Wuhan University of Technology Undergraduate Graduation Design (Thesis)

Design (Thesis) Title:

Lightweight Design for Tailgate

School: School of International Education

Specialty amp; Class: Automotive Engineering gj1603

Name: Yu Weilun

Tutor: Wang Xiaoli

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Abstract

As an important part of the car body assembly, the tailgate plays a very important role. The tailgate is not only a passage connecting the trunk of the car with the outside world, but also an important guarantee for the safety and comfort of passengers in the car. In the design and development of passenger car doors, it is necessary to consider the manufacturing cost, manufacturing cycle and quality of the doors, and the rigidity performance of the doors, which affect the comfort and safety of the car. In the current environment where the demand for energy conservation and environmental protection is increasing, the lightweight design also needs to be taken into account. Under the condition of ensuring the rigidity and various indexes of the doors, how to realize the requirements of the door structure design and how to realize the lightweight at the same time is particularly important. Based on the above problems, the main research content of this paper is divided into three parts. Firstly, the main contents and main research methods of the structural performance of passenger car doors are summarized, and the current situation of stiffness analysis and lightweight design of passenger car doors at home and abroad is introduced. Based on an existing car model, a three-dimensional model of a certain car tailgate is established. Secondly, a finite element analysis model is established. According to the operating conditions of the passenger car door, the finite element model of the door is calculated and analyzed, and the stiffness value of the passenger car door is calculated. Finally, on the basis of finite element analysis, through the static stress analysis, the tailgate designed can reduce the weight of the vehicle door, reduce the maximum stress of the vehicle door and realize improvement without increasing the weight of the vehicle door.

Key Words: lightweight; three-dimensional modeling; door stiffness; finite element analysis; stiffness optimization

