1 Introduction
After a new model is determined, it is necessary to quickly achieve mass production and seize the market. Whether automotive molds, especially automobile body molds, can be manufactured quickly is the key. In China, the production of a car of a model requires more than 4,000 sets of molds, worth 20,000 to 300 million yuan, but in general, the investment in body stamping dies is the largest, only the body-in-white accounts for 70% to 80%.
Automobile cover moulds generally have low levels, insufficient capacity and long production cycle. This has become the bottleneck of China's automobile development, which has greatly affected the development of vehicles. How to break this inferior situation and form core competitiveness is the development focus of the 11th Five-Year Plan of China's auto industry, and it is also a problem that needs to be solved before us.
At present, the rapid manufacture of automotive body panel molds and new sheet metal forming methods are two directions to solve this problem. Advanced sheet metal forming technology and equipment to improve production efficiency, reduce mold usage and save costs are undoubtedly an effective way.
2. Body panel forming technology and equipment
Due to the rapid development of advanced energy-saving technologies and lightweight technologies, new methods and processes for automobile manufacturing are emerging one after another. Automobile manufacturing technologies and equipment will develop in the direction of high speed, automation and flexibility, and the demand for virtual manufacturing, green manufacturing and cleaner production will become more urgent. .
As an indispensable auxiliary means, the numerical simulation analysis technology of sheet metal forming has become an important means to improve stamping quality, reduce waste, defective rate and reduce automobile manufacturing cost. With the increasing level of computer-aided design, numerical analysis and simulation, the manufacturing technology is provided with strong soft support, and new forming methods are constantly emerging for use in automotive panels.
(1) Liquid-filled forming Since the 1990s, with the breakthrough of related technologies, some new technologies of liquid-filled forming have emerged, making its application in the automotive, aerospace and other manufacturing fields expanding. For ordinary body panel stamping process, generally, large and medium-sized stamping parts require an average of 4 sets of molds. The use of sheet metal single-form hydroforming requires only the use of punches (Fig. 1), so mold manufacturing costs can be saved by more than 50%, while manufacturing The time is shortened by 35% to 75%; the mold is simple to repair, and the repair cost is reduced by 80%; the integration between the stamping processes, such as the integration of the drawing and bending processes, reduces the forming and testing time by about 50%; The process is a flexible and uniform deformation process, which does not scratch the surface of the workpiece, and the quality and precision of the formed workpiece are high; no matching adjustment between the convex and concave molds is required; the time for replacing the mold is short; several materials forming processes can be performed The merging is done in one flexible forming, reducing the number of stamped and formed parts, the number of stampings and manual repairs. Sheet flexible forming technology can be used not only for single-piece body manufacturing, but also for small-volume or even medium-volume body manufacturing. It is one of the most critical technologies in automotive trial production technology.
Figure 1 Schematic diagram of liquid filling
Many well-known automakers, including Toyota and Audi, have applied this technology to the production of automotive panels. In China, research institutes such as Beijing University of Aeronautics and Astronautics and Harbin Institute of Technology have also carried out research on this process, and have been applied in the field of aviation and aerospace manufacturing. However, the development of liquid-filled forming as a new technology is still immature, and many key technologies require further research.
Beijing University of Aeronautics and Astronautics has many years of experience in hydraulic flexible forming technology, solving the application problems of ultra-high pressure, and on this basis, the development of sheet metal filling molding machine and pipe hydraulic flexible forming machine. The plate tonnage flexible forming machine has a total tonnage of 550t, which can realize real-time variable pressure side force control and non-uniform blank holder force control. The internal pressure reaches 150MPa, which can realize complex forming.
(2) Multi-point moldless forming Dieless multi-point forming is a method of forming a discrete curved surface by using a height-adjustable numerical control hydraulic loading unit to replace the traditional mold to form a three-dimensional curved surface. It is a multi-point rolling processing technology with a broad The application prospects are not only suitable for the production of large-volume parts, but also for the production of single-piece and small-sized parts, reflecting the concept of agile manufacturing. At present, typical moldless molding methods include spin forming, forming hammer progressive forming, multi-point forming, and digital progressive forming. Spin forming is one of the most commonly used sheet metal forming techniques. Its forming technology is mature and has reached the level of CNC forming, but it can only process axisymmetric workpieces.
