This book summarizes the advanced manufacturing technology of original innovations in hot stamping of lightweight car body. A detailed description of the technical system and basic knowledge of sheet metal forming is given, which helps readers quickly understand the relevant knowledge in the field. Emphasis has been placed on the independently developed hot stamping process and equipment, which help describe the theoretical and experimental research on key problems involving stress field, thermal field and phase transformation field in hot stamping process. Also, a description of the formability at elevated temperature and the numerical simulation algorithms for high strength steel hot stamping is given in combination with the experiments. Finally, the book presents some application cases of hot stamping technology such as the lightweight car body design using hot stamping components and gradient hardness components, and the cooling design of the stamping tool.
This book is intended for researchers, engineers and graduate students in vehicle engineering, mechanical engineering, especially in the field of advanced manufacturing technology. The book also provides a useful reference for other new technology related temperature and phase transformation, such as aluminum-magnesium alloy hot stamping.

Since the reform and opening up more than 30 years ago, automobile industry, as the pillar industry of national economy in our country. has played an impo11ant role in improving the national standard of living and rhe quality of travel. The support from all fields has also contributed to the unprecedented development of our country 's automobile industry. Two oil crises in 1970s made automobile industry face three big challenges: safety. energy saving and environmental protection. How to design and manufacture cars featured with energy saving and safety is the eternal pursuit goal of automobile industry in the furure.The automobile in new ages not only needs to meet all kinds of collision safety laws and regulations such as front crash. side impact offset collision. etc .. but also has co reduce their own curb weight in order to get belier fuel economy and achieve energy conservation and emssioo reduction. Studies have indicated that using new materials with high specific strength and good lightweight effect, such as high-strength steel. aluminum alloy, magnesium alloy and carbon fiber enhanced composite material. in automobile lightweight design and manufacture is the most effective way to achieve this goal. However, new materials such as high-strength steel plate. aluminum alloy and magnesium alloy all have disadvantage of poor toughness and plasticity, which has limited its application in car body, and new technology and new method therefore must be adopted to realize the design .and manufacture. High-strength steel hot stamping technology emerges in this new situation.
Hot stamping technology is a new manufacturing technology combining the new material and new technology effectivcly to manufacture automobile parts. In hot stamping, the original steel plate of boron alloy steeI is heated to a temperature of about 950℃ ，then transferred to the water-cooling tools for stamping, quenching and forming, finally obtaining the lightweight components with satisfying perfor-mance. Hot stamping technology not only can solve the problem of poor formability. unmanageable springback and manufacture precision of high-strength steel sheet. but also can obviously improve the strength and hardness of steel during the fom1ing and quenching process, and obtain ultrahigh-strengd1 hot stamping car body struc1ural parts with tensile strength as high as 1500 MPa. In addition. carbody parts with hardness gradient composite prope11ies bnsed on the optimization of forming process can also effectively improve the characterisrics of anti-collision and energy absorption. to improve the safetyof the car. Based on the background of automobile lighrweight and the a.dvantages introduced above, high-strength steel hot stamping technology is booming in the global automotive body manufacturing industry. From the perspective of making China the world ’s biggest automobile producer with annual production up to 20 million in 2015, the development prospect of th is technology is extremely broad, the corporate demand is also very big.
At present, the study of high-strength steel hot stamping technology abroad is very mature. The hot stamping technology was used in the aviation industry such as Unired States NASA (National Aeronautics and Space Administration)， and nuclear industry at the beginning of the last century. The hot stamping technology suitable for auto parts production was first developed by N. Jemverkin 1973. and opened up its industrialiwtion tour in the 1990s. It has been gradually applied and popularized on a global scale in big companies such as BMW and Volvo. As the mature hot stamping technology has been strictly closed in China, it had to be researched and developed from the very beginning in China. the AMT (Advanced Manufacture of Technology) rese.arch team led by Prof. Ping Hu in Dalian University of Technology have been studying on山e hot stamping technology for more than 10 years， starting from the research field of mechanics for manufacturing process. focusing on the establishment of basic mechanics theory and the constitutive equation and the finite element algorithm for hot stamping. They have developed the KMAS_HF hot stamping sheet forming software with independent intellectual property rights, being the first to break the foreign monopoly and successfully develop a complete set of hot stamping process database and complete sets of production line with completely independent intellectual propeerty rights.
The related scientific research achievements have been published in journals at home nnd abroad under the premise of not leaking the core technology. The research results have also been successfully applied and demonstrated in the indusoγin Japan KOSBELCO Steel Company. China's Chery Automobile Co .. Ltd .. FAW Technology Center. JiLin VAFT Lightweight Technology Co .. Ltd .. and other related units.
