RU2247639C1 - Method for friction welding of aluminum alloy butt joints - Google Patents

Abstract

FIELD: processes of butt joining of parts of aluminum alloy with low welding capability.

SUBSTANCE: method comprises steps of preliminarily making through opening in butt of parts and introducing into it bit of rotating tool until tool shoulder touches surface of parts; inclining axis of opening by angle α = (0.8 -1.0)δ (δ - thickness of parts) relative to line normal to surface of parts in plane of their butt; setting diameter of opening D = d +(0.10 -0.15) mm; immersing bit of tool into butt by value consisting (0.90 - 0.95)δ; regulating motion speed of tool along butt of parts in range 0.20 - 0.35 mm/rev.

EFFECT: enhanced quality of butt joints, decreased number of tool failures.

4 dwg, 1 tbl

Description

The invention relates to the field of welding and can be used in butt joints of aluminum alloys having low weldability.

A known method of friction welding of cylindrical parts (WMThomas, EDNicholas, ERWatts and DGStaines. Friction Based Welding Technology for Aluminum. Materials Science Forum Vols. 396-402 (2002) pp. 1543-1548. 2002. Trans Tech Pablications, Switzerland Fig. 1a). The parts to be joined are arranged to provide dry friction in contact between them. With rapid rotation on abutting surfaces, surface contaminants are destroyed, the joints are heated to the plastic state of the material and a joint is formed during upsetting. The disadvantage of this welding method is its limited use only for connecting cylindrical parts and the formation of burrs in the connection zone. The formation of burrs requires mechanical processing of the joint after welding.

A known method of friction stir welding (UK patent No. 9125978.8), in which welding is carried out in three stages. At the first stage, a cylindrical or step-shaped tool with a shoulder rotating at high speed is immersed in the joint of the parts to be joined to a depth approximately equal to their thickness. When the shoulder of the tool comes into contact with the surface of the parts, immersion is stopped and the tool is moved along the connection line. At the third stage (at the end of welding), the rotating tool is lifted and removed from the joint. The disadvantage of this method of friction stir welding is the increased wear of the tool when it is inserted into the joint of the parts, as well as its breakage during welding of sheets 5-6 mm thick due to insufficient heating of the root part of the joint.

The closest in technical essence to the claimed one is a method of friction stir welding, in which a through hole with a diameter greater than the diameter of the tool tip is preliminarily made at the junction of the parts to be joined (WMThomas, EDNicholas, ERWatts, DGStaines. Friction Based Welding Technology for Aluminum. Materials Science Forum Vols. 2002. pp. 1543-1548). Then the rotating tool is immersed in the hole until the shoulder contacts the surface of the parts. When the shoulder of the tool comes into contact with the surface of the parts, immersion is stopped and the tool is moved along the connection line. The disadvantage of this method is the frequent failure of the tool due to chipping of the tip in the root of the connection, as well as the layer-by-layer arrangement of oxide films in the weld. The latter phenomenon leads to a significant decrease in the strength properties of the compounds, especially with cyclic loads.

The proposed method of friction welding of butt joints of aluminum alloys ensures complete penetration of the parts, forms the root of the seam of a more uniform shape with minimal technological allowance. This technique does not require an increase in the thickness of the workpieces, which reduces the cost of subsequent machining of the welded joint. The selected ratio of the speed of rotation of the tool and the speed of its movement along the junction of the parts to be joined promotes the qualitative formation of their connection and the finely dispersed distribution of fragments of oxide films.

The technical result to which this invention is directed is achieved by making a through hole at the joint of the parts to be welded at an angle α to the normal to the surface of the parts into which a rotating tool consisting of a tip in the form of a body of revolution with a shoulder is immersed until the latter contacts the surface of the parts moreover, the angle α of the axis of the through hole is determined by the ratio α = (0.8-1.0) δ, with the hole diameter specified in the range D = d + (0.10-0.15) mm, the immersion depth of the tip of the rotating tool and the hole is (0,90-0,95) δ, where δ - thickness of the parts and movement speed of the rotary tool along the joint parts is adjustable between 0.20-0.35 mm / rev.

In more detail the essence of the proposed method is illustrated by drawings:

figure 1 - shows a schematic diagram of the method (the beginning of the process);

figure 2 - shows a diagram of the formation of the connection in the process of moving the tool;

figure 3 - appearance of the root part of the connection with different values of the depth of the tool;

figure 4 - microstructure in the joint zone of the alloy 1460.

The proposed method of friction welding is as follows.

