RU2418664C1 - Method of friction welding with mixing of tee joints and tool to this end - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention may be used for making T-section parts and ribbed thin-sheet panels mainly from aluminium alloys. Proposed tool comprises mandrel with support collar accommodating two-step working rod aligned therewith. Smaller-diametre additional rod arranged on lower end face of the main rod features narrowing taper working surface. Additional rod base diametre makes 0.5-0.6 of the main rod base diametre. Diametre of end face nearby its top makes 0.4-0.5 of rib thickness while height makes 0.8-1.0 of tee joint rib thickness. Larger-diametre working surface is intended for processing flange while smaller-diametre serves to process rib. Working rod is lowered allows additional rod to penetrate the rib to depth equal to 0.7-0.9 of rib thickness.

EFFECT: smooth conjugation between rib surface and flange with angle chamfers.

2 cl, 7 dwg

Description

Technical field

The invention relates to technological processes, more specifically to a technique for the production of welded structures, namely to friction welding of stirring by a rotating tool, and can be used to manufacture parts, mainly from aluminum alloys, with a cross section in the form of a profile, for example, T-shaped, as well as in the form of finned thin-sheet panels in aerospace, engineering, construction and other industries.

State of the art

The manufacture of profile parts, including finned panels, faces a number of difficulties: the high complexity of machining, especially hard-to-process materials; the lack of large blanks of the required shape, low material utilization.

There is a well-known practice of manufacturing ribbed panels from a titanium alloy by arc welding through penetration of a brand shelf (A. S. Zazhigin et al. “Technology for welding and heat treatment of a center section panel of an airplane made of VT20 alloy.” “Aviation Industry”, 1982, No. 6, p. 9-11). However, arc welding is associated with the melting of metal and can hardly be used to connect structurally difficult to weld by fusion.

In recent years, it has received practical application, in particular for producing T-profiles, the process of welding in the solid phase by friction with stirring, which proceeds without melting the metal.

A known method of manufacturing parts by friction stir welding, including fixing the elements to be welded, introducing a rotating working rod into contact with the parts to be joined, moving the working rod relative to the elements being welded so that the heat generated by friction translates the elements into a plastic state. The method is also characterized in that one of the elements to be welded is insulated to prevent heat dissipation (see US Pat. No. 6,380,937, B23K 20/12, 2002).

The traditional friction stir welding tool (Fig. 1) is a mandrel mounted in the spindle and bearing a cylindrical or conical working rod on its support collar. The surface of the working rod may have a relief of various shapes (for example, screw cutting, protrusions, etc.). In a traditional friction welding tool, the main parameters are as follows: the length L of the working rod of the tool, which is approximately equal to the thickness of the metal being welded; diameter d of the base of the working shaft of the tool (usually more than 5 mm for reasons of strength of the tool); the diameter of the support collar D is approximately 2.5-3 the diameter of the working rod; the taper of the working rod is approximately no more than 3%, which ensures uniform friction along the entire length of the rod and facilitates the removal of the tool from the hole at the end of welding (Shtrikman M.M. “Status and development of the friction welding process of linear joints (overview). 4.2. Tool improvement and technological schemes of welding. ”“ Welding Production ”, 2007, No. 10, p.25-32).

The friction stir welding process involves three main steps. At the first stage, the working shaft of the tool rotating at a high speed is brought into contact and immersed in welded sheets, rigidly fixed in a snap, to a depth approximately equal to its thickness. When the tool shoulder comes into contact with the surface of the welded sheet, stop immersion and proceed to the second stage of the process - moving the rotating welding tool along the entire length of the connection. At the third stage (at the end of welding), the rotating welding tool is lifted and removed from the hole and the parts are cooled.

A known method of welding T-joints is Raj Talwar, Dave Bolser: “Friction Stir Welding of airframes structures”, 2 International Symposium on Friction Welding with Stirring, Session 9, June 26-28, 2000, Sweden. However, the resulting parts with this method do not have a smooth pairing of the surfaces of the ribs and shelves (the presence of fillets in the corners of the brand). The connection with a sharp intersection of the surfaces of the flange and the rib (stress concentrator), as well as with the cracks between the flange and the flange, cannot work for a long time under cyclic loading, especially in an aggressive environment due to the development of crevice corrosion.

In (G. Buffa, L. Fratini: “Material flow in FSW of T-joints: experimental and numerical analysis”, ESAFORM. Conference on materials forming, France, 2008), the authors propose a circuit with a traditional tool for friction welding connection with fillets (prototype). However, at least two drawbacks of such a scheme raise doubts about its applicability for welding thin-sheet structures.

