国内外冷、热冲压技术回顾于综述

A review on hot stampingThe production of high strength steel components with desired properties by hot stamping (also called press hardening) requires a profound knowledge and control of the forming procedures. In this way, the final part properties become predictable and adjustable on the basis of the different process parameters and their interaction. In addition to parameters of conventional cold forming, thermal and microstructural parameters complicate the description of mechanical phenomena during hot stamping, which are essential for the explanation of all physical phenomena of this forming method.In this article, the state of the art in the thermal, mechanical, microstructural, and technological fields of hot stamping are reviewed. The investigations of all process sequences, from heating of the blank to hot stamping and subsequent further processes, are described. The survey of existing works has revealed several gaps in the fields of forming-dependent phase transformation, continuous flow behavior during the whole process, correlation between mechanical and geometrical part properties, and industrial application of some advanced processes. The review aims at providing an insight into the forming procedure backgrounds and shows the great potential for further investigations and innovation in the field of hot sheet metal forming.Development of tribo-simulator for hot stamping冲压工艺过程仿真开发Coefficients of friction were measured at elevated temperatures using a hot flat strip drawing test machine newly developed by the authors for the purpose of confirming the coefficients of friction used for the FEM simulation of hot stamping. To examine the functions of the tribo-simulator, the coefficients of friction are measured using hot rolling oil with an emulsion, which is supplied continuously, while varying the drawing speed, drawing pressure and temperature. From the experimental results, it was shown that the coefficient of friction in hot stamping can be measured using this tribo-simulator. The measured coefficients of friction can be used as values in the FEM simulation of hot stamping. Moreover, the tribological behavior at the interface between the die and strip in hot stamping can be evaluated from the coefficient of friction, because it is one of the quantitative values used to represent the tribological behavior between the die and blank.Die design for stamping a notebook case with magnesium alloy sheetsIn the present study, the stamping process for manufacturing a notebook top cover case with LZ91 magnesium–lithium alloy sheet at room temperature was examined using both the experimental approach and the finite element analysis. A four-operation stamping process was developed to eliminate both the fracture and wrinkle defects occurred in the stamping process of the top cover case. In order to validate the finite element analysis, an actual four-operation stamping process was conducted with the use of 0.6 mm thick LZ91 sheet as the blank. A good agreement in the thickness distribution at various locations between the experimental data and the finite element results confirmed the accuracy and efficiency of the finite element analysis. The superior formability of LZ91 sheet at room temperature was also demonstrated in the present study by successful manufacturing of the notebook top cover case. The proposed four-operation process lends itself to an efficient approach to form the hinge in the notebook with less number of operational procedures than that required in the current practice. It also confirms that the notebook cover cases can be produced with LZ91 magnesium alloy sheet by the stamping process. It provides an alternative to the electronics industry in the application of magnesium alloys.Improving the accuracy of contact-type drawbead elements in panel stamping analysis面板冲压的材料与接触类型A finite element modeling technique is proposed to improve the accuracy of contact-type drawbead elements in panel forming analyses, and a performance assessment in terms of part border and thickness predictions is presented in conjunction with panel stamping experiments of two automotive sheets. Inherent model limitations causing incorrect part geometry and thickness predictions are, firstly, evaluated considering blank deformations on a plain–strain section of a stamping die. The influence of omitted drawbead geometry and overestimated drawbead exit thickness are described analytically, and a closed form expression is obtained to correct draw-in model error. Then a sectional deformation model is used to calculate restraint force and drawbead exit thickness for a particular blank and drawbead design. The proposed technique is applied in process modeling of polygon shaped panels made of draw-quality and bake-hardenable steels. Three bead penetrations were investigated in process simulations as well as in stamping experiments. The same blankholder force was applied in all process conditions. Computed draw-in and thickness distributions were compared with on-part measurements using an experimental panel-draw die. It was determined that drawbead models based on force parameters only resulted in remarkably high thickness values at the die entry and mostly overestimated draw-in along panel border lines. An evaluation of thickness distributions computed with proposed technique showed an improved correlation with experiment results of both blank materials and confirmed the use of the drawbead exit thickness as a drawbead modeling parameter. Effects of bead penetration on panel border lines were also simulated in accord with stamping experiments.