Friction stir welding seam forming mechanism research model and seam forming evaluation method

Abstract

The invention discloses a friction stir welding seam forming mechanism research model and a welding seam forming evaluation method. The model comprises a frame and a stirring friction tool, a bottom plate capable of ascending and descending is arranged in the frame, a base metal model is arranged in the frame and located on the bottom plate, the base metal model is formed by stacking a plurality of metal particle layers of different colors, and a cover plate used for pressing the metal particle layers is arranged on the top layers of the metal particles. The cover plate is provided with a strip-shaped hole through which the stirring head can just pass, and the position of the strip-shaped hole corresponds to the simulated welding seam; the method comprises the steps that the bonding plate is adopted for bonding and removing particles of the metal particle layer layer by layer, shooting is carried out before the bonding plate is adopted for bonding the metal particles every time so as to obtain an image of the welded metal particle layer, a base metal model and a welding seam model are reconstructed according to the obtained image, and the welding seam forming mechanism is evaluated. According to the method, the material flow evolution characteristics of the whole welding seam area can be rapidly obtained, and a blind area between the characterization sections of the adjacent welding seams is avoided.

Description

Technical Field

[0001] The invention relates to the technical field of evaluation of a friction stir welding weld formation process, and in particular to a friction stir welding weld formation mechanism research model and a weld formation evaluation method. Background Art

[0002] In order to gain an in-depth and systematic understanding of the theories of friction stir welding weld formation mechanism, defect evolution law, interface structure regulation, and joint performance improvement, Ke Liming and his colleagues conducted research on the plastic fluidity of friction stir welding weld metal and proposed the "suction-extrusion" theory of friction stir welding weld formation for the first time. This theory reveals the intrinsic relationship between "stirring needle size-welding process parameters-plasticized metal flow-weld formation characteristics", providing theoretical guidance for welding process optimization, and thus raising friction stir welding process optimization and defect control from experience and trial and error to a theoretical level.

[0003] The above-mentioned existing scheme is to alternately stack copper foil and aluminum alloy (the upper and lower surfaces are 2 mm thick aluminum alloy, and the middle is 1 mm thick aluminum alloy and 0.02 mm thick copper foil alternately stacked), and use copper foil as a marking material. After welding, cut the cross-sectional sample of the joint and observe it, forming a "visualization" scheme that uses the deformation characteristics of copper foil and the change of the distance between adjacent copper foils to analyze the flow direction of the plasticized metal in the weld. Although this scheme can feedback the flow results of the material through the cross-sectional morphology, it cannot quickly obtain the flow evolution characteristics of the material in the entire weld area. The key is that it cannot accurately characterize the flow evolution of the material in the weld area. There is at least a 5mm blind area between all adjacent weld characterization sections (referring to the weld section processed to observe the color, position and other characteristics of the weld material) that cannot be observed (because obtaining a single weld characterization section requires sawing, the section of the saw seam itself cannot be characterized, and there must be a gap between adjacent saw seams). Summary of the invention

[0004] At least in view of the problems mentioned in the background technology, the present invention aims to provide a friction stir welding weld formation mechanism research model and a weld formation evaluation method.

[0005] The present invention adopts the following technical solution.

[0006] A research model for the formation mechanism of a friction stir welding weld includes a frame and a friction stir tool. The stirring head of the friction stir tool is made of metal material. A lifting bottom plate is provided in the frame. A base material model is provided in the frame and on the bottom plate. The base material model includes several layers of metal particles of different colors stacked together. A cover plate for pressing the metal particle layer is provided on the top layer of the metal particles. The cover plate is provided with a strip hole that can just allow the stirring head to pass through. The position of the strip hole corresponds to the simulated weld. The particle size of the particles in the metal particle layer is not greater than 1 mm.

[0007] Preferably, the metal particle layer is formed by paving titanium alloy particles.

[0008] Preferably, the particle size of the metal particle layer is 0.3-0.8 mm.

[0009] Preferably, it further comprises a plurality of independent bonding plates for bonding the metal particles, and the bonding area of ​​each bonding plate is equal to the top surface area of ​​the metal particle layer.

[0010] Furthermore, an adjusting mechanism for adjusting the height position of the cover plate and for pressing the cover plate is provided on the frame. With such a structure, it is possible to prevent metal particles from running around during the friction stir welding process.

[0011] A weld formation evaluation method using the aforementioned friction stir welding weld formation mechanism research model comprises the following steps: Step 1, firstly, laying a target number of metal particle layers in the frame to obtain a base material model, and then covering it with a cover plate and pressing the cover plate tightly; Step 2, insert the stirring head of the friction stir tool into the starting position of the strip hole, and then simulate the friction stir welding according to the set parameters. The shoulder of the stirring head is always in contact with the upper surface of the top layer of the metal particles during the welding process. After the welding is completed, the friction stir tool is removed; Step 3, remove the cover; Step 4, in a top-down order, using an adhesive plate to bond and peel off the particles of the metal particle layer layer by layer, and taking pictures before bonding the metal particles with the adhesive plate each time to obtain an image of the metal particle layer after welding; Step 6, reconstructing the base material model and the weld model according to the obtained image; Step 7: Analyze the displacement of metal particles in the metal particle layer according to the obtained model and evaluate the weld formation mechanism.

[0012] As a preferred solution, the step of laying a metal particle layer in a frame to obtain a parent material model includes: Step 11, raising the bottom plate in the frame to the upper limit position, where the top surface is close to the top edge of the frame; Step 12, first evenly spread the first layer of particles on the bottom plate and scrape it flat, then drop a certain amount of mucus on the first layer of particles to obtain a first metal particle layer; Step 13, controlling the bottom plate to move downward by a set distance, then spreading a second layer of particles on the surface of the first metal particle layer and scraping it flat, and then dripping a certain amount of mucus on the second layer of particles to obtain a second metal particle layer; Step 14, refer to step 13 several times until the top layer of metal particles is obtained, and then lock it; Step 15, drying the frame with the metal particle layer in an oven, and obtaining a base material model after the water in the mucus in the metal particle layer evaporates.

[0013] As a preferred embodiment, the mucus is rice soup or milk.

[0014] Furthermore, during the friction stir welding process, the area around the stirring head shoulder of the top layer of metal particles is pressed by the movable cover plate. This solution mainly serves to more accurately simulate the flow field of the plasticized material in friction stir welding and prevent the unwelded stirred metal particles around the shoulder from shifting.

[0015] Beneficial effect: By adopting the scheme of the present invention, not only can the material flow evolution characteristics of the entire weld area be quickly obtained, especially the time required for obtaining the data model for the material flow evolution in the weld area can be greatly shortened, but also the material flow evolution in the weld area can be accurately characterized, and the spacing between adjacent weld characterization sections can be reduced to within 1 mm, effectively avoiding the blind spots between adjacent weld characterization sections. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 It is a three-dimensional schematic diagram of the research model of the friction stir welding weld formation mechanism in Example 1; Figure 2 It is a top view schematic diagram of the research model of the friction stir welding weld formation mechanism in Example 1; Figure 3 This is a schematic diagram of the bonding plate in Example 1; Figure 4 This is a schematic diagram of the framework in Example 1; Figure 5 A schematic diagram of laying a top layer of metal particles on the bottom plate in Example 1; Figure 6 A schematic diagram of laying a multi-layer top layer of metal particles on the bottom plate in Example 1 and covering it with a cover plate; Figure 7 This is a schematic diagram of the parent material model in Example 1; Figure 8 Schematic diagram of the flow evolution of metal particle material in the welding area in Example 1; Fig. 9 This is a schematic diagram of the welding process in Example 1. DETAILED DESCRIPTION

[0017] The technical solution of the present invention is described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work belong to the scope of protection of the present invention. In the present invention, the welding mentioned refers to simulated stir friction welding, and the flow of plasticized material in the actual stir friction welding process is simulated by the flow of granular material. In particular, after the metal granular material is pressed by the cover plate 5 and the movable cover plate 21, the flow of plasticized material in stir friction welding can be better simulated when the stirring head is used for stirring; in the present invention, when selecting the rotation speed of the stirring head, the requirement that the metal particles in the metal particle layer are not plasticized should be met, otherwise the movement of the metal particles between adjacent layers cannot be accurately judged. Example 1

