RU2708724C1 - Method of electron-beam welding of annular connection of thin-wall shell with cylindrical cover, made of high-strength aluminum alloys - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention relates to a method of electron-beam welding of annular connection of thin-walled structures from high-strength aluminum alloys. In cylindrical cover top surface peripheral part annular groove is made with section of at least 3×3 mm. Shell is installed on the cover with a gap of not more than 0.1 mm, the shell edge is shifted down at distance δ from cover upper surface. On external surface of shell is tightly installed copper ring with width of at least 2δ and height of not less than 20δ, shifted down at distance δ from shell of shell ring. Shell is pre-fixed on the side surface of the cylinder with an electron beam at 12 diametrically opposite points. Annular seam is made in vacuum chamber at orientation of shell-centered shell at distance of 0.4δ from its inner surface of the electron beam at angle of 30 degrees to the surface of the shell during rotation of the welded article around the axis of symmetry. Thickness of the cover wall in the groove area, angular rotation speed of the article being welded, accelerating voltage, electron beam current and linear welding speed are selected in accordance with preset ratios related to thickness of shell δ and cover radius R.

EFFECT: invention can be used for making light structures with high strength and tightness requirements.

1 cl, 5 dwg, 1 ex

Description

The invention relates to a technology for electron beam welding of an annular connection of thin-walled structures from high-strength aluminum alloys, in particular for the manufacture of assemblies consisting of a thin-walled shell and a cylindrical cover. The inventive method can be used in the manufacture of lightweight welded structures for aviation and space technology with increased requirements for strength and tightness of joints (for example, gyroscopes for artificial Earth satellites).

A known method of electron beam welding of a thin-walled pipe with a thin-walled bimetallic adapter [1]. Before welding, the welded end of the pipe is distributed into a cone, no larger than 14 degrees, and a centering ring protrusion is performed at its end. The welded end of the bimetallic adapter is given a similar conical shape and a centering ring groove is made at its end under the annular protrusion at the end of the pipe. Welding is performed by the heating spot of the electron beam with a welding speed of not more than 20 m / h (5.6 mm / s), while the heating spot of the electron beam is oscillated with a frequency of not more than 50 vibrations per second symmetrically to the junction line.

The proposed method is time-consuming and requires the completion of parts before welding (cone, annular groove and protrusion), which is not allowed in the manufacture of precision products.

A known method of electron beam welding of thin-walled pipes made of molybdenum alloys [2]. The proposed method is characterized in that before joining the pipes, filler material is placed between them in the form of an insert of a molybdenum-rhenium alloy, the dimensions of which provide a rhenium content of at least 11%. The pipes are joined with axial force and the insert is fixed by an electron beam at several points. The joint is heated with a defocused beam to a temperature of (80 ÷ 900) ° C. Welding is carried out at a speed of (24 ÷ 26) mm / s.

The closest in technical essence is the selected for the prototype method of electron beam welding of ring compounds of titanium alloys [3]. The method includes preparing the edges for welding, assembling the joint and welding with an electron beam with the beam focus above the surface of the welded product. In this case, an electron beam with a circular scan is focused on a distance from the surface of the welded edges of at least two and not more than three thicknesses of the welded joint.

A common disadvantage of the methods [1-3] is the lack of requirements for the temperature of the heating units of the welded product, which are presented to welding as a finishing operation of the process. In this case, it is unacceptable to heat the components inside the product (printed circuit boards, microcircuits, radioelements, etc.) above 80 ° C.

In addition, when welding precision manufactured parts, their additional machining for welding without subsequent stress relieving during processing is unacceptable. This can lead to a change in the size of structural elements (misalignment, the appearance of an ellipsoidal configuration, etc.).

The technical result of the present invention is the development of a method of electron beam welding of thin-walled structures made of hardened aluminum alloys, which provides high-quality ring joints with increased requirements for strength and tightness.

The technical result is achieved by the fact that a method of electron beam welding of an annular connection of a thin-walled shell with a cylindrical cover made of hardened aluminum alloys is developed, including preparing the connection for welding, assembling the joint and welding it with an electron beam. In the peripheral region of the upper surface of the cylindrical cover, an annular groove is made with a cross section of at least 3 × 3 mm. The shell and lid are heat treated to relieve residual stresses. The shell is mounted on the cover with a gap of not more than 0.1 mm; the cut of the shell is shifted downward by a distance δ from the top surface of the cover. On the outer surface of the shell tightly install a copper ring with a width of at least 28 and a height of at least 20δ, shifted downward by a distance δ from the cut of the shell. The casing is preliminarily fixed on the lateral surface of the cylinder by an electron beam at 12 diametrically opposite points evenly spaced around the circumference of the ring joint. The ring joint is welded in a vacuum chamber when the shell is focused on the end of the shell at a distance of 0.4δ from its inner surface of the electron beam at an angle of 30 degrees to the shell surface when the article being welded rotates around the axis of symmetry. The wall thickness of the lid in the groove area and the angular velocity of rotation of the welded product are determined in accordance with the ratios