As the industry’s first monograph that systematically introduces the hot stamping technology from aspects of experiment. theory. method, and industrial application, this book comprehensively introduces the developing situation.equipment and process mechanism of the hot stamping technology. Th book mainly introduce., the related basic theory about multi-field coupled relatiooship among heat. stress and phase transformaLion. Lhe finite element simuJacion technology and the actual engineering application of hot i;tamping products in automotive lightweight. toge1her with the theoretical background for sheet metal hot stamping technology and its engineering significance in the field of auto parts.the book also provides a useful reference for other new technology related temperature and phru.e unnsfor-macion, such as aluminun-magnesium alloy hot stamping. We sincerely hope山e book will be beneficial for advanced manufacturing engineers. automotive design engineers. and researchers in olher related fields.
The latest achievements and progress of hot stamping technology in the last 5 years are included in this book, which is organized in ten chapters. The contents include the research achievements and patents of the author and the AMT group for years. and have referred to the related scientific papers published in recent years. Chapter I introduces the basic knowledge of sheet metal stamping. includirng the development of stamping technology, the core basic knowledge such as process, tools, press machine production process. as well as the basic requirement of ，stamping process for material property，which lays a foundation for the subsequent introduction of hot stamping technology. Chapter 2 provides a systematic and concise introduction about the high-strength steel hot stamping technology and the main single equipment technology based on mass production line to make the readers have a macrolevel understanding of the technology. Chapter 3 expounds the process factors that affect the perfom1ance of high-strength steel and the orginal results of process optimization by authors ’ team in recent years. It also puts emphasis on illustrating the process mechanism to produce auto body parts wit11 tailored properties. Chapter4 mainly elabomtes the hot stamping mechanical (heory and constitutive equation for high-strength steel plate from a phenomenological level. Through experiments and theoretical analysis., quantitative research on multi-field coupling heat, stress, and phase transfonnations in hot stamping process is introduced. together with the stress-strain relationship derived from the law of mixrure. and the hot stamping constitutive model of total strain theory and focre-mental theory, which have established rhe basic mechanics theo1y of hot scamping based on phenomenological significance. Chapter 5 establishes the single crystal and polycrystalline finite defonnation constinuive integration algorithm under the condition of variable temperature based on the finite element algorithm by taking elastic-plastic deformation gradient and stress as basic vadables. Combined with the thermal tensile curves numerical simulation and experimental verification under thermal coupling are carried out. Chapter 6 focuses on the heat transfer theory in hot stamping process, including the mixed heat transfer theory between blank-tools and tools-channel in the process of Lransfer, punching, and quenching. The heat transfer coefficient berween blank-tools and tools-channel is measured by inverse calculation and experiments. The factors such as high-temperarure oxidation and the steel blank surface I。ughness are also studi.ed in this chapter. Chapter 7 dis-cusses the factors influencing the plasticity a111d deformation resistance of hot stamping materials, and establishes the high-tempemture material constitutive model, which is suitable for multi-field coupling analysis. based on high-temperature material mechanics perfom1ance. Combined with thefim set high-temperature forming limit TFLD test equipment developed independemly in China，the 30 fo1ming limit surface 30-TFLD suitable for high-temperature formability prediction is obtained. In Chap. 8, rhe high-strength steel hot stamping FEM simulation algorithm is discussed from the four key problems of numerical simulation: the discussion of the variational叫uation in temperature field modeling and sumrlation. cell division transient spatial domain, and discrete time domain. Meanwhile the fundamental equation and the solving method of the hot stamping pha.e transformation are analyzed and described. Based on the hot stamping multi-field coupling numerical simulation needs, this paper expounds the static explicit algorithm and dynamic explicit a.lgorithm. Chapter 9 mainly intrαluces the application of hot stamping components and hardness gradient parts in lightweight car body. Acco1’ding to practical engineering. the hot stamping technology is applied to the typical body bearing pans such as door anti-collision beam. side wall, body beam frame, and the school bus pillars. And the application and optimization of typical body structures such as B Pillar are conducted with the harrness gradient composite properties of hot stamping. Chapter 10 mainly intreduces the key technologies involving tool optimization design and manufacture in hot stamping technology. It also analyzes the fatigue and life of hot stamping die.
the relevant research work in this book is strongly supported by projects such as the Key Project of the National Natural Science Foundation of China，973 ”National Basic Research Projcet of China and “ 04 ”Great Projectof the Ministry of Industrialization and Information of China. After years of interdisciplinary collaboration research，from scientific theory to process practice, from the scientific problems to product research and development, the systemic research progress has been made. To promote the new technology of hot stamping automotive compo-nents manufacturing combining new material, new process and new equipment and to guide the innovation and development of auto pans manufacturing industry and then provide a new train of thought for 1he design and development of new cars are the purpose and motivation for the author to write the book. Errors are inevitable in this book due to the continuous development of hot stamping technology and the limitations of the author. Any comments from readers will be appreciated.
Dalian, China
Ping Hu
Liang Ying
Bin He

