CN107876966A - It is a kind of to reduce welding method of the agitating friction welding to lap joint defect - Google Patents

Abstract

The invention provides a welding method for reducing defects of lap joints in friction stir welding, which belongs to the technical field of friction stir welding. The welding method of the present invention comprises the following steps: Step 1, measuring the geometric parameters of the workpiece to be welded and the stirring head; Step 2, fixing the workpiece to be welded; Step 3, determining the welding position; Step 4, friction stir welding. The welding method of the invention is used for friction stir welding of overlapping structures. In the method, the overlapping bonding surface in the butt-lapping structure is used as the backward side of the friction stir welding, and the other side is used as the advancing side. Mainly through the method of biasing the conical stirring pin on the forward side, with high welding heat input, to avoid the oxide film at the lap joint surface in the lap joint structure from entering the stirring zone, thereby avoiding the hook on the forward side Under the premise of the formation of shape defects, the cold lap defects generated in the stirring zone on the retreating side are reduced, and the purpose of improving the quality of welded joints is achieved.

Description

A Welding Method for Reducing Defects of Friction Stir Welded Lap Joints

technical field

The invention relates to the field of friction stir welding, in particular to a welding method for reducing defects of lap joints in friction stir welding.

Background technique

Friction Stir Welding (FSW) technology, as a solid-phase joining technology, can effectively avoid welding defects such as pores and inclusions caused by metallurgical problems in fusion welding during the welding process. However, when friction stir welding is applied to the welding of overlapping structures, due to the plastic flow of the weld metal, hook-shaped defects will appear on both sides of the stirring zone of the joint, especially on the retreating side, there will be cold laps extending into the stirring zone. Joint defects (thermal processing Vol.46, No.3(2017) p189-194; J Mater Process Technol, Vol.238(2016) p244-254), seriously endanger the quality of joints, and are urgently needed in friction stir lap welding. solved problem.

Butt-lap joint structure is a common structure with the characteristics of both butt joint structure and lap joint structure. For example, in the friction stir welding of side walls of high-speed rail and light rail trains, it is often necessary to weld this kind of butt-lap joint structure (JMSE International Journal, Vol.47, No.3(2004) p502-511; Technology and New Technology, Vol.42, No.5(2013) p31-36). For the friction stir welding of this kind of butt joint structure, at present, it is mainly welded by placing the stirring pin at the center of the butt joint surface. This method puts forward very high requirements for the selection of the length of the stirring needle and the control of the welding process. When the end of the stirring pin does not touch the lap joint surface, it will cause incomplete penetration defects, and repair welding is required (welding, Vol.11, (2016) p37-40); if the end of the stirring pin touches the lap joint The bonding surface (similar to lap joint structure welding) will cause hook defects or cold lap defects similar to those in lap welding (Li Hong, research on friction stir welding technology for urban rail aluminum alloy car body side walls, Harbin Institute of Technology Master's Thesis, 2014, p35-36), thus affecting joint performance. Analysis of the characteristics of the lap joint structure shows that only one side of this structure is similar to the lap joint structure. When a longer stirring pin is used for welding, only hook-shaped defects or cold joint defects will appear on one side of the joint during the welding process. Because there is no overlapping interface on one side, the above-mentioned defects will not occur. Studies have shown that when the overlapping interface is used as the retreating side, the joint is less adversely affected by defects, and the performance of the joint is better than that of the joint when the overlapping interface is used as the advancing side (Welding Technology, Vol.16, (2014) p57- 60,64). However, when this method is used, cold lap defects will form in the stirred zone, which will still adversely affect the performance of the joint.

In view of the fact that the hook defects on the forward side have a greater adverse effect on the performance of the joint than the cold connection defects (patent application number: 201410705553.7), how to eliminate the hook defects in the lap joint structure in a simple way while minimizing the cold in the stirring zone Overlapping defects are of great significance for improving the quality of overlapping structural joints.

Contents of the invention

In order to solve the problem that the hook defects and cold lap defects in the welding of friction stir lap joints in the prior art seriously affect the performance and quality of the joints, the present invention provides a welding method for reducing the defects of friction stir welding lap joints .