Where

B is the wall thickness of the cylindrical cover in the groove area, m;

δ is the shell thickness, m;

n is the angular velocity of rotation of the welded product (revolution / s);

R is the radius of the cylindrical cover, m;

u is the linear welding speed, m / s.

The values of the accelerating voltage, electron beam current, and linear welding speed are selected in accordance with the ratios

U = 28⋅10 ³ V; I = 25⋅10 ^-3 A; u = 25⋅10 ^-3 m / s.

The positive effect of the invention is due to the following factors.

1. An annular groove made in the peripheral region of the upper surface of the cylindrical lid limits heat removal from the welding site deep into the lid, which reduces the required value of the electron beam power, eliminates shell burn-through and heating of the product to temperatures above 80 ° C. The cross section of the groove (at least 3 × 3 mm) was determined experimentally.

2. Heat treatment of the shell and lid before the welding operation relieves residual stresses arising from the machining of product parts. This prevents possible deformation of the elements of the product during welding.

3. The gap between the shell and the cylindrical cover (not more than 0.1 mm) ensures high-quality formation of the weld.

4. The offset of the cut of the shell from the upper surface of the lid eliminates the burn through of the shell and allows you to get a tight welded joint. The amount of displacement equal to the shell thickness δ was selected experimentally.

5. The installation of a copper ring on the outer surface of the shell provides intensive conductive heat removal (due to the high value of the coefficient of thermal conductivity of copper) from the welding zone to prevent overheating of the product and reduce deformation and welding stresses. The dimensions of the ring (height not less than 20δ and width not less than 2δ), as well as the magnitude of its displacement from the end of the shell (by a distance of δ) were selected experimentally.

6. Preliminary fixing of the shell on the side surface of the cylinder at 12 diametrically opposite points prevents the displacement of parts during welding.

7. The operation of welding in a vacuum chamber increases the efficiency of electron beam welding, because in this case, there are no energy losses in the collision of electrons with gas molecules. In addition, when welding in vacuum, the quality of the joint increases (the absence of the introduction of impurities of atmospheric air components into the molten metal).

8. Orientation of the electron beam at an angle of 30 degrees to the surface of the shell, focused on the end of the shell at a distance of 0.4δ from its inner surface, provides the required penetration depth and eliminates the formation of lack of penetration or through burns. The specified beam parameters are determined experimentally.

9. The wall thickness of the lid in the groove area, defined by relation (1), is selected according to the results of testing the welding technology and ensures high-quality weld penetration.

10. The angular velocity of rotation of the welded product, defined by relation (2), is selected from the condition of ensuring the necessary linear welding speed u. It is known that the tangential speed of rotation of a point located at a distance R from the axis of rotation is determined by the formula

From (3) follows the relation (2):

11. The values of the accelerating voltage U = 28 kV and the current strength of the electron beam I = 25 mA were determined experimentally during the development of the welding mode, as optimal when welding hardened aluminum alloys.

12. The linear welding speed u = 25 mm / s, selected according to the results of the development of the technology, is one of the important operating parameters providing crystallization of the molten weld metal, eliminating the possibility of the formation of hot cracks in the weld and in the weld zone. With the selected optimal value of the welding speed, the resulting product does not require cooling and additional heat treatment.

An example implementation of the method

The installation diagram for implementing the proposed method is shown in FIG. 1. The welded assembly, including the shell 1 and the cylindrical cover 2, is placed in the vacuum chamber 5.

The vacuum chamber 5 is equipped with a loading door 6, an inspection window 7, a vacuum gauge 8, and an air evacuation system through the nozzle 9. In the upper part of the vacuum chamber, an electron beam installation 10 of the ELS-0.5-6 type is installed with the possibility of varying the welding angle in the range α = (0 ÷ 45) degrees. The welded product is installed on the slipway 11.

As an example of the implementation of the method, welding of a shell with a thickness of δ = 1.1 mm and a cylindrical cover with a thickness of h = 30 mm and a radius of R = 200 mm made of hardened aluminum alloy grade 1370 was given. The shell, the lower part of which has a hemispherical shape, is made by drawing from an aluminum sheet and the lid - by milling from an aluminum plate. In the peripheral region of the upper surface of the cylindrical cover 2, an annular groove 3 is made with a cross section of 3 × 3 mm (Fig. 2).

