The role of the frame is to support and connect all parts of the car, bear the weight of the car's own parts, and bear the impact, distortion, inertia force and so on. When driving, the frame is the key core component of the whole vehicle. In particular, the second cross beam of the frame needs to provide mounting points for the front axle and steering gear on the basis of ensuring the strength and rigidity of the frame. The cracking problem of a certain vehicle occurred at the chamfer of the steering gear installation point. In order to solve this problem, our department conducted the following investigation and analysis.

1 problem source

In CAE formability analysis, the upper plate of the second cross beam of a frame is partially cracked, which will seriously affect the quality of parts, the quality and safety of the whole vehicle.

2 Cause analysis

By benchmarking the relevant structures of various models and reviewing and analyzing the design structure of the upper plate of the secondary beam, it is concluded that the causes of local cracks are as follows: (1) The upper plate structure of the secondary beam is vertical flanging, and the flanging height is 33.5mm, which is large and easy to draw thin steel plates; (2) The flanging contour near the cracking part is complex, and the adjacent side is a convex structure with a steering gear support tube, and the arc structure extending to the cracking part is concave, so the flanging contour fluctuates greatly and it is difficult to form; (3) The upper plate of the secondary beam is made of high-strength steel plate, made of SAPH440, with a thickness of 3mm, which has limited formability and is prone to forming cracking or thinning cracking at complex profiles.

To sum up, the main reasons for the cracking of the upper plate of the second beam are: the limited formability of the steel plate of the selected brand and thickness, the high flanging height of the parts, and the sharp fluctuation of the flanging profile, which leads to local cracking during forming.

3 Scheme formulation and verification

3. 1 Program formulation

Seek the best solution by analyzing the real reasons. In order to ensure that the upper plate of the second cross beam meets the requirements of the frame rigidity and strength, it is not allowed to change the material, so it is necessary to optimize the profile structure, and two schemes are formulated as follows: Scheme 1: Restore the convex profile near the cracking position, move the R angle of the convex surface inward by 8mm, and solve the cracking problem through CAE forming analysis, but additionally set the steering gear support tube on the convex surface. Scheme 2: Straighten the concave cambered surface of the cracking part into a plane, so that the flanging surface is gentle and undulating, and the convex surface is connected with the straight edge. After CAE forming analysis, the cracking problem has also been solved, and the change has no effect on the installation area, so the scheme is feasible.

3.2 verification

Through CAE formability analysis, the cracking area disappears, the problem is solved, and there is no stress concentration at the original cracking position.

4 conclusion

This problem reflects that the structure of design parts should be combined with its material characteristics. In order to ensure its properties, it is necessary to use materials with higher mechanical properties, but while improving its mechanical properties, its formability will decrease, which requires avoiding designing too complicated profile structures. At the same time, it is necessary to combine the process formability analysis in the design process, eliminate the problem in the design stage, and standardize this solution to provide reference for similar structures in the later stage.

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