The welding method of the present invention comprises:

Step 1. Measure the geometric parameters of the workpiece to be welded and the stirring head:

The workpiece to be welded includes a flat plate to be welded and a step to be welded. The flat plate to be welded includes a first abutting surface and a first overlapping surface, and the step to be welded includes a second abutting surface and a second overlapping surface; the flat plate to be welded The first butt joint surface of the step welded workpiece is closely attached to the second butt joint surface to form a butt joint surface, and the first lapped surface of the flat plate welded workpiece is closely attached to the second lapped surface of the stepped welded workpiece to form a lap joint The mating surface; the stirring head includes interconnected shoulders and stirring needles;

Measure the plate thickness H1 of the welded area of the flat welded workpiece, the plate thickness H2 of the welded area of the step welded workpiece, the diameter D1 of the shaft shoulder, and the lateral width L1 of the overlapping joint surface; the shoulder is pressed down to the welding The distance L2 from the shoulder surface to the lap joint surface in the state, L2 is the difference between the thickness H1 and the preset shoulder pressure, and the diameter D2 of the stirring needle at the L2 is measured; the diameter D1 Half of the difference from the diameter D2 should be greater than or equal to the width L1, that is, L1 is not less than 0.5 (D1-D2); the length L3 of the stirring needle is greater than the thickness H1 and less than the thickness H2; the diameter of the root of the stirring needle D3 at least 2 mm smaller than the diameter D1; the diameter D4 of the end of the stirring needle away from the shaft shoulder is at least 2 mm smaller than the diameter D3;

Step 2. Fix the workpiece to be welded:

Use the clamp to fix the workpiece to be welded on the workbench, and make the flat workpiece to be welded closely overlap the top of the workpiece to be welded on the step, so that both the butt joint surface and the lap joint surface can be closely fitted, and the flat plate is welded The welding workpiece and the highest upper surface of the step welded workpiece are kept at the same level to complete the assembly of the welded workpiece;

Step 3. Determine the welding position:

First, move the stirring head above the butt joint surface of the workpiece to be welded so that the centerline of the stirring needle is directly above the butt joint surface; then horizontally shift the centerline of the stirring needle to the advancing side by 0.5D2 distance, so that the outer wall of the stirring needle at the lap joint surface is tangent to the intersection line formed by the butt joint surface and the lap joint surface, and the positioning of the stirring head is completed;

Step 4. Friction stir welding:

The stirring head is pressed into the workpiece to be welded, and the outer wall of the stirring pin at the lap joint surface is always tangent to the intersection line formed by the butt joint surface and the lap joint surface; Walk in the direction of the intersection line between the butt fitting surface and the upper surface of the workpiece to be welded until the welding is completed.

The stirring needle described in step 1 is a tapered stirring needle.

The preset press-in amount of the shoulder mentioned in step 1 is controlled within the range of 0.1-0.3mm.

The insertion amount of the stirring needle should be greater than H1 and less than 5/6H2.

When the stirring head is pressed down in step 4, the speed is controlled at 2-300mm/min.

During the welding process in step 4, the friction stir lap welding is carried out in the form of high welding heat input, that is, the rotation speed of the stirring head is controlled between 800-3000rpm/min, and the rotation speed and the stirring head travel The speed ratio should not be lower than 3.

The present invention mainly adopts the way that the conical stirring needle is biased on the forward side, and performs friction stir lap welding with high welding heat input. The amount should be greater than H1 and less than 5/6H2. Using this method of biasing the stirring needle prevents the oxide film at the lap joint surface from entering into the stirring zone of the joint. On the basis of skillfully avoiding the occurrence of hook-shaped defects on the forward side of the joint of the lap joint structure, it also reduces the Formation of cold lap defects in the stirred zone in the retreating side.