[0018] Combination Figures 1 to 9 As shown, a research model for the formation mechanism of a friction stir welding weld comprises a frame 1 and a friction stir tool. The stirring head of the friction stir tool is made of metal material (a conventional frustum-shaped stirring head can be used), the stirring head adopts a conventional frustum-shaped structure, the length of the stirring head is 5 mm, a lifting bottom plate 9 is arranged in the frame 1 (specifically, a screw lifting mechanism 6 is arranged at the bottom of the bottom plate 9. When it is necessary to control the lifting and lowering of the bottom plate 9, the bottom plate 9 is pre-connected to the lifting rod of the screw lifting mechanism 6, and then the screw lifting mechanism 6 is controlled to work to adjust the height of the bottom plate 9), a base material model 2 is arranged in the frame 1 and on the bottom plate 9, the base material model 2 comprises a plurality of layers of metal particle layers 3 of different colors stacked together, and a cover plate 5 for pressing the metal particle layer 3 is arranged on the top layer 4 of the metal particles, the cover plate 5 adopts a polytetrafluoroethylene plate, and a strip hole 7 is arranged on the cover plate 5 for just allowing the stirring head to pass through, and the position of the strip hole 7 corresponds to the simulated weld. Among them, the metal particle layer 3 is paved with titanium alloy particles. The particles of the metal particle layer 3 are in a polygonal structure, and the particle size (size) is 0.5±0.1mm (that is, the edge length of the particles is 0.5±0.1mm). The particles with this polygonal structure can cooperate well with the stirring head, and can effectively avoid the particles from slipping during the stir friction welding process and causing the particles to not flow and shift. The model also includes a number of independent bonding plates 8 for bonding metal particles, and the bonding area area of ​​each bonding plate 8 is equal to the top surface area of ​​the metal particle layer 3. An adjustment mechanism 10 for adjusting the height position of the cover plate 5 and for pressing the cover plate 5 is provided on the frame 1. In this embodiment, one end of the strip hole 7 extends to the outer wall of the frame 1, so that the stirring head and the movable cover plate 21 can smoothly enter the welding area and move smoothly. The top of the movable cover plate 21 is connected to the mounting seat of the stirring head through a connecting rod. During the stir friction welding process, the stirring head and the shaft shoulder 22 rotate synchronously, and the movable cover plate 21 moves laterally with the stirring head ( Fig. 9 The hollow arrow indicates the moving direction of the stirring head, that is, the welding direction). The area around the stirring head shoulder 22 at the top layer 4 of the metal particles is always pressed by the movable cover plate 21, and a stirring head with an outer diameter of the shoulder equal to the width of the strip hole 7 is selected (such as Fig. 9 as shown).

[0019] A weld formation evaluation method using the friction stir welding weld formation mechanism research model in this embodiment comprises the following steps: Step 1: firstly lay a target number of metal particle layers 3 in a frame 1 to obtain a base material model 2, and then cover the cover plate 5 and press the cover plate 5 tightly; wherein, the step of laying the metal particle layer 3 in the frame 1 to obtain the base material model 2 includes: Step 11, lift the bottom plate 9 in the frame 1 to the upper limit position, at which the top surface of 9 is close to the top edge of the frame 1; Step 12, first evenly spread the first layer of particles on the bottom plate 9 and scrape it flat (such as Figure 5 As shown), a certain amount of mucus is then dripped onto the first layer of particles to obtain a first metal particle layer 11; the mucus is rice soup (rice and pure water are boiled in a volume ratio of 1:5). In the present invention, the mucus mainly plays a role in taking into account the fluidity of the metal particles during the friction stir welding process, while improving the stability and uniformity of the particles during spreading, and preventing the metal particles of adjacent layers from shifting relative to each other during the spreading process; Step 13, controlling the bottom plate 9 to move downward by a set distance, then spreading the second layer of particles on the surface of the first metal particle layer 11 and scraping it flat, and then dripping a certain amount of mucus on the second layer of particles to obtain the second metal particle layer 12; Step 14, refer to step 13 several times until the top layer 4 of metal particles is obtained, and then lock it (such as Figure 6 shown); Step 15, the frame 1 with the metal particle layer laid is dried in an oven, and after the water in the mucus in the metal particle layer evaporates, a base material model 2 (such as Figure 7 shown); Step 2, such as Fig. 9 As shown, the stirring head of the friction stir tool is inserted into the starting position of the strip hole 7, and then the friction stir welding is simulated according to the set parameters. The shoulder of the stirring head is always in contact with the upper surface of the top layer 4 of the metal particles during the welding process. After the welding is completed, the friction stir tool is removed; Step 3, remove the cover 5; Step 4, in a top-down order, use the adhesive plate 8 to bond and peel off the particles of the metal particle layer 3 layer by layer (specifically, first align the bonding area of ​​the adhesive plate 8 in a horizontal state and press it on the top surface of the metal particle layer 3, then remove the adhesive plate 8, at this time, only part of the metal particles of the same metal particle layer 3 can be bonded, then use another new adhesive plate 8 to gently place it on the top surface of the metal particle layer 3, and then remove the adhesive plate 8. Experiments show that using two new adhesive plates 8 per layer (that is, each metal particle layer 3 is bonded twice) can almost bond all the metal particles of the same metal particle layer 3), and use a high-definition camera terminal to shoot before each use of the adhesive plate 8 to bond metal particles, so as to obtain the surface image of the metal particle layer after welding; Step 6, reconstructing the base metal model and the weld model according to the obtained image, that is, forming a three-dimensional weld model in digital space by stacking the obtained metal particle layer image, such as Figure 8 As shown; Step 7: Analyze the displacement of metal particles in the metal particle layer 3 according to the obtained model, and evaluate the weld formation mechanism.

