A clamp and method for friction stir welding of a skin to a stringer

Abstract

The application provides a clamp for skin and stiffener friction stir welding, which comprises: a base arranged on a machine tool; a plurality of I-beams arranged on the base; wherein the stiffener is arranged on the I-beam, and the skin is arranged on the stiffener; a plurality of clamping top frames, the clamping top frames are located above the corresponding skins, the two ends of the clamping top frame are arranged on the base, and the middle part of the clamping top frame is used for pressing the skin and the stiffener; meanwhile, the application also provides a method for skin and stiffener friction stir welding; the application solves the problem that the traditional clamp is difficult to clamp the to-be-welded part when welding a plurality of welds on the same plane, and reduces the possibility of welding deformation.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of aircraft skin manufacturing, and particularly relates to a clamp and method for friction stir welding of a skin and a stiffener. BACKGROUND

[0002] The stiffened skin is a typical structure form on an aircraft, which has been applied to a wing surface and a fuselage, etc. The stiffener greatly enhances the rigidity of the skin, and also bears part of the air force acting on the skin and transmits it to other components of the fuselage.

[0003] Riveting is the most commonly used connection method of the skin and the stiffener, which has been tested for a long time, and has high connection strength and is easy to replace. However, the rivet has a large number of structures, and the weight is obviously increased, so that the aircraft bears a large load, and stress concentration or cracks of the fuselage are easily caused, which causes a safety hazard.

[0004] The friction stir welding is a new solid-phase connection technology, which generates heat on the friction surface by using the relative movement between the welding contact end faces under the action of constant or increasing pressure and torque, so that the temperature in the welding seam area is increased, but the temperature is generally lower than the melting point of the material. The deformation resistance of the material is reduced, plastic flow occurs in the welding seam under the action of the top forging pressure of the stirring head, and the solid-state welding method is realized by molecular diffusion and recrystallization of the interface. The welding seam has good forming, and defects such as pores and cracks generated in traditional fusion welding are not easy to occur. The friction stir welding is particularly suitable for the connection of non-ferrous metals such as aluminum alloy, and has a wide application in the welding of spacecraft cryogenic containers, large light alloy structural parts, skin, and high-speed trains.

[0005] In the prior art, the locking and clamping are realized in the friction stir welding or the flat plate welding, so that the two plates in the middle are not cracked and the two plates are not warped during the flat plate welding process, and a welding joint with good performance is obtained. However, when multiple welds are present on the same flat plate, clamping cannot be performed, and welding cannot be performed. SUMMARY

[0006] The application aims to provide a clamp and method for friction stir welding of a skin and a stiffener, which are used to solve the problems of difficult clamping and welding deformation when the skin and the stiffener are welded.

[0007] In a first aspect, the application provides a clamp for friction stir welding of a skin and a stiffener, which comprises:

[0008] A pedestal is arranged on a machine tool.

[0009] A plurality of I-beams are arranged on the pedestal, wherein the stiffener is arranged on the I-beam, and the skin is arranged on the stiffener.

[0010] A plurality of clamping top frames are arranged above the corresponding skins, two ends of the clamping top frames are arranged on the pedestal, and the middle part of the clamping top frames is used for pressing the skins and the stiffeners.

[0011] Preferably, the pedestal comprises:

[0012] A bottom plate;

[0013] A plurality of first rectangular grooves are uniformly arranged in the middle region of the bottom plate, and the first rectangular grooves are used for mounting the I-beams.

[0014] Two second rectangular grooves are arranged on both sides of the bottom plate, and the second rectangular grooves are used for fixing two ends of the clamping top frame.

[0015] A rectangular clamping groove is arranged at the first end and the second end of the bottom plate, the first end is symmetrical to the second end, and the first end and the second end are close to the second rectangular groove; wherein the rectangular clamping groove is matched with the T-shaped groove of the machine tool, and the pedestal is fixed on the upper surface of the machine tool workbench through the first T-shaped bolt.

[0016] Preferably, the clamping top frame comprises a first top frame and a second top frame, and the first top frame and the second top frame are the same; wherein the first top frame is a π-shaped structure.

[0017] Preferably, the first top frame comprises:

[0018] A horizontal rod, the front end face of the horizontal rod is provided with a protrusion, and the protrusion is provided with a first threaded hole;

[0019] A vertical rod, one end of the vertical rod is connected with one end of the horizontal rod perpendicularly, and the other end of the vertical rod is horizontally provided with a connecting plate, and the connecting plate is provided with a bolt hole; wherein the horizontal rod and the vertical rod are coplanar.

[0020] Preferably, the pedestal further comprises:

[0021] A T-shaped groove is arranged below the second rectangular groove, and the connecting plate can be accommodated in the second rectangular groove;

[0022] A second T-shaped bolt, the head of the second T-shaped bolt can be accommodated in the T-shaped groove;

[0023] Wherein, the second T-shaped bolt passes through the bolt hole, and the cooperating nut fixes the first top frame and the second top frame at a suitable position on the pedestal.

