Micro-plastic-forming process and its research progress
Abstract: With the electronics, biotechnology and the development of micro-electro-mechanical systems, light, thin, short, