The main causes of bolt misalignment are as follows: First, after the roof welding is completed, the deflection of the roof and the tire type do not match, leading to vertical displacement of the bolts. Even if the side bead is installed smoothly, it still does not align with the roof's deflection, resulting in an unattractive interior appearance. Second, when the roof is lowered, if the left and right sides are not accurately aligned, the bolt assembly shifts left or right. This causes the end of the strip to fail to reach its proper position, making it difficult to load the strip. In some cases, one end of the bead is cut off while the other is not, which greatly affects the visual quality and increases labor time.
To address this issue, technicians attempted to solve the problem by adjusting the process. During testing, the roof top welding tire was precisely adjusted, and the bolt positioning gear was also modified and reinforced before assembling the roof side beam bolts. The initial test results were promising—the first car showed a significant reduction in bolt misalignment. However, by the second car, the problem began to reappear, and the misalignment returned to its original severity. Analysis revealed that the adjustment of the tire type could not be sustained over time, so the positioning gear had to be readjusted after each roof drop. This increased the workload significantly.
In order to effectively resolve the issue of side beam bolt misalignment, it became clear that the current process and positioning method needed to be changed. The goal was to allow the positioning gear to adapt to the roof's deflection and avoid collisions during the vehicle's lowering. To achieve this, the positioning gear had to be separated from the reversing tire, creating an independent positioning system. One possible solution was to use a template. A tracking test was conducted on 471 cars using the model set, where the roof side beams were observed according to the improved method. It was found that during the side bead assembly, there was no bolting issue, and even the knocking was less frequent. This demonstrated that using the model set significantly improved the dimensional accuracy of the roof side beam bolt sets. Additionally, the templates were durable and could be used for a long time, making this process feasible for mass production.
Due to the large tolerance in roof length, the model could not rely on a single end for positioning. Instead, it was centered and grouped in the middle of a set of bolts, then paired toward both ends. The design of the bolt set to the sample included two main aspects: 123mm positioning and 540mm and 104mm size positioning. Previously, the process involved integrating the upper side beam with the roof, which made it impossible to position the 123mm mark from the lower part of the roof side beam. Therefore, the model used a Z-beam profiled plate to locate the 123mm, and the 540mm and 104mm dimensions were achieved through the sample holes. The overall size was realized through a schematic combination of the middle set's centerline and the upper side beam centerline.
During the bolt welding process, the roof side beam bolts are welded together during the roof reversal welding. The center line of the upper side beam is reflected to the inner side in the stock preparation workshop in advance, allowing for accurate alignment when setting the middle set of bolts. First, the middle template group is used to position the middle set of bolts and apply tack welds. Then, the left template is used to hook the last bolt of the previous set and position it at a 104mm distance. The left set of bolts is then grouped until the end, following this method. At the same time, another operator uses the right template to group the four sets of bolts on the right side. Once all the bolt sets are completed, the entire assembly is ready for further processing.
By using the template group for the side rail bolts, it ensures that the bolts on each side bead are aligned in a straight line, minimizing misalignment between the beads and maintaining the overall aesthetic quality of the side bead. After implementing this technical breakthrough, the long-standing issue of bolt misalignment in production was fundamentally resolved. Not only was the dimensional accuracy of the roof bolt sets ensured, but the post-process also proceeded more smoothly. The pass rate of the side beam bolts significantly improved, reducing material waste and saving cutting work time.
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