribution of residual stresses throughout the volume, the formation of goals for applying high tempering to a specific product, determining the permissible level of residual stresses, as well as the appointment of high tempering modes is even more difficult than in most engineering structures . The process of thermal dressing is similar directly to welding, and in case of non-compliance with the conditions for the distribution of strains from dressing, deformations in metal structures will not only not decrease, but will increase, similar to welding ones. Thermal dressing does not contribute to relaxation or reduction of residual stresses, but rather contributes to their increase.

At the same time, there are mechanical dressing methods, which, like thermal dressing methods, are based on plastic deformation of the weld zone after welding, but have significantly higher energy efficiency: rolling by rollers, cold forging, high-speed pulsating deformation, ultrasonic impact processing; low frequency vibration processing.

Thus, stresses and strains are currently studied in sufficient detail, and there are also many ways to relieve residual stresses and eliminate strains, which have their own characteristics and advantages. The criteria for their selection, integrated use and implementation in the technological chain of production of metal structures, including large ones, deserve further study.

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