Front cover assembly tool capable of automatically screwing bolts

Abstract

The invention relates to the field of body-in-white automatic assembly, in particular to a front cover assembly tool capable of automatically screwing bolts, which comprises a C-shaped hanging bracket, a frame is fixed at the bottom of the hanging bracket, a tool positioning component and a front cover positioning component are detachably and symmetrically arranged on the frame, two screwing guns are detachably and symmetrically arranged on the frame, and the screwing guns are connected with floating mechanisms. A centering mechanism is arranged on the frame, a gravity center adjusting mechanism is arranged on the top of the hanging bracket and comprises an adjusting sliding rail fixed to the top of the hanging bracket and an adjusting sliding seat connected to the adjusting sliding rail in a sliding mode, and a connecting seat is installed on the adjusting sliding seat and used for being externally connected with transfer equipment. The hanging bracket is provided with a locking assembly used for locking the adjusting sliding seat. The gravity center of the tool can be adjusted according to different vehicle types through the gravity center adjusting mechanism, so that the tool can adapt to various vehicle types, the application range is wide, and the flexibility is high.

Description

Technical Field

[0001] The invention relates to the field of automatic assembly of body-in-white, and in particular to a front cover assembly tool for automatic bolt tightening. Background Art

[0002] In the process of assembling the front cover of the body in white, the tooling used in the prior art includes built-in and split types. The built-in tooling is installed in the body when in use. After the front cover of the body is closed, the bolts on the front cover are tightened manually, which requires a lot of manual labor and is inefficient. The split tooling needs to be fixed at multiple positions of the front cover and the consistency of the fixation must be ensured, which requires a lot of work and is difficult to operate. Therefore, the applicant intends to develop an integrated assembly tool for automatically tightening the bolts of the front cover to achieve automatic tightening of the bolts of the front cover and improve assembly efficiency.

[0003] The prior art discloses an automatic closing nailing assembly device for the front cover of a vehicle body (publication number: CN217394261U; application date: 2021-12-30), including a welding frame, a floating cylinder, a handle, a guide pin, a linkage centering mechanism, a floating mechanism and a tightening gun. The welding frame includes an upper frame and a lower frame. A floating cylinder and a guide block are arranged between the upper frame and the lower frame. A linkage centering mechanism is arranged in the upper middle position of the upper frame. A floating mechanism is also arranged on the upper part of the upper frame. The floating mechanism includes connecting block I, connecting block II, connecting block III, connecting block IV, spring guide column, switch control cylinder, clamp block I and clamp block II. Support blocks for supporting the front cover of the vehicle body are arranged on the sides of the upper frame and the lower frame, and a suspension is also arranged on the side of the welding frame. The fixture is connected to the body frame by inserting the guide pin into the mounting hole of the body spring leg through the guide pin, and then inserting the positioning pin on the linkage centering mechanism into the body process pin hole to achieve precise positioning and fixture alignment; the body hood is placed on the fixture by hanging, and the relative position of the body hood and the fixture is also fixed by the guide block on the fixture. During the placement of the hood, the floating cylinder is compressed by the weight of the hood, and the floating mechanism generates an upward thrust through the spring guide column to achieve the engagement of the nut on the hood with the tightening gun head. The existing technology can realize the automatic assembly of the body hood, but the existing technology still has the following problems:

[0004] 1. The welding frame includes an upper frame and a lower frame. A floating cylinder and a guide block are arranged between the upper frame and the lower frame. The tightening gun, the linkage centering mechanism and other components are installed on the upper frame. Such a structure causes the welding frame to occupy more vertical space, increases the overall volume and weight of the welding frame, makes it difficult to apply it to models with a compact body head structure, and also puts forward higher requirements for transfer equipment such as robots. Therefore, the scope and flexibility of the use of the existing technology are limited.

[0005] 2. The existing technology uses a spring guide column to achieve the floating of the tightening gun, and the spring is exposed to the outside. During long-term use, the spring part is prone to rust and is easily attached with dust and impurities, resulting in a stuck phenomenon. This seriously reduces the service life of the spring guide column and increases the replacement frequency of the spring guide column, which in turn leads to an increase in equipment maintenance costs. Summary of the invention

[0006] The present invention aims to provide a front cover assembly tool for automatically tightening bolts, so as to solve the problem that the existing automatic assembly equipment for the front cover of a vehicle body has narrow applicability and can only be adapted to the same type of vehicle model.

[0007] In order to achieve the above object, the present invention adopts the following technical scheme:

[0008] A front cover assembly tool for automatically tightening bolts, including a C-shaped hanger, a frame fixed at the bottom of the hanger, a tool positioning component and a front cover positioning component detachably and symmetrically arranged on the frame, two tightening guns detachably and symmetrically arranged on the frame, the tightening guns are connected with a floating mechanism, a centering mechanism is arranged on the frame, a center of gravity adjustment mechanism is arranged on the top of the hanger, the center of gravity adjustment mechanism includes an adjustment slide rail fixed on the top of the hanger and an adjustment slide seat slidably connected to the adjustment slide rail, a connecting seat is installed on the adjustment slide seat, the connecting seat is used for external transfer equipment, and a locking assembly for locking the adjustment slide seat is arranged on the hanger.

[0009] Preferably, as an improvement, the locking assembly includes a locking pin hole provided on the side of the adjusting slide rail and a spring plunger fixed on the adjusting slide seat, and the spring plunger is used to be inserted into the locking pin hole to lock the adjusting slide seat.

[0010] Preferably, as an improvement, an adjustment scale is provided on the hanger, and a reading pointer for reading on the adjustment scale is provided on the positioning slide.

[0011] Preferably, as an improvement, C-shaped reinforcing sheet metal is fixed on both sides of the hanger.

[0012] Preferably, as an improvement, the tool positioning assembly includes a tool positioning block and a body fixture, there are four tool positioning blocks and four body fixtures, and the four tool positioning blocks and four body fixtures are symmetrically arranged on both sides of the frame.

[0013] Preferably, as an improvement, the front cover positioning assembly includes a front cover positioning pin and a front cover clamp, the front cover positioning pins are arranged on both sides of the frame, and the front cover clamps are arranged on the front side and the rear side of the frame.

[0014] Preferably, as an improvement, a tightening gun mounting plate is fixed on the frame, the tightening gun is fixed on the tightening gun mounting plate, and the floating mechanism includes a floating cylinder and a floating guide rail mounted on the tightening gun mounting plate.

[0015] Preferably, as an improvement, the centering mechanism includes a rocker arm, the middle part of the rocker arm is rotatably connected to the frame, the rocker arm can swing in a vertical plane, connecting rods are hinged at both ends of the rocker arm, sliders are hinged at both ends of the connecting rod, a centering slide rail is fixed on the frame, the slider is horizontally slidably connected to the centering slide rail, the slider is connected to a vertical body locating pin, the connecting rod includes a sleeve and connecting heads threadedly connected to both ends of the sleeve, the two connecting heads are respectively hinged to the rocker arm and the slider, and the distance between the two body locating pins is the same as the distance between the locating holes on the body when the rocker arm and the connecting rod are under force balance.

[0016] Preferably, as an improvement, a slide groove is provided on the slider, the slider is slidably connected to the centering slide rail via the slide groove, and the slider is connected to an oil filling pipe joint for injecting lubricating oil into the slide groove.

[0017] Preferably, as an improvement, two limit plates are fixed on the frame, the slider is connected to the limit block, the limit block is located between the two limit plates, and pads are fixed on both sides of the limit block and the inner side of the limit plate.

[0018] The principles and beneficial effects of this scheme are:

[0019] 1. A C-shaped hanger is used, and a connecting seat is set on the top of the hanger to connect to an external robot or other lifting and transporting equipment. The solution is lifted to the position above the front cover of the vehicle body by the robot or other transporting equipment, and then lowered into the vehicle body. The centering mechanism is used to center the tooling and place it in the vehicle body. The tooling is then connected and positioned with the vehicle body by the tooling positioning assembly. After positioning, the front cover is connected and positioned with the tooling by the front cover positioning assembly under the cover. Finally, the bolts on the front cover are automatically tightened by a tightening gun to complete the automatic assembly of the front cover.

