Researcher, Ph.D., Director, Institute of Metal Research, Chinese Academy of Sciences
Stamping is a traditional production technique that has been tested for more than a thousand years. The traditional stamping technology is mainly for mold and process design problems, with copper and copper alloys, steel, aluminum and aluminum alloy as the main materials. Due to the long history of development and application of these materials and the mature performance, the stamping process relies mainly on the cooperation of the molds, and the dependence on the materials is not obvious.
In recent years, with the development of industries such as automobiles and aerospace, many new materials have been used more and more, such as some difficult-to-deform stamping materials: titanium alloys, magnesium alloys, composite materials and high-strength aluminum alloys. The development of materials science and plastic mechanics has led to advances in stamping technology, and the development of computer technology and control technology has made it possible to implement processes that were difficult to achieve in the past. Since the beginning of the 21st century, stamping technology has gradually developed into a technical science, showing the development characteristics of integration of technology, materials and control. The integration of process, material and control requires the physical test, simulation and numerical simulation to master the optimization and matching of materials and processes, and realize process control or online measurement and control according to specific process requirements.
(1) Quantitative control of material properties. Physical simulation technology is a necessary means to master the quantitative law of material properties. Earlier physical simulation techniques used simulated materials and test methods that were similar in performance to the formed material, primarily to address process feasibility issues. Some Gleeble and other test equipment developed in recent years offer a wider range of possibilities for testing material properties. It can be tested by compression and torsion, simulate deformation processing under various temperature, different friction conditions and different deformation speeds, and obtain various performance data of materials. According to these data, the material forming limit and material constitutive relationship can be obtained. The expression makes the plastic deformation process of the calculated or simulated material more accurate and reliable, and provides a material basis for the quantitative control of the stamping process.
(2) Intelligent control technology for stamping production. In recent years, the intelligent control technology for stamping production is also an area that has developed rapidly. On the basis of the integration of materials and processes, it realizes on-line control or intelligent control (also called adaptive control) of the stamping process based on existing materials and process databases. First, an on-line detection system is established for the material or process parameters. When the material properties or process parameters change or fluctuate, the automatic detection system (sensor and signal conversion system) determines the instantaneous magnitude of the relevant parameters online, and through computer simulation analysis and Optimization software (such as artificial neural network methods, expert systems) determine the optimal combination of process parameters after parameter changes. After the automatic control system adjusts the process parameters, adaptive control of the stamping process can be achieved. The new production data is gradually accumulated, which can further become the basis for process optimization of the subsequent processing.
(3) Scientific stamping production technology is the coupling control of various field quantities. Stamping forming of complex parts requires field quantity control of stamping process parameters. Some materials require field quantity to achieve gradient distribution. This is the need of combining plastic mechanics principle with material properties; temperature field, deformation speed field, friction lubrication field, material flow trend, Material deformation sequence (yield order) and deformation path.
These field quantities are not constant and are process variables, so heating and cooling measures, lubrication methods and lubricants, mold structure, crimping method (variable pressure side force and multi-point crimping), draw ribs and loading methods are all controlled. Important measures of the amount of field. Temperature field control can realize differential temperature stamping; friction gradient field (lubrication gradient field) is also an important means to control stamping deformation. Friction can provide some resistance to the flow of stamped deformed materials. Generally, friction is required to be minimized. However, sometimes friction also helps to increase the forming limit of materials. Moreover, the force state of the blank can be controlled by the die structure, the fillet radius, the crimping mode, the die gap, the drawbead and the die block, and the internal stress state of the blank, the material flow tendency, the material yield order, and the material deformation sequence can be further changed. And material strain history. For example, when the blank welded blank is pressed, in order to reduce the movement of the blank weld and make the blank deformation uniform, the stamping deformation process is generally controlled by the die die boss and the variable pressure force mode; and the automobile cover stamping is very deep. General measures. The movable die hydroforming technology proposed by the author uses a split structure to change the deformation order of each part of the blank, avoiding excessive local deformation, significantly increasing the forming limit, and forming very complicated stamping parts one after another.
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