[0020] In one of the application schemes of this embodiment, the thickness of the base material model 2 is set to 5 mm, and the particle size of the metal particle layer 3 is 0.5±0.1 mm. Then the corresponding metal particle layer is ten layers. The metal particle layers 3 laid in the frame 1 are as follows from top to bottom: Figure 7 As shown, the red first metal particle layer 11, the orange second metal particle layer 12, the yellow third metal particle layer 13, the green fourth metal particle layer 14, the cyan fifth metal particle layer 15, the blue sixth metal particle layer 16, the purple seventh metal particle layer 12, the silvery eighth metal particle layer 18, the black ninth metal particle layer 19, and the gray tenth metal particle layer 20. The colors of the metal particles in each layer before friction stir welding are set. During the friction stir welding process, the metal particles in each layer of the weld area will shift under the stirring action of the stirring needle. Therefore, it is only necessary to observe the color of each layer of metal particles after the friction stir welding is completed (the difficulty lies in how to accurately and quickly obtain the color of each layer of metal particles after the welding is completed) to know the flow evolution of the metal particles during the welding process. In this embodiment, the metal particle layer 3 is bonded and peeled off layer by layer using the bonding plate 8, and each metal particle layer 3 is photographed before the metal particles are bonded by the bonding plate 8 for the first time to obtain an image of the metal particle layer after welding, so that the color of each layer of metal particles after welding can be accurately and quickly obtained. Figure 8As shown, in the process of friction stir welding, if the metal particles are in a flow field as shown by the solid arrow in the figure under the action of the stirring needle (the hollow arrow indicates the welding direction, i.e., the moving direction of the stirring head), the metal particles in the area 36 on the sixth metal particle layer 16 move up to the area 35 of the fifth metal particle layer 15, the metal particles in the area 35 move up to the area 34 of the fourth metal particle layer 14, the metal particles in the area 33 move down to the area 32, and the metal particles in the area 32 move down to the area 31, then, the metal particle layer image after welding will be obtained: the fifth metal particle layer 15 is mostly cyan, but its area 35 is blue, and the area 32 is green; the fourth metal particle layer 14 is mostly green, but its area 34 is cyan, and the area 33 is green; the sixth metal particle layer 16 is mostly blue, but its area 31 is cyan, and the area 36 is blue. It should be noted that the figure and description only schematically represent the core idea of ​​the simplest metal particle flow evolution. In actual situations, the corresponding metal particle color and position changes are more complicated, and the actual shooting and statistical results shall prevail.

[0021] By adopting the scheme of the present invention, not only can the material flow evolution characteristics of the entire weld area be quickly obtained, especially the time required for obtaining the data model for the material flow evolution of the weld area can be greatly shortened, but also the material flow evolution of the weld area can be accurately characterized, and the spacing between adjacent weld characterization sections can be reduced to less than 1mm. The key is to effectively avoid the blind area between adjacent weld characterization sections. For the ten layers of metal particle layers in this embodiment, it is only necessary to implement according to the aforementioned steps 1-6 (making a parent material model, usually only eighteen times of bonding metal particles, taking ten images, and then importing the obtained images into a computer and reconstructing the parent material model and the weld model). In this process, obtaining ten weld characterization sections can be completed within half a day, and the spacing between the obtained adjacent weld characterization sections is approximately equal to the metal particle size (0.5±0.1mm), and there is no material flow blind area between adjacent weld characterization sections. However, the method of alternately stacking copper foil and aluminum alloy and sawing and polishing the weld section in the existing scheme (background technology) takes at least five days to process ten weld characterization sections, and there is at least a 5mm blind area between adjacent weld characterization sections, and the accuracy is very low.