[0020] In this solution, the tightening gun, tool positioning assembly, front cover positioning assembly, centering mechanism and other structures are detachably integrated on the frame at the bottom of the hanger. The center of gravity of the entire tool is located at the bottom of the hanger, and the top of the hanger is connected to the lifting and transfer equipment such as the robot. Since the positions of the tightening gun, tool positioning assembly, front cover positioning assembly, centering mechanism and other structures corresponding to different vehicle models are different, the center of gravity of the tool is different. Therefore, this solution sets an adjustment slide at the top of the hanger. By adjusting the position of the adjustment slide so that it is aligned with the center of gravity of the tool on the vertical plane, the center of gravity of the tool can be stabilized when it is hoisted, and the entire tool can be lowered into the vehicle body horizontally and steadily. In conjunction with the centering of the centering mechanism, the accuracy of the tooling is guaranteed, and the accuracy of the subsequent front cover assembly is guaranteed.

[0021] In summary, this solution adopts a C-shaped hanger, and all structures are detachably integrated at the bottom of the hanger. The center of gravity adjustment mechanism at the top of the hanger can adjust the center of gravity of the tooling according to the different integrated structural positions of different vehicle models, so that the tooling can adapt to a variety of vehicle models, with a wide range of uses and high flexibility.

[0022] Since the center of gravity of the tooling is located at the bottom, this solution uses a C-shaped hanger and sets the center of gravity adjustment mechanism at the top of the hanger. By using the principle of center of gravity alignment, the center of gravity of the tooling after being hoisted can be easily adjusted by simply adjusting the position of the sliding seat. This is more convenient than the traditional method of adjusting the center of gravity by adjusting the tightening gun, floating mechanism and other structures. Furthermore, the tightening gun, tooling positioning assembly, front cover positioning assembly, etc. are all symmetrically arranged on the frame, which can further ensure the stability of the center of gravity of the tooling.

[0023] 2. During the adjustment of the slide, the moving distance of the slide can be visually observed by adjusting the scale and the reading pointer, which is convenient for the operator to observe and record. This design improves the visualization of the operation, allowing the operator to more accurately grasp the position information of the slide, thereby more accurately adjusting the center of gravity of the tooling.

[0024] 3. The hanger of this tooling is assembled through porous hexagonal metal tubes, and an integrated C-shaped reinforced sheet metal is fixed on both sides of the hanger, which can provide better bending rigidity and out-of-plane stability, thereby further improving the structural strength of the hanger. The use of porous metal tubes can also reduce the weight of the tooling and facilitate lifting.

[0025] 4. When the tool is placed in the vehicle body during actual use, the vehicle body locating pins on the centering mechanism can drive the two connecting rods to move synchronously outward or inward by the same distance through the swing of the rocker arm, so as to achieve fine adjustment of the positions of the two vehicle body locating pins and compensate for the position deviation of the vehicle body locating holes caused by processing errors, so that the two vehicle body locating pins can be inserted into the locating holes of the vehicle body correspondingly, thereby making the front cover assembly tooling fixed in a center on the vehicle body, completing the centering and fixation of the front cover assembly tooling.

[0026] The centering mechanism of this tool sets the rocker arm to swing in the vertical plane. The rocker arm and the connecting rod reach a force balance state under the action of gravity. In actual use, the distance between the two body locating pins in this balance state is set to be equal to the distance between the two locating holes on the body. This setting makes it unnecessary to add a swinging drive member to drive the rocker arm to swing. Instead, during the lowering process, the weight of the front cover assembly tool (200-300 kg) is used to squeeze the two body locating pins into the body locating holes, thereby driving the rocker arm to swing. In summary, the design of the centering mechanism of this tool does not require additional configuration of a drive member to drive the rocker arm, which saves equipment costs and reduces the volume and space occupied by the front cover assembly tool.

[0027] 5. In addition to the range of motion of the three-link mechanism composed of the rocker arm and the two connecting rods, the range of motion of the vehicle body locating pin can also be adjusted by adjusting the length of the connecting rod itself. The length of the connecting rod itself can be adjusted by adjusting the length of the connecting head on the connecting rod, so that the adjustment range of the centering mechanism can be reduced or expanded on the basis of the range of motion of the three-link mechanism, which can meet the centering needs of different vehicle models.

