Formation of bulges on hollow cylindrical products made of non-ferrous difficult-to-deform alloys

Formation of thickened elements on the edge parts of hollow cylindrical products, which serve as the elements of fuel lines of various power plants, can be applied to ensure a significant quality of their welding connection. The article deals with the formation of such thickening elements on tubes made of special non-ferrous alloys. Due to the mechanical features of these materials, these processes were investigated under narrow temperature and speed conditions causing short-term creep of the material. To analyze these operations, mathematical models have been created that describe power modes. Quantitative rules of the influence of the geometric parameters of the process on the pressure during the upsetting have been obtained. The materials obtained during the analysis can be used to create similar technologies.


Introduction
For high-quality welding of hollow cylindrical products, it is necessary to have thickenings on the edge elements [1][2][3][4]. The most rational method of their production is plastic forming, that is, upsetting and forging of the workpieces. The upsetting process is accompanied by barrel formation [1, 2, 5,6]. When it comes to making critical parts from special metal materials using this method, then, when they are deformed, there is a risk to decrease the stability, as well as to significantly increase the loads on the tool [7][8][9][10][11]. Therefore, it is important to implement this process in narrow temperature and speed conditions, under which short-term creep of the material takes place [12][13][14][15]. In this case, such factors as the velocity and time of deformation determine the modes of technology application and need to be calculated.
are respectively the equivalent stress, strain, strain rate; n m А , , are the material constants.
The calculation assumes that the process scheme is axisymmetric. To perform calculations for this operation of modes, we use the power balance [1], and its equation: (2) In expression (2) N is the power of forces on the deforming tool, The powers in block 1, which is also the block of deformations are represented as follows: "12" line power is [1]: The power on friction areas is [1]: The pressure for the formation of the internal thickening by upsetting is determined by the equation (2)    The analysis of this graphical dependence showed that with a decrease in the relative size of the flange (with an increase in the relative punch stroke), the upsetting pressure increases by 1.8 times for the materials under study. In general, the dependences of change for both studied alloys are identical. Fig. 3 shows the dependence of the change in the upsetting force on the relative value of the flange radius. The analysis of this graphical dependence showed that with a decrease in the relative value of the flange radius from 0.5 to 0.9, the pressure decreases by 2.3 times for a chromium-nickel alloy and by 2.8 times for AA586 aluminum. Figure 4 shows the dependence of the change in the upsetting force on the velocity of the tool movement.

Fig. 4. Dependences of the change in the upsetting force on the velocity of the tool movement
The analysis of this graphical dependence showed that with an increase in the velocity of the tool movement, the pressure increases by 20% for material AA5086 and by 28% for 304 L. Having analyzed the obtained dependences, it can be said that the intensity of pressure growth during the upsetting for a chromium-nickel alloy is greater than for alloy AA5086.
Upsetting of external thickenings. The upsetting scheme for making external thickenings is shown in Fig. 5. The equation of state of the material in the deformation zone is described by the following expression The pressure during the upsetting of the external thickenings is estimated by the following inequation [2]: Here q is the pressure on the punch; ep σ is the value of the equivalent stress at the boundaries of the velocity gap; 0  After the substitution of these constants and dimensional ratios into formula (11), we obtained the dependences of the pressures on the deforming tool on its velocity 6) and those of the pressures on the deforming tool on the relative thickness of the workpiece ) / ( 2 1 r r q (Fig. 7). The analysis of the results of the dependences shown in Fig. 6 and 7 suggest that increasing the pressure tool velocity for alloy AA5086 results in a 20% increase in the upsetting pressure. For a titanium-containing alloy, the intensity of the pressure growth in the same velocity range is 28%. Increasing the relative thickness of the workpiece from 0.6 to 0.9 leads to a 44% decrease in pressure for AA5086. For the 6Al-4V alloy in the same range, changes in the relative pressure thickness are reduced by 40%.

Conclusion
Thus, after the analysis of the research results concerning the upsetting of external and internal thickenings, it can be said that compliance with high-speed deformation modes has a positive effect on reducing power loads. Dependences between the degrees of deformations during the upsetting and the force of the process have been established. The results can be used as recommendations for the manufacture of thickened tube elements.
The work was carried out within the framework of the grant of the rector of Tula State University and grant NSH-2601.2020.8.