Assembly jig for a frame and method of assembling a frame

Abstract

The application provides an assembling tool and method for a framework. The assembling tool is provided with a guide cylinder, and can adjust and lock the guide cylinder to a position coaxial with a connecting piece mounting hole of the framework, and ensure coaxiality of the guide cylinder and the connecting piece mounting hole through positioning effect of a positioning column. The assembling method first cold shrinks the connecting piece, and then assembles the cold shrunk connecting piece into the connecting piece mounting hole under guidance of the guide cylinder of the assembling tool. The assembling method can ensure assembly quality, and compared with interference press fitting, the assembling efficiency is improved, and for a carbon fiber material side beam and cross beam, the connecting piece is not easy to cause delamination of the carbon fiber material during assembly. Further, the assembling method performs overall finishing on each pair of rough machining holes, which is more conducive to ensuring assembly quality.

Description

Technical Field

[0001] This application relates to the field of rail vehicle technology, and in particular to an assembly tooling for a frame and a method for assembling the frame. Background Technology

[0002] The frame is a crucial component of a rail vehicle. The frame includes side beams and crossbeams. In one type of frame, the side beams and crossbeams are connected together by connectors, which are interference-fitted with mounting holes on the side beams and crossbeams.

[0003] Previously, connectors were typically pressed into the mounting holes of the side beams and cross beams using a press. This assembly method was inefficient. Furthermore, for carbon fiber side beams and cross beams, this assembly method was prone to causing carbon fiber delamination, which adversely affected the strength of the frame.

[0004] Therefore, how to improve the assembly method of connectors is a technical problem that needs to be solved by those skilled in the art. Summary of the Invention

[0005] To address the aforementioned technical problems, this application provides an assembly fixture for a frame, comprising a guide cylinder, a fixing structure, a position adjusting structure, a position locking structure, and a positioning post. The inner diameter of the guide cylinder is the same as the diameter of the mounting hole for the connecting parts of the frame. The fixing structure is used to fix and connect to the fixture fixing hole of the frame. The position adjusting structure is movably connected to the fixing structure. The guide cylinder is connected to the position adjusting structure, which is used to adjust the position of the guide cylinder. The position locking structure is used to lock the guide cylinder. The positioning post is positioned and engaged with the inner hole of the guide cylinder and can be pulled out from the inner hole of the guide cylinder.

[0006] One embodiment of the assembly fixture for the frame includes a fixing structure comprising a fixing base, a fixing shaft, a fixing claw, and a fixing claw adjusting device. The fixing shaft, the fixing claw, and the fixing claw adjusting device are all assembled on the fixing base. The fixing shaft is parallel to the guide cylinder. The fixing claw is used to extend into the fixing hole of the fixture and abut against the inner wall of the fixing hole. The fixing claw adjusting device is used to adjust the opening diameter of the fixing claw.

[0007] In one embodiment of the assembly fixture for the frame, the end of the fixing claw away from the fixing seat is provided with a limiting part, which is used to abut against the end of the fixture fixing hole away from the fixing seat.

[0008] One embodiment of the assembly fixture for the frame includes a position adjustment structure comprising a rotating bracket and a position locking structure comprising a first locking part. The rotating bracket is rotatably and axially movable and is sleeved outside the fixed shaft. The guide cylinder is connected to the rotating bracket, and the first locking part is used to lock the rotating bracket.

[0009] One embodiment of the assembly fixture for the frame includes a position adjustment structure comprising a sliding bracket and a position locking structure comprising a second locking part. The sliding bracket is connected to the rotating bracket and can slide along a direction perpendicular to the rotation axis of the rotating bracket. The guide cylinder is connected to the sliding bracket, and the second locking part is used to lock the sliding bracket.

[0010] In one embodiment of the assembly tooling for the frame, the guide cylinder is detachably connected to the position adjustment structure.

[0011] In addition, this application also provides a method for assembling a framework, the assembly method comprising the following steps:

[0012] S1. Machine tool fixing holes on the frame;

[0013] S2. Multiple connector mounting holes are machined on the side beams and cross beams of the frame. Each connector mounting hole on the side beam and each connector mounting hole on the cross beam correspond to multiple pairs of connector mounting holes.