Figure 2 Multi-point moldless forming equipment and mold
In the 1970s, the Japanese shipbuilding industry began to study multi-point forming presses and successfully applied to the surface forming of hull plates. Since then, many scholars have carried out a lot of research and research on the development of multi-point forming technology, and have produced different prototypes, but most of them can only perform the overall deformation with small deformation. The multi-point forming method developed by Li Mingzhe and others from Jilin University of Technology (Fig. 2) has initially realized moldless forming. It can not only process thin plates, but also process large-scale thick-covering parts. It has independently designed and manufactured the internationally leading level. Multi-point forming equipment is currently being developed for application.
(3) Sheet hot forming technology Hot stamping technology has been applied in Europe in the early 1990s and has become the main technology for producing high-strength automotive parts. At present, steel sheets processed by hot stamping technology in Europe each year reach 1 million tons. In 2003, Toyota Motors began to use hot stamping technology to produce reinforcing materials for the center pillar of hybrid vehicles. In Europe, hot stamping technology is used in a wide range of applications, mainly for the production of bumpers, center pillars, strong pillars and roof reinforcements, and door impact beams (Figure 3). The next development plan is to use it for production buffers and chassis.
Figure 3 Schematic diagram of high-strength automotive stamping parts
In recent years, sheet metal forming technology has been applied to actual production in the foreign automobile industry. According to relevant information, Volkswagen AG has adopted hot stamping technology for some body parts in its newly developed PASSSATB6 model. In addition, with the application of high-strength steel plates, the unique advantages brought by the safety and light weight of automobiles have become prominent. Warm forming technology and forming equipment have received widespread attention. At present, the hot forming equipment used in the automobile manufacturing industry is mainly from abroad. The company provides that key equipment such as continuous heating systems are not sold separately and are sold in the form of a complete production line, which is quite expensive.
(4) Laser tailor welding and cutting technology In the international automotive industry, laser processing technology has been widely used in automotive body manufacturing, laser cutting and welding has gradually become a standard processing technology. At present, the company mainly introduces a complete set of laser processing equipment and technology for the manufacture of laser tailor welded blanks, white body laser three-dimensional cutting and group welding. According to statistics, using laser technology to manufacture the body can save about 2/3 of the prototype new body development mold and about 70% of the fixture, shortening the production cycle by 50%, reducing the weight of the body-in-white by 20%, manufacturing precision (shape, size, etc.) And the overall quality (stiffness, strength, etc.) of the body-in-white is significantly improved.
Since the mid-1980s, laser tailor welding has been used as a new technology in the manufacture of complete vehicles in major automobile factories in Europe, America and Japan. According to the latest research by ULSAB (World Lightweight Steel Body Association), 50% of the latest steel body structures are made of tailor welded blanks. In North America, the application of laser tailor welding is increasing at a rate of 1.5 to 200 million pieces per year. Laser tailor welding has enabled North American automotive manufacturing to save $1 billion in processing costs per year.
In October 2002, the first professional commercial production line for laser tailor welded blanks was officially put into operation in Wuhan. At present, the demand for domestic laser tailored blanks is rising rapidly. High-quality models such as Passat, Buick, Audi, and Accord have begun to use laser tailor welded blanks. In 2004, Baosteel Group established a laser tailor welded blank production company in Shanghai and Changchun through joint ventures, but 90% of equipment and technology still rely on imports. Shenyang Institute of Automation developed laser tailor welding equipment through international cooperation. As equipment and process technology matures and batches expand, the cost and price of laser tailor welded blanks will gradually decrease.
(5) Electromagnetic forming Electromagnetic forming is a plastic deformation in which metal is subjected to high-strength electromagnetic force in a very short period of time, and is a high-energy rapid forming. The electromagnetic forming technology has the characteristics that the processing energy is easy to accurately control, the forming speed is fast, the tooling is simple, the forming precision is high, and the plasticity of some materials can be improved. It has been widely used in many fields, such as machinery, electronics, automotive industry, light chemicals and instrumentation, aerospace, weapons industry and so on. In the use of electromagnetic forming technology for composite stamping and forming parts, the Ohio State University in the United States and the PULSAR company in Israel have done a lot of research, and made the automotive door test samples of 6011Al materials, the appearance and strength have basically met the requirements of use. As a non-polluting and energy-efficient green processing technology, the electromagnetic forming process will be more and more widely used.
