Monorail vehicle side wall central panel assembly welding tool and gantry automatic welding process using same
By using gantry automatic welding and welding fixtures for the central panel assembly of monorail vehicle side walls, the problems of welding quality and efficiency of rail transit vehicle body components have been solved, realizing a high-quality, low-skill welding process and improving product consistency and production efficiency.
Patent Information
- Application Number
- CN202511714641.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-11-21
- Publication Date
- 2026-01-09
AI Technical Summary
The welding quality of rail transit vehicle body components is difficult to guarantee, especially the welding of aluminum alloys, which has many defects. In addition, the manual welding operation requires high skills, which leads to difficulties in recruitment, low production efficiency, poor product size consistency, and inconsistent weld joint forms, which affect production efficiency.
Automatic gantry welding was adopted to replace manual welding. We developed a welding fixture for the central panel assembly of the side wall of the monorail vehicle, which includes a fixture frame, positioning blocks, contour support blocks, quick clamping devices and gap plugs. By machining the arc-starting plate and the lead-out plate before welding and adjusting the welding process, we ensured the consistency and quality of the weld.
It improved welding quality and production efficiency, reduced the skill requirements for welders, avoided welding defects, ensured product dimensional consistency and stability, and improved overall production efficiency.
Smart Images
Figure CN121289910A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of rail transit technology, specifically relating to a welding fixture for assembling the central panel of the side wall of a monorail vehicle and an automatic gantry welding process using the fixture. Background Technology
[0002] Urban rail transit has become the preferred mode of transportation for the public due to its high speed and large passenger capacity.
[0003] The rail transit industry has extremely high requirements for product welding quality. Since the welding of car body components such as the central panel of the side wall is generally done by hand, the welding skills of the welders are required to be high. It is difficult to recruit intermediate and senior welders, and there are certain risks to the product welding quality. Compared to steel, aluminum alloys offer advantages such as lightweight and superior corrosion resistance, making them a popular choice for rail transit vehicle body components. However, aluminum alloy welding is prone to defects such as incomplete penetration and crater cracks during the arc initiation and termination stages. Furthermore, the weld joint types at the ends of the product differ from those in the middle section (see...). Figure 1 As shown in the figure, in order to ensure welding quality and avoid burn-through, stainless steel backing is required when welding the weld seams at both ends. This operation is troublesome and affects production efficiency.
[0004] The welding of the central panel of the side wall is carried out on a general work platform or bench without dedicated welding fixtures. Therefore, it is difficult to guarantee the consistency of product dimensions. Due to fluctuations in the heat input of manual welding, the deformation of the product after welding is uncontrollable, and the product dimensions are difficult to stably control within the range required by the drawings, resulting in a large workload for subsequent shaping. In addition, according to the drawings, the weld is a full penetration butt weld. If the bevel gap is too small during part assembly, welding defects such as incomplete penetration may occur. Summary of the Invention
[0005] The technical problem to be solved by this invention is as follows: (1) Using gantry automatic welding to replace manual welding can alleviate the problem of difficulty in recruiting intermediate and senior welders and solve the problem of product welding quality risks caused by insufficient welder skills. (2) Adjust the production process, and process the arc-starting plate and the arc-starting plate (e.g., before welding) on the profile during the pre-welding machining process. Figure 2 As shown), this avoids welding defects that are prone to occur during the arc initiation and arc termination stages of aluminum alloys from appearing on the product weld. Additionally, some pre-welding machining operations will be moved to post-welding (see details). Figure 1 , Figure 2 As shown), the joints of the entire weld are exactly the same, and the weld can be completed in one go. When welding the welds at both ends, stainless steel backing is no longer used, which improves welding quality and production efficiency. (3) Develop a group welding fixture clamp, solve the problem of poor consistency of product size after welding, large workload of model adjustment; Solve the problem of poor control of weld groove gap and thus produce incomplete penetration and other welding defects; The purpose of the present application is to provide a monorail car side wall central panel group welding fixture and a gantry automatic welding process using the same, to solve the above problems.