[0028] 6. The oil filling pipe joint is used to connect the external lubricating oil pipeline to inject lubricating oil into the dovetail groove, thereby lubricating the centering rail and the slider to avoid sticking and improve the smoothness of sliding.

[0029] 7. The tightening gun is supported by a floating cylinder. After the front cover is closed, the floating cylinder drives the tightening gun to move up close to the inner wall of the front cover. When the tightening gun contacts the front cover, it continues to move up, so that the two floating cylinders are pressed down to form a pre-tightening force. During the tightening process, the two tightening guns can move up as the nut is screwed upward under the action of the floating cylinder, always keeping the gun head of the tightening gun in close contact with the front cover to ensure that the nut is tightened smoothly. This solution uses a floating cylinder to provide pre-tightening force for the tightening gun. Compared with the prior art, this solution can precisely adjust the air pressure of the floating cylinder through a precision pressure regulating valve, thereby precisely adjusting the pre-tightening force of the tightening gun. This design can be applied to the assembly requirements of various vehicle models, and has high adjustment accuracy, ensuring the tightening quality and accuracy. In addition, this solution also provides a floating guide rail, which can guide the tightening gun, improve its vertical floating stability, ensure the stability and accuracy of the tightening gun during operation, and enhance the reliability and durability of the equipment.

[0030] 8. This solution uses a floating cylinder to provide floating and restoring force. Compared with the spring sleeve, the floating accuracy is higher and more controllable. It can also effectively avoid the problems of jamming and rapid rusting of the spring sleeve due to exposure, effectively extending the service life of the parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 It is a schematic structural diagram of an embodiment of the present invention.

[0032] Figure 2 Schematic diagram of the structure of the hanger in the embodiment of the present invention.

[0033] Figure 3 for Figure 2 Schematic diagram of part of the structure.

[0034] Figure 4 for Figure 1 Schematic diagram of part of the structure.

[0035] Figure 5 It is a partial top view of an embodiment of the present invention.

[0036] Figure 6It is a structural schematic diagram of the centering mechanism of the present invention.

[0037] Figure 7 for Figure 6 Schematic diagram of part of the structure. DETAILED DESCRIPTION

[0038] The following is further described in detail through specific implementation methods:

[0039] The figure marks in the drawings of the specification include: hanger 1, porous hexagonal steel pipe 11, reinforced sheet metal 12, center of gravity adjustment mechanism 13, connecting seat 130, reading pointer 131, adjustment scale 132, spring plunger 133, adjustment slide 134, locking pin hole 135, adjustment slide rail 136, frame 2, tooling positioning block 3, body fixture 31, front cover positioning pin 4, front cover positioning cylinder 41, hook pin cylinder 42, hook pin cylinder driving cylinder 43, hook pin 44, clamping cylinder 45, tightening gun 5, floating guide rail 51, floating cylinder 52, centering mechanism 6, centering slide rail 60, rocker arm 61, connector 62, sleeve 63, slider 64, body positioning pin 65, oil filling pipe joint 66, limit plate 67, cushion block 68, limit block 69.

[0040] Example:

[0041] like Figure 1 and Figure 2 As shown, a front cover assembly tool for automatically tightening bolts includes a C-shaped hanger 1, which is composed of a plurality of porous hexagonal steel pipes 11 connected together. C-shaped reinforcing sheet metal 12 is bolted to both sides of the hanger 1 to improve the structural strength of the entire hanger 1. A center of gravity adjustment mechanism 13 is installed on the top of the hanger 1. Figure 3 As shown, the center of gravity adjustment mechanism 13 includes an adjustment rail 136 bolted to the top of the hanger 1 and an adjustment slide 134 slidably connected to the adjustment rail 136. A connection seat 130 is bolted to the adjustment slide 134. The connection seat 130 is used to connect to an external lifting and transportation device. In this embodiment, the transportation device is a robot. The hanger 1 is provided with a locking assembly for positioning the adjustment slide 134. The locking assembly includes a locking pin hole 135 opened on the side of the adjustment rail 136 and a spring plunger 133 bolted to the adjustment slide 134. The spring plunger 133 is used to be inserted into the locking pin hole 135 to lock the adjustment slide 134. An adjustment scale 132 is also bolted to the side of the top of the hanger 1, and a reading pointer 131 for sliding reading on the adjustment scale 132 is bolted to the positioning slide.

