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 ℃.

In order to reduce stamping cost from perspective of material cost control, this article discussed the cost control strategy for automotive stamping material from three aspects: improving material utilization rate, applying new sheet metal manufacturing processes, and selecting materials rationally, combined with specific application cases. Firstly, material utilization can be improved by product collaborative development, stamping process optimization, and reusing stamping waste materials. Secondly, in the application of new sheet metal manufacturing processes, processes such as roller pressing and integrated heat forming can be used to replace the process of single stamping or multiple separate stamping followed by spot welding. Finally, in terms of rational material selection, principles for selecting steel with the same strength, using bake-hardening steel instead of interstitial-free steel, and recommendations for the application of high-strength steel are provided.

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.

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.

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.

Research on the fatigue performance and failure modes of H340LAD+Z (1.2 mm)-H340LAD+Z (1.2 mm) spot welding cross joints and spot welding stripping joint was conducted. The study identifies that the maximum force of the spot welding cross joint tensile test is 9.0 kN, the maximum force of the spot welding stripping joint tensile test is 1.9 kN, and the maximum hardness of the spot welding joint is 348 HV 1 located at the nugget area, the spot welding cross joint and the maximum force-fatigue life curve of the spot welded stripping joint show a linear relationship under the logarithmic coordinate axis, and the fatigue performance of the spot welding cross joint is better than that of the spot welding stripping joint. Finally, the fatigue failure modes and fatigue fracture morphology characteristics of the spot welding cross joint and the spot welding stripping joint were observed. The failure modes of the two joints are slightly different, and the fatigue fracture morphology is composed of crack sources and expansion zones.

Based on the material consistency and mechanical properties, fracture morphology analysis, structure analysis, stress analysis, failure simulation, broken door handle shell material consistency and mechanical properties met the design requirements, it was found that the parts away from the tip of the modeling of gate structure was prone to stress fracture. Clearance between shell and skeleton was increased from 0.2 mm to 1.2 mm, handle tip comer with rectangular links was changed to bevel and circular arc transition, the position of mold feeding mouth was changed, temperature of the mold was fixed at 50~60 ℃, the drying time of baking material before injection was increased from 1 h to 2 h, the baking stress relief of 80 ℃ for an hour was increased after injection, and the pressure holding time was reduced from 7 s to 4 s, the stress could be reduced which eliminated handle fracture. After the rectification, the parts were verified and tracked, and no similar failure occurred again.

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.

To explore the differences in energy properties between natural gas commercial vehicles and traditional commercial vehicles (diesel), this paper described natural gas characteristics, the cost of refueling equipment, common leakage scenarios, and the emissions of pollutants and greenhouse gases from commercial vehicles, as well as their driving range, then analyzed and explained the gas cylinder and gas route structure and principles of the natural gas commercial vehicle supply system. Arrangement of gas supply system for a domestic heavy-duty commercial vehicle was dissected, and the assembly process and technical specifications for natural gas heavy duty commercial vehicle were developed. Finally, the paper studied the leakage test operation procedures of the GB 19239-2022 “Gas Vehicle Gas System Installation Specifications”, and summarized the nitrogen displacement operation procedures and production processes for natural gas heavy-duty trucks from assembly to storage.

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.