[0014] S2. Fix the fixing structure of any of the above-mentioned assembly tooling to the tooling fixing hole of the frame, then use the position adjustment structure of the assembly tooling to adjust the guide cylinder of the assembly tooling to the target position, and make the positioning pin inserted in the inner hole of the guide cylinder also inserted in a pair of target connector mounting holes of the frame, then use the position locking structure of the assembly tooling to lock the guide cylinder in the target position, and then pull the positioning pin out from the inner hole of the guide cylinder and the target connector mounting hole;

[0015] S4. Shrink the connector by cold so that its outer diameter is smaller than the diameter of the connector mounting hole. Insert the shrunken connector into the target connector mounting hole from the end of the guide cylinder away from the connector mounting hole along the inner hole of the guide cylinder.

[0016] In one embodiment of the frame assembly method, in S1, the tooling fixing holes are set within the circumference of the mounting holes of multiple pairs of connectors.

[0017] In one embodiment of the frame assembly method, in S3, when the guide cylinder is adjusted to the target position, one end face of the guide cylinder abuts against the frame.

[0018] In one embodiment of the framework assembly method, S2 includes the following sub-steps:

[0019] S21. Roughly machine multiple rough-machined holes on the side beams and cross beams of the frame. Each rough-machined hole on the side beam and each rough-machined hole on the cross beam correspond to multiple pairs of rough-machined holes.

[0020] S22. Threaded fasteners are passed through at least two pairs of the rough-machined holes to secure the side beam and the cross beam together;

[0021] S23. Finish each pair of rough-machined holes that are not connected to the threaded fasteners into mounting holes for the connectors;

[0022] S24. Threaded fasteners are passed through at least two pairs of mounting holes for the connectors to secure the side beam and the cross beam together.

[0023] S25. Finish the remaining pairs of rough-machined holes into mounting holes for connectors.

[0024] The assembly fixture provided in this application has a positioning fit between the positioning pin and the inner hole of the guide tube, and the inner hole diameter of the guide tube is the same as the mounting hole diameter of the connecting part of the frame. Therefore, when the positioning pin inserted into the inner hole of the guide tube can be inserted into the mounting hole of the connecting part, it indicates that the inner hole of the guide tube and the mounting hole of the connecting part are coaxial.

[0025] The assembly method provided in this application involves cold shrinking the connector so that its outer diameter is smaller than the diameter of the connector mounting hole. Then, the cold-shrink connector is inserted into the connector mounting hole. This improves assembly efficiency compared to interference fit. Moreover, for carbon fiber side beams and cross beams, the connector insertion process is less likely to cause carbon fiber delamination, thus preventing the structural strength from being affected by carbon fiber delamination.

[0026] The assembly method provided in this application ensures that the positioning pin inserted into the inner hole of the guide cylinder is also inserted into a pair of target connector mounting holes in the frame, thus guaranteeing that the inner hole of the guide cylinder is coaxial with the pair of target connector mounting holes. After ensuring the coaxiality of the inner hole of the guide cylinder with the pair of target connector mounting holes, the position of the guide cylinder is locked to stabilize it in the coaxial position. Then, the positioning pin is pulled out from the pair of connector mounting holes and the inner hole of the guide cylinder. Subsequently, the cold-shrinkable connector is inserted into the pair of connector mounting holes from the end of the guide cylinder away from the connector mounting holes along the inner hole of the guide cylinder. In this way, the coaxiality of the cold-shrinkable connector after being inserted into the pair of connector mounting holes is high, and the interference fit between the connector and different circumferential positions of the pair of connector mounting holes after thermal expansion is highly consistent, thereby ensuring assembly quality. Attached Figure Description

[0027] Figure 1 A schematic diagram showing the locations of tooling fixing holes and connector mounting holes on the frame;

[0028] Figure 2This is a perspective view of one embodiment of the assembly fixture for the framework provided in this application.

[0029] The annotations in the attached figures are explained as follows:

[0030] 1 Assembly fixture, 11 Guide cylinder, 12 Fixing structure, 121 Fixing seat, 122 Fixing shaft, 123 Fixing claw, 123a Limiting part, 124 Fixing claw adjusting device, 13 Rotating bracket, 14 Sliding bracket, 15 First locking part, 16 Second locking part, 17 Clamp, 18 Guide cylinder;

[0031] 2 side beams;

[0032] 3 crossbeams;

[0033] A is the tooling fixing hole, and B is the connector mounting hole. Detailed Implementation

[0034] To enable those skilled in the art to better understand the technical solution of this application, the technical solution of this application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0035] like Figure 1 As shown, the frame includes a crossbeam 2 and a side beam 3. Both the crossbeam and the side beam are provided with connector mounting holes B. Each connector mounting hole B on the side beam and each connector mounting hole B on the crossbeam correspond to a pair of connector mounting holes B. Figure 1 In the middle, eight pairs of connector mounting holes B are provided at each of the two horizontal ends of the frame. Figure 1 Only eight pairs of connector mounting holes B are shown at one end. The same connector (not shown) is assembled within the same pair of connector mounting holes B. The connector is interference-fitted with the connector mounting holes B, securing the crossbeam and side beam together via the connector.