[0006] To achieve the above object or other object, the technical scheme of the present application is as follows: The monorail car side wall central panel group welding fixture comprises a monorail car side wall central panel positive assembly welding fixture and a monorail car side wall central panel reverse assembly welding fixture; The monorail car side wall central panel positive assembly welding fixture comprises a fixture frame, an end positioning stopper, a profiling support block, a quick clamping device and a plurality of gap plugs arranged on the fixture frame; the fixture frame comprises a support column, a cross beam and a longitudinal beam arranged on the support column; the end positioning stopper is protrudingly arranged at one end of the fixture frame, and is used for positioning the monorail car side wall central panel in X direction; the profiling support block is arranged on the longitudinal beam, and is used for supporting and positioning the monorail car side wall central panel in Y direction and Z direction, and the profiling support block is also used for welding reverse deformation adjustment; the quick clamping device is used for clamping and fixing the monorail car side wall central panel; the gap plugs are temporarily placed between the four parts of the monorail car side wall central panel, and are used for controlling the weld groove gap; The monorail car side wall central panel reverse assembly welding fixture also comprises the fixture frame, the end positioning stopper, the profiling support block and the quick clamping device arranged on the fixture frame.
[0007] Further, the gap plugs are all machined, and each comprises an upper handle and a lower plug-in end; the upper handle is welded by two round bars; and the lower plug-in end is plugged between parts to control the gap.
[0008] Further, the gap plugs comprise a first gap plug, a second gap plug and a third gap plug; the first gap plug is plugged from the side between the first part and the second part of the monorail car side wall central panel; the second gap plug is plugged from the side between the third part and the fourth part of the monorail car side wall central panel; and the third gap plug is plugged from above the connection of the four parts. The lower plug-in end structures of the first gap plug and the second gap plug are symmetrical to each other; and the lower plug-in end of the third gap plug is provided in T-shaped structure.
[0009] Further, the profiling support block is adjusted by the thickness of the adjusting gasket for welding reverse deformation adjustment; the adjusting gasket is arranged between the profiling support block and the fixture frame. Each of the longitudinal beams is provided with the profiling support blocks arranged oppositely; and the profiling support blocks are fixed on the longitudinal beams by bolts.
[0010] Further, two pairs of profiled supporting blocks are arranged on each longitudinal beam of the single-track vehicle side wall central panel front assembly and welding tooling; One pair of profiled supporting blocks is arranged on each longitudinal beam of the single-track vehicle side wall central panel back assembly and welding tooling, and the profiled supporting blocks are located at the two ends of the longitudinal beam. Further, the profiled supporting blocks of the front assembly and welding tooling and the back assembly and welding tooling are different in structure and size and match the front and back profiles of the central panel respectively.
[0011] Further, the quick clamping devices are arranged opposite to each other and press and fix the single-track vehicle side wall central panel from above.
[0012] Further, the quick clamping devices of the single-track vehicle side wall central panel front assembly and welding tooling are arranged on the outer sides of the longitudinal beams at the two ends of the tooling frame and at the two ends of each longitudinal beam to clamp and fix from the four sides of the tooling frame. The quick clamping devices of the single-track vehicle side wall central panel back assembly and welding tooling are arranged at the two ends of each longitudinal beam.
[0013] The gantry automatic welding process of the single-track vehicle side wall central panel assembly and welding tooling comprises the following steps: (1) Machining before welding: arc leading plates and leading-out plates are directly machined on the two ends of the central panel welds. (2) Front assembly: the components of the single-track vehicle side wall central panel are assembled on the single-track vehicle side wall central panel front assembly and welding tooling in sequence: X-direction positioning is performed by end positioning blocks, Y-direction and Z-direction supporting positioning and welding reverse deformation adjustment are performed by profiled supporting blocks; a plurality of gap plugs are inserted between the components to control the weld gap; the quick clamping devices are closed to clamp and fix the four components, and then tack welding is performed. (3) The gap plugs are removed, and the gantry automatic welding equipment is started to perform front weld welding. (4) Back assembly and back weld welding: the components after front welding are lifted by a crane and turned over by 180°, and are assembled on the single-track vehicle side wall central panel back assembly and welding tooling: X-direction positioning is performed by end positioning blocks, Y-direction and Z-direction supporting positioning and welding reverse deformation adjustment are performed by profiled supporting blocks; the quick clamping devices are closed to clamp and fix the components; the gantry automatic welding equipment is started to perform back weld welding. (5) After the welding process is completed, the arc leading plates and leading-out plates at the two ends of the central panel welds are machined and removed, so that the entire weld joint is completely the same.