热冲压机床与设备及其冷却系统设计Design of Hot Stamping Tools with Cooling SystemHot stamping with high strength steel is becoming more popular in automotive industry. In hot stamping, blanks are hot formed and press hardened in a water-cooled tool to achieve high strength. Hence, design of the tool with necessary cooling significantly influences the final properties of the blank and the process time. In this paper a new method based on systematic optimization to design cooling ducts in tool is introduced. The optimization procedure was coupled with FE analysis and a specific evolutionary algorithm. Through this procedure each tool component was separately optimized. Subsequently, the hot stamping process was simulated both thermally and thermo-mechanically with the combination of optimized solutions.热冲压的材料机械性能Investigation of the thermo-mechanical properties of hot stamping steelsWithin the innovative hot forming process for sheet metals, called hot stamping, it is possible to combine forming and quenching in one process step. This affords the opportunity to manufacture components with complex geometric shapes, high strength and a minimum of springback which currently find applications as crash relevant components in the automotive industry. As standard material for hot stamping the quenchenable high strength steel 22MnB5 is commonly used. With regard to the numerical modeling of the process, the knowledge of thermal and thermo-mechanical properties of the material is required. To determine the thermo-mechanical material characteristics, the flow behavior of the steel 22MnB5 in the austenitic state has been investigated by conductive, hot tensile tests with a Gleeble 1500 system dependent on the time–temperature characteristic of the hot stamping process.金属钣金快速冲压先进系统Fast FE analysis system for sheet metal stamping—FASTAMPFASTAMP is a fast FE analysis system for sheet metal stamping, which is based on an improved inverse approach and dynamic explicit method. The improved algorithm successfully avoids the strain localization problem existing in plastic deformation theory to lay foundation for the inverse approach. Quadrilateral membrane elements together with DKQ bend element are used in the algorithm to considering bending effect. More accurate model is built in the system so that the process parameters, such as blank-holding force, friction and drawbead restriction, can be taken into account. Press types, eject plate and other influence factors on sheet metal forming are also considered. As a result, the system can be applied to potential defects detection, formability analysis, material selection and process verification. Product design, process planning and die design can be integrated by FASTAMP, so that product formability can be ensured, optimization of stamping process and die structure achieved.钣金冲压的电子电磁辅助自控设施Electromagnetically assisted sheet metal stampingA new approach, electromagnetically assisted sheet metal stamping, has been developed to alter strain distribution and improve formability in sheet metal stamping. In this study,this new approach was applied to form a non-symmetric panel from Al 6111-T4. The results show that this new approach greatly increased the draw depth of the formed panel, compared with conventional stamping. A detailed analysis of strain distribution, stretching and draw-in shows that both a more homogeneous strain distribution and enhanced draw-in contribute to producing deeper pans in a single press operation. This work demonstrates the feasibility of electromagnetically assisted sheet metal stamping, which offers a much improved ability to make complex components in a single press stroke as compared to conventional stamping.多步钣金冲压中的材料厚度变化率保证使用的优化软件Minimization of the thickness variation in multi-step sheet metal stampingThis paper presents an efficient method to optimize the intermedial tool surfaces in the multi-step sheet metal stamping process to obtain improved quality of a product at the end of forming. The proposed method is based on a combination of finite element modeling (FEM) and the response surface method (RSM). The objective of the optimization is to minimize the thickness variation of the part at the final stage. The constraint function of local fracture is introduced by the use of the forming limit curve (FLC). With acceptable accuracy and high efficiency, the multi-step inverse method is used together with RSM to check various intermediate surfaces to search for the optimal shape parameters. After the convergence of the optimization, the result is validated using commercial software DYNAFORM®.Application of a feasible formability diagram for the effective design in stamping processes of automotive panels图表化冲压过程柔性化设计方法的应用自动面板控制The