Description of drawings

Fig. 1 is the schematic diagram of friction stir welding process of lap joint structure among the present invention;

Fig. 2 is a schematic view of the structure of the flat plate of the workpiece to be welded in the present invention;

Fig. 3 is a schematic diagram of the structure of the workpiece to be welded by the step of the welded workpiece in the present invention;

Fig. 4 is the metallographic diagram of the aluminum alloy joint of overlapping structure obtained by adopting the welding method of the present invention: wherein Fig. a is the macroscopic appearance diagram of the joint obtained by adopting the welding method of the present invention, and Fig. b is the joint obtained by adopting the welding method of the present invention Microstructure diagram of the receding side of the joint obtained by the welding method;

Figure 5 is a metallographic diagram of an aluminum alloy joint with a lap joint structure obtained by using the existing friction stir welding method: Figure a is the macroscopic appearance of the joint obtained by the existing welding method, and Figure b is the joint obtained by the existing welding method The microstructure map of the receding side of the joint obtained by the method.

In the figure: 1 flat plate to be welded, 2 steps to be welded, 3 the first butt surface, 4 the first lap surface, 5 the second butt surface, 6 the second lap surface, 7 shaft shoulder, 8 stirring pin; A Butt fitting surface, B lap fitting surface, C-axis shoulder surface; H1 plate thickness of the welded area of the flat workpiece to be welded, H2 plate thickness of the welded area of the step welded workpiece, H3 flat plate welded workpiece away from the welded area The plate thickness of the H4 step to be welded is far away from the plate thickness of the welded area; L1 is the lateral width of the lap joint surface (B) L1, L2 when the shoulder is pressed down to the welding state from the shoulder surface connected to the root of the stirring needle (C) The distance to the lap joint surface (B), the length of L3 stirring needle; D1 the diameter of the shaft shoulder, D2 the diameter of the stirring needle at L2, the diameter of D3 the root of the stirring needle, and the diameter of D4 the end of the stirring needle away from the shoulder diameter.

Detailed ways

In order to solve the problems existing in the prior art, as shown in Figures 1 to 5, the present invention provides a welding method for reducing the defects of friction stir welding lap joints, the steps of the friction stir welding lap welding method are as follows :

Step 1. Measure the geometric parameters of the workpiece to be welded and the stirring head:

The workpiece to be welded includes a flat plate to be welded (1) and a step to be welded (2), the flat plate to be welded (1) includes a first abutting surface (3) and a first overlapping surface (4), and the step to be welded ( 2) Including the second butt surface (5) and the second overlapping surface (6); the first butt surface (3) of the plate to be welded (1) and the second butt surface (5) of the step to be welded (2) ) closely fit to form the butt joint surface (A), and the first lap surface (4) of the flat plate workpiece (1) and the second lap surface (6) of the step weld workpiece (2) closely adhere to form a lap connected to the mating surface (B); the stirring head includes an interconnected shoulder (7) and a stirring needle (8): the shoulder (7) is a cylindrical shoulder, and the stirring needle (8) is a tapered stirring needle;

Measure the plate thickness H1 of the plate welded workpiece (1) near the butt joint surface area, that is, the welded area, the plate thickness H2 of the step welded workpiece (2) near the butt joint surface area, that is, the welded area, and the shaft shoulder (7) The diameter D1 of the lap joint surface (B) and the transverse width L1; the plate thickness H3 of the plate welded workpiece away from the welded area should be less than or equal to H1, and the plate thickness H4 of the step welded workpiece away from the welded area should be less than or equal to H2 ; The distance L2 from the shoulder surface (C) to the lap joint surface (B) when the shoulder (7) is pressed down to the welding state is the difference between the plate thickness H1 and the preset shoulder pressing amount, and the preset The set shoulder pressure should be controlled within the range of 0.1-0.3mm; measure the diameter D2 of the stirring needle (8) at L2; half of the difference between the diameter D1 and the diameter D2 should be greater than or equal to the transverse width L1, that is, L1 should not be less than 0.5 (D1-D2); the length L3 of the stirring needle (8) is greater than the thickness H1 of the plate and less than the thickness H2 of the plate; the diameter D3 of the root of the stirring needle (8) is at least 2 mm smaller than the diameter D1 of the shoulder (7); the stirring needle (8) The diameter D4 of the end away from the shoulder (7) is at least 2mm smaller than the diameter D3;

Step 2. Fix the workpiece to be welded:

