Vehicle body side wall skin tensioning method

Abstract

The invention provides a vehicle body side wall skin tensioning method which comprises the following steps: step S10, tensioning pretreatment: checking the straightness of a vehicle body framework by using a guiding rule, pasting a sponge strip on the vehicle body framework, and improving the subsequent installation fitting degree of the side wall skin and the vehicle body framework through the tensioning pretreatment; s20, skin tensioning is conducted, specifically, the two sets of process skins are welded to the two ends of the side wall skin correspondingly, two sets of skin tensioning devices are arranged to conduct tensioning on the two sets of process skins correspondingly, and then tensioning of the side wall skin is achieved; and S30, tensioning post-treatment is conducted, specifically, after the side wall skin is tensioned, reinforcing welding and polishing finishing are conducted on the side wall skin. According to the technical scheme, the problem that in the prior art, the side wall skin is low in tension flatness is effectively solved.

Description

Technical Field

[0001] This application relates to the technical field of skin stretching, and particularly to a method for stretching the skin of a vehicle body side wall. Background Art

[0002] With the continuous development of the bus industry market, product quality and lightweight are one of the most important ways for each bus industry to survive in the competition. High-quality side wall skins can effectively improve the sealing and noise reduction effects of the whole vehicle. Stretching the side wall skin makes the side wall skin reach the plastic deformation zone, resulting in deformation strengthening, so that the yield limit of the side wall skin is improved, the ability to resist deformation is enhanced, the stiffness of the whole vehicle is increased, and the safety performance of the whole vehicle is improved. At the same time, the natural frequency of the side wall skin can be increased, effectively reducing the noise generated by the side wall skin during driving. During the automobile manufacturing process, there are many welding processes. When the surface of the side wall skin is uneven, during the painting production process, putty needs to be filled. The part where the putty is filled is prone to cracking during the vehicle operation due to vehicle vibration and bumping, and then the topcoat cracks and peels off.

[0003] In some existing stretching methods (for example: the application number is 202111671871.2, and the name is: Bus Side Wall Aluminum Skin Stretching Process), it includes: Step S1, paste high-temperature resistant sponge on the vehicle body frame; Step S2, attach the aluminum skin to the high-temperature resistant sponge, and at the same time fix the front end of the aluminum skin to the vehicle body frame; Step S3, clamp the tail end of the aluminum skin by a stretching device, and synchronously heat the aluminum skin by a heating device while stretching the aluminum skin; Step S4, fix the tail end of the aluminum skin to the vehicle body frame after stretching. This stretching method can reduce obvious defects such as wrinkles and waves on the skin, but the small uneven defects on the surface of the side wall skin cannot be eliminated, so the flatness of the side wall skin still needs to be improved. Summary of the Invention

[0004] One technical problem to be solved by this application is: to improve the flatness of the stretching of the side wall skin.

[0005] To solve the above technical problem, the embodiment of this application provides a method for stretching the skin of a vehicle body side wall, including the following steps: Step S10: Pretreatment before stretching, use a straightedge to check the straightness of the vehicle body frame, paste a sponge strip on the vehicle body frame, and improve the installation fit degree of the subsequent side wall skin and the vehicle body frame through the pretreatment before stretching; Step S20: Skin stretching, weld two groups of process skins to both ends of the side wall skin respectively, set two groups of skin stretching devices to stretch the two groups of process skins respectively, and then realize the stretching of the side wall skin; Step S30: Post-treatment after stretching, carry out reinforcement welding and grinding and trimming on the side wall skin after the stretching of the side wall skin is completed.

[0006] In some embodiments, the skin stretching includes the following steps: Step S21, loading the side skin, lifting the side skin onto the support frame, and flattening the side skin against the vehicle body frame, and temporarily fixing the upper edge of the side skin to the side frame using a fixture; Step S22, welding the process skin, welding two groups of process skins to both ends of the side skin respectively; Step S23, opening holes in the side skin, using a plasma cutting machine to cut notches at the interference between the side skin and the vehicle body frame so that the side skin can closely adhere to the side frame; Step S24, stretching operation, stretching the two groups of process skins respectively through two groups of skin stretching devices, thereby realizing the stretching of the side skin.

[0007] In some embodiments, the skin stretching further includes the step: Step S25, obtaining the stretching amount. Before the stretching operation, mark a straight line on the side skin and the corresponding vehicle body frame. After the stretching operation, measure the distance between the straight line on the side skin and the straight line on the vehicle body frame using a tape measure or a displacement sensor, and this distance is the stretching amount.

[0008] In some embodiments, the skin stretching further includes the step: Step S26, fixing the side skin. Fix one end of the side skin and the vehicle body frame in order from top to bottom. First, use a single-sided electric welding machine for spot welding, and then use a CO2 shielded welding machine for plug welding, and grind the welds smooth.

[0009] In some embodiments, during the welding of the process skin, fix the two groups of process skins on the two groups of skin stretching devices respectively. Adjust the two groups of process skins to the height of the side skin through the skin stretching devices. The process skin and the side skin overlap, and use a CO2 welding machine to perform intermittent welding on the overlapping part of the process skin and the side skin.

[0010] In some embodiments, the overlapping range of the process skin and the side skin is 50 - 100 mm.

[0011] In some embodiments, the post-stretching treatment includes the following steps: Step S31: Welding operation, perform CO2 shielded welding on the back of the side skin, and perform CO2 spot welding along the extension direction of the side skin inside the upper stop edge of the side skin. First, perform skip welding, and then perform CO2 fold-back spot welding to complete the welding points; Step S32: Reinforcement welding, perform plug welding on the door pillar part using a CO2 shielded welding machine, check the unpenetrated positions during the single-sided spot welding of the side skin, and perform repair welding; Step S33: Weld point grinding, grind the high welding nodules flat with a hard grinding piece, and then use an angle grinder to polish all the welding points; Step S34: Side skin trimming, check whether the side skin has bulging phenomena, perform annealing treatment on the bulging parts through a skin recovery machine, and polish and flatten after confirming no bulging.

[0012] In some embodiments, the pre - stretching treatment includes the following steps: Step S11: Check the straightness of the body frame. Use a straightedge to check the straightness of the body frame and correct the unqualified positions. Step S12: Paste sponge strips. Paste sponge strips on the body frame. Step S13: Paste heat - insulating cotton. Paste heat - insulating cotton between the side - wall panel and the body frame. The heat - insulating cotton is as high as the side - wall panel and is arranged closely against the body frame. Step S14: Apply sealant. Apply sealant at the central positions of the lower window cross - beam and the waist beam.

[0013] In some embodiments, the thickness of the sponge strip is 10 - 12.5 mm.

[0014] In some embodiments, before the post - stretching treatment, cut the process skin from the side - panel skin.

[0015] Through the above - mentioned technical solution, the method for stretching the side - panel skin of the vehicle body provided by the present application includes steps of pre - stretching treatment, skin stretching, and post - stretching treatment. Through the pre - stretching treatment, the straightness and surface flatness of the body frame can meet the requirements, laying a good foundation for the subsequent installation of the side - panel skin. During skin stretching, weld the process skin at both ends of the side - panel skin. The skin stretching device realizes the stretching of the side - panel skin by stretching the process skin. The process skin can be reused, and the introduction of the process skin can reduce the waste of the side - panel skin. The side - panel skin is evenly stressed and has high flatness during the stretching process. Through the post - stretching treatment, the installation of the side - panel skin can be made more stable, and the flatness of the side - panel skin can be further improved after grinding and trimming. The technical solution of the present application effectively solves the problem of poor flatness of the side - panel skin in the prior art when stretching the side - panel skin. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following - described drawings are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0017] Figure 1 Shows the schematic flow - chart of the method for stretching the side - panel skin of the vehicle body in the embodiment of the present application;

[0018] Figure 2 Shows the schematic flow - chart of skin stretching in the embodiment of the present application;

[0019] Figure 3 Shows the schematic flow - chart of the post - stretching treatment in the embodiment of the present application;

[0020] Figure 4The figure shows a schematic diagram of the process steps for pre - tensioning in the embodiments of the present application;

[0021] Figure 5 The figure shows a schematic diagram of the structure of the vehicle body frame in the embodiments of the present application;

[0022] Figure 6 The figure shows a schematic diagram of the connection structure when the skin tensioning device in the embodiments of the present application tensions the side - wall skin;

[0023] Figure 7 The figure shows a welding schematic diagram of the side - wall skin, the lower window cross - member, and the waist beam in the embodiments of the present application.

[0024] Among them, the above - mentioned drawings include the following reference numerals:

[0025] 10, vehicle body frame; 11, lower window cross - member; 12, waist beam; 13, waist - beam column; 14, diagonal brace; 20, sponge strip; 30, process skin; 40, side - wall skin; 50, vehicle window; 100, skin tensioning device. Detailed implementation manners

[0026] The following further describes the implementation manners of the present application in detail with reference to the drawings and embodiments. The detailed description and drawings of the following embodiments are used to exemplarily illustrate the principle of the present application, but cannot be used to limit the scope of the present application. The present application can be implemented in many different forms, is not limited to the specific embodiments disclosed in the text, but includes all technical solutions falling within the scope of the claims.