[0014] Further, during the front weld welding and back weld welding, stainless steel gaskets are not used for welding the two ends of the welds.
[0015] Furthermore, in step (2): a first gap block is inserted from the side between the first component and the second component, a second gap block is inserted from the side between the third component and the fourth component, and a third gap block is inserted from above at the connection point of the four components; there is no requirement for the order of placement of the first gap block, the second gap block, and the third gap block.
[0016] The present invention has the following advantages: (1) Compared with manual welding, the gantry automatic welding of the present invention has lower requirements for the welding skills of the welder, the welding quality is more stable and reliable, the product quality and stability are improved, and the pressure of recruiting welders can be alleviated at the same time. (2) When welding the welds at both ends of the present invention, stainless steel backing is no longer used, thus improving production efficiency; the arc-starting plate and the arc-ending plate are directly processed on the profile, eliminating the need for additional installation of the arc-starting plate and the arc-ending plate, thus avoiding the welding defects that are easily generated during the arc-starting and arc-ending stages of aluminum alloys from appearing on the product welds, thereby improving welding quality and production efficiency. (3) The welding fixture of the present invention is positioned and fixed by positioning blocks, support blocks, gap plugs, quick clamping devices, etc., which makes assembly convenient and ensures high consistency of assembly dimensions. It can adjust the welding deformation according to the actual deformation of the product after welding. Moreover, manual welding is changed to gantry automatic welding, which makes the heat input more stable and the product dimensions after welding more stable. The product after welding no longer needs to be reshaped, and the product quality and production efficiency are improved.
[0017] Furthermore, when using the tooling of this invention, the weld groove gap is ensured by the gap plug, avoiding welding defects such as incomplete penetration caused by an excessively small groove gap.
[0018] In addition, the welding fixture of the present invention can realize the simultaneous assembly and welding of two lengths of side wall central panels, thereby improving welding efficiency (products of different lengths can be assembled and welded at the same time on the fixture: the first component 8 and the second component 9 are side wall central panels of one length, and the third component 10 and the fourth component 11 are side wall central panels of another length). Attached Figure Description
[0019] Figure 1 This is a schematic diagram illustrating the difference between the weld joint forms at both ends of the product and the weld joint forms in the middle section, as mentioned in the background art. Figure 2 This invention is for Figure 1 A schematic diagram of the optimized welding area (with arc-starting plate and arc-exiting plate fabricated). Figure 3 This is a diagram illustrating the use of gap plugs. Figure 1 ; Figure 4 This is a diagram illustrating the use of gap plugs. Figure 2 ; Figure 5is a schematic diagram of the positive assembly and welding tooling of the monorail car side wall central panel of the present application; Figure 6 is a schematic diagram of the reverse assembly and welding tooling of the monorail car side wall central panel of the present application; Figure 7 is a schematic diagram of the assembly and welding using the positive assembly and welding tooling of the monorail car side wall central panel of the present application; Figure 8 is a schematic diagram of the assembly and welding using the reverse assembly and welding tooling of the monorail car side wall central panel of the present application; Figure 9 is a first gap block perspective view; Figure 10 is a second gap block perspective view; Figure 11 is a third gap block perspective view; Figure 12 is a third gap block bottom view; Wherein, 1-tooling frame, 2-end positioning stopper, 3-profiling support block, 4-quick clamping device, 5-first gap block, 6-second gap block, 7-third gap block; 8-first component part, 9-second component part, 10-third component part, 11-fourth component part; 12-arc guide plate, lead-out plate. DETAILED DESCRIPTION
[0020] The present application will be further described in detail below in conjunction with the drawings and examples. Example 1:
[0021] Referring to Figures 5 to 8 Fig. 1, the assembly and welding tooling of the monorail car side wall central panel of the present embodiment includes positive assembly and welding tooling of the monorail car side wall central panel and reverse assembly and welding tooling of the monorail car side wall central panel, respectively used for positive assembly and welding of the monorail car side wall central panel and reverse assembly and welding of the monorail car side wall central panel.
[0022] As shown in Figure 5 Fig. 2, the positive assembly and welding tooling of the monorail car side wall central panel includes tooling frame 1, end positioning stopper 2, profiling support block 3, quick clamping device 4, first gap block 5, second gap block 6 and third gap block 7.