[0024] Preferably, a protruding part is arranged on the vertical rod, and a second threaded hole is arranged on the protruding part, and the clamp further comprises:

[0025] A pin is arranged in the second threaded hole, wherein the pin is threaded;

[0026] A locking washer is connected with the pin, and is used to lock the first and second top frames to avoid shaking.

[0027] Preferably, the first rectangular groove is horizontally arranged in the middle region of the bottom plate, and the second rectangular groove is vertically arranged on both sides of the bottom plate.

[0028] Preferably, the clamp further comprises:

[0029] A pressing strip is arranged on the skin;

[0030] A pressing bolt is arranged in the first threaded hole, and the lower end surface of the pressing bolt abuts against the pressing strip.

[0031] Preferably, the reinforcing rib is Z-shaped, and the reinforcing rib is invertedly arranged on the I-beam.

[0032] In a second aspect, the application further provides a method for friction stir welding of a skin and a reinforcing rib, and the method comprises:

[0033] The reinforcing rib is invertedly arranged on the upper top surface of the I-beam, the skin is arranged on the reinforcing rib, and the pressing strip is arranged on the skin;

[0034] The reinforcing rib and the skin are pressed by the clamping top frame;

[0035] A friction stir welding tool obtains a working instruction, wherein the friction stir welding tool comprises a stirring head and a stirring needle, and the working instruction comprises a preset welding speed, a preset rotation speed and a preset inclination angle;

[0036] The stirring needle is inserted into the skin surface of the middle region based on the preset inclination angle, and the stirring head starts to weld the skin and the reinforcing rib of the middle region based on the preset welding speed and the preset rotation speed with the stirring needle;

[0037] After the skin and the reinforcing rib of the middle region are welded, the skin and the reinforcing rib of both sides are welded.

[0038] The application has the following beneficial technical effects:

[0039] The application plays a main positioning role on the skin and the reinforcing rib to be welded by the clamping top frame above and the I-beam below, solves the problem of difficulty in clamping the workpiece to be welded when the traditional clamp faces multiple welds on the same plane, reduces the possibility of welding deformation, and has high versatility when facing different weld widths because the distance between the clamping top frames is adjustable. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 is the overall structure assembly provided by the embodiment of the present application;

[0041] Figure 2 is the overall structure assembly provided by the embodiment of the present application;

[0042] Figure 3 is Figure 2 the side view of the explosion diagram;

[0043] Figure 4 is the schematic diagram of the clamping top frame provided by the embodiment of the present application;

[0044] Figure 5 is the main view of the pedestal provided by the embodiment of the present application;

[0045] Figure 6 is the top view of the pedestal provided by the embodiment of the present application;

[0046] Figure 7 is the schematic diagram of the I-beam provided by the embodiment of the present application;

[0047] Figure 8 is the schematic diagram of the limiting shell provided by the embodiment of the present application;

[0048] Figure 9 is the schematic diagram of the locking piece 2 provided by the embodiment of the present application;

[0049] Figure 10 is the schematic diagram of the locking piece 1 provided by the embodiment of the present application;

[0050] Figure 11 is the welding process flowchart provided by the embodiment of the present application;

[0051] Figure 12 is the multi-pass welding sequence schematic diagram provided by the embodiment of the present application Figure 1 ;

[0052] Figure 13 is the multi-pass welding sequence schematic diagram provided by the embodiment of the present application Figure 2 ;

[0053] Figure 14 is the multi-pass welding sequence schematic diagram provided by the embodiment of the present application Figure 3 . DETAILED DESCRIPTION

[0054] Please refer to Figures 1 to 14The application provides a friction stir welding clamp, which comprises two protruding rectangular clamping grooves arranged on the two sides of a base, the rectangular clamping grooves are matched with T-shaped grooves of a machine tool, the base is fixed on the upper surface of a workbench of the machine tool through T-shaped bolts, the upper surface of the base is provided with second rectangular grooves on the two sides, and the two sides of the base of a pair of clamping top frames are arranged in the second rectangular grooves on the upper surface of the base.

[0055] The lower side of the second rectangular groove is further provided with a T-shaped groove, the base of the clamping top frame is provided with a through hole, the T-shaped bolt is fixed on the upper surface of the base through a nut after passing through the through hole, and two clamping top frames are required for each weld to complete the clamping work.

