Research Progress on new technology of lightweight

Research progress of new technology of body lightweight and steel aluminum integrated structure

preface

focusing on sustainable development, saving resources and reducing environmental pollution have become two major problems to be solved urgently in the world automotive industry. For every 10% weight reduction, the fuel consumption can be reduced by 6% - 8%. Therefore, reducing vehicle weight is one of the most basic ways to save energy and improve fuel economy. The mass of the vehicle body accounts for about 40% of the total mass of the vehicle. The lightweight of the vehicle body plays an important role in the lightweight of the whole vehicle. The lightweight of the vehicle is becoming the forefront and hotspot of Automotive Technology in the 21st century

there are two main ways to realize the lightweight of body structure: first, choose new materials with higher strength and lighter weight, such as aluminum alloy, high-strength steel, etc; The second is to design a more reasonable body structure, making the parts thin-walled, hollow, miniaturized, composite, and improving the structure and process of body parts. At present, the first way should be the mainstream of body lightweight. For the needs of large-scale production, many lightweight materials have been used in the body manufacturing industry, such as high-strength steel, aluminum alloy and carbon fiber. The second way is to use finite element method and optimization design methods to carry out structural analysis and optimization design of the car body, so as to reduce the mass of the car body skeleton and car body steel plate

the above two approaches complement each other, and the combination of material replacement and structural improvement must be adopted in order to minimize the mass of various parts on the premise of ensuring that the overall quality and performance of the vehicle will not be affected. The steel aluminum integrated body frame structure is that in the traditional body frame steel structure, some components or components are replaced by aluminum alloy materials, and the different proportions of steel and aluminum and the parts where aluminum replaces steel are determined through optimization design and performance simulation methods, so as to realize the lightweight and high strength of the body frame structure. This structure is a typical application of the combination of two fundamental ways of body lightweight, which fully conforms to the development technical route of body lightweight

1 development status of body lightweight technology at home and abroad

1.1 new materials realize body lightweight

since the oil crisis in 1973, the world's automobile manufacturers have made obvious progress in lightweight research on cars. The six types of materials that account for 90% of the dead weight of modern cars are generally: Steel 55% - 60%, cast iron 12% - 15%, plastic 8% - 12%, aluminum 6% - 10%, composite 4%, ceramics and glass 3%. Using new plates and light materials (such as magnesium, aluminum, plastic and composite materials) to replace the original steel of the body frame and inner and outer wall panels to achieve lightweight is one of the important ways of body lightweight technology, which is mainly reflected in the following aspects

1.1.1 new steel plate

at present, many automotive industry enterprises are committed to reducing the weight of automotive steel materials in order to achieve the purpose of automotive lightweight. Automobile steel is gradually developing towards high strength. When the thickness of steel plate is reduced by 0.05, 0.10 and 0.15mm respectively, the weight of car body is reduced by 6%, 12% and 18% respectively. The use of advanced high-strength steel increases safety, reduces noise and vibration, improves fuel efficiency, and reduces the total mass of the vehicle. The cost has not increased, but the acceleration and driving performance have improved

with the great improvement of steel quality and performance, it is expected that the use of new steel will exceed 70% by 2010. Sport of Mitsubishi Corporation of Japan has designed a new body structure for its latest SUV. 70% of the components of the body are made of high-strength steel plates. The torsional stiffness of the whole vehicle is even 45% higher than that of the Grand Cherokee, and the bearing capacity of the body can reach more than 2T. The sonata body structure of Hyundai Corporation of Korea is also strengthened with high-strength steel plates, and 800MPa high-strength steel is used for beams and columns. Mercedes Benz uses a lot of high-strength steel in the SLK body frame, which increases the torsional stiffness by 70%, greatly improves the safety and reduces the quality of the body. The BMW 3 Series body frame introduced in 1999 uses 50% high-strength steel. 60% of Ford's Windstar body frame is made of high-strength steel. High strength steel accounts for 48% of the body structure of Toyota's latest model Vitz, which is 17kg lighter than the starlet produced by the company. Jaguar pe2.5 adopts a whole piece cabin structure in the body structure, achieving a significant lightweight effect

1.1.2 aluminum and aluminum alloy

as automotive materials, aluminum has many advantages, such as reducing the mass by 60% compared with steel under the condition of meeting the same mechanical properties, and it is easy to recover, absorbing 50% more energy than steel in the process of collision, and no rust prevention treatment is required. The successful research and development of aluminum metal matrix composites with excellent specific strength and specific stiffness provides a way for the further development of automotive lightweight. It is predicted that the average aluminum use quality of each car will further rise to 130kg in 2008, an increase of 53% compared with 1998. The world Aluminum Association announced in a research report recently that the amount of aluminum in cars has exceeded (CAST) iron, becoming the second largest automotive material after steel. The average aluminum consumption per vehicle of North America, Europe and Japan is shown in Figure 1. The application level of aluminum in North America is the highest. The average aluminum consumption per vehicle of passenger cars has reached 145kg, and the average aluminum consumption per vehicle in Europe is 118kg. The situation in Japan is close to that in Europe