Use the clamp to fix the workpiece to be welded on the workbench, and make the flat plate to be welded (1) closely overlap the top of the step to be welded (2), so that the butt joint surface (A) and the lap joint surface ( B) all achieve close fit, the flat plate to be welded (1) and the highest upper surface of the step to be welded (2) are kept at the same level, and the assembly of the welded workpiece is completed;

Step 3. Determine the welding position:

Set one side of the overlapping joint surface as the backward side, and the other side, that is, the side of the stepped workpiece (2) as the forward side; first, move the stirring head above the butt joint surface (A) of the workpiece to be welded so that The center line of the stirring needle (8) is located directly above the butt joint surface (A); then, the center line of the stirring needle (8) is horizontally shifted to the forward side by a distance of 0.5D2, so that the stirring needle (8) is in the lap The outer wall at the joint surface (B) is tangent to the intersection line formed by the butt joint surface (A) and the lap joint surface (B), as shown in the dotted line position in Figure 1, to complete the positioning of the stirring head;

Step 4. Friction stir welding:

The stirring head is pressed into the workpiece to be welded at a pressing speed of 2-300mm/min, and the outer wall of the stirring pin (8) at the lap joint surface (B) is always in contact with the butt joint surface (A) and the lap joint The intersection line formed by the surface (B) is tangent; the speed of the stirring head is controlled between 800-3000rpm/min by means of high welding heat input, and the speed (rpm/min) is related to the speed of the stirring head (mm/min). The ratio is not lower than 3, so that the stirring head moves along the direction parallel to the intersection line between the butt joint surface (A) and the upper surface of the workpiece to be welded until the welding is completed.

Example 1

The aluminum alloy plate to be welded plate 1 with H1 = 4mm and the aluminum alloy stepped welded plate 2 with H2 = 6mm are assembled for lap joint structure, the height of the joint surface is the same as H1, that is, 4mm, and the lap joint The surface length L1 is selected as 15mm, and then the welding method of the present invention is used to carry out friction stir welding: the length of the stirring needle L3=5.4mm, the amount of pressure=0.2mm, the root diameter of the stirring needle D3=6mm, the diameter of the end D4=4mm, The diameter of the stirring needle at the junction of the joint and fitting surface is D2=4.6mm, the diameter of the shaft shoulder D1=18mm, the rotation speed is 800r/min, the welding speed is 200mm/min, and the distance between the center of the butt fitting surface of the stirring needle is 0.5×4.6mm = 2.3 mm. Microstructural analysis showed that no hook-shaped defects appeared on the advancing side of the joint, especially no cold lap defects were found in the stirring zone on the retreating side (as shown in Figure 4), so the quality of the joint was significantly improved.

Comparative example 1

The aluminum alloy plate to be welded plate 1 with H1 = 4mm and the aluminum alloy stepped welded plate 2 with H2 = 6mm are assembled for lap joint structure, the height of the joint surface is the same as H1, that is, 4mm, and the lap joint The surface length L1 is selected as 15mm, and then the existing friction stir welding method is adopted: the stirring needle L3=5.4mm, the pressing amount is 0.2mm, the root diameter of the stirring needle D3=6mm, the end diameter D4=4mm, and the shaft shoulder diameter D1 =18mm, rotating speed 800r/min, welding speed 200mm/min, the center line of the stirring needle is placed directly above the butt joint surface. Microstructural analysis showed that although there were no hook-shaped defects on the advancing side of the joint, cold lap defects extending to the stirring zone were found in the stirring zone on the retreating side (as shown in Figure 5), which affected the quality of the joint.

On the basis of the traditional friction stir welding of lap joints, the present invention takes the side of the lap joint surface as the retreat side, and proposes a method of offsetting the conical stirring needle to the forward side for welding, which is a reduction in the application Friction stir welding is a welding method for lap joint defects. On the basis of cleverly avoiding the hook-shaped defects on the forward side of the lap joint structure joints, it also reduces the cold lap defects formed in the stirring zone on the retreating side.

The invention has a simple operation process and is easy to realize, and is suitable for friction stir welding of overlapping joint structures with various thicknesses, and the quality of joints is significantly improved.

The above descriptions are only preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included in the protection of the present invention. within range.