1 The Basis of Sheet Metal Forming Technology 1

1.1The Development of Stamping Technology 2

1.2 The Basics of Sheet MetalForming 4

      1.2.1 The Process of Traditional Cold Stamping 4

      1.2.2 The Cold Stamping Tool 5

      1.2.3Stamping Press 7

      1.2.4 The Production Process of Stampings 9

1.3 Materials for Cold Stamping and Its Formability 11

      1.3.1Requirements on Materials for Cold Stamping 11

      1.3.2 The Fo1mability of Materials12

1.4 Summary17

References 18

2Hot Stamping Technology and the Main Equipment 19

2.1 The Hot Stamping Technology of High Strength Steel19

      2.1.1 Brief Introduction of Hot Stamping Technology19

      2.1.2 Hot Stamping Process 21

      2.1.3 Finite Element Simulation Analysis of Hot Stamping Technology 28

      2.1.4 The Research Status of Hot Stamping 30

2.2 Hot Stamping Production Lines and the Key Equipments 32

      2.2.1 Continuous Ring Heating Furnace. 33

      2.2.2 High-Temperature Resistant Robot Arm and Automatic Transfer Device for Loading and Unloading . 35

      2.2.3 Key Technologies for Design and Manufacture of Hot Stamping Dies 36

      2.2.4 High-Speed HydraulicPress for Hot Stamping 38

      2.2.5 Central Intelligence Control Automaiic Integrated System 39

      2.2.6 Subsequent Shot Blasting. Trimming. and PunchingEquipment 40

2.3 Summary. 42

References.. 42

3 Performance of Hot Stamping High Strength Steel (HSS) Technology45

3.1Processand Principle of Hot Stamping HSS45

      3.1.1 Hot Stamping Plate. 45

      3.1.2 Hot Stamping Technology and Mechanism 48

3.2 Research in the basic technology of hot stamping . 50

      3.2.1 Mechanical Properties of Hot Stamping Steel 50

      3.2.2Effect of Heating Temperature on the Mechanical Properties of Hot Stamping Steel 53