Parts 1 are installed in a welding fixture (not shown in the drawing). In the plane of their junction of parts at an angle α to the normal to their surface, a through hole 2 with a diameter of 0.1-0.15 mm is larger than the diameter of the tip of the tool 3. The angle is set in the range (0.8-1.0) δ, where δ is the thickness of the parts. Then a tool 3 is placed in the hole 2, consisting of a tip 4 in the form of a body of revolution and a shoulder 5. The tip 4 is buried in the hole 2 by 0.90-0.95 of the thickness of the parts until the shoulder 5 contacts the surface of the part. Then the tool 3 is brought into rotation and set its movement along the joint line of the parts within 0.20-0.35 mm / rev. When moving the rotating tool 3, the metal 6, heated by friction of the shoulder 5 on the surface of the parts, in a solid-liquid state enters along the generatrix of the tip 4 and forms a melt 7. The formation of the melt 7 is carried out due to the metal of the technological allowance 8 (Fig. 2).

When the angle α is less than 0.8δ, the frequency of breakdowns and tool wear is observed, which is typical for the case of welding without first making a through hole. If the angle exceeds 1.0δ, disturbances are observed in the metal transfer on the peripheral part of the shoulder 5 and the formation of discontinuities in the central part of the seam.

The depth of the rotary tool 3 in the thickness of the part determines the quality of formation of the root part of the seam. With a depth of less than 0.90δ, incomplete penetration of parts is observed, which is unacceptable for critical structures. When the rotary tool 3 is deepened more than 0.95δ, the metal is intensively displaced into hole 2 and the root of the weld is formed of an uneven shape with a penetration height of up to 2-3 mm. This leads to an increase in the necessary technological allowance from the impact of the shoulder 5 and a corresponding increase in the thickness of the workpieces and the cost of machining them after welding. In some cases, when limiting the thickness of the workpieces, this condition cannot be fulfilled. Therefore, the deepening of the tool 0.90-0.95 of the thickness of the parts should be considered optimal.

The quality of the formation of the compound and the distribution of fragments of oxide films in it is significantly affected by the ratio of the rotation speed of the tool 3 and the speed of its movement along the junction of parts. When the specified tool moves along the joint with a speed of less than 0.20 mm / rev, overheating of the metal in the joint zone, the formation of zones with a high content of oxide film fragments in the weld metal are observed. Ultimately, these phenomena affect the reduction of the mechanical properties of welded joints. The increase in the speed of movement of the tool 3 more than 0.35 mm / rev leads to the formation of microvoids in the seam and increase the frequency of exit of the said tool from failure due to breakage.

Experiments were conducted on welding samples of alloys D16 and 1460 with a thickness of 3 mm. Welding of samples was carried out on a milling machine equipped with a special fixing device for installing samples. For welding, tool 3 was used, consisting of a conical tip 4 with a height of 3.5 mm (with bases 3.0 and 3.5 mm) and a shoulder 5 with a diameter of 12 mm. The tool was made of heat-resistant alloy ХН55ВМКТЮ. The working part of the shoulder 5 was polished. When welding, the rotation speed of the tool 3 was 900 rpm. The results are shown in the table.

The experiments showed that when the depth of the tool 3 into the hole 2 changes, the nature of the formation of the root of the seam changes. So when the depth of the tool is less than 0.90 δ (2.7 mm) in the root of the seam is formed lack of penetration (figa). When deepening at the level of (0.90-0.95) δ, a uniform bead is formed in the root of the seam (Fig.3b), and the allowance on the front side of the joint is 1-1.5 mm. With a depth of more than 0.95 δ (2.85 mm), the root bead is formed uneven with separate thickenings, and the size of the necessary allowance on the front side increases to 2.7-3.1 mm (Fig.3c).

Using this method allows to obtain high quality welded joints from aluminum alloys with low weldability. The quality of the compounds obtained is confirmed by studies of the microstructure of welded joints of alloy 1460 (figure 4).

Claims (1)

A method of friction welding of butt joints of aluminum alloys, in which a through hole is preliminarily made at the junction of the parts, into which a rotating tool consisting of a tip in the form of a body of revolution with a shoulder is immersed until the shoulder contacts the surface of the parts, characterized in that the axis of the hole is placed under angle α to the normal to the surface of the parts in the plane of their junction, defined by the relation α = (0.8 ÷ 1.0) δ, the hole diameter is set within D = d + (0.10 ÷ 0.15) mm, the tip is buried in the joint by (0.90 ÷ 0.95) δ, where δ is the thickness on the parts, and the speed of movement of the tool along the junction of the parts is regulated within 0.20 - 0.35 mm / rev.

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