Contents

Abstract III

Chapter 1 Introduction 1

1.1 The Background and Significance of Topic Research 1

1.2 Research Status at Home and Abroad 3

1.3 Basic Contents, Objectives, Proposed Technical Scheme and Measures of Design 4

1.3.1 Basic Contents of Design 4

1.3.2 Design Objectives 5

1.3.3 Proposed Technical Scheme and Measures 5

Chapter 2 Structure design of automobile tailgate 6

2.1 Design Standard of Automobile Tail Door 6

2.2 Importance of Door Stiffness 7

2.3 Overall Structure of Tailgate 8

2.4 Three-dimensional Modeling of Vehicle Tailgate 9

2.4.1 Tailgate Inner Panel and Outer Panel Structure 9

2.4.2 Add weight reduction hole design to inner plate 11

2.5 Summary of this Chapter 11

Chapter 3 Establishment of Finite Element Model of Tailgate 12

3.1 Brief Introduction of Finite Element Theory 12

3.2 Flow and Grid Division of Finite Element Analysis for Tailgate 13

3.2.1 Finite element process 13

3.2.2 Meshing 13

3.3 Summary of this Chapter 15

Chapter 4 Finite Element Analysis of Tailgate 16

4.1 Background 16

4.2 Finite element analysis software 17

4.3 Design and Finite Element Analysis of Various Working Conditions 17

4.3.1 Modal analysis of tailgate 17

4.3.2 Vertical Stiffness Analysis 19

4.3.3 Torsional stiffness analysis 21

4.4 Finite Element Analysis and Optimal Design Direction of Automobile Tailgate 22

4.5 Summary of this Chapter 23

Chapter 5 Conclusion 24

Acknowledgement 25

References 26

Chapter 1 Introduction

1.1 The Background and Significance of Topic Research

China's automobile industry has developed rapidly in recent decades, and is also facing fierce competition at home and abroad. On the surface, the content of its competition is the competition of quality and design concept. However, in fact, technological innovation is the focus of this competition and the key to obtain competitive advantages in the market. As an important part of the car body, the car door is an extremely important assembly in the opening and closing parts of the car, and it is an important channel for passengers in the car to communicate with the outside world. From the perspective of ergonomics, the car door has an important impact on the comfort and safety of the car. At the same time, the quality of door manufacturability directly affects the manufacturing cost, manufacturing cycle and door quality. Therefore, the passenger car door should have sufficient strength, rigidity and vibration characteristics to meet various performance requirements such as impact resistance when opening and closing the door and impact resistance when touching the side. So how to meet the requirements of door structure design is extremely important under the condition of ensuring door rigidity and various indexes. As an important part of the vehicle body, the door is of great significance to the safety and comfort of the vehicle. In the design of automobile body, the design of door is rather complicated, especially the design of tailgate. Because the door must not only meet certain strength, rigidity and concavity resistance, but also meet the requirements of ergonomics, sensory quality, etc. For the tailgate, due to the use of gas spring device, it is more complicated than the left and right side doors. However, with the rapid development of CAE technology, these performances can be simulated and analyzed by CAE software, so that designers can objectively evaluate the design results, propose improvement directions for product structure optimization, shorten product design and development cycle, and save design and development costs. Taking the concrete analysis of CAE in the structural design of the tailgate of a certain vehicle as an example, this paper briefly describes the concrete application of CAE in the structural design of the tailgate of the vehicle. The subject is proposed based on the above background. The objective is to make the structural design of the vehicle door more reasonable. On the premise of increasing the weight of the vehicle door, the rigidity of the vehicle door meets the requirements. In the initial design stage, the rigidity of the vehicle door is taken as one of the criteria for the design of the vehicle door and the secondary design of the vehicle door is avoided. In addition, in order to continuously innovate the technology, add product development and design, and improve the structural performance of the door, CAE is used to analyze the rigidity of the door structure and calculate the rigidity value of the door to verify whether the door meets the requirements, which is conducive to shortening the product development cycle and saving the development cost.

However, due to the need of environmental protection and energy conservation, the lightweight of automobiles has become the development direction of automobiles in the world. On the premise of ensuring the strength and safety performance of the automobile, through the lightweight structural optimization design of the core components and the application of lightweight materials such as high-strength steel, aluminum/magnesium alloy, carbon fiber composite materials and advanced manufacturing and forming processes, the preparation quality of the automobile is reduced as much as possible, thus improving the power performance of the automobile, reducing fuel consumption and reducing exhaust pollution. It can be seen that improving fuel economy is an inevitable development trend of automobiles. Under the same technical conditions, the fuel consumption of automobiles has an obvious linear relationship with the weight of automobiles. The fuel consumption of automobiles increases with the increase of the weight of automobiles. Therefore, adopting lightweight design for automobiles is undoubtedly a development direction for improving fuel economy [1]. According to the report of the World Aluminum Association, for every 10% reduction in the weight of automobiles, the fuel consumption can be reduced by 6%~8%, and the emission can be reduced by about 4%.As an important part of the car body, the car door is also an independent assembly on the car body, which is a frequently used part of the car. The car body is directly related to the comfort and safety of passengers, so lightweight design of car doors is an effective method to reduce fuel consumption and carbon emissions on the premise of ensuring comfort and safety. The concept of light weight originated from racing, which brings good power and maneuverability with low weight, and is not aimed at fuel economy. Later, with the proposal of energy saving and environmental protection, light weight is also widely applied to ordinary cars. Today’s car lightweight, of course, also includes the door lightweight, mainly from the structural optimization design, the application of lightweight materials and advanced manufacturing technology in three aspects [2]. In addition, the design of vehicle doors should be considered comprehensively from the aspects of safety and comfort.