[0023] The tool frame 1 comprises a support column, a cross beam and a longitudinal beam, and the remaining components of the tool are mounted on the tool frame 1, which is a mounting platform for other components. The support columns are parallel to each other and vertically fixed on the bottom surface. Preferably, four pairs of support columns are arranged in the embodiment. The cross beam and the longitudinal beam are arranged above the support columns to form a stable frame structure. The longitudinal beam is arranged above each pair of support columns, and the width of the longitudinal beam is larger than that of the cross beam, which facilitates the subsequent arrangement of the profiled support block 3 and the quick clamping device 4 and other structures. Preferably, in order to further stabilize the structure, a cross beam and a longitudinal beam are also arranged below the support columns. Preferably, the tool frame 1 is welded by square tubes, rectangular tubes and the like.
[0024] The end positioning block 2 is arranged on the longitudinal beam at one end of the tool frame 1, and is used for X-direction positioning of the product (the side wall central panel of the monorail vehicle). The end positioning block 2 comprises a block mounting seat and a rubber block, and the rubber block is vertically arranged and faces the product.
[0025] The profiled support block 3 is used for Y-direction and Z-direction support positioning of the product. As shown in Figure 5 , the profiled support blocks 3 are arranged in pairs, and two pairs of profiled support blocks 3 are arranged on each longitudinal beam. The profiled support block 3 comprises a machined profiled block, and the profiled support block 3 in the embodiment is arranged in an “L” shape.
[0026] The profiled support block 3 is fixed on the longitudinal beam of the tool frame 1 by bolts.
[0027] Preferably, the profiled support block 3 can be adjusted by adjusting the thickness of the gasket (arranged between the profiled support block 3 and the tool frame 1) to adjust the welding reverse deformation of the product. Preferably, the material of the profiled support block 3 is aluminum alloy.
[0028] The quick clamping device 4 is used for clamping and fixing the product. The quick clamping device 4 is arranged in pairs and protrudes outward from the longitudinal beams at both ends of the tool frame 1 and at both ends of each longitudinal beam, so as to clamp and fix the product from all around the tool frame 1. The quick clamping device 4 comprises a base and a clamping structure above the base, and a general quick clamp in the market is adopted in the embodiment.
[0029] The first gap plug 5, the second gap plug 6 and the third gap plug 7 are used for controlling the gap of the weld bevel, and are temporarily arranged between the four part panels of the side wall central panel of the monorail vehicle.
[0030] Specifically, the first gap plug 5 is inserted between the first part 8 and the second part 9 (as shown in Figure 3 from the side); and the second gap plug 6 is inserted between the third part 10 and the fourth part 11 (as shown in Figure 3The third gap block 7 is inserted into the joint of the four parts of the first part 8, the second part 9, the third part 10 and the fourth part 11 (as shown in the figure, inserted from the side). Figure 4 The third gap block 7 is inserted into the joint of the four parts of the first part 8, the second part 9, the third part 10 and the fourth part 11 (as shown in the figure, inserted from the side).
[0031] The first gap block 5, the second gap block 6 and the third gap block 7 are made of stainless steel and are machined, and each includes an upper handle and a lower insertion end. The upper handle is welded by two round bars, and the lower insertion end is inserted between the parts to control the gap between the parts.
[0032] The lower insertion end structures of the first gap block 5, the second gap block 6 and the third gap block 7 are slightly different, according to the product structure design, such as Figures 9 to 12 The lower insertion end structures of the first gap block 5 and the second gap block 6 are symmetrical to each other, and the lower insertion end of the third gap block 7 is provided in a T-shaped structure, as shown in the figure. Figure 6 The monorail car side wall central panel reverse assembly welding tool includes a tool frame 1, an end positioning stop block 2, a profiling support block 3 and a quick clamping device 4.
[0033] The tool frame 1 and the end positioning stop block 2 of the monorail car side wall central panel reverse assembly welding tool are consistent with the tool frame 1 and the end positioning stop block 2 of the monorail car side wall central panel forward assembly welding tool.