objective of this study is to propose a method of process design that uses a feasible formability diagram, which denotes the safe region without fracture and wrinkle, for the effective and rapid design of stamping processes. To determine the feasible formability diagram, FE-analyses have been performed for combinations of process variables that correspond to the orthogonal array of design of experiments. Subsequently, thecharacteristic values for fracture and wrinkle have been estimated from the results of FE-analyses on the basis of the forming limit diagram. The characteristic values for all combinations within a whole range of process variables have been predicted through the training of an artificial neural network. The feasible formability diagram has been finally determined for all combinations of process variables. The stamping processes of automotive panels to support suspension module, such as the turret suspension and the wheel house, have been taken as examples to verify the effectiveness of process design through feasible formability diagram. A comparison of the FE-simulation results with the experimental results reveals that the design of stamping processes through feasible formability diagram is efficient and suitable for actual processes.Development of nano-columnar carbon coating for dry micro-stampingTwo-stage cold stamping of magnesium alloy cups having small corner radius杯型零件的两步化冲压方法A two-stage cold stamping process for forming magnesium alloy cups having a small corner radius from commercial magnesium alloy sheets was developed. In the 1st stage, a cup having large corner radius was formed by deep drawing using a punch having large corner radius, and the corner radius of the cup was decreased by compressing the side wall in the 2nd stage. In the deep drawing of the 1st stage, fracture was prevented by decreasing the concentration of deformation with the punch having large corner radius. The magnesium alloy sheets were annealed at 500 °C to increase the cold formability. Circular and square cups having small corner radii were formed by the two-stage cold stamping. For the circular cup, the height of the cup was increased by ironing the side wall in the 1st stage. The radii of the bottom and side corners of the square cup were reduced by a rubber punch for applying pressure at these corners in the 2nd stage. It was found that comparatively shallow magnesium alloy square cups used as cases of laptop computers and mobile phones can be satisfactorily formed at room temperature without heating by the two-stage stamping.Numerical simulation of hot stamping of quenchable boron steelQuenchable boron steel is a new type of ultra-high-strength steel used for automotive parts to reduce the weight of automobiles and maintain the safety requirements. On the basis of experimental data of mechanics and thermal physical properties, a material model under hot stamping condition of quenchable steel was set up, and the numerical simulation to the whole hot stamping process of hot forming, quenching and spring-back of bending parts was made with ABAQUS software. The results show that the springback of hot stamping parts increases when the blank-holder force (BHF) decreases; and it increases when the clearance between punch and dies increases and when the die radius increases. The simulation results are basically in agreement with experimental results.热冲压工艺过程的数字化仿真A numerical investigation to the strategies of the localised heating for micro-part stampingLocal heating renders attractive characteristics for achieving high efficiency of metal forming. With reference to micro-part stamping, two localised-heating methods, electrical heating and laser-heating, are investigated with FE simulation. Results show that electrical heating would result in an advantageous distribution of the temperature in a steel work-material. A desired temperature distribution may also be achievable for a copper work-material, if a high-powered laser beam is used. Both electrical heating and laser-heating enable reduction of the stamping force and increase of the aspect ratio that is achievable by stamping. The simulation also demonstrates that both electrical heating and laser-heating are able to result in the desired temperature-distributions at sufficiently high heating-rates and that the methods are easy to be implemented. The comparison further shows that electrical heating is more favourable for engineering applications.微小零件的冲压过程策略与方式仿真Prevention of oxidation in hot stamping of quenchable steel sheet by oxidation preventive oilOxidation in hot stamping of quenchable steel sheets heated in an electrical furnace was prevented by coating the sheets with oxidation preventive oil. A solid film is generated on the surface of the sheet by drying the coated sheet, and the film changes i nto a liquefied film having an oxidation barrier at elevated temperatures. Hot hat-shaped bending of the coated sheet was performed to examine the properties of the products. For the bent products, the oxidation preventive oil was effective, the shape accuracy was very high and the hardness increased to a level of 1.5 GPa in tensile strength.热冲压用油防止氧化。