The primer-topcoat syncretic cathode electrophoretic coatings on the base of Baosteel Mechanical Descaling (BMD) or Eco Pickled Surface (EPS) plates have poor resistance to neutral salt spray. In order to solve this problem, the SA-207/3 green Zirconium-silane phosphorus-free conversion agent was developed which used on BMD or EPS plates before cathodic electrocoating, various performance tests were carried out, performances including adhesion, water resistance, acid resistance, alkali resistance, oil resistance and diesel resistance and phosphorus-free treatment were comparable to that of phosphating treatment. After 500 h salt spray test, the expansion width of phosphorus-free treatment was obviously less than phosphating treatment. The salt spray resistance of the phosphorus-free conversion treatment coatings was better.

With the development of automobile lightweight technology, the substrates of truck body have changed from cold-rolled steel sheet to aluminum alloy mixed with cold-rolled steel, which has brought about the demand for co-line coating of steel and aluminum alloy. Therefore, this paper, based on the tests of the degreasing, surface conditioning, phosphating and electrophores, discussed the pretreatment process scheme of steel-aluminum co-line phosphating. The research results show that the degreasing corrosion of aluminum alloy should be controlled below 100 mg/m² when the co-line coating of steel and aluminum is carried out, and the surface conditioner XG, by contrast, has a more significant effect on the phosphating of aluminum alloy. When the concentration of fluoride ions in phosphating solution is 150~240 mg/L, the corrosion resistance of electrophoresis films on DC04 cold-rolled steel plate, 5052 and 6061 aluminum alloy substrate can meet 1 000 h of neutral salt spray test requirements. The research results provide technical support for the application of steel-aluminum co-line coating technology.

To solve the shortcomings of silane film technology in covering ability and adhesion, this paper proposed a method to control silane film weight. Firstly, reduce the risk of excessive film weight by optimizing the start and stop procedures of the silane tank circulation pump, secondly, effectively prevent excessive accumulation of zinc hydroxide on the workpiece surface by selecting appropriate degreasing agents, to improve the adhesion between the silane film layer and the substrate, the problem of insufficient electrophoretic adhesion in the silane film process is thus solved.

This paper used the Synchronization Engineering (SE) analysis method to comprehensively evaluate the fixed engine hood scheme, and proposed 2 process schemes, i.e., the traditional scheme of passing through the paint shop using the hinge tooling, and the scheme of passing through the paint shop with the hood fixed and opened at a certain angle. Comparing the impacts of each scheme on manufacturing cost, anti-corrosion impact, deformation impact, appearance impact, assembly impact, etc., it is determined that a certain angle of fixed opening is the optimal scheme. Through the Alsim simulation software, the problems of gas and liquid accumulation of the engine hood after opening at a certain angle, the influence of deformation control and the influence on spraying appearance were analyzed, and the opening angle of 30° was determined as the best scheme.

To obtain the optimal milling process parameters of vermicular graphite cast iron, milling test was conducted by using the BP neural network optimization design method at various combinations of cutting speed, feed rate and back feed volume, the chip formation of vermicular graphite cast iron (RU450) and the influence of process parameters on surface quality during high-speed milling was studied and analyzed. The results indicate that the optimal milling process parameters, as optimized by the BP neural network, consist of a cutting speed range of 2.8~3.1 m/s, a feed rate of 760~780 mm/min, and a back feed rate of 0.1 mm. The milling process resulted in chips with a helical and "C"-shaped curved shape, as observed by Scanning Electron Microscope (SEM). The graphite on the workpiece surface has a complete worm-like and spherical shape, with the graphite edge clearly visible. The milling surface roughness measures 1.0~2.0 μm, and the milling samples meet all process indicator requirements.

A cross beam of instrument cluster was welded automatically. In order to eliminate the influence of weld seam position deviation on welding quality, it is necessary to explore the control method and application of weld seam tracking. Several common control methods of welding seam tracking were studied and compared, laser position identification technology was applied in the automatic welding of commercial vehicle’s instrument panel cross beam. The scheme design, system architecture, working process, using effect and other aspects were expounded in detail. Through the verification of the actual production, the laser position identification technology effectively realized the tracking and positioning of the welding seam. By giving feedback and correcting the movement trajectory of the welding robot, it improved the welding accuracy of the instrument panel cross beam, and provided strong guarantee for improving the assembly quality of the cab interior.