[0056] The upper surface of the base is provided with five first rectangular grooves for mounting the I-beam, the I-beam is fixed on the base through the bolts after being arranged in the first rectangular grooves, the reinforcing rib is arranged on the upper surface of the I-beam, the skin is arranged on the reinforcing rib, the distance between the clamping top frames in the same group is adjusted according to the width of the required weld, the pressing bolt is screwed into the first threaded hole in the side surface of the clamping top frame, the pressing strip is arranged on the skin, the lower end surface of the pressing bolt abuts against the pressing strip, and the skin and the reinforcing rib are pressed on the I-beam by screwing the pressing bolt.

[0057] In other embodiments of the application, the application further discloses the following:

[0058] Process parameters

[0059] The main process parameters of the friction stir welding of the skin and the reinforcing rib include a welding speed, a rotating speed, a pressing amount and a welding angle. Process tests should be performed on each specification of the welded part according to the requirements of the technical document, and the welding process parameters are determined. The typical process parameters of the friction stir welding of the skin and the reinforcing rib of aluminum alloy and titanium alloy are shown in Table 1 and Table 2.

[0060] Table 1

[0061]

[0062] Table 2

[0063]

[0064] Process flow

[0065] A typical process flow for skin-to-stringer friction stir welding is shown in Fig. 1, which generally includes process verification, pre-weld preparation, assembly, welding, inspection, post-weld treatment, and acceptance. Figure 11

[0066] Process verification

[0067] Before each trial or batch production welding, a test piece or simulation piece with the same material grade, heat treatment state, and thickness as the welded parts is prepared, and the recommended size of the test piece is 400 mm x 100 mm x δ, where δ is the welding thickness, and the thickness should represent the maximum and minimum dimensions of the product; the surface roughness Ra value of the test piece or simulation piece to be welded should be less than 6.3 μm. According to the appearance quality, internal quality, and mechanical properties of the welded joint, the welding process parameters can be adjusted appropriately, but the adjustment range should not be more than 10%.

[0068] Pre-weld preparation

[0069] Before welding, the surface of the parts should be cleaned of oil stains, and then the oxide film on the surface of the parts to be welded is cleaned by mechanical methods such as stainless steel brushes (steel wire diameter not more than 0.1 mm) and scrapers, or chemical cleaning methods.

[0070] The surface cleaned welded parts can be directly welded within 3 h (2A12) and 12 h (TA2). The welded parts exceeding 6 h (2A12) and 24 h (TA2) should be re-cleaned mechanically. The surface of the welded parts to be welded and the surface of the tooling fixture in contact with the material must be wiped with white cloth or fine white cloth dipped in industrial alcohol or industrial acetone, and there should be no oil stains, paint, rust spots, fusible metals, and other contaminants that affect the welding quality and welding process.

[0071] Assembly

[0072] During the installation of the parts to be welded, the centering of the stir pin to the joint should be checked, and the deviation should be adjusted, with a requirement that the full length deviation be ≤0.3 mm.

[0073] The pre-welding overlap gap of the weld should be ≤0.05 mm. For parts that do not meet the assembly accuracy, mechanical grinding within the range of the dimensional tolerance of the parts is allowed to meet the pre-welding assembly requirements.

[0074] In order to ensure the positioning of the parts, positioning welding can be performed by friction stir welding. The positioning weld points or sections should be symmetrical and uniform, have no cracks, and be covered by the weld. ​

[0075] Welding

[0076] If the welding lead-in plate and the welding lead-out plate are used, their material grade, thickness and state should be the same as the parts, and their pre-welding preparation is also performed according to the above, and they are removed after welding.

[0077] Before TA2 welding, the argon jet is ventilated for 3 to 5 seconds, and then placed at 10 to 20 mm from the welding position, and the output pressure is not less than 0.3 MPa. The argon jet moves with the stirring head, and the gas is turned off after staying for 3 to 5 seconds after welding is completed. (Note: The purity of argon should be more than 99.999%)

[0078] The friction stir welding process of the skin and the stiffener should be continuous. If interruption occurs, the welding is restarted at the interruption position, and the area is treated as a defect.

[0079] The welding sequence of the whole plate multi-pass welding should be performed by using the "Z" type welding sequence. The pre-welding deformation suppression is described in Figure 12 , Figure 13 and Figure 14 .

[0080] The stiffener welding component of the skin and the stiffener friction stir welding often produces buckling instability deformation due to the eccentric arrangement of the weld. Reasonable design should try to arrange the weld on or close to the neutral axis of the structural section, and try to make the deformations on both sides of the neutral axis equal in size and opposite in direction, so as to offset each other.

[0081] For large and complex welded structures, if conditions permit, they can be divided into several simple components, and then welded separately, and then assembled into a whole. The divided components should be easy to control the welding deformation, the welding amount is small when assembling, and it is also convenient to control the total deformation. For the welding seam being welded, it should be as close to the neutral axis of the structural section as possible. For the structure with asymmetrically arranged welds, the side with fewer welds should be welded first during assembly welding. For the structure with symmetrically arranged welds, an even number of weld passes should be symmetrically welded.