[0036] Traditionally, connectors are press-fitted into the connector mounting holes B using a press machine. This method is inefficient and, for carbon fiber side beams and cross beams, can easily cause carbon fiber delamination, affecting the structural strength. Therefore, this application provides a structural assembly fixture and a structural assembly method based on this fixture. This method improves assembly efficiency, ensures assembly quality, and prevents carbon fiber delamination during connector assembly.

[0037] like Figure 2 As shown, the assembly fixture for the frame provided in this application includes a guide cylinder 11, a fixing structure 12, a position adjustment structure, a position locking structure, and a positioning column 18.

[0038] The inner diameter of the guide cylinder 11 is the same as the diameter of the mounting hole B of the connecting part of the frame.

[0039] The fixing structure 12 is used for fixed connection with the tooling fixing hole A of the frame, such as... Figure 1 As shown, the tooling fixing hole A is pre-machined on the frame before assembling the connecting parts.

[0040] The position adjustment structure is used to adjust the position of the guide cylinder 11.

[0041] The position locking structure is used to lock the guide cylinder 11.

[0042] The positioning pin 18 is positioned and engaged with the inner hole of the guide cylinder 11 and can be pulled out from the inner hole of the guide cylinder 11.

[0043] The assembly method of the framework provided in this application includes the following steps:

[0044] S1. Machine tool fixing holes A on the frame.

[0045] S2. Multiple connector mounting holes B are machined on the side beams and cross beams of the frame.

[0046] S3. Fix the fixing structure 12 of the assembly tooling to the tooling fixing hole A of the frame. Then, use the position adjustment structure of the assembly tooling to adjust the guide cylinder 11 of the assembly tooling to the target position, and make the positioning pin 18 inserted in the inner hole of the guide cylinder 11 also inserted in the pair of target connector mounting holes B of the frame. Then, use the position locking structure of the assembly tooling to lock the guide cylinder 11 in the target position, and then pull the positioning pin 18 out from the inner hole of the guide cylinder 11 and the target connector mounting hole B.

[0047] S4. Shrink the connector by cold so that the outer diameter of the connector is smaller than the diameter of the connector mounting hole B. Insert the shrunken connector into the connector mounting hole B from the end of the guide cylinder 11 away from the connector mounting hole B along the inner hole of the guide cylinder 11.

[0048] The above assembly method involves cold shrinking the connector so that its outer diameter is smaller than the diameter of the connector mounting hole B. Then, the cold-shrink connector is inserted into the connector mounting hole B. Compared with interference fit, this method improves assembly efficiency and makes it less likely to cause carbon fiber material delamination during the insertion process, thus preventing the structure strength from being affected by carbon fiber material delamination.

[0049] In the above assembly fixture, since the positioning pin 18 is positioned and fitted with the inner hole of the guide cylinder 11, and the inner hole diameter of the guide cylinder 11 is the same as the diameter of the connecting component mounting hole B of the frame, the positioning pin 18 inserted in the inner hole of the guide cylinder 11 can only be inserted into the connecting component mounting hole B when the inner hole of the guide cylinder 11 is coaxial with the connecting component mounting hole B. In other words, when the positioning pin 18 inserted in the inner hole of the guide cylinder 11 can be inserted into the connecting component mounting hole B, it indicates that the inner hole of the guide cylinder 11 is coaxial with the connecting component mounting hole B.