The wall thickness of the lid in the area of the groove 3 is determined in accordance with the relation (1):

B = 2δ = 2⋅1.1 = 2.2 mm.

After machining, the shell and lid underwent additional heat treatment to relieve residual stresses.

The shell 1 was mounted on the cover 2 with a gap of 0.1 mm, while the cut of the shell 1 was shifted downward by a distance δ = 1.1 mm from the upper surface of the cover 2 (Fig. 3). On the outer surface of the shell 1, a copper ring 4 was tightly mounted with a width of 2δ = 2.2 mm and a height of 20δ = 22 mm (Figs. 2, 3). In this case, the ring 4 was shifted downward by a distance δ = 1.1 mm from the cut of the shell (Fig. 3).

After assembly, the welded assembly was mounted on the rotating stock 11 and fixation (tacking) of the shell 1 by the electron beam to the shell 2 was carried out at 12 diametrically opposite points evenly spaced around the circumference of the ring joint.

The product prepared for welding was placed in a vacuum chamber 5, which was pumped out through a pipe 9 to vacuum (10 ^-4 Torr).

Using the control unit of the slipway 11, the welding angle α = 30 degrees was established (Fig. 2, 3) and the ring joint was welded when the slipway 11 was rotated with the product installed on it. The angular speed of rotation of the slipway is determined in accordance with the relation (2):

A general view of the installation for implementing the proposed method is shown in FIG. 4. A photograph of the welded ring joint is shown in FIG. 5.

Obtained using the proposed method of electron beam welding, the product (gyroscope case for an artificial Earth satellite) passed a cycle of strength and leak tests, which confirmed the required qualities of the ring connection presented to space products.

LITERATURE

1. RF patent №2329127, IPC В23К 15/00, В23К 31/02, В23К 33/00. The method of electron beam welding of a thin-walled pipe with a thin-walled bimetallic adapter / A.N. Semenov, E.F. Kartashev, A.A. Karpunin, V.N. Tyurin, V.P. Proudly, G.N. Shevelev; publ. 07/20/2008 Bull. No. 20.

2. RF patent No. 2664746, IPC V23K 15/04, V23K 9/23, V23K 33/00, V23K 35/32. The method of electron beam welding of thin-walled pipes from molybdenum alloys / A.R. Abitov, V.I. Retired, E.G. Kolesnikov A.V. Arriving, V.A. Tolechennikov; publ. 08/22/2018 Bull. Number 24.

3. RF patent No. 2644491, IPC V23K 31/02, V23K 15/02, V23K 33/00, V23K 101/06. The method of electron beam welding of ring compounds of titanium alloys / A.V. Grebenshchikov, A.I. Tailors, L.P. Shuvaev, M.V. Eremin; publ. 02/12/2018 Bull. No. 5.

Claims (3)

A method for electron beam welding of an annular connection of a thin-walled shell with a cylindrical cover made of hardened aluminum alloys, including preparing the connection for welding, assembly and electron beam welding, characterized in that when preparing the connection for welding, an annular groove is made in the peripheral region of the upper surface of the cylindrical cover with a cross section of at least 3 × 3 mm, and the wall of the lid in the groove area with a thickness of B = 2δ, where δ is the shell thickness, m, and the shell is heat-treated and cr shanks to relieve residual stresses, then the shell is mounted on the cover with a gap of not more than 0.1 mm, while the cut of the shell is shifted downward by a distance δ from the top surface of the cover, a copper ring is tightly installed on the outer surface of the shell with a width of at least 2δ and a height of at least 20δ with an offset downward by a distance δ from the cut of the shell, and the shell is pre-fixed on the lateral surface of the cylinder with an electron beam at 12 diametrically opposite points evenly spaced around the circumference of the ring connection, and the welding of the ring joint is performed in a vacuum chamber with the orientation of the electron beam focused on the end of the shell at a distance of 0.4δ from its inner surface and at an angle of 30 degrees to the surface of the shell during rotation of the welded product around the axis of symmetry with an angular rotation speed n = u / 2πR where n is the angular velocity of rotation of the welded product (revolution / s), R is the radius of the cylindrical cover, m, u is the linear welding speed, m / s, and the values of the accelerating voltage U, current I of the electron beam and linear welding speed u are selected in according to the ratios: U = 28⋅10 ³ V; I = 25⋅10 ^-3 A; u = 25⋅10 ^-3 m / s.

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