This article analyzes the lightweight body materials gradually promoted in the new energy automobile industry, from the performance of aluminum sheet raw materials, aluminum stamping process analysis and review standards, mold structure design, and aluminum stamping production to the plant planning and the differences between production organizations and steel plates. Analysis and comparison of the impact of aluminum stamping technology have further strengthened the research on aluminum stamping technology and promoted the development and application of aluminum stamping technology.
With the development of the automobile industry and the gradual maturity of the promotion of new energy vehicles, new materials are the first of the four new technologies, and the applications of new processes, new technologies, and new equipment brought by them are constantly being updated and transformed. The first of the four major processes plays a pivotal role in cost and quality control. Colleagues in the automotive industry once thought that the stamping process was sufficiently perfect. However, with the application of new materials, practitioners in the stamping field realize that the development of technology will never stop, and continuous innovation is required to make continuous innovations in the stamping industry.
In the traditional automobile industry, the application of steel is relatively mature, and the development of the domestic steel industry is becoming more and more perfect. Whether it is automobile OEMs or sheet metal factories, the performance of steel plates is very thorough. However, as the development and application of new energy vehicles have gradually stepped onto the core stage, the economic and dynamic indicators of new energy vehicles have become more and more demanding, and the lightweight of the body has always played a vital role in the development of automobiles. Especially in the new energy vehicle industry in recent years, experts in many industries have begun to put forward the four new concepts of electrification, intelligence, connectivity, and lightweight. Lightweight is a major trend in the development of new energy electric vehicles.
As practitioners in the automotive industry, everyone is familiar with how to implement lightweight, such as lightweight material selection and lightweight structural design optimization. In the development process of the aluminum body project, both the main engine factory and the mold factory talked about aluminum discoloration. This is understandable. After all, the development history of aluminum is about 200 years. On the one hand, the performance of aluminum is not sufficiently studied. On the other hand, the application of aluminum plates in the automotive industry has not yet been widely promoted and applied. This reason is largely constrained by cost, quality and production organization. This article uses the H company’s R project to stamp steel and aluminum bodies. To compare the representative differences of stamping materials, let more stamping people fully understand the difference and uniqueness of steel and aluminum stamping, and make reasonable plans for material selection, process design, and production organization.
The application of steel plate in the automotive industry has been very mature, and the performance of the plate is more stable. Compared with steel plate, the main disadvantages of aluminum plate are: ⑴ aluminum plate is more sensitive to aging, especially 6 series aluminum; ⑵ aluminum plate is soft, In the production process, it is easy to cause bumps and scratches, resulting in additional surface quality defects, which increases the workload of rework and polishing, and derives the need for aluminum plate repair and dust removal equipment; (3) The performance difference of aluminum plate leads to instability of stamping and forming. Rebound and easy to crack. The advantage of aluminum plate and steel plate is that aluminum plate has better anti-corrosion performance than steel plate. The density of aluminum plate is 2.7g/cm3, and the density of steel is 7.85g/cm3, and the lightweight effect is very obvious. See Table 1 for specific comparison.
The elongation rate of aluminum sheet is lower than that of steel, and the fracture surface is generally brittle cracks. The yield ratio (yield/tension) of aluminum sheet is higher. Compared with steel, aluminum sheet has the same uniform elongation, but low local elongation and poor deformability . The tensile curve of aluminum plate and steel plate is shown in Figure 1.
Figure 1 Tensile curve of aluminum plate and steel plate
Table 1 Performance comparison between aluminum plate and steel plate
In view of the differences in the properties of aluminum sheets, there are also certain discrepancies in the product process review standards. For example, the R angle of the aluminum sheet should generally be greater than 5t, and the aluminum cladding should generally be designed as a water drop edging. Generally, the n (hardening index) and r value (plasticity ratio) of aluminum sheet will be greatly reduced after 3 months, which requires high mold safety margin, so it has a greater impact on the simulation performance of CAE. Therefore, in the process of aluminum stamping CAE analysis, generally at least Need to pass Dynaform and Autoform two software for comparative analysis and verification. Table 2 shows the performance and process review standards of aluminum and steel plates. When the aluminum plate is at the minimum drawing convex R angle, the thickness of the outer plate is generally 1.0mm, R ≥ 5t; the thickness of the outer plate of steel plate is 0.7mm, R ≥ 2.8mm.
Due to the difference in performance parameters of aluminum plates, there is a big difference between aluminum stamping die and steel die regardless of die material or structure design. For example, the comparison of die matrix and convex and concave die selection is shown in Table 3.
At the same time, because the quality of the aluminum plate surface is more sensitive, in principle, the mold does not allow repair welding. Therefore, when designing the mold structure, a thickness of 10mm is reserved so that the mold can be changed by a second reduction process instead of repair welding. . The drawing of aluminum stamping die style is shown in Figure 2.
Table 2 Performance and process review standards of aluminum and steel plates
Table 3 Steel stamping die material and aluminum stamping die material requirements
Figure 2 Aluminum stamping die style
The trimming of aluminum molds is easy to produce aluminum scraps, and the aluminum scraps in the production process will cause quality defects of the noodles. Therefore, the structure design of the aluminum plate to minimize the scrap knife is shown in Figure 3.
Impact on production planning
Because aluminum plates are light and non-magnetic, traditional demagnetization can no longer be split during the unstacking and splitting process of the stamping production line. Aluminum splitting generally uses air knife splitting, as shown in Figure 4.
Due to the softness of the aluminum plate, the friction of the sliding belt of the sheet material is prone to surface quality defects in the production and transportation process. Therefore, high friction vacuum belts are used in the planning. At the same time, considering the difference in raw materials between aluminum and steel plates, it is necessary to separate and collect aluminum plates and steel plates. . Therefore, the waste collection of the general steel-aluminum mixed line is mostly collected by double hoppers (Figure 5). Taking into account the rework of aluminum plates, the grinding dust needs to be planned for dust removal and explosion protection, so it is necessary to plan a closed grinding room in the stamping workshop to meet the product rework, as shown in Figure 6.
At the same time, due to the timeliness requirements of aluminum sheets, it is necessary to specify first-in, first-out in the production organization to ensure the timely use of sheet materials. The sheet materials in the workshop need to be planned and informatized, and the sheet materials must be monitored in time to avoid over-aging of sheet materials.