[0042] Combination Figure 4 and Figure 5As shown, the frame 2 is fixed with bolts at the bottom of the hanger 1, and the frame 2 is symmetrically provided with a tooling positioning assembly and a front cover positioning assembly which are detachably provided. The tooling positioning assembly includes a tooling positioning block 3 and a body fixture 31. There are four tooling positioning blocks 3 and four body fixtures 31, and the four tooling positioning blocks 3 and the four body fixtures 31 are symmetrically provided on both sides of the frame 2. The body fixture 31 is a clamping cylinder, and the clamping cylinder and the tooling positioning block 3 are detachably fixed to the frame 2 by bolts. The positions of the tooling positioning block 3 and the body fixture 31 are different according to different vehicle models. The function of the tooling positioning block 3 is to support and position the tooling at the corresponding position of the body after the tooling is hoisted and lowered into the body.

[0043] The front cover positioning assembly includes a front cover positioning pin 4 and a front cover clamp. The front cover positioning pin 4 is connected to a front cover positioning cylinder 41, and the front cover positioning cylinder 41 is fixed to both sides of the frame 2 by bolts. The front cover clamp is provided on the front side (the side away from the hanger 1) and the rear side of the frame 2. The front cover clamp on the front side of the frame 2 adopts a hook pin cylinder assembly. The hook pin cylinder assembly is divided into two groups. The two groups of hook pin cylinder assemblies are symmetrically fixed to the frame 2 by bolts. The hook pin cylinder assembly includes a hook pin cylinder 42 and a hook pin cylinder driving cylinder 43 for driving the hook pin cylinder 42 to rise and fall. The hook pin cylinder 42 is used to insert into the positioning hole on the inner side of the front cover and clamp. The front cover clamp on the rear side of the frame 2 adopts a clamping cylinder 45. The number of the clamping cylinders 45 is two and the two clamping cylinders 45 are symmetrically installed on the frame 2 by bolts. The two clamping cylinders 45 are used to clamp the front side edge of the front cover after the front cover is closed.

[0044] Two tightening gun mounting plates are bolted to the front side of the frame 2, and tightening guns 5 are fixed to the tightening gun mounting plates. The two tightening guns 5 are symmetrically arranged, and the two tightening guns 5 are both equipped with a floating mechanism. The floating mechanism includes a floating cylinder 52 and a floating guide rail 51 bolted to the tightening gun mounting plates. The floating cylinder 52 adopts a slide cylinder.

[0045] Combination Figure 6 and Figure 7As shown, a centering mechanism 6 is installed on the top of the frame 2. The centering mechanism 6 includes a swing rod 61. The middle part of the swing rod 61 is rotatably connected to the frame 2. The swing rod 61 can swing on a vertical plane. Connecting rods are hinged at both ends of the swing rod 61. Slide blocks 64 are hinged at both ends of the connecting rod. The slide block 64 is bolted to a vertical body positioning pin 65. A centering slide rail 60 is bolted to the frame 2. A slide groove is provided on the slide block 64. The slide block 64 is slidably connected to the centering slide rail 60 through the slide groove. The slide block 64 is connected to an oil filling pipe joint 66 for injecting lubricating oil into the slide groove. The connecting rod includes a sleeve 63 and a connector 62 threadedly connected to both ends of the sleeve 63. The two connectors 62 are hinged to the swing rod 61 and the slide block 64 respectively. The distance between the two body positioning pins 65 of the swing rod 61 and the connecting rod in a force-balanced state is the same as the distance between the positioning holes on the body. Two limit plates 67 are bolted to the frame 2 , the slider 64 is bolted to the limit block 69 , the limit block 69 is located between the two limit plates 67 , and pads 68 are bolted to both sides of the limit block 69 and the inner side of the limit plate 67 .

