The main causes of bolt misalignment are as follows: First, after the roof welding is completed, there is a mismatch between the roof deflection and the tire type deflection, which leads to vertical displacement of the bolts. Even if the side bead is installed smoothly, it still doesn’t align with the roof deflection, resulting in an unattractive interior finish. Second, when the roof is lowered, the left and right positioning of the roof is inaccurate, causing the bolt assembly to shift sideways. This misalignment makes it difficult to press the side strips properly, leading to incomplete end alignment and uneven cuts on both ends. These issues severely impact the appearance quality and increase labor time.
To address this issue, the technical team attempted to solve the problem through process improvements. During testing, the roof top welding tire was precisely adjusted, and the bolt positioning gear was also fine-tuned and reinforced before assembling the roof side beam bolts. The initial test results were promising—the first car showed a significant improvement with fewer misaligned bolts. However, by the second car, the misalignment problem returned to its previous level. Analysis revealed that adjusting the tire type alone wasn’t enough to maintain consistent alignment over time. Therefore, the positioning gear had to be re-adjusted after each roof drop, which significantly increased the workload.
To effectively resolve the side beam bolt misalignment, it became clear that the current process and positioning method needed to change. The new approach required the positioning gear to adapt to the roof's deflection without colliding during the vehicle’s drop. To achieve this, the positioning gear needed to be independent from the reversing tire. A template-based solution was proposed, and a tracking test was conducted on 471 cars using the model set. The results showed that with the improved method, no bolting issues occurred during side bead installation, and even less knocking was observed. This indicated that the template set was more effective in ensuring dimensional accuracy for the roof side beam bolts. Additionally, the templates were durable and could be reused for a long time, making the process feasible for mass production.
Due to the large tolerance in roof length, positioning could not rely solely on one end. Instead, the middle group of bolts was centered, and then paired toward the ends. The design of the bolt set to the sample included two main positioning points: 123mm and 540mm/104mm. Previously, the upper side beam and roof were integrated, making it impossible to position the 123mm mark from the lower part of the roof side beam. To overcome this, a Z-beam profiled plate was used to locate the 123mm, while the 540mm and 104mm dimensions were achieved through sample holes. The overall size was ensured by combining the middle set centerline with the upper side beam centerline.
In the bolt welding process, the roof side beam bolts were welded during the roof reversal stage. The center line of the upper side beam was pre-marked in the stock preparation workshop so that it could be used for centering the middle set of bolts. First, the middle template group was used to position the middle set of bolts and apply tack welds. Then, the left-side template was used to hook the last bolt of the previous set, and it was positioned at a 104mm distance. The left set of bolts was grouped until the end, following the same method. At the same time, another operator used the right-side template to group the four sets of bolts on the right side. Once all the bolt groups were completed, the process was complete.
By using the template group to position the side rail bolts, it was possible to ensure that the bolts on each side bead were aligned in a straight line, reducing misalignment between beads and improving the overall appearance of the side bead. After implementing this technical breakthrough, the long-standing issue of bolt misalignment was fundamentally resolved. Not only was the dimensional accuracy of the roof bolt set ensured, but the subsequent processes also ran more smoothly. The pass rate of the side beam bolts improved significantly, raw material waste was reduced, and cutting work time was saved.
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