Processes of isothermal formation of hollow t-shaped tubes made of high-strength alloys

Slow hot deformation makes it possible to achieve a significant growth of deformation without the destruction of the material and avoiding a significant decrease in pressure when forming difficult-to-deform nonferrous alloys. This is especially important when it is necessary to obtain products that operate in severe conditions, for example, in propulsion systems. The article discusses the manufacture of hollow T-shaped connectors by means of forming, namely, by means of extrusion in orthogonal planes and piercing. It was assumed that these operations took place under isothermal conditions. Expressions for calculating the force values of the processes are obtained. Using these expressions, the influence of the degrees of deformation on the forces of extrusion and piercing was investigated.


Introduction
In piping systems of power plants, T-shaped tubes are used to connect heat pipes [1][2][3][4]. Their operating conditions determine the requirements for materials and their properties for the manufacture of these T-tubes. They are mainly made from resistant non-ferrous alloys that resist treatment [5][6][7][8][9]. The deformation of such alloys in a special viscoplastic mode looks very promising. Hydraulic press in split dies, providing forming in orthogonal planes, can be used as the equipment that allows implementing this mode [1,2,8,10].
An important value here is the rate of deformation [11][12][13][14], which ultimately affects the intensity of the deformation. In this article, two particular operations for obtaining hollow T-shaped tubes are considered: orthogonal extrusion and piercing.
To determine the pressures, we will use the energy calculation methods [1][2][3]. The scheme of operations will be assumed to be axisymmetric. Using the energy calculation methods [4], we obtained the expressions for calculation of powers in various elements of the selected velocity field [2].
The deformation block's power is [2] ∫ ∫ ∫ where W , gr.c. y are respectively the volume of the block and the transverse center of gravity of its cross-sectional area. The power on the considered lines of velocity gaps is [2]: Here p S is the area of the velocity gap's surfaces; τ     The friction power on the contact lines between the tool and the workpiece is [2]: Here 2 1 0 0 is the value of the velocity of the edge elements of the material at the output end of the tool; 1 S , 2 S are the friction zones at the input and output areas of the tool; µ is the Coulomb friction coefficient.
Taking into account formulas (2)(3)(4)(5), the value of the extrusion pressure in orthogonal planes is [2]: To find the pressure substituting formulas (2-5) into expression (6) An increase in the relative value of the extrusion diameter for alloy AA5086 results in a 65% reduction of pressures. For alloy 6Al-4V it leads to a 50% decrease of the pressures on the punches. Fig. 3 shows the dependence, which makes it possible to reveal the change in the pressure of the bar extrusion in the orthogonal planes, depending on the relative pressing punch stroke. An increase in the relative strokes of the deforming punches for titanium 6Al-4V leads to an increase in pressures on the deforming tool by 20%, and for aluminum AA5086 -by 45%. Fig. 4 shows the dependence that reveals the change in the bar extrusion pressure in orthogonal planes with an increase of the Coulomb friction coefficient.

Fig. 4. Graphs for the extrusion of a bar in orthogonal planes
The growth of Coulomb friction coefficient leads to an increase in pressures on the deforming tool by 15% for titanium 6Al-4V, and for aluminum AA5086 -by 17%.
Isothermal piercing. Piercing operation is used for the formation of holes in solid metal bodies. It is the second stage in the cycle of operations for the manufacture of connectors after the extrusion of the bar in orthogonal planes. Fig. 5. shows the scheme of the analyzed process.
Using the energy calculation methods [3], we obtained the expressions for calculating the powers in various elements of the selected velocity field [3].
The power of the internal forces in the deformation block is: where gr.c.. .
The powers of the internal forces on line "13" is [3]: The friction power of workpiece material is [3]: Here q is the piercing pressure; п S , м S are the areas of friction surfaces on the punch and the die.
The maximum piercing pressure is [3]: To find the pressure substituting formulas (7-11) into expression (12) After performing the calculations, the piercing pressure was estimated depending on the degrees of deformation and the velocity of piercing punches for alloys AA5086 and 6Al-4V. Their temperature modes were С°450 and С°930 respectively. Fig. 6 shows the obtained dependences of the pressure change during the piercing, depending on the speed of movement of the piercing punches for the investigated nonferrous alloys.  Fig. 6, with an increase in the velocities of piercing punches' movement, a 27% increase in pressure on them is observed for the AA5086 alloy and 35% increase -for the 6Al-4V alloy. Fig. 7 shows the obtained dependences of the change in pressure during piercing, depending on the relative value of the diameter of the pierced hole. The growth of the relative value of the pierced hole diameter, according to Fig. 6, leads to an increase in pressures on the deforming punches by 1.9 ... 2.1 times for the alloys under study. It should be said that the lines of pressure change first demonstrate a decrease in their values by 5%, and then a 2-fold increase.

Conclusion
This mathematical modeling made it possible to obtain expressions describing the power parameters of the T-shaped tubes' production from high-strength alloys. On the basis of the modeling results, the studies of the influence of the deformation on the pressure of the processes were carried out. The studies have confirmed their significance for the growth of