[0034] The profiling support block 3 of the monorail car side wall central panel reverse assembly welding tool is different from the profiling support block 3 of the monorail car side wall central panel forward assembly welding tool in that: (1) the size is slightly different, because the product front and back profiles are opposite, according to the product profile design, the reverse profiling support block of the present embodiment is provided in a stepped type; (2) the profiling support block 3 of the monorail car side wall central panel reverse assembly welding tool is provided with only one pair on each longitudinal beam, located at both ends of each longitudinal beam.
[0035] The quick clamping device 4 of the monorail car side wall central panel reverse assembly welding tool is consistent with the quick clamping device 4 of the monorail car side wall central panel forward assembly welding tool, and the difference lies in that the quick clamping device 4 of the monorail car side wall central panel reverse assembly welding tool is located at both ends of each longitudinal beam.
[0036] Example 2: The monorail car side wall central panel assembly welding process using the monorail car side wall central panel assembly welding tool of Example 1 is as follows: (1) Welding before machining process: an arc guide plate and a lead-out plate 12 (as shown in the figure) are machined on the profile, without the need for additional installation of the arc guide plate and the lead-out plate 12, to avoid welding defects that are prone to occur during the arc striking and arc collecting stages of the aluminum alloy from appearing on the weld. Figure 2
[0037] (2) Forward assembly: As shown in Figure 7 , four parts are sequentially assembled on the monorail car side wall central panel front assembly welding tooling: X-direction positioning is performed by end positioning stopper 2, Y-direction and Z-direction support positioning and welding reverse deformation adjustment are performed by profiling support block 3; First gap plug 5 is inserted between first part 8 and second part 9, second gap plug 6 is inserted between third part 10 and fourth part 11, and third gap plug 7 is inserted at the connection points of the four parts (as shown in Figure 7 ), and the weld gap is controlled (first gap plug 5, second gap plug 6, and third gap plug 7 have no placement order requirements); Close quick clamping device 4 to clamp and fix the four parts; Then spot welding is performed.
[0038] (3) Remove the gap plug and perform front weld welding: start the gantry automatic welding equipment to perform front weld welding, and preferably, stainless steel backing pads are not used when welding the two ends.
[0039] (4) Assemble and weld the reverse weld: After the front weld welding is completed, the part after front welding is lifted by the crane and turned over by 180°, as shown in Figure 8 , and then the part is assembled on the monorail car side wall central panel reverse assembly welding tooling: X-direction positioning is performed by end positioning stopper 2, Y-direction and Z-direction support positioning and welding reverse deformation adjustment are performed by profiling support block 3; Close quick clamping device 4 to clamp and fix the part; Perform reverse weld welding: start the gantry automatic welding equipment to perform front weld welding, and preferably, stainless steel backing pads are not used when welding the two ends.
[0040] (5) After all the welding processes are completed, some existing technology pre-welding machining contents are adjusted to be performed after welding (after welding is completed, the two ends of the central panel are machined into the shape as shown in Figure 1 ), so that the entire weld joint form is exactly the same, and the entire weld can be welded at one time after welding.
[0041] In the existing technology, Figure 1 the green box area is machined before welding, and stainless steel backing plates need to be placed under it before welding, otherwise it will be welded through.
[0042] In the present embodiment, Figure 1 the green box area is not machined before welding but is directly machined into an arc guide plate 12 (as shown in Figure 2 ), and is machined intoFigure 1 Green region shape.
[0043] The above embodiments only illustrate the technical idea of the present application, and cannot limit the protection scope of the present application. Any modification made according to the technical idea of the present application on the basis of the technical scheme falls within the protection scope of the present application. The technology not involved in the present application can be realized by the prior art.
Claims
1. A monorail car side wall center panel assembly welding fixture, characterized in that: The tooling includes a monorail car side wall central panel positive assembly welding tooling and a monorail car side wall central panel reverse assembly welding tooling; The monorail car side wall central panel positive assembly welding tooling includes a tooling frame and end positioning blocks, profiled support blocks, quick clamping devices and a plurality of gap plugs arranged on the tooling frame; the tooling frame includes struts and transverse beams and longitudinal beams arranged on the struts; the end positioning blocks are protrudingly arranged at one end of the tooling frame to position the monorail car side wall central panel in the X direction; the profiled support blocks are arranged on the longitudinal beams to support and position the monorail car side wall central panel in the Y direction and the Z direction, and the profiled support blocks also perform welding reverse deformation adjustment; the quick clamping devices clamp and fix the monorail car side wall central panel; the gap plugs are temporarily placed between the four parts of the monorail car side wall central panel to control the gap of the weld bevel. The monorail car side wall central panel reverse assembly welding tooling also includes the tooling frame and the end positioning blocks, profiled support blocks and quick clamping devices arranged on the tooling frame.