In this work, the authors use the following welding parameters for the T-profile: with a rib thickness of 3 mm and a maximum fillet radius of 3.5 mm, a traditional tool with a working rod of 4 mm in length and 4 mm in diameter, immersed to a depth of 4.2 mm, is used. If we take into account possible deviations of the tool from the axis of the ribs during welding, we can conclude that the working rod of the tool is immersed over the entire thickness of the shelf and it cannot be embedded in its end of the ribs to the depth necessary to obtain a strong connection. Thus, in the zone of mating surfaces creates a zone of non-fusion due to its greatest distance from the heat source (working core of the tool). It is impossible to reduce the diameter of the working rod for reasons of its operability, especially considering the presence of a deep relief on its surface; to increase the radius of the fillets (to increase the space for deeper immersion of the tool in the rib) is also not possible due to the following prototype disadvantage.

To smoothly pair the flanges 4 and ribs 5 during assembly and fixation for welding of the brand from sheet blanks, pads 6 and 7 are used (see figure 2). The edge of the brand is installed between the forming pads in such a way that its upper end is located approximately at the level (not lower) of the upper surface of the pads and compress them. In this case, the edge of the rib from the pinch line of its linings to the upper end remains free like a console. As a result of the influence of a traditional rotating working tool rod on the edge of the edge of the rib, it heats up and experiences high stresses from compression forces and torque. Thus, conditions are created for uncontrolled deformation of the edge of the rib, the greater the greater the radius of the fillet, and, as a result, the violation of the accuracy of the assembly and the stability of the quality of the T-joint.

Thus, the known methods of welding T-joints do not allow to obtain parts such as high-quality brands.

SUMMARY OF THE INVENTION

The objective of the invention is the development of such a method of friction welding with mixing of T-joints and a tool for its implementation, which provided the possibility of manufacturing thin-sheet parts and units of profile section such as T-bars or ribbed panels with smooth conjugation of the surfaces of the ribs and shelves (with fillets in the corners).

The solution to the problem is achieved in that in a method of friction welding with stirring of T-joints containing a shelf and a rib, including immersing in a tool’s parts to be welded in the form of a working core of high strength material rotating at a high speed, moving it along the entire length of the joint, and removing the core from the joint and part cooling, immersion and movement of the tool is carried out with a working core having a working surface of a larger diameter for processing the shelf and a working surface of a smaller diameter meter for processing the ribs, while immersing the working core is performed before the additional rod is immersed in the rib to a depth equal to 0.7-0.9 thickness of the rib.

In addition, in a tool for friction welding with stirring of T-pieces, including a shelf and a rib, containing a mandrel with a supporting collar, bearing a working core coaxially mounted with it, the working core is made in two stages with a main rod bearing an additional rod at its lower end having a smaller than the diameter of the main rod, while the additional rod is conical, tapering to the bottom, with a base diameter equal to (0.5-0.6) the diameter of the end face of the main rod, and the diameter at the apex are 0.4-0.5 rib thickness.

This embodiment of the method and the tool allows to obtain high quality T-joints by eliminating the causes of discontinuities between the fillet and the rib and providing parts with fillets at the junction.

List of figures

The invention is illustrated by drawings, in which:

Figure 1 shows a General view of a tool for welding with a traditional working rod;

Figure 2 shows a traditional assembly and fixing pattern for welding sheet elements;

Figure 3 shows a General view of the tool for friction welding of the T-joints, made in accordance with the invention;

Figure 4 shows the working rod (on an enlarged scale) of a friction welding tool of a T-joint made in accordance with the invention;

Figure 5 shows a view along arrow A of Figure 4;

Figure 6 shows the welding circuit before starting it;

Figure 7 shows a tool immersed in a rib (during welding);

The implementation of the invention

In accordance with the invention, a method of friction welding with stirring of T-joints containing a shelf and a rib includes immersing a tool in the form of a working core of high strength material rotating at a high speed and moving it along the entire length of the joint, removing the core from the joint and cooling the part.

The tool is immersed and moved with a working core having a larger diameter working surface for processing the shelf and a smaller diameter working surface for processing the rib. Immersion of the working core is carried out before its introduction into the rib. In this case, the working core is immersed with its penetration into the rib material to a depth equal to 0.7-0.9 of the rib thickness.

A tool for friction welding with stirring of T-pieces, including a shelf and a rib, contains a mandrel 8 with a supporting collar 9, carrying a working core 10 mounted coaxially with it (see Figs. 3, 4).

The working core 10 is made in two stages, with the main shaft 11 bearing an additional shaft 12 at its lower end, having a diameter smaller than that of the main shaft. The additional rod 12 is made conical, tapering to the bottom, with a base diameter equal to (0.5-0.6) of the end diameter of the main rod, a diameter at the apex equal to 0.4-0.5 of the thickness of the rib of the welded T-joint, and a height of equal to 0.8-1.0 thickness of the ribs.

When the diameter of the base of the additional shaft D is less than 0.5 · d _PC , the strength is lost, which entails a reduction in the working life of the tool. When the diameter of the base of the additional rod D is greater than 0.6 · d _PC , on the one hand, the fillet is less compacted by the annular platform of the end of the support collar, and on the other, the edges of the end of the rib begin to bend, which leads to a decrease in the friction force, heating and, as a result, the quality of the connection.

When the diameter of the end face of the additional rod at its apex is d _P , less than 0.4 · δ _P , the volume of the processed material is reduced, thereby reducing the thermal effect of the friction forces. A value greater than 0.5 · δ _P can lead to loss of stability of the free edge of the rib, its deformation, and there is also a danger of bending the edges of the edges from the end of the rib, which entails their exit from the processing zone of the tool and a decrease in heating. Thus, the specified interval provides a good entry of the tool into the end face of the rib and keeps the edge from moving off axis.

The selected height of the additional rod L _P allows thermomechanical study and formation of the connection of the ribs with the fillet.

To increase the intensity of thermomechanical processes in the joint zone in order to improve the structure of the weld material and its properties, the surface of the additional rod may have a different relief.

A tool with an additional rod for welding the T-joints of aluminum alloys can be made of tool steel (for example, 4X4 VMFS, 4HZVMF, etc.) or high-speed tool (P18, P6M5, etc.) with subsequent hardening according to reference data. The welding tool with an additional core is made by high-precision milling on a CNC machine. After the heat treatment, the desired relief (for example, screw thread) is cut on the surface of the working rod.

The welding method is implemented as follows.

Sheet blanks: the shelf 13 and rib 14 are assembled for welding (see figure 6), for which a blank of rib 14 is installed between two linings 15 and 16 of heat-resistant steel with rounded upper, inner corners forming fillets 17 in the corners of the brand, so that the end face of the rib was at the level of the upper surface of the linings 15, 16, and compress it with the linings 15, 16. Then lay the shelf 13 on the upper end of the ribs 14 and on the linings 15, 16 and in this position press the shelf 13 to the linings 15, 16 and to the end ribs.

At the beginning of the welded joint, the rotating tool 18 is brought up with the top of the additional rod 20 to the surface of the shelf 13 at a point opposite the midline of the end face of the rib 14 until it touches the surface of the shelf 13 (Figure 6) and is immersed until the support collar 21 contacts the surface of the shelf 13 (Figure 7). In this case, the additional rod with the vertex is immersed in the end face of the rib 14 to a depth of h = (0.6 ... 0.8) · r.

When the additional rod is immersed in the end of the rib to a depth h of less than 0.7 · δ _P , stable fusion of the rib with the fillet in the zone of their conjugation is not achieved. If the immersion depth is greater than 0.9 · δ _P , the contact of the working shaft of the tool with the fillet-forming surface of the pads and a violation of the process are possible.

Then, without stopping the rotation of the tool, move it in the direction along the end face of the ribs 2 with a welding speed. At the end of the welded joint, the tool 5 is stopped moving along the rib and, continuing to rotate, is withdrawn from the shelf 13 until the contact with it ceases. After that, the rotation of the tool is stopped and it is removed from the finished seam and the welded part is cooled.

Feasibility

The use of friction welding for the manufacture of T-welds from sheet blanks of predominantly aluminum alloys, including high-strength and difficult to weld, compared to traditional methods of fusion welding, will increase the working life of the joint and reduce and / or eliminate:

- special methods of surface preparation before welding (chemical milling, mechanical cleaning, etc.);

- costs of additional welding consumables (filler wire, shielding gas, etc.);

- repair operations to remove defects in welded joints;

- operations of editing the structure after welding due to the absence of melting temperatures in the thermal cycle during welding and, accordingly, significant welding stresses that cause deformation and warping.

Claims (2)

1. A method of welding a T-joint with friction with stirring, containing a shelf and a rib, comprising immersing a tool in the form of a rotating working core in the parts to be welded, moving it along the length of the connection, removing the core from the connection and cooling the part, characterized in that they use a tool having a working a core containing a main rod for processing the shelf and an additional rod of a smaller diameter placed on its lower end for processing the ribs, while the working core is immersed lead with the penetration of an additional rod into the material of the ribs to a depth equal to 0.7-0.9 thickness of the ribs. 2. A tool for welding a T-joint with friction with stirring, containing a shelf and a rib, including a mandrel with a support collar and a working core installed coaxially with it, characterized in that the working core contains a main core and an additional core of a smaller diameter placed on its lower end, having a tapering cone-shaped working surface, while the diameter of the base of the additional rod is 0.5-0.6 of the diameter of the said end of the main rod, the diameter of the end of the additional rod at e vertex is 0.4-0.5 rib thickness and the height of the rib thickness of 0.8-1.0 tee connections.

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