      3.2.3 Effect of Holding Time on the Mechanical Properties of Hot Stamping Steel Plate 57

      3.2.4 Effects of Cooling Rate on the Mechanical Behavior of Hot Stamping Steel Plate 59

3.3 The Study of Hot Stamping Material Toughness Process Experiment63

      3.3.1 Hot Stamping Steel Strength-Toughness Tempering Process 63

      3.3.2 Hot Stamping Steel Strength-Toughness High Temperanrre Quenching Process70

3.4 Tailored Proper1ies of Hot Stamping Part74

      3.4.l Forming Mechanism of Hot Stamping Gradient StrengthSteel 75

      3.4.2 Experimental Research on District Cooling Process of Gradient Strength Pa11 76

      3.4.3 Exponential Relation Between

      Strength-Hardness-Cooling Rate

      of Hot Stamping Steel 83

3.5 Summary 90

References91

4 The Basic Theory and Constitutive Equation of High Strength Steel for Hot Forming95

4.1 Multifield Coupled Relationship Among Heat, Stress and Phase Transformation.95

      4.1.1 Theoretical Analysis 95

      4.1.2 The Detem1ination of the Parameters97

      4. 1.3 The Analysis and Discussion on the Experiment Results 100

      4.1.4 Thermal-Mechanica1 1Transfonnation Coupled Constitutive Model 102

4.2 Hot Forming Stress and Strain Analysis 104

      4.2.l Mixed Law 104

      4.2.2 Strain Analysis104

      4.2.3 Stress Analysis 105

4.3 Constitutive Model of Hot Forming 107

      4.3.1 Hot Fonning Constitutive Relation of Total Strain Theory107

      4.3.2 Hot Forming Constitutive Relation of Incremental Theory107

4.4 Summary108

References.109

5 Constitutive fotegrition Algorithm of Crystal Thermal Deformation111

5.1 The Cons1itutive Integration Method of Single Crysial Fini1e Defonnation at Variable Temperature Conditions111

      5.1.l Elastic Deformation Gradient as Basic Variable 111

      5.1.2 Plastic Defonnation Gradient as Basic Variable 114

      5.1.3 Stress as the Basic Variable in the Algori山m.116

5.2 Comarison Between Two Deformation Gradient Algorithms.120

      5.2.1 Elastic and Plas1ic Defom1ation Gradient120

      5.2.2 The Implicit and Explici1 Algorithms 121

5.3 The Constitutive Integration Method of Polycrystalline 122

      5 .3. I The Construction of Taylor Model 123

      5.3.2 The Muhiscale Finite Element Model 124

5.4 The Numerical Calculation and Experimental Verification of Thermal Tensile of the High Strength Steel 127

      5.4.1 The Thennal-Mechanical Coupling Tensile Experiment127

      5.4.2 Comparison Analysis of the Numerical Simulation130

5.5 Summary 133

References133

6 Heat Transfer in Hot Stamping Process of High-Strength Steel 135

6.1 Hent Transfer Theory and Behavior Analysis.135

      6.1.1 Basic Principle [I. 2]135

      6.1.2 Heat Transfer Behavior Annlysis 137

6.2 Determination of Heat Transfer Coefficient in Hot Stamping Process 138

      6.2.1 Method 138

      6.2.2 Determination of lnterfacial Heat Transfer Coefficient Between Blank and Tool139

      6.2.3 Determination of Convectional Heat Transfer Coefficient Between Tool and Cooling Water143

6.3 The Other Factors lnflue『icing the Heat Transfer Coefficient of Hot Stamping Process150

      6.3.1 The Effecrof High-Temperature Oxidized Scale150

      6.3.2 The lnRuence of Hear Transfer Coefficient About Steel Sheet Su巾ce Roughness 160

6.4 Summary 163

References163

7 The Formability of High-Strength Steel for Hot Stamping 165

7.1 The Concepts of Plasticity and Deformation Resistance 165

7.2 Factors Influencing Plasticity and Deformation Resistance of Hot Stamping Stee 166

      7.2.1 Chemical Composition166

      7 .2.2 Metallic Structure 167

      7 .2.3 Defom1ation Temperarure and Work Hardening 167

      7 .2.4 Defomlation Rate 168

      7.2.5 Cooling Rate.170

      7.2.6 Defom1ation Degree 170

      7 2.7 Size Factor 171

7.3 Material Propeties of High-Strength Steel at Elevated Temperature171

      7 .3.1 Uniaxial Tensile Experiment of High-Strength Steel at Elevated Temperature 171