[0050] Therefore, the above assembly method ensures that the positioning pin 18, which is inserted into the inner hole of the guide cylinder 11, is also inserted into the pair of target connector mounting holes B of the frame, thus guaranteeing that the inner hole of the guide cylinder 11 is coaxial with the pair of target connector mounting holes B. After ensuring that the inner hole of the guide cylinder 11 is coaxial with the pair of target connector mounting holes B, the position of the guide cylinder 11 is locked to stabilize it in the coaxial position. Then, the positioning pin 18 is pulled out from the pair of connector mounting holes B and the inner hole of the guide cylinder 11. After that, the cold-shrinkable connector is inserted into the pair of connector mounting holes B from the end of the guide cylinder 11 away from the connector mounting hole B along the inner hole of the guide cylinder 11. In this way, the coaxiality of the cold-shrinkable connector after being inserted into the pair of connector mounting holes B is high, and the interference fit between the connector and the pair of connector mounting holes B at different circumferential positions after thermal expansion is highly consistent, thereby ensuring the assembly quality.

[0051] In one specific embodiment of the assembly method, in S1, the tooling fixing hole A is set within the circumference of multiple pairs of connector mounting holes B, preferably coaxial with the circumference. For example... Figure 1 In the diagram, the tooling fixing hole A on the left is located within the circumference of the four pairs of connector mounting holes B, and the tooling fixing hole A on the right is located within the circumference of the other four pairs of connector mounting holes B. Thus, during assembly, when the previous pair of target connector mounting holes B and the next pair of target connector mounting holes B are on the same circumference, the guide cylinder 11 only needs to move a small distance to quickly move from a position coaxial with the previous pair of target connector mounting holes B to a position coaxial with the next pair of target connector mounting holes B, thereby improving assembly efficiency.

[0052] In one specific embodiment of the assembly method, S2 includes the following sub-steps:

[0053] S21. Roughly machine multiple rough-machined holes on the side beams and cross beams of the frame. Each rough-machined hole on the side beam and each rough-machined hole on the cross beam correspond to multiple pairs of rough-machined holes.

[0054] S22. Threaded fasteners are passed through at least two pairs of rough-machined holes to secure the side beams and cross beams together.

[0055] To ensure reliable fixation of the side beams and crossbeams, it is preferable to threaded fasteners through at least one pair of rough-machined holes at one end of the frame and at least one pair of rough-machined holes at the other end of the frame. For example, Figure 1 In the middle, threaded fasteners can be threaded through the four pairs of rough-machined holes at one end of the frame and through the four pairs of rough-machined holes at the other end of the frame.

[0056] S23. Finish each pair of rough-machined holes that are not connected to the threaded fasteners into mounting holes B for the connectors;

[0057] S24. Threaded fasteners are passed through at least two pairs of connector mounting holes B to secure the side beam and cross beam together;

[0058] To ensure reliable fixing of the side beams and cross beams, it is preferable to threaded fasteners through at least one pair of connector mounting holes at one end of the frame and at least one pair of connector mounting holes at the other end of the frame. For example, Figure 1 In the middle, threaded fasteners can be threaded through the four pairs of connector mounting holes at one end of the frame and through the four pairs of connector mounting holes at the other end of the frame.

[0059] S25. Finish the remaining pairs of rough-machined holes into mounting holes B for the connector.

[0060] This design allows for overall finishing of each pair of rough-machined holes. Compared to finishing the rough-machined holes on the side beams and cross beams separately, this design is more conducive to improving the coaxiality of each pair of connector mounting holes B, thereby further improving assembly quality.

[0061] In one specific embodiment of the assembly method, in S3, when the guide cylinder 11 is adjusted to the target position, one end face of the guide cylinder 11 abuts against the frame. In this way, the stability of the guide cylinder 11 is better, which is more conducive to the precise guidance of the connecting parts.

[0062] The above-described specific embodiments of the assembly method can be freely combined without conflict.

[0063] A specific embodiment of the assembly tooling, such as Figure 2 As shown, the fixing structure 12 includes a fixing base 121, a fixing shaft 122, a fixing claw 123, and a fixing claw adjusting device 124. The fixing shaft 122, fixing claw 123, and fixing claw adjusting device 124 are all assembled onto the fixing base 121. The fixing shaft 122 is parallel to the guide cylinder 11. The fixing claw adjusting device 124 is used to adjust the opening diameter of the fixing claw 123; a common rotary adjusting device can be used for the fixing claw adjusting device. In application, the fixing claw 123 extends into the tooling fixing hole A, and the fixing claw 123 abuts tightly against the inner wall of the tooling fixing hole A. This fixing structure 12 can quickly connect to and quickly separate from the tooling fixing hole A, which helps improve assembly efficiency. Moreover, the connection with the tooling fixing hole A has high stability.