[0046] A method for using a front cover assembly tool for automatically tightening bolts:

[0047] 1. Adjust the center of gravity: manually push the adjustment slide 134 to slide on the adjustment slide rail 136, and refer to the position of the adjustment reading pointer 131 on the adjustment scale 132 to accurately adjust the position of the adjustment slide 134, so that it slides to a position where its center of gravity is aligned with the overall center of gravity of the bottom of the hanger 1 in the vertical direction, and then press the spring plunger 133 so that the spring plunger 133 is inserted into the locking pin hole 135 to lock the adjustment slide 134, thereby completing the center of gravity adjustment of this tooling. When the tooling with adjusted center of gravity is subsequently connected to the robot and hoisted, the tooling can be in a horizontal and vertical state, that is, the top and bottom of the hanger 1 are both horizontal, without left and right or front and back tilts, which is convenient for subsequent accurate fixing of the tooling to the vehicle body.

[0048] 2. Tool hoisting and alignment: The front cover is preliminarily installed on the body manually. The bolts of the front cover are screwed into the bolt holes in advance but not tightened. When the front cover is open, it is connected to the robot or other hoisting and transportation devices through the connection seat 130 on the top of the hanger 1. In this embodiment, the robot is used as an example. The robot hoists the tool just above the front cover of the car body, with the front side of the frame 2 facing the car body. After the robot finds the position, it slowly lowers the tool vertically into the car body. Although the robot has found the position, due to the machining error of the positioning holes on the car body, there is a slight deviation in the position of the positioning holes on the car body. Therefore, when the tool is lowered to the car body, the two body positioning pins 65 cannot be completely aligned with the positioning holes, but are pressed against the edges of the positioning holes. Therefore, during the lowering process, the two body locating pins 65 are squeezed into the body locating holes under the deadweight of the front cover assembly tooling, so that the two body locating pins 65 simultaneously move the same distance inward or outward under the swinging action of the rocker arm 61 and the two connecting rods, thereby achieving fine adjustment of the two body locating pins 65, so that the two body locating pins 65 can be accurately inserted into the corresponding body locating holes, and then the tooling is placed in a center on the body, completing the centering of the tooling, facilitating the subsequent assembly of the front cover, and ensuring the assembly accuracy of the front cover.

[0049] 3. Tool positioning: After the tool is hoisted into place, four body positioning blocks are supported on the body. After the centering is completed, the body is clamped from both sides by four body clamps 31, thereby fixing the tool on the body, providing a stable foundation for the subsequent assembly of the front cover.

[0050] 4. Front cover positioning: Cover the front cover, the front cover positioning cylinder 41 drives the front cover positioning pin 4 to rise and insert into the positioning holes on both sides of the front cover, and at the same time, the two hook pin cylinder driving cylinders 43 on the front side of the frame 2 drive the hook pin cylinder 42 to move up, so that the hook pin 44 on the hook pin cylinder 42 is inserted into the positioning hole at the hinge of the front cover, and after the insertion, the hook pin cylinder 42 drives the positioning hook on the hook pin 44 to move up and clamp the front cover. At the same time, the two clamping cylinders 45 on the rear side of the frame 2 clamp the front cover from the outside of the front cover, thereby completing the positioning of the front cover and fixing the front cover on the tooling.

[0051] 5. Automatically tighten the bolts: After the front cover is positioned, the floating cylinder 52 drives the tightening gun 5 to move upward so that the gun head of the tightening gun 5 is pressed against the bolt in the threaded hole on the front cover. After the gun head contacts the bolt, it continues to move upward so that the floating cylinder 52 is compressed to form a pre-tightening force. Then the tightening gun 5 acts to tighten the bolt. During the tightening process, the tightening gun 5 moves upward as the bolt is tightened upward under the action of the pre-tightening force of the floating cylinder 52, and the gun head of the tightening gun 5 is always kept in close contact with the bolt to ensure smooth tightening of the bolt.

[0052] This solution adopts an integral tooling, with symmetrical positioning on both sides and front and back, to stably connect the body-tooling-front cover. Compared with the split tooling, this tooling structure has strong integrity and high consistency, and can position both sides of the front cover at the same time, ensuring the accuracy and efficiency of the front cover assembly. In addition, the tooling is also centered by driving the centering mechanism 6 to move when the tooling is lowered, without the need to use additional driving parts to drive the centering mechanism 6, saving equipment costs, reducing equipment size and weight, facilitating hoisting, and facilitating use in assembly in narrow spaces.

