OBRABOTKAMETALLOV TECHNOLOGY Vol. 24 No. 2 2022 and fi ller metals, the weld has a cast structure. A partial melting zone of the base metal is located near the fusion boundary, which is followed by a heat-affected zone characterized by a structure changed by temperature taking place with increasing the distance from the center of the welding zone [3]. Due to structural differences, the transitions between the considered zones are accompanied by changes in mechanical properties, which is especially pronounced in the transition over the fusion boundary, which is a weak point of the weld joint. Along with structural non-uniformity, welding issues also include residual stresses, welding deformations and weld porosity [4–7]. Various methods are used today to avoid these drawbacks that can be classifi ed into those applied during and after welding. The methods used during welding include strain balancing by means of a reasonable sequence of weld passing, creating initial distortions and rigid fi xing the elements to be welded. The methods used after welding include weld heat treatment, mechanical leveling of structures, thermal leveling, and surface plastic deformation (SPD) [8]. Another effi cient method to minimize the consequences of these drawbacks is the vibration treatment of metal in a molten state [9–10]. This method was proposed in 1950 as applicable to crystallizing metal by Chernov in order to improve the ingot structure after casting. Vibrations increase the homogeneity of ingots by dispersing the growing dendrites [11–12]. To ensure effi cient action on the structural formation of the weld, the crystallization of which is several times faster, it is reasonable to use high-frequency vibrations of ultrasonic frequency, which will make it possible to exert a signifi cant impact in a limited time interval. There are the following methods of using ultrasonic vibrations during welding: – applying vibrations to the electrode [13]; – applying vibrations to the non-consumable electrode [14]; – transferring vibrations to the gas burner body [15]; – transferring vibrations to non-weldable structural elements [16]; – using the arch as a source of ultrasonic radiation [17]. The studies considering these methods show a positive effect on the welding process and weld structure. In particular, depending on the method, the depth of penetration of the base metal can be increased, the porosity of the weld can be decreased, the conditions for the transfer of molten metal drops from the electrode to the workpiece can be improved, the microstructure of the weld can be refi ned, the proportion of dendritic segregation in the weld metal can be decreased, and the mechanical properties can be improved [18–22]. More detailed results can be found in overview papers on this subject [23, 24]. The effect of ultrasonic machining on the structure of the crystallizing weld metal has a clear positive effect. Nevertheless, these technologies are not widely used in welding processes, for example, as compared to ultrasonic SPD that is applied for post-treatment of welds [25-27]. This can be explained by a number of reasons: 1. Additional equipment is required: ultrasonic generator and vibration system. 2. Complex organization of the process related to coordination between welding conditions and acoustic process parameters of ultrasonic machining. 3. It is preferable to use more complex and larger magnetostrictive transducers requiring forced cooling since piezo-ceramic ones lose its effi ciency at high temperatures. 4. Increased power consumption for the welding process. Despite the diffi culties, opportunities of using ultrasonic vibrations make the development of these technologies attractive. This paper describes the research of applying ultrasonic vibrations on the elements to be welded and selecting the vibration application spot and the welding zone.
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