1.2 Research Status at Home and Abroad

Structural optimization design technology for automobiles is the earliest and most mature lightweight technology at present. After 1970, U.S. General Motors and other companies began to apply finite element analysis to automobile design. With the development of various technologies, CAE technology has been increasingly applied in the field of automobiles ^[3]. Xu Xiaofeng used CATIA software to carry out door simulation analysis and verification to verify the design rationality of the door structure. Through the simulation analysis of the door structure, the development cycle of the automobile appearance design can be effectively shortened and the development cost can be reduced ^[4]. Li Mengfan and others used Hyperworks software to mesh the tailgate assembly with shell elements, and carried out free mode analysis, torsional stiffness analysis, dead weight analysis when fully opened, force analysis when closed and sag analysis ^[5]. At present, most of the methods used are the combination of size optimization, material optimization, topology optimization and multi-objective optimization. Jianguang Fang proposed a reliability-based multi-objective design optimization method to study the design of vehicle doors. Response surface method was used instead of time-consuming finite element simulation, which improved the efficiency. Monte Carlo simulation and descriptive sampling technology were combined, and probability adequacy factor was used as the design constraint. Multi-objective particle swarm optimization algorithm was adopted for optimization ^[6]. Gao Yunkai of Tongji University ^[7] and Deng Junhong of South China University of Technology ^[8] introduced in detail the application of multi-objective optimization in vehicle door lightweight design. Most of Zhen Wang's researches on vehicle door lightweight were single-objective optimization, which not only realized lightweight, reduced 0.97kg, but also had good robustness ^[9]. Hua Huangwei of Guangdong University of Technology chose pure electric vehicle doors for lightweight design research and proposed a lightweight extension design method for doors to reduce the weight of doors and enrich the extension design theory and method system ^[10]. In terms of material optimization, Xing haobin used composite materials for lightweight design of tailgate. The inner plate was made of PP LGF material, the outer plate was made of PP EPDM TD20 material, and the inner and outer plates were connected by polyurethane adhesive. Compared to the sheet metal tailgate, there was no corrosion problem with the plastic tailgate, and the plastic tailgate showed stronger environmental adaptability. In addition, it has better elasticity and less damage under low-speed collision ^[11]. According to Kang Bin ^[12], the light-weight status of foreign automobiles was studied. At present, the proportion of high-strength steel and ultra-high-strength steel in automobile steel is increasing, while ArcelorMittal used high-strength steel to optimize the lightweight of many automobile parts. Wang Wei of Chongqing Jiaotong University used aluminum alloy to replace the ordinary steel plate of the inner and outer panels of the car door to carry out lightweight optimization ^[13]. In addition, Novita Sakundarini et al. adopted multi-material technology to realize light weight and cost control ^[14]. ULSAC Consortium used 6 kinds of high-strength steel and adopted traditional stamping technology to make high-quality door outer panel ^[15]. In addition, the multi-material connection technology researched by Martin Ivanjko^[16] et al. is a new type of lightweight connection technology. Manufacturing lightweight refers to the adoption of appropriate manufacturing technology to reduce manufacturing steps and additional weight in the manufacturing process on the premise of certain body design and material lightweight. At present, many manufacturing technologies are widely used, such as laser tailor welding technology, hot forming technology of high strength steel, hydraulic forming technology, roll forming technology of high strength steel, surface cutting treatment technology, electromagnetic forming and other advanced joining and forming technologies. The tailgate guard is mainly used to cover the door panel to provide a beautiful appearance for the car, and can meet the relevant requirements of ergonomics to the greatest extent, striving for comfort and functionality. The most important thing is that the car tailgate guard can effectively block dust and rain from entering the interior of the car, and at the same time it can also block noise from outside the car to prevent adverse effects on drivers ^[17]. KEE H.IM introduced the characteristics of two different types of wedges, their effects on the liftgate system, and the design methods to improve the wedge performance ^[18].

1.3 Basic Contents, Objectives, Proposed Technical Scheme and Measures of Design

1.3.1 Basic Contents of Design

First of all, through the research and analysis of existing cars, determine the research benchmark. The design of the car tailgate and the drawing of the three-dimensional model should take into account the safety, comfort and other indicators in the process of establishing the three-dimensional model. The crashworthiness and light weight of the car door assembled by modeling are optimized, and the car door is further improved through finite element analysis.

1.3.2 Design Objectives

This design aims to realize the lightweight design of the car door through the structural optimization of the car tailgate and the rational use of new materials. On the premise of ensuring safety and comfort, the weight of the car door is reduced, thus reducing the fuel consumption rate of the car and reducing the pollution of the environment.

1.3.3 Proposed Technical Scheme and Measures

The following technical scheme is to be adopted: determining the design basis → determining the tailgate style → designing the outer panel of the vehicle door → designing the inner panel of the vehicle door→ checking the strength and rigidity → modeling and assembling the vehicle door → optimizing the finite element analysis → completing the design.