[0053] The above is only an embodiment of the present invention, and the common knowledge such as the known specific technical solutions and / or characteristics in the solution is not described in detail here. It should be pointed out that for those skilled in the art, without departing from the technical solution of the present invention, several modifications and improvements can be made, which should also be regarded as the protection scope of the present invention, and these will not affect the effect of the implementation of the present invention and the practicality of the patent. The scope of protection required by this application shall be based on the content of its claims, and the specific implementation methods and other records in the specification can be used to interpret the content of the claims.

Claims

1. A front cover assembly tool for automatically tightening bolts, characterized by: It includes a C-shaped hanger, a frame is fixed at the bottom of the hanger, a tool positioning component and a front cover positioning component are detachably and symmetrically arranged on the frame, two tightening guns are detachably and symmetrically arranged on the frame, the tightening guns are connected with a floating mechanism, a centering mechanism is arranged on the frame, a center of gravity adjustment mechanism is arranged on the top of the hanger, the center of gravity adjustment mechanism includes an adjustment slide rail fixed on the top of the hanger and an adjustment slide seat slidably connected to the adjustment slide rail, a connecting seat is installed on the adjustment slide seat, the connecting seat is used for external transfer equipment, and a locking assembly for locking the adjustment slide seat is arranged on the hanger.

2. The front cover assembly tool for automatic bolt tightening according to claim 1, characterized in that: The locking assembly comprises a locking pin hole arranged on the side of the adjusting slide rail and a spring plunger fixed on the adjusting slide seat. The spring plunger is used for being inserted into the locking pin hole to lock the adjusting slide seat.

3. The front cover assembly tool for automatic bolt tightening according to claim 2, characterized in that: An adjusting scale is arranged on the hanger, and a reading pointer for reading on the adjusting scale is arranged on the positioning slide.

4. The front cover assembly tool for automatic bolt tightening according to claim 3, characterized in that: C-shaped reinforcement plates are fixed on both sides of the hanger.

5. The front cover assembly tool for automatic bolt tightening according to claim 1, characterized in that: The tooling positioning assembly comprises a tooling positioning block and a vehicle body fixture. There are four tooling positioning blocks and four vehicle body fixtures, and the four tooling positioning blocks and four vehicle body fixtures are symmetrically arranged on both sides of the frame.

6. The front cover assembly tool for automatic bolt tightening according to claim 5, characterized in that: The front cover positioning assembly comprises a front cover positioning pin and a front cover clamp. The front cover positioning pins are arranged on both sides of the frame, and the front cover clamps are arranged on the front side and the rear side of the frame.

7. The front cover assembly tool for automatic bolt tightening according to claim 6, characterized in that: A tightening gun mounting plate is fixed on the frame, the tightening gun is fixed on the tightening gun mounting plate, and the floating mechanism comprises a floating cylinder and a floating guide rail which are installed on the tightening gun mounting plate.

8. The front cover assembly tool for automatic bolt tightening according to any one of claims 1 to 7, characterized in that: The centering mechanism includes a rocker arm, the middle part of which is rotatably connected to the frame, the rocker arm can swing on a vertical plane, connecting rods are hinged at both ends of the rocker arm, sliders are hinged at both ends of the connecting rod, a centering slide rail is fixed on the frame, the slider is horizontally slidably connected to the centering slide rail, the slider is connected to a vertical body locating pin, the connecting rod includes a sleeve and connecting heads threadedly connected to both ends of the sleeve, the two connecting heads are respectively hinged to the rocker arm and the slider, and the distance between the two body locating pins is the same as the distance between the locating holes on the body when the rocker arm and the connecting rod are under force balance.

9. The front cover assembly tool for automatic bolt tightening according to claim 8, characterized in that: A slide groove is provided on the slide block, and the slide block is slidably connected to the centering slide rail through the slide groove. The slide block is connected to an oil filling pipe joint for injecting lubricating oil into the slide groove.

10. The front cover assembly tool for automatic bolt tightening according to claim 9, characterized in that: Two limit plates are fixed on the frame, the slider is connected with the limit block, the limit block is located between the two limit plates, and cushion blocks are fixed on both sides of the limit block and the inner side of the limit plate.

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