[0027] These embodiments of the present application are provided to make the present application thorough and complete, and to fully express the scope of the present application to those skilled in the art. It should be noted that: unless otherwise specifically stated, the relative arrangements of components and steps, the components of materials, numerical expressions, and numerical values described in these embodiments should be construed as merely exemplary, rather than as limitations.

[0028] It should be noted that in the description of the present application, unless otherwise stated, the meaning of "a plurality" is greater than or equal to two; the orientation or positional relationships indicated by the terms "upper", "lower", "left", "right", "inner", "outer", etc. are only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be construed as a limitation of the present application. When the absolute position of the described object changes, the relative position relationship may also change accordingly.

[0029] In addition, the "first", "second" and similar terms used in this application do not denote any order, quantity or importance, but are only used to distinguish different parts. "Vertical" does not mean strictly vertical, but within the allowable error range. "Parallel" does not mean strictly parallel, but within the allowable error range. Words such as "include" or "comprise" mean that the elements before this word cover the elements listed after this word, and do not exclude the possibility of also covering other elements.

[0030] It should also be noted that in the description of this application, unless otherwise clearly specified and defined, the terms "install", "connect", and "couple" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances. When it is described that a specific device is located between a first device and a second device, there may or may not be an intermediate device between the specific device and the first device or the second device.

[0031] All terms used in this application have the same meanings as understood by those of ordinary skill in the art to which this application pertains, unless otherwise specifically defined. It should also be understood that terms defined in a general dictionary, such as, should be interpreted as having meanings consistent with their meanings in the context of the relevant art, and should not be interpreted in an idealized or overly formal sense, unless specifically defined as such here.

[0032] Technologies, methods and devices known to those of ordinary skill in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods and devices should be regarded as part of the specification.

[0033] As Figure 1 shown, in the technical solutions of some embodiments, the method for stretching the body side skin includes the following steps: Step S10: Pretreatment before stretching, use a straightedge to check the straightness of the body frame 10, paste a sponge strip 20 on the body frame 10, and improve the installation fit degree of the subsequent side skin 40 and the body frame 10 through the pretreatment before stretching; Step S20: Skin stretching, weld two groups of process skins 30 to both ends of the side skin 40 respectively, set two groups of skin stretching devices 100 to stretch the two groups of process skins 30 respectively, and thus realize the stretching of the side skin 40; Step S30: Post-treatment after stretching, after the side skin 40 is stretched, perform reinforcement welding and grinding and trimming on the side skin 40.

[0034] The present embodiment provides a method for stretching the side skin of a vehicle body, which includes the steps of pre-stretching treatment, skin stretching and post-stretching treatment. The pre-stretching treatment can make the straightness and surface flatness of the vehicle body frame 10 meet the requirements, laying a good foundation for the subsequent installation of the side skin 40. When the skin is stretched, the process skin 30 is welded at both ends of the side skin 40, and the skin stretching device 100 stretches the side skin 40 by stretching the process skin 30. The process skin 30 can be reused, and the introduction of the process skin 30 can reduce the waste of the side skin 40. The side skin 40 is evenly stressed during the stretching process and has high flatness. The post-stretching treatment can make the installation of the side skin 40 more stable, and the flatness of the side skin is further improved after grinding and finishing. The technical solution of this embodiment effectively solves the problem of poor flatness of the side skin 40 when the side skin 40 is stretched in the prior art.

[0035] like Figure 2 As shown, in some embodiments, the skin expansion and pulling includes the following steps: Step S21, side enclosure skin loading, lifting the side enclosure skin 40 onto the support frame, and flattening the side enclosure skin 40 on the vehicle body frame 10, using a clamp to temporarily fix the upper edge of the side enclosure skin 40 to the side frame. The clamp is a U-shaped clamp, and a plurality of U-shaped clamps are arranged along the extension direction of the side enclosure skin 40 to achieve clamping. Step S22, process skin welding, welding two groups of process skins 30 to the two ends of the side enclosure skin 40 respectively. The purpose of introducing the process skin 30 is to achieve reuse and reduce the waste of the side enclosure skin 40. Step S23, side enclosure skin opening, using a plasma cutting machine to open a notch at the interference between the side enclosure skin 40 and the vehicle body frame 10, so that the side enclosure skin 40 can be close to the side frame, thereby improving the fit between the subsequent side enclosure skin 40 and the vehicle body frame 10 after expansion and pulling. Step S24, expansion and pulling operation, two sets of skin expansion and pulling devices 100 are used to expand and pull the two sets of process skins 30 respectively, thereby expanding and pulling the side wall skins 40. Before the expansion and pulling operation, the U-shaped clip is removed.