      7.3.2 Hardening Model of High-Strength Steel at Elevated Temperature173

      7.3.3 Effects of Hardening Capacity on Formability175

      7.3.4 Effects of Directional Anisotropy on Formability177

7.4 Preclictiom of Forming Limit for H。l Stamping 179

7.4.1 Lntroduction of Forming Limit and Instability Theory179

7.4.2 Test Principle of Forming Limit at Elevated Temperature182

7.4.3 Test Equipment and Test Procedure of Forming Limit at Elevated Temperatur 184

7.4.4 Three-Dimension Thermal Forming Limit Diagram and Its Application186

7.5 Summary 190

References 190

8 Hot Stamping Simulation Algorithms of High-Strength Steels 193

8.1 Basic Descriptions of the Hot Stamping Simulation 193

8.2 Several Key Points in Numerical Simulation of Hot Stamping195

      8.2.1 Key technology of Multi-field Coupled Problem.195

      8.2.2 Problems of High Temperaiure Coniact Friction 196

      8.2.3 The Simulation Technology of Temperature Field. 197

      8.2.4 The Simulation Technology of Phase Field 198

8.3 The Model Building and Simulation of Temperarure Field in Hot Stamping199

      8.3.1 Summary of Temperature Field FEA in Hot Stamping Process 199

      8.3.2 Variational Equation of Temperature Field 203

      8.3.3 The Basic Equation of Temperature Shell Elements 207

      8.3.4 Discreteness of Space Domain and Time Domain in Shell Transi巳nt Temperature Field213

8.4 The Model in and Simularion of Phase Field in Hot Stamping 214

      8.4.1 Summary of Phase Field 2l4

      8.4.2 The Basic Exqua1ion of Phase Field 215

      8.4.3 The Solving Mechod of Phase Field 217

8.5 Hot Stamping Multi-Field Coupled Numerical Simulation 218

      8.5.1 Static Explicit Algorithm for Hot Stamping Multi-Field Coupled Numerical Simulation 218

      8.5.2 Dynamic Explicit Finite Element Fonnulation of Multi-Filed Coupled Hot Stamping Simulation 226

8.6 Summary 240

References 241

9 Lighhveight of Car Body Structure Applied by Hot Stamping Part 243

9.1 Lightweight of Car Body Structure Applied by Hot Stamping Parts 243

      9.1.1 HOt Stamping Door Anti-crash Beam and Its Process Optimization 243

      9.1.2 Application of Hot stamping Pans Based on CAE Crash of Whole Vehicle 247

      9.1.3 Application of Hot stamping Pans in Concept Body Lightweight Design 251

      9.1.4 The Application of Hor stamping Component in Lightweight Design of Large School Bus 260

9.2 The Application of Gradient Hardness Hot stamping Component in Vehicle Bodywork264

      9.2.1 The Research of Crashεnergy Absorptiom Propertyof Gradlient Hardness Hot stamping Component265

      9.2.2 The Application of Gradient Hardness Hot stamping 8-Pillar in Vehicle Bodywork and Optimiization Design.269

9.3 Summary 275

References 276

10 The 0Ptimization Design and Manufacture of Hot Stamping Mold 279

10.1 The Key Technology of Hot Stamping Mold Design279

      10.1.1 The Whole Stmcture of Mold 279

      10.1.2 The Selectionof Material 280

      10.1.3 Surface Engineering of Mold. 281

      10.1.4 Optimization Design of Mold Cooling System 283

10.2 The Optimization of Cooling System in Hot Stamprng Dies 284

      10.2.1 Optimization of Subsystem Decomposition 284

      10.2.2 Vinual Protol?'pe of tJ1e Optimization of Mold Cooling285

      10.2.3 Optimizin Core Technology Decomposition288

      10.2.4 Optimization Examples 289

10.3The Manufacturing of HotStampjng Mold 292

      10.3.1 Mold Heat Treatment 292

      10.3.2 Mold Surface Strengthening T1气eacment 292

10.4 The Thermomechanica.l Fatigue Test allld Life Prediction Simulatio,n of Hot Stamping Die. 294

      10.4.1 Fatigue Type of Hot Stamping Die 294

      10.4.2 Thermomechanical Fatigue Test Device 295

      10.4.3 Experimental Principle and Content. 295

      10.4.4 Experimental Results297

      10.4.5 Life PredJction Simulation 303

10.5 Summary308

References308

Index 311

Ping Hu PA\ Liang Ying PA\ Bin He PA\

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