[0064] A specific embodiment of the assembly tooling, such as Figure 2 As shown, the end of the fixing claw 123 away from the fixing seat 121 is provided with a limiting part 123a. In the application state, the limiting part 123a abuts against the end of the tooling fixing hole A away from the fixing seat 121. In this way, the axial movement of the fixing claw 123 in the tooling fixing hole A can be restricted, which is conducive to further improving the connection stability between the fixing structure 12 and the tooling fixing hole A.

[0065] A specific embodiment of the assembly tooling, such as Figure 2 As shown, the position adjustment structure includes a rotating bracket 13. The rotating bracket 13 is rotatably and axially movable around the fixed shaft 122. The guide cylinder 11 is connected to the rotating bracket 13, thus allowing it to rotate and move axially with the rotating bracket 13. In this way, the rotating bracket 13 can adjust both the angular position of the guide cylinder 11 relative to the fixed shaft 122 and its axial position relative to the fixed shaft 122, providing multiple uses and simplifying the assembly tooling structure. The position locking structure includes a first locking part 15. After the rotating bracket 13 rotates and moves axially into position, the first locking part 15 locks the rotating bracket 13 in place.

[0066] A specific embodiment of the assembly tooling, such as Figure 2 As shown, the first locking part 15 includes a bolt. In the locked state, the bolt is threadedly connected to the threaded hole on the rotating bracket 13, and one end of the bolt abuts against the outer periphery of the fixed shaft 122. Of course, the structure of the first locking part 15 is not limited to this, as long as it can lock the rotating bracket 13.

[0067] A specific embodiment of the assembly tooling, such as Figure 2 As shown, the position adjustment structure includes a sliding bracket 14. The sliding bracket 14 is connected to the rotating bracket 13 and can slide along a direction perpendicular to the rotation axis of the rotating bracket 13. The guide cylinder 11 is connected to the sliding bracket 14, and can slide with the sliding bracket 14. In this way, the radial distance between the guide cylinder 11 and the fixed shaft 122 is adjustable, so as to accommodate both situations where the target connector mounting hole B and the tooling fixing hole A are far apart and situations where the target connector mounting hole B and the tooling fixing hole A are close together. The position locking structure includes a second locking part 16. After the sliding bracket 14 slides into place, the sliding bracket 14 is locked by the second locking part 16.

[0068] A specific embodiment of the assembly tooling, such as Figure 2 As shown, the second locking part 16 includes a stud and two nuts. In the locked state, the stud passes through the through hole on the rotating bracket 13 and connects to the sliding bracket 14. The two nuts are connected to the stud and abut against the two sides of the rotating bracket 13 respectively. Of course, the structure of the second locking part 16 is not limited to this, as long as it can lock the sliding bracket 14.

[0069] A specific embodiment of the assembly tooling, such as Figure 2 As shown, the position adjustment structure is detachably connected to the guide cylinder 11, for example, by means of a clamp 17 or a threaded connection. This makes it easy to replace guide cylinders 11 with different diameters to accommodate the installation of connectors with different diameters.

[0070] A specific embodiment of the assembly tooling, such as Figure 2As shown, a handle 18a is provided at the end of the positioning post 18 to facilitate the removal of the positioning post 18.

[0071] One specific embodiment of the assembly fixture is provided with multiple guide cylinders 11, which are arranged sequentially at intervals on the circumference surrounding the fixed shaft 122, so that multiple connectors can be installed simultaneously.

[0072] The above-described specific embodiments of the assembly tooling can be freely combined without conflict.

[0073] The above examples illustrate the principles and implementation methods of this application. The descriptions of these embodiments are merely for the purpose of helping to understand the method and core ideas of this application. It should be noted that those skilled in the art can make various improvements and modifications to this application without departing from its principles, and these improvements and modifications also fall within the protection scope of the claims of this application.

