As the pace of product updates accelerates, the flexible roll forming process has garnered widespread attention within the industry. However, due to the inherent complexity of its forming process, inevitable defects arise. To address this, numerical simulation and analysis of the forming process of variable cross-section panels along a three-point bending curve were conducted, examining the impact of material, thickness, and flange height on warping. The results indicate that the warping defect in the panels is related to longitudinal strain, with the minimum warping defect occurring when the longitudinal strain distribution is uniform. Orthogonal simulation design analysis determined the primary and secondary order of process parameters affecting warping height as thickness, flange height, and panel material. The conclusion is that compared to aluminum alloy materials, the warping height is reduced when using high-strength steel with a high yield strength ratio, whereas the warping height increases when using high-strength steel with a low yield strength ratio.

To address the issue of batch cracking of seat crossbeam parts stamped with 2 GPa hot forming material after welding, this article analyzed and found that this part was cracked caused by hydrogen embrittlement. Through tracing the parts process, it was found that hydrogen embrittlement cracking was caused by factors such as high heating temperature, long heating time, and long part transfer time. Through orthogonal design, different hot stamping process combinations of parts were improved to verify the prototyped parts, it was finally confirmed that for the 2 GPa hot formed parts with hot stamping process window in hot-formed austenitizing furnace, dew point temperature shall be under -5 ℃, heating time of 3~13 min, and heating temperature of 880~940 ℃.

As a new type of ultra-fine grained high-strength steel, UF340 has the potential to replace HC180BD in automotive exterior panels. This paper investigated its mechanical properties and formability. The results indicate that UF340 and HC180BD have similar mechanical properties in terms of plasticity, processing hardening index, and anisotropy, but UF340 does not exhibit significant bake hardening properties. The formability of the two materials is similar. There is certain difference between the forming limit curve calculated by the Keeler model and the forming test results. The forming limit diagram obtained by linear segment fitting data has a higher degree of agreement with the experiment, the forming limit curve obtained by this method can provide a reference on the forming application of new materials.

This article studied laser welding of the coating-free press hardened steels (CFPHS) with low carbon footprint and laser welding of aluminum-silicon coating press hardened steels (CFPHS). The study shows that both CFPHS-to-CFPHS and CFPHS-to-AlSi-coated PHS do not require filler wire and laser ablation. Both weldments demonstrate good tensile ductility, with fracture occurring away from the weld seam. Besides, CFPHS-to-AlSi-coated PHS shows high Charpy V-notch impact toughness of 86% of bulk metal. Furthermore, microstructure analysis was conducted on CFPHS-to-AlSi-coated PHS: Microstructure of weld zone is mainly martensite with very small amount of ferrite, consistent with the hardness being as high as bulk metal. Finally, thermodynamics and phase transformation kinetics were used to study the weld seam between CFPHS and AlSi-coated PHS: (1) CFPHS reduces the Al and Si content from coating contamination during weld fusion, avoiding or reducing the formation of brittle AlSi-rich ferrite at high temperatures; (2) Cr alloying improves the hardenability of the weld seam, thus full martensitic microstructure can be obtained during die quenching of hot forming, which guarantees the high hardness of the weld seam.

The effect of cooling water between rolling mills on the surface microstructure uniformity of UF340 was investigated using hot rolling experiments and full-process tracking. The results show that the cooling water between rolling mills has certain effect on the organization uniformity of the hot rolled coil along the transverse direction, and will be partially inherited to the final UF340 strip organization. When the cooling water between rolling mills is fully open, a small amount of non-recrystallized grain is retained on the surface of the final UF340 strip located at about 1/4 from the edge. When the latter part of water between rolling mills is closed, due to the full recrystallization during hot rolling, the final product has a better consistency of the organization along the transverse direction, presenting a fine and fully recrystallized tissue on the surface, which is beneficial to improving surface Distinctness of Image (DOI) of the material. The extraordinary uniformity of the microstructure makes the waviness of the UF340 after painting and deforming is as low as 0.169 μm, and DOI value reaches 92, which fully meets the requirements of the surface quality for the intercoat-free coating process.

It is difficult to solve the problem of exterior quality control of PVC bubbles in doors and covers in the production process. To eliminate the drawbacks in PVC bubble quality by empirical qualitative management, a free sliding wooden plug closed space model for PVC bubbles generation was constructed, and combined with the Ideal Gas Law, the quantitative formula for characterizing the quality state of PVC bubbles was attained, and the formation mechanism of PVC bubbles was analyzed from the perspective of mathematical models. Based on mathematical model and quantitative characterization formulas, the impact of factors including original cavity volume of the sheet metal fold, the highest temperature of PVC drying room, PVC materials, and other environmental factors on the positive or negative correlation and degree of influence of PVC bubbles can be objectively reflected, thereby the direction of quality control of PVC bubbles is more explicit from design and process.

To ensure the adhesion reliability of door sealing strip in the whole life cycle of the product, the Failure Tree Analysis (FTA) model of door sealing strip degumming was established considering the whole process of part design, manufacturing, assembly etc., to analyze various failure events, and 40 corresponding bottom events were identified, which were used to conduct Failure Mode and Effect Analysis (FMEA), to evaluate risk index and Action Priority (AP) of each degumming mode. 2 high priorities and 4 medium priorities for improvement were identified that were implemented to solve degumming.

In view of the characteristics of randomness, diversity and complexity of discrete manufacturing systems, efficiently and accurately identifying system quality risk factors and conducting quantitative assessment of quality risks are crucial to developing corresponding quality control activities and improving product quality. In this research, firstly a product quality risk assessment model for Fuzzy Colored Petri Nets was constructed. Then the fuzzy inference rules were determined, and the confidence of the intermediate library and the terminating library was calculated by fuzzy reasoning through the confidence empirical value obtained at the scene. Finally, the automotive top cover stamping process was analyzed as an example to verify the rationality of the model proposed in this paper, which can be applied to other similar discrete process manufacturing.

In order to solve the existing problems of too many processes in the In-Mold Graining Lamination (IMGL) process, the IMGL process based on Thermoplastic Olefin (TPO) skin was optimized and applied in practice. Compared with the existing problem of too long processes, this paper proposed the reduction of some processes and optimization of the forming equipment and mold, which were put in production. Compared with the existing IMGL process flow chart, the new flow reduced 6 processes, saved 35 m² production site, shortened the IMGL forming cycle by 15 s, reduced glue usage, and improved the utilization rate of glue by 90%.

In order to solve the problem of microcracks in the ceramic chips causing failure of the sensor assembly, this article studied and analyzed a simple and non-destructive method for detecting the microcracks in the ceramic chips, which can be filled in the middle of the crack by using the good wettability of alcohol to the ceramic, and the difference between the conductivity of alcohol and air was used to quickly determine whether there were microcracks in the chips by detecting the change of the current of the ceramic chips. This method was applied to the case study of the failure of the front oxygen sensor of a vehicle model. The cause of microcracks was further proved by optical microscopy and high-precision CT. The results show that the alcohol detection method could accurately determine the occurrence of microcracks inside ceramic chips, and the cause of cracks is excessively high heater voltage, and the uneven internal thermal stress, which cause the heater electrode to detach from the chips’ body, which in turn leads to microcracks inside the chips.