In order to improve the welding quality of the laser welding process in the processing of polymer materials, this paper explored the principle of laser plastic welding technologies, welding process and its application in the automotive lighting industry. Several influencing factors of laser welding effect were designed and tested to explore its actual influence in production practice. For the defects easily occur in the production process such as virtual welding, over-welding and poor appearance, this paper proposed improvement measures from the aspects of welding materials, power, pressure, speed, welding times, in combination with production practice, which provided a reference for the subsequent application and research of laser plastic welding technology in the automotive lighting industry.

This article studied and analyzed the basic principle of electron beam welding and the main factors affecting welding quality. In combination with the developing project case, this paper, taking the sixth driven gear of a 6-speed manual transmission of a commercial vehicle as the research object, introduced the optimization of welding process parameters and structural design to solve the welding crack problem. The experiment finds that when the welding structure remains unchanged, it is difficult to eliminate welding cracks by changing the process parameters when the welding depth is deeper; Simultaneously optimizing the welding structure and matching it with appropriate welding processes can eliminate welding cracks and meet technical requirements such as welding depth.

In response to the problem of significant fluctuations in the Y-direction dimension of the door, this paper analyzed the influencing factors one by one by using an online measurement system Perceptron, and identified key factors such as the impact of key welding point positions and mismatched under copper welding operation. 2 optimizations were carried out: firstly, by adding a welding plier guiding mechanism to optimize the key welding spot positions; secondly, by adjusting the height of the support block for the under copper welding and optimizing the adhesion between the support surface and the outer panel, the problem of Y-direction dimensional instability of door is solved.

In order to achieve a good fixing effect and reduce the internal stress between fixings, it is necessary to accurately measure the deviation of the stud position after welding on the Body In White (BIW). Based on the ATOS Scanbox (ATOS optical measurement system), this paper investigated the feasibility of direct measurement of studs when using the system for stud position degree measurement, and compared it with 2 commonly used measurement methods (screwing auxiliary cylinder and spraying developer) to study the differences in measurement accuracy between the 3 methods, and analyzed the advantages and disadvantages of different measurement methods from the viewpoint of measurement efficiency and economy.

This paper studied the twinning behavior of AZ31 magnesium alloy in the high cycle fatigue process and the microscopic characteristics of twins, and studied systematically the influence of orientation and fatigue load on twinning in the high cycle fatigue deformation process of magnesium alloy and the role of twins in the fatigue deformation process with the help of metallographic observation, fatigue performance analysis, fracture morphology observation, Transmission Electron Microscope (TEM) and other analysis methods. The results show that twinning could play an important role to the fatigue deformation of magnesium alloy at room temperature, the ratio of twinning varies in different fatigue loading directions, the radio of twinning is the highest for loading perpendicular to the extrusion direction.

Based on the fracture analysis of the screw spring fracture in durability test, the paper determined that the fracture originated from the surface decarburization layer and further analyzed the harmfulness of the surface decarburization layer on the spring life from the perspective of surface microstructure and fatigue crack initiation, the paper concluded that the surface decarburization was the main cause for the early spring fracture. The problem of surface decarburization was solved by improving the heat treatment technology of spiral spring. The durability test of the improved spiral spring was carried out again. The life of the improved spiral spring was greatly improved, the durability test number was increased from failing to meet the technical requirements before the improvement to exceeding 2 times of the technical requirements before the improvement without breaking.

In order to improve manufacturing technology capabilities and production preparation efficiency of production lines in the digital era, this article studied the use of industrial simulation PDPS software for virtual process design of automotive door sealing strip rolling (including simulation of production line design, virtual simulation verification of process and equipment). The results indicate that simulation and validation in the virtual environment can verify the rationality of design schemes in advance, identify design problems, optimize design schemes, shorten installation and debugging time, simulation is an efficient means for factories to achieve rapid intellectualization and digital transformation.