[0036] It should be noted that one side of the side panel skin 40 may be welded to the vehicle body frame 10 , and then a set of process skins 30 may be welded to the other side of the side panel skin 40 , and a set of skin expansion and tensioning devices 100 may be provided accordingly for expansion and tensioning.

[0037] like Figure 2 As shown, in some embodiments, the skin expansion and pulling further includes the following steps: Step S25, obtaining the expansion and pulling amount, before performing the expansion and pulling operation, marking straight lines on the side panel skin 40 and the corresponding vehicle body frame 10, as the side panel skin 40 expands and pulls, the straight lines marked thereon will gradually be offset from the straight lines marked on the vehicle body frame 10, after the expansion and pulling operation, the distance between the straight lines on the side panel skin 40 and the straight lines on the vehicle body frame 10 is measured by a tape measure or a displacement sensor, and this distance is the expansion and pulling amount.

[0038] The following table shows the stretching amount of the side skin of the welded body (unit of length: mm)

[0039]

[0040] According to δ = R / L * 100%, where

[0041] R is the stretching amount

[0042] L is the length of the side skin before stretching by 40, that is, the effective length of the side skin 40

[0043] δ is the stretching rate of the side skin

[0044] It can be calculated that the stretching rate of the side skin is between 0.08% - 0.1%. Compared with the previous 0.05% - 0.08%, the stretching rate is increased. After the stretching rate is reasonably increased, the side skin 40 can be fully extended, releasing the residual stress inside the material, thereby improving the surface flatness

[0045] As Figure 2 shown, in some embodiments, the skin stretching further includes the steps: Step S26, fixing the side skin. One end of the side skin 40 and the vehicle body frame 10 are sequentially spot-welded by a single-sided electric welding machine from top to bottom, and then plug-welded by a CO2 shielded welding machine, and the weld seam is polished flat. After stretching is completed, the side skin 40 is welded and fixed by the above welding method. It should be noted that before fixing the side skin 40, it is necessary to measure and correct the size of the window

[0046] As Figure 6 shown, in some embodiments, in the welding of the process skin, two groups of process skins 30 are respectively fixed on two groups of skin stretching devices 100. The two groups of process skins 30 are adjusted to the height of the side skin 40 by the skin stretching device 100. The process skin 30 and the side skin 40 overlap, and the overlapping part of the process skin 30 and the side skin 40 is intermittently welded by a CO2 welding machine. After welding is completed, the process skin 30 is stretched by the skin stretching device 100 to achieve the stretching of the side skin 40. This stretching method is double-sided stretching. It is also possible to weld one end of the side skin 40 to the vehicle body frame 10 and the other end to the process skin 30, and the skin stretching device 100 stretches one group of process skins 30, that is, single-sided stretching

[0047] It should be noted that without welding the process skin 30, the skin stretching device 100 directly stretches the side wall skin 40. To achieve the connection between the side wall skin 40 and the skin stretching device 100, the length of the side wall skin 40 is longer than the actual requirement. After stretching, the excess length is cut off, which results in waste of some side wall skins 40. By welding the process skin 30 on the side wall skin 40 and completing the stretching operation, then cutting off the process skin 30, the process skin 30 can be reused in the stretching operation of the next group of side wall skins 40.

[0048] It should also be noted that when the skin stretching device 100 performs the stretching operation, the skin stretching device 100, i.e., the hydraulic stretching machine, is adjusted to the manual mode.

[0049] In some embodiments, the overlapping range of the process skin 30 and the side wall skin 40 is 50 - 100 mm. If the overlapping length is less than 50 mm, the process skin 30 and the side wall skin 40 may break under the action of the stretching force; if the overlapping length is greater than 100 mm, some of the side wall skins 40 need to be cut, resulting in waste. In this embodiment, the overlapping length is 65 mm.