2. The monorail car side wall center panel assembly fixture of claim 1 wherein: The gap plugs are all machined and each includes an upper handle and a lower plug-in end; the upper handle is welded from two round bars; and the lower plug-in end is plugged between parts to control the gap.
3. The monorail car side wall center panel assembly fixture of claim 2 wherein: The gap plugs include first gap plugs, second gap plugs and third gap plugs; the first gap plugs are plugged from the side between the first part and the second part of the monorail car side wall central panel; the second gap plugs are plugged from the side between the third part and the fourth part of the monorail car side wall central panel; and the third gap plugs are plugged from above the connection of the four parts; The lower plug-in end structures of the first gap plugs and the second gap plugs are symmetrical to each other; and the lower plug-in end of the third gap plug is provided in a T-shaped structure.
4. The monorail car side wall center panel assembly fixture of any one of claims 1-3, wherein: The profiled support blocks perform welding reverse deformation adjustment by adjusting the thickness of the adjusting shims: the adjusting shims are arranged between the profiled support blocks and the tooling frame; Each of the longitudinal beams is provided with two pairs of profiled support blocks arranged opposite to each other, and the profiled support blocks are fixed on the longitudinal beams by bolts.
5. The monorail car side wall center panel assembly fixture of claim 4 wherein: Each longitudinal beam of the monorail car side wall central panel positive assembly welding tooling is provided with two pairs of profiled support blocks; Each longitudinal beam of the monorail car side wall central panel reverse assembly welding tooling is provided with one pair of profiled support blocks, which are located at the two ends of the longitudinal beam; And the profiled support block structures of the positive assembly welding tooling and the reverse assembly welding tooling are different in size and match the positive and reverse profiles of the central panel respectively.
6. The monorail car side wall center panel assembly fixture of any one of claims 1-3, wherein: The quick clamping devices are arranged opposite to each other and press and fix the monorail car side wall central panel from above.
7. The monorail car side wall center panel assembly fixture of claim 6 wherein: The quick clamping devices of the monorail car side wall central panel positive assembly welding tooling are protrudingly arranged outside the longitudinal beams at the two ends of the tooling frame and at the two ends of each longitudinal beam to clamp and fix from all around the tooling frame; The quick clamping devices of the monorail car side wall central panel reverse assembly welding tooling are located at the two ends of each longitudinal beam.
8. The gantry automatic welding process using the monorail car side wall central panel assembly welding tooling of any one of claims 1-7, characterized in that: The process includes: (1) A pre-welding machining process: directly machining an arc leading plate and a plate leading plate on the two ends of the central panel; (2) Assemble the components of the monorail car side wall central panel in sequence on the monorail car side wall central panel front assembly welding tool: position in the X direction by the end positioning block, support and position in the Y and Z directions by the profiling support block, and perform welding reverse deformation adjustment; insert a plurality of gap blocks between the components to control the weld gap; close the quick clamping device, clamp and fix the four components, and then tack weld; (3) Remove the gap blocks and start the gantry automatic welding equipment to weld the front welds; (4) Assemble and weld the reverse welds: use the crane to lift the welded components and turn them over by 180°, assemble them on the monorail car side wall central panel reverse assembly welding tool: position in the X direction by the end positioning block, support and position in the Y and Z directions by the profiling support block, and perform welding reverse deformation adjustment; close the quick clamping device, clamp and fix the components; start the gantry automatic welding equipment to weld the reverse welds; (5) After the welding process is completed, remove the arc guide plates and the lead-out plates at both ends of the central panel.
9. The process of claim 8, wherein: During the front weld welding and the reverse weld welding, stainless steel gaskets are not used for welding the welds at both ends.
10. The process according to claim 8 or 9, characterized in that: In step (2), the first gap block is inserted from the side between the first component and the second component, the second gap block is inserted from the side between the third component and the fourth component, and the third gap block is inserted from above at the connection point of the four components; the first gap block, the second gap block, and the third gap block have no placement order requirement.