[0022] Example 2: Refer to Example 1, except that the mucus is commercially available pure milk.

Claims

1. A friction stir welding weld formation mechanism research model, characterized by: The invention comprises a frame (1) and a friction stir tool, wherein the stirring head of the friction stir tool is made of metal material, a bottom plate (9) capable of being raised and lowered is arranged in the frame (1), a base material model (2) is arranged in the frame (1) and on the bottom plate (9), the base material model (2) comprises a plurality of metal particle layers (3) of different colors stacked together, and a cover plate (5) for pressing the metal particle layer (3) is arranged on the top layer (4) of the metal particles, and a strip hole (7) is arranged on the cover plate (5) so as to allow the stirring head to pass through, and the position of the strip hole (7) corresponds to the simulated weld.

2. The friction stir welding weld formation mechanism research model according to claim 1, characterized in that: The metal particle layer (3) is formed by paving titanium alloy particles.

3. The friction stir welding weld formation mechanism research model according to claim 1, characterized in that: The particle size of the metal particle layer (3) is 0.3-0.8 mm.

4. The friction stir welding weld formation mechanism research model according to any one of claims 1 to 3, characterized in that: It also includes a plurality of independent bonding plates (8) for bonding the metal particles, and the bonding area of ​​each bonding plate (8) is equal to the top surface area of ​​the metal particle layer (3).

5. The friction stir welding weld formation mechanism research model according to claim 4, characterized in that: An adjustment mechanism (10) for adjusting the height position of the cover plate (5) and for pressing the cover plate (5) is provided on the frame (1).

6. A weld formation evaluation method using the friction stir welding weld formation mechanism research model according to any one of claims 1 to 5, characterized in that the steps include: Step 1, firstly laying a target number of metal particle layers (3) in the frame (1) to obtain a base material model (2), then covering it with a cover plate (5), and pressing the cover plate (5); Step 2, inserting the stirring head of the friction stir tool into the starting position of the strip hole (7), and then simulating the friction stir welding according to the set parameters, wherein the shoulder of the stirring head is always in contact with the upper surface of the top layer (4) of the metal particles during the welding process, and removing the friction stir tool after the welding is completed; Step 3, remove the cover (5); Step 4, in a top-down order, using an adhesive plate (8) to bond and peel off the particles of the metal particle layer (3) layer by layer, and taking a picture before bonding the metal particles with the adhesive plate (8) each time, so as to obtain an image of the metal particle layer after welding; Step 6, reconstructing the base material model and the weld model according to the obtained image; Step 7, analyzing the displacement of metal particles in the metal particle layer (3) according to the obtained model, and evaluating the weld formation mechanism.

7. The weld formation evaluation method according to claim 6, characterized in that: The steps of laying a metal particle layer (3) in a frame (1) to obtain a parent material model (2) include: Step 11, raising the bottom plate (9) in the frame (1) to the upper limit position, at which the top surface of (9) is close to the top edge of the frame (1); Step 12, firstly, evenly spread a first layer of particles on the bottom plate (9) and scrape it flat, and then drip a certain amount of mucus on the first layer of particles to obtain a first metal particle layer (11); Step 13, controlling the bottom plate (9) to move downward by a set distance, then spreading a second layer of particles on the surface of the first metal particle layer (11) and scraping it flat, and then dripping a certain amount of mucus on the second layer of particles to obtain a second metal particle layer (12); Step 14, refer to step 13 for multiple times until the top layer of metal particles (4) is obtained, and then lock it; Step 15, the frame (1) with the metal particle layer laid thereon is dried in an oven, and after the water in the mucus in the metal particle layer evaporates, a base material model (2) is obtained.

8. The weld formation evaluation method according to claim 7, characterized in that: The mucus is made of rice soup or milk.

9. The weld formation evaluation method according to claim 6, characterized in that: During the friction stir welding process, the area around the stirring head shoulder (22) of the top layer (4) of the metal particles is pressed by the movable cover plate (21).

10. The weld formation evaluation method according to claim 6, characterized in that: The metal particles have a polygonal structure.

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