[0050] As Figure 3 and Figure 7 shown, in some embodiments, the post - stretching treatment includes the following steps: Step S31: Welding operation. CO2 shielded welding is used on the back of the side wall skin 40, and the welding spacing is 150 - 200 mm. The welding area between the back of the side wall skin 40 and the waist beam is large. Inside the upper stop edge of the side wall skin 40, CO2 spot welding is carried out along the extending direction of the side wall skin 40. First, skip welding is used, and then CO2 folded - back spot welding is used to fill the weld spots, and the spot welding spacing is 100 - 120 mm. The welding area at the upper stop edge with the lower window cross - beam 11 is small, and the CO2 spot welding method is used. There is a fold at the position where the side wall skin 40 is close to the lower window cross - beam 11, forming a stepped shape. The purpose of this setting is that after the lower window cross - beam 11 installs the window and applies sealant in the subsequent process, it can be aligned with the sealant surface, making the overall flatness better. Step S32: Reinforcement welding. Plug welding is carried out at the column part of the car door with a CO2 shielded welding machine. Check the un - welded penetration positions during the single - side spot welding of the side wall skin 40 and perform repair welding to ensure that the side wall skin 40 will not have the phenomenon of warping. Step S33: Weld spot grinding. Grind the high weld beads flat with a hard grinding disc, and then use an angle - type polishing disc to polish all the welding points to improve the flatness at the weld spots. Step S34: Side wall skin trimming. Check whether the side wall skin 40 has bulging. Use a skin recovery machine to perform annealing treatment on the bulging part. After confirming no bulging, polish it flat.

[0051] As Figure 4 and Figure 5As shown, in some embodiments, the pre-tensioning treatment includes the following steps: Step S11: Checking the straightness of the vehicle body frame. Use a straightedge to check the straightness of the vehicle body frame 10, and correct the unqualified positions. Step S12: Pasting sponge strips. Paste sponge strips 20 on the vehicle body frame 10. The specific pasting positions are the waist beam columns 13, the diagonal braces 14, and the square tubes with sunk platforms. Figure 5 Only some of the sponge strips are shown in Figure 5 . Step S13: Pasting heat insulation cotton. Paste heat insulation cotton between the side wall panel and the vehicle body frame 10. The heat insulation cotton is as high as the side wall panel and is closely attached to the vehicle body frame 10. The heat insulation cotton and the sponge strips are respectively arranged on the two opposite sides of the vehicle body frame 10. Step S14: Applying sealant. Apply sealant at the central positions of the lower window cross beam 11 and the waist beam 12, and apply spot welding sealant at the corresponding spot welding parts on the vehicle body frame 10.

[0052] It should be noted that the side wall panel, the heat insulation cotton, the vehicle body frame 10, the sponge strips 20, and the side panel skin 40 are arranged in sequence from the inside to the outside of the vehicle body frame 10. The vehicle body frame 10 includes structures such as the waist beam columns 13, the diagonal braces 14, the square tubes with sunk platforms, the lower window cross beam 11, and the waist beam 12.

[0053] In some embodiments, the thickness of the sponge strips 20 is 10 - 12.5 mm. The length of the sponge strips 20 is 200 - 300 mm. When the thickness of the sponge strips 20 is less than 10 mm and the length is less than 200 mm, the sponge strips 20 cannot effectively fit the surface of the side panel skin 40; when the thickness of the sponge strips 20 is greater than 12.5 mm and the length is greater than 300 mm, the sponge strips 20 will push up the side panel skin 40, affecting the welding quality. In this embodiment, the thickness of the sponge strips 20 is 12 mm and the length is 230 mm.

[0054] In some embodiments, before the post-tensioning treatment, the process skin 30 is cut off from the side panel skin 40, and then the side panel skin 40 is welded to the vehicle body frame 10. The process skin 30 can also be cut off after the tensioning operation in step S24.

[0055] So far, the embodiments of the present application have been described in detail. To avoid obscuring the concept of the present application, some details well known in the art have not been described. Those skilled in the art can fully understand how to implement the technical solutions disclosed here based on the above description.

[0056] Although some specific embodiments of the present application have been described in detail by way of examples, those skilled in the art should understand that the above examples are for illustrative purposes only and are not intended to limit the scope of the present application. Those skilled in the art should understand that the above embodiments can be modified or equivalent substitutions can be made for some technical features without departing from the scope and spirit of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in each embodiment can be combined in any way.

Claims

1. A method for stretching the body side skin, characterized in that, It includes the following steps: Step S10: Pretreatment before stretching. Use a straightedge to check the straightness of the vehicle body frame (10), paste a sponge strip (20) on the vehicle body frame (10), and improve the fitting degree of the subsequent side skin (40) and the vehicle body frame (10) through the pretreatment before stretching; Step S20: Skin stretching. Weld two groups of process skins (30) to both ends of the side skin (40) respectively, set two groups of skin stretching devices (100) to stretch the two groups of process skins (30) respectively, and thus realize the stretching of the side skin (40); Step S30: Post-treatment after stretching. After the side skin (40) is stretched, perform reinforcement welding and grinding and trimming on the side skin (40).

2. The method for stretching the skin of the vehicle body sidewall according to claim 1, characterized in that, The skin stretching includes the following steps: Step S21, Loading the side skin. Lift the side skin (40) onto the support frame, and press the side skin (40) flat on the vehicle body frame (10), and temporarily fix the upper edge of the side skin (40) to the side frame using a fixture; Step S22, Welding the process skin. Weld the two groups of process skins (30) to both ends of the side skin (40) respectively; Step S23, Drilling holes in the side skin. Use a plasma cutting machine to cut a notch at the interference between the side skin (40) and the vehicle body frame (10), so that the side skin (40) can closely adhere to the side frame; Step S24, Stretching operation. Stretch the two groups of process skins (30) respectively through the two groups of skin stretching devices (100), and thus realize the stretching of the side skin (40).

3. The method for stretching the body side skin according to claim 2, wherein The skin stretching further includes the steps: Step S25, Obtaining the stretching amount. Before the stretching operation, mark a straight line on the side skin (40) and the corresponding vehicle body frame (10). After the stretching operation, measure the distance between the straight line on the side skin (40) and the straight line on the vehicle body frame (10) with a tape measure or a displacement sensor, and this distance is the stretching amount.

4. The method for stretching the body side skin according to claim 2, characterized in that The skin stretching further includes the steps: Step S26, Fixing the side skin. Fix one end of the side skin (40) and the vehicle body frame (10) in the order from top to bottom. First, use a single-sided electric welding machine for percussion welding, and then use a CO2 shielded welding machine for plug welding, and grind the weld seam flat.

5. The method for stretching the body side skin according to claim 2, characterized in that, In the process skin welding, fix the two groups of process skins (30) on the two groups of skin stretching devices (100) respectively, adjust the two groups of process skins (30) to the height of the side skin (40) through the skin stretching devices (100), overlap the process skin (30) and the side skin (40), and perform intermittent welding on the overlapping part of the process skin (30) and the side skin (40) with a CO2 welding machine.

6. The method for stretching the body side skin according to claim 5, wherein The overlapping range of the process skin (30) and the side skin (40) is 50 - 100 mm.

7. The method for stretching the body side skin according to claim 1, wherein The post-treatment after stretching includes the following steps: Step S31: Welding operation. Perform CO2 shielded welding on the back of the side skin (40). Along the upper stop edge of the side skin (40) and in the extending direction of the side skin (40), perform CO2 spot welding. First, perform skip welding, and then perform CO2 folded-back spot welding to complete the welding points. Step S32: Reinforcement welding. Use a CO2 shielded welding machine to perform plug welding at the pillar part of the door. Check the positions where incomplete penetration occurs during the single-sided spot welding of the side skin (40) and perform repair welding. Step S33: Weld bead grinding. Grind the high weld beads flat with a hard grinding disc, and then use an angle grinder to polish all the welding points. Step S34: Side skin trimming. Check whether the side skin (40) has bulging. Use a skin recovery machine to perform annealing treatment on the bulging part. After confirming no bulging, polish it flat.

8. The method for stretching the body side skin according to claim 1, characterized in that The pre-tensioning treatment includes the following steps: Step S11: Straightness inspection of the vehicle body frame. Use a straightedge to inspect the straightness of the vehicle body frame (10) and correct the unqualified positions. Step S12: Paste the sponge strip. Paste the sponge strip (20) on the vehicle body frame (10). Step S13: Paste the heat insulation cotton. Paste the heat insulation cotton between the side wall panel and the vehicle body frame (10). The heat insulation cotton is at the same height as the side wall panel and is closely attached to the vehicle body frame (10). Step S14: Sealant application. Apply sealant at the center positions of the lower window cross member (11) and the waist beam (12).

9. The vehicle body side skin expansion and pulling method according to claim 1, characterized in that: The thickness of the sponge strip (20) is 10 - 12.5 mm.

10. The method for stretching the body side panel skin according to claim 1, characterized in that Before performing the post-tensioning treatment, cut the process skin (30) from the side skin (40).

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