(6) Digitally formed rapid digital forming technology for automotive panel parts is a flexible processing technology, which eliminates the time and money spent on complex processes such as mold design, manufacturing, experiment, modification, etc. in the product development process, and reduces the new The cycle and cost of product development are suitable for the development of new models and the verification of concept car design. Moreover, the processed cover can be used as a prototype to reproduce simple molds and use these molds for small batch production. At present, there are two main methods for making simple molds: one is to make a mold from a resin material, and its life can reach several hundred pieces, but the material can not be reused; the other is to use a low-middle melting point alloy material to make a mold, and its life can reach Thousands of pieces, the material can be used repeatedly, is a green material. The common features of these two methods are: short production cycle, low cost and easy modification. This mold can also be used as a process validation before making a formal steel mold. The combination of digital forming technology of automobile cover parts and rapid mold-making technology can be used not only for the trial production of new automobiles, but also for the development of multi-variety and small-volume products such as airplanes and satellites. It has great economic value and broad industrial application prospects.
3. Development of superplastic forming technology for aluminum alloy automotive panels
The aluminum alloy automobile cover has a good effect on the weight reduction. At present, the mainstream process is still the traditional cold stamping process, and the yield is low and the cost is high. In order to change this situation, in the mid-to-late 1990s, international research on superplastic forming of aluminum alloy automotive panels began. Car companies in Europe and the United States have cooperated with universities and research institutes to conduct research in this area. For example, ForTech AG of Switzerland has been superplastic forming automotive covers for more than a decade. A professional superplastic forming company (AREOMET) in the UK also forms aluminum alloy automotive covers for automotive companies. Recently, General Motors Corporation of the United States established a special thermoforming workshop for the production of aluminum alloy automotive panels. Ford is working with some universities to study the superplastic hot forming of aluminum alloy automotive panels. At present, all the published super-plastic forming of aluminum alloy automotive cover parts use 5083 aluminum alloy plate, which is a special plate developed by some aluminum alloy companies for superplastic forming. Its best elongation is over 400%, which is easy to exceed. Plastic forming automotive aluminum alloy cover parts. However, such panels have not yet been put into mass production and are more expensive.
Since ordinary industrial aluminum alloy sheets do not have this condition, the use of superplastic special 5083 aluminum alloy sheets requires a high material cost. Another solution is to solve the problem by improving the forming process. The connotation of this kind of scheme is to reduce the requirements of the superplastic properties of the parts by improving and optimizing the forming process, and selecting ordinary industrial grade aluminum alloy plates according to actual needs to achieve the purpose of low cost and high efficiency. This idea of ​​solving problems has received the attention of the automotive industry. At present, research in this area has achieved certain success. Some people call this process a rapid plastic forming. Professor Jin Quanlin, the Advanced Manufacturing Technology Research Center of the Institute of Mechanical Science Research, called sub-superplastic forming, which has great potential in reducing material requirements and increasing productivity.
4. Conclusion
In 2006, China's automobile output was 7.28 million, and in 2007 it reached 8,882,400, ranking third in the world. In recent years, the rapid improvement of China's automobile mold manufacturing level has attracted the attention of the European and American automotive industry. The use of advanced forming technology and equipment to manufacture automotive body panels, or reduce the use of body molds, or with rapid mold manufacturing technology, greatly promoted the improvement of automotive body manufacturing levels, shortened the cycle, and enhanced the product brand Image.
With the fierce competition in China's auto market, whether it is the introduction of auto products or independent research and development, the manufacture of the corresponding tooling equipment will be completed in the country as far as possible. Then, the tooling equipment manufacturer and the OEM will keep up with the pace of the international body manufacturing process. It is imperative to improve the digital level as soon as possible and realize the digitization of design, manufacturing equipment, production process and management. Only in this way can we fully enhance the competitiveness of the automotive and automotive equipment industry.
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