Figure 1 Average aluminum consumption per car in North America, Europe and Japan

1.2 structural optimization to achieve body lightweight

1.2.1 aluminum alloy body frame structure

from the concept cars launched by automobile manufacturers in various countries, most of the body structure adopts frameless structure and space frame structure, and most of them are aluminum extruded profiles. As shown in Figure 2, although the strength and stiffness of aluminum is much smaller than that of steel, this deficiency is compensated by the frame structure design and the use of thicker plates. The mass of the body space frame structure after the use of aluminum is reduced by 47%. At the same time, the use of improved section form increases the torsional and bending resistance of the body by 13%

Figure 2 frame structure legend

Audi A2 car adopts an all aluminum frame body and aluminum alloy skin structure, reducing the total mass to 895kg. The body is composed of body frame, rigid sections, cast iron joints and shell plates, which is 43% lighter than the traditional steel body, and the mechanical property can be improved by 40%. In addition, Audi A8 series' good crash safety is also based on its ASF (aluminum alloy space frame structure 1 body structure. This kind of body adopts high-strength aluminum alloy skeleton, which surrounds the entire passenger compartment, like a protective cage. BMW Z8 also adopts skeleton structure and aluminum alloy skin body, which not only improves the rigidity of the whole vehicle, but also reduces the vibration of the vehicle, making Z8 the most popular model in the BMW family. It can be seen that the use of aluminum alloy skeleton and its skin body is increasing the Stiffness, improve the passive safety of the car, while greatly reducing the total weight of the body

however, due to the large springback of aluminum materials and easy to crack, it is more difficult to punch aluminum plates than steel plates, and aluminum plates have not been completely used in large quantities to produce cars. At present, the all aluminum body is generally a small batch of cars with an annual output of several thousand, and a medium-sized car body produced in large quantities The proportion of aluminum structure in China only accounts for 3% - 7%

1.2.2 parts integration and structure optimization

integrating parts and reducing their number is also an effective way to realize the lightweight of parts structure. The number of body frame parts of some models has been reduced from 400 to 75, and the mass reduction has reached about 30%. As the connection between parts is reduced, the rigidity of the car body is strengthened, and the purpose of weight reduction is achieved while improving the comfort of the car body. Audi A6 adopts an integral hood structure (the hood and radiator cover are made into a whole), which is made of aluminum plate with a thickness of 1.1mm. While retaining the shape characteristics of Audi, it has the advantages of light weight, corrosion resistance and so on

combining finite element method and structural optimization method to optimize the structure of parts is also an important research direction to realize the lightweight of parts. At present, the theory and method of structural section optimization have been relatively mature, and shape optimization has been greatly developed. People have shifted the research focus to higher-level structural optimization problems such as topology optimization

at present, there are analytical and numerical methods for structural topology optimization. Analytical methods are not suitable for engineering applications, and numerical methods are often used in engineering applications. At present, continuum structure has become the main research object of structural topology optimization. The topological optimization design of continuum structure has two different solution systems. Domestic scholars mainly study the topological optimization design of strength under local stress constraints, while foreign scholars mainly study the topological optimization design of stiffness under global volume constraints

topology optimization method has been widely used in the optimization design of automobile lightweight structure. Yang et al. 114j studied the topology optimization design of automobile body, chassis, weld joint location, etc. based on the finite element software MSC/NASTRAN and CSA/NASTRAN. Wang et al. Used the finite element method and topology optimization method to optimize the stiffener part of the car body. Through the optimization design, the overall stiffness of the car body can be fully improved under the given cost. Fredricson et al. Summarized the application of topology optimization design in automotive design, focusing on the progress of topology optimization in body design. EOM and other 117J have optimized the topology of the body solder joint configuration, and obtained the best position of the solder joint under the condition of ensuring the overall stiffness requirements of the body, so as to minimize the number of solder joints. Volz introduced the method of applying the combination of linear topology optimization and nonlinear shape optimization to study the crash performance of vehicle body in the early stage of product development. Lyu et al. Applied the topology optimization method of multi-objective genetic algorithm to study the optimization of aluminum alloy space frame structure. Shi Qin and others introduced topology optimization theory at the beginning of structural design. First, the layout of the structure was optimized to obtain a more reasonable initial structural scheme, and then through the optimization design of structural parameters, the optimal structure meeting its strength, stiffness and design process requirements was obtained. Yang Shukai and others established the mathematical model of topological optimization of automobile support structure by using the variable density method, and carried out the topological optimization design of the structure by using the finite element method. Wang Hongyan et al. Optimized and improved the structure by using topological method, and optimized the design of automobile hood through finite element structural simulation calculation. Gao Yunkai and others introduced the topology optimization design theory into the load-bearing body design of an electric refitted vehicle, realized the topology optimization design under the conditions of multiple working conditions and multiple state variables, and determined the best structural scheme of the lower body. Chen ruwen and others used the topology optimization technology based on the finite element method to design the topology structure of the body skeleton, and the characteristic parameters of the body skeleton after topology optimization have been improved to varying degrees

it can be seen that topology optimization is becoming an important means of structural optimization in body lightweight design, and its wider application needs to be further studied

1.3 new manufacturing process and forming technology

in the process of continuing to promote automobile lightweight, we should strive to develop new manufacturing methods, and reform the traditional manufacturing process and forming technology, which is also one of the research directions of automobile body structure lightweight. Aiming at the new materials developed at present, such as high-strength steel plate, ultra-high strength steel plate, light metal materials such as magnesium aluminum alloy, plastic and composite materials, the new forming methods mainly include tailor welded blanks forming, hydroforming and semi-finished products developed for light metal materials