Claims (6)

1. a kind of reduce welding method of the agitating friction welding to lap joint defect, it is characterised in that the welding method bag Include：

Step 1: the geometric parameter of measurement welded piece and stirring-head：

Welded piece includes flat board welded piece (1) and step welded piece (2), and flat board welded piece (1) includes the first docking Surface (3) and the first overlap joint surface (4), step welded piece (2) include the second butting surface (5) and the second overlap joint surface (6)； The first butting surface (3) of flat board welded piece (1) is brought into close contact group with the second butting surface (5) of step welded piece (2) Faying face (A), the first overlap joint surface (4) of flat board welded piece (1) and the second overlap joint table of step welded piece (2) are connect in pairs Face (6) is brought into close contact composition overlap joint binding face (B)；Stirring-head includes the shaft shoulder (7) and mixing needle (8) interconnected；

Flat board welded piece (1) is measured by the sheet metal thickness H1 in welding zone domain, step welded piece (2) by the sheet metal thickness in welding zone domain H2, the diameter D1 of the shaft shoulder (7), the transverse width L1 of the overlap joint binding face (B), from axle when the shaft shoulder (7) presses to welding state The distance L2, L2 of shoulder face (C) to overlap joint faying face (B) are the difference of the thickness H1 and default shaft shoulder volume under pressure, and are measured The diameter D2 of mixing needle (8) at the L2；The half of the diameter D1 and the diameter D2 difference should be greater than being equal to the width L1, i.e. L1 are not less than 0.5 (D1-D2)；Mixing needle (8) length L3 is more than the thickness H1 and is less than the thickness H2；Mixing needle (8) the diameter D3 of root is at least smaller 2mm than the diameter D1；The diameter D4 of end of the mixing needle (8) away from the shaft shoulder (7) at least compares The small 2mm of diameter D3；

Step 2: fixed welded piece：

The welded piece is fixed on the table using fixture, and makes flat board welded piece (1) closely to taking in step quilt The top of welder's part (2), docking binding face (A) and overlap joint binding face (B) is set all to realize and be brought into close contact, flat board welded piece (1) Same level is maintained at step welded piece (2) highest upper surface, completes the assembling of welded piece；

Step 3: determine welding position：

First, stirring-head is moved to above the docking binding face (A) of the welded piece, is located at the center line of mixing needle (8) Dock the surface of binding face (A)；Then the center line of mixing needle (8) is marched forward side horizontal-shift 0.5D2 distance, makes to stir It is tangent with docking the intersection that binding face (A) and overlap joint binding face (B) are formed to mix outer wall of the pin (8) at overlap joint faying face (B) place, it is complete Into the positioning of stirring-head；

Step 4: agitating friction welds：

Stirring-head is pressed into the welded piece, keep the mixing needle (8) overlap joint faying face (B) place outer wall all the time with institute It is tangent to state the intersection that docking binding face (A) and overlap joint binding face (B) are formed；Stirring-head is along parallel to the docking binding face (A) Walked with the direction of the intersection of the welded piece upper surface, until welding is completed.

2. a kind of reduction agitating friction welding as claimed in claim 1 exists to the welding method of lap joint defect, its feature In mixing needle described in step 1 (8) is taper mixing needle.

3. a kind of reduction agitating friction welding as claimed in claim 1 exists to the welding method of lap joint defect, its feature In default shaft shoulder intrusion control is in the range of 0.1-0.3mm described in step 1.

4. a kind of reduction agitating friction welding as claimed in claim 1 exists to the welding method of lap joint defect, its feature In the insertion of the mixing needle (8) should be greater than H1 and be less than 5/6H2.

5. a kind of reduction agitating friction welding as claimed in claim 1 exists to the welding method of lap joint defect, its feature In speed control is in 2-300mm/min when stirring-head pushes described in step 4.

6. a kind of reduction agitating friction welding as claimed in claim 1 exists to the welding method of lap joint defect, its feature In in step 4 during welding, friction being stirred in a manner of high thermal weld stress and connects welding, that is, controls the stirring-head Rotating speed between 800-3000rpm/min, and the ratio of the rotating speed and the stirring-head gait of march is not less than 3.