Claims

1. An assembly fixture for a frame, characterized in that, The assembly fixture includes a guide cylinder (11), a fixing structure (12), a position adjustment structure, a position locking structure, and a positioning post (18). The inner diameter of the guide cylinder (11) is the same as the diameter of the connecting mounting hole (B) of the frame. The fixing structure (12) is used to fix and connect to the fixture fixing hole (A) of the frame. The position adjustment structure is movably connected to the fixing structure (12). The guide cylinder (11) is connected to the position adjustment structure. The position adjustment structure is used to adjust the position of the guide cylinder (11). The position locking structure is used to lock the guide cylinder (11). The positioning post (18) is connected to the guide cylinder (11). The inner hole is positioned and can be pulled out from the inner hole of the guide cylinder (11); the fixing structure (12) includes a fixing seat (121), a fixing shaft (122), a fixing claw (123) and a fixing claw adjustment device (124). The fixing shaft (122), the fixing claw (123) and the fixing claw adjustment device (124) are all assembled on the fixing seat (121). The fixing shaft (122) is parallel to the guide cylinder (11). The fixing claw (123) is used to extend into the tooling fixing hole (A) and abut against the inner wall of the tooling fixing hole (A). The fixing claw adjustment device (124) is used to adjust the opening diameter of the fixing claw (123).

2. The assembly fixture for the frame according to claim 1, characterized in that, The fixing claw (123) has a limiting part (123a) at one end away from the fixing seat (121), and the limiting part (123a) is used to abut against the end of the tooling fixing hole (A) away from the fixing seat (121).

3. The assembly fixture for the frame according to claim 1, characterized in that, The position adjustment structure includes a rotating bracket (13), and the position locking structure includes a first locking part (15). The rotating bracket (13) is rotatably and axially movable and sleeved outside the fixed shaft (122). The guide cylinder (11) is connected to the rotating bracket (13), and the first locking part (15) is used to lock the rotating bracket (13).

4. The assembly fixture for the frame according to claim 3, characterized in that, The position adjustment structure includes a sliding bracket (14), and the position locking structure includes a second locking part (16). The sliding bracket (14) is connected to the rotating bracket (13) and can slide along a direction perpendicular to the rotation axis of the rotating bracket (13). The guide cylinder (11) is connected to the sliding bracket (14), and the second locking part (16) is used to lock the sliding bracket (14).

5. The assembly fixture for the frame according to any one of claims 1-4, characterized in that, The guide cylinder (11) is detachably connected to the position adjustment structure.

6. A method for assembling a frame, characterized in that, The assembly method includes the following steps: S1. Machine tool fixing holes (A) on the frame. S2. Multiple connector mounting holes (B) are machined on the side beams and cross beams of the frame. Each connector mounting hole (B) on the side beam and each connector mounting hole (B) on the cross beam correspond to multiple pairs of connector mounting holes (B). S3. Fix the fixing structure (12) of the assembly tooling according to any one of claims 1-5 to the tooling fixing hole (A) of the frame, and then use the position adjustment structure of the assembly tooling to adjust the guide cylinder (11) of the assembly tooling to the target position, and make the positioning pin (18) inserted in the inner hole of the guide cylinder (11) also inserted in a pair of target connector mounting holes (B) of the frame, and then use the position locking structure of the assembly tooling to lock the guide cylinder (11) in the target position, and then pull the positioning pin (18) out from the inner hole of the guide cylinder (11) and the target connector mounting hole (B); S4. Shrink the connector by cold so that the outer diameter of the connector is smaller than the diameter of the connector mounting hole (B). Insert the shrunken connector from the end of the guide cylinder (11) away from the connector mounting hole (B) into the target connector mounting hole (B) along the inner hole of the guide cylinder (11).

7. The assembly method of the frame according to claim 6, characterized in that, In S1, the tooling fixing hole (A) is set within the circumference of the multiple pairs of connector mounting holes (B).

8. The assembly method of the frame according to claim 6, characterized in that, In S3, when the guide cylinder (11) is adjusted to the target position, one end face of the guide cylinder (11) abuts against the frame.

9. The method for assembling the frame according to any one of claims 6-8, characterized in that, S2 includes the following sub-steps: S21. Roughly machine multiple rough-machined holes on the side beams and cross beams of the frame. Each rough-machined hole on the side beam and each rough-machined hole on the cross beam correspond to multiple pairs of rough-machined holes. S22. Threaded fasteners are passed through at least two pairs of the rough-machined holes to secure the side beam and the cross beam together; S23. Finish each pair of rough-machined holes that are not connected to the threaded fasteners into mounting holes for the connectors (B). S24. Threaded fasteners are passed through at least two pairs of the connecting mounting holes (B) to secure the side beam and the cross beam together; S25. Finish the remaining pairs of rough-machined holes into mounting holes for connectors (B).

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