[0082] Welding deformation suppression

[0083] During welding, the heat dissipation method can be used for deformation suppression. By adding pneumatic load, liquid cooling and other methods, the heat at the welding position is quickly dissipated, reducing the heated area of the weld and its vicinity, and also greatly reducing the heating degree of the heated area, so as to reduce the welding deformation. During welding, the deformation suppression can also be performed by applying a welding impact device.

[0084] Post-weld deformation treatment

[0085] After welding, the post-weld deformation correction can be performed by manual correction method, mechanical correction method, flame heating correction method, post-weld heat treatment, etc.

Claims

1. A fixture for friction stir welding of a skin to a stringer, characterized by, The clamp comprises: a pedestal arranged on a machine tool; a plurality of I-beams arranged on the pedestal; wherein a reinforcing rib is arranged on the I-beam, and a skin is arranged on the reinforcing rib; a plurality of clamping top frames, the clamping top frames being located above the corresponding skins, two ends of the clamping top frames being arranged on the pedestal, and a middle part of the clamping top frames being used for pressing the skin and the reinforcing rib; wherein the pedestal comprises: a bottom plate; a plurality of first rectangular grooves arranged uniformly in a middle region of the bottom plate, the first rectangular grooves being used for mounting the I-beams; two second rectangular grooves arranged on two sides of the bottom plate, the second rectangular grooves being used for fixing two ends of the clamping top frames; the clamping top frame comprises a first top frame and a second top frame; the first top frame comprises: a horizontal rod, a front end surface of the horizontal rod being provided with a protrusion, and a first threaded hole being arranged on the protrusion; a vertical rod, one end of the vertical rod being connected perpendicularly to one end of the horizontal rod, and a connecting plate being horizontally arranged on the other end of the vertical rod, and a bolt hole being arranged on the connecting plate; wherein the horizontal rod and the vertical rod are coplanar; the pedestal further comprises: a T-shaped groove arranged below the second rectangular groove, the connecting plate being capable of being accommodated in the second rectangular groove; a second T-shaped bolt, a head of the second T-shaped bolt being capable of being accommodated in the T-shaped groove; wherein the second T-shaped bolt passes through the bolt hole, and a nut is used to fix the first top frame and the second top frame at a suitable position on the pedestal; a protruding part is arranged on the vertical rod, a second threaded hole is arranged on the protruding part, and the clamp further comprises: a latch arranged in the second threaded hole; wherein the latch has a thread; a locking washer connected with the latch; the locking washer is used to lock the first top frame and the second top frame to avoid shaking; the first rectangular grooves are horizontally arranged in the middle region of the bottom plate, and the second rectangular grooves are vertically arranged on the two sides of the bottom plate; the clamp further comprises: a pressing strip arranged on the skin; a pressing bolt arranged in the first threaded hole, a lower end surface of the pressing bolt abutting against the pressing strip; wherein two clamping top frames are used as a group to complete the clamping work for each weld, and the two clamping top frames are connected through a first locking washer, a second locking washer and a latch, the first locking washer and the second locking washer each having a threaded hole, and the first locking washer is inserted into a suitable position of the second locking washer and then the latch is inserted to connect the first locking washer and the second locking washer.

2. The clamp of claim 1, wherein the pedestal further comprises: a rectangular clamping groove arranged at a first end and a second end of the bottom plate, the first end being symmetrical to the second end, and the first end and the second end being close to the second rectangular groove; wherein the rectangular clamping groove is matched with a T-shaped groove of the machine tool, and a first T-shaped bolt is used to fix the pedestal on an upper surface of a workbench of the machine tool.

3. The clamp of claim 2, wherein the first top frame and the second top frame are the same; wherein the first top frame is a π-shaped structure.

4. The clamp of claim 1, wherein The reinforcing rib is Z-shaped, and the reinforcing rib is inverted on the I-beam.

5. A method of friction stir welding of a skin to a stringer, characterized by, The method is applied to the clamp for friction stir welding of the skin and the reinforcing rib according to any one of claims 1-4, and the method comprises: The reinforcing rib is inverted on the upper top surface of the I-beam, the skin is laid on the reinforcing rib, and the pressing strip is laid on the skin; The reinforcing rib and the skin are pressed by the clamping top frame; The friction stir welding tool obtains a working instruction; wherein the friction stir welding tool comprises a stirring head and a stirring needle, and the working instruction comprises a preset welding speed, a preset rotating speed and a preset inclination angle; The stirring needle is inserted into the skin surface of the middle region based on the preset inclination angle, and the stirring head starts to weld the skin and the reinforcing rib of the middle region based on the preset welding speed and the preset rotating speed; After the skin and the reinforcing rib of the middle region are welded, the skin and the reinforcing rib of the two side regions are welded.

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