Abstract: In view of the frequent falling off of a M5 steel stud on the body in assembly shop, this paper analyzes the fracture phenomenon of the body and the falling off stud. Also the welding process and assembly process of the M5 stud near the issue stud and the shape of the assembly hole of the interior trim are compared. And carries out a large number of tests with different tightening torques and different tightening methods in body shop. The result analysis shows that the root cause of frequent falling off of M5 welding stud is that the selection of stud and the matching of interior trim mounting holes are unreasonable. Due to the excessive depth of the internal groove of the mounting hole and the thin plate, the plate is overstretched and deformed during the tightening process, and finally the plate is tear and the studs fall off. Two solutions are proposed, such as changing the type of stud and changing the depth of recessed groove of interior trim mounting hole. The two solutions can almost completely avoid the occurrence of bolt detachment in the assembly shop and greatly improving the quality of the body in white. It provides new ideas for stud type selection and welding process quality control of white body stud welding.

Key words: Body in white; Stud welding; Stud fall off; Torque detection; Interior trim

摘要： 针对总装工厂频繁出现的车身上某颗 M5 钢焊接螺栓脱落问题，文章分析了螺栓脱落 后车身及脱落螺栓的断裂现象，对比了相邻位置 M5 螺栓的焊接工艺、安装工艺及内饰件安 装孔形状，同时在焊装工厂进行大量不同拧紧扭矩、不同拧紧方式的试验。结果分析表明， 造成该 M5 焊接螺栓频繁脱落的根本原因为车身螺栓选型与内饰件安装孔搭配不合理、安装 孔内部凹槽深度过大时，车身板材过薄，在拧紧过程中板材被过度拉伸变形，最终板材被撕 裂，从而导致螺栓脱落。文章提出的变更焊接螺栓类型、变更内饰件安装孔凹槽深度两种解 决方案，可几乎完全避免总装工厂该螺栓脱落问题的发生，极大提高了车身质量，为白车身 螺柱焊接的螺栓选型和焊接过程质量控制提供了新思路。

关键词: 白车身；螺柱焊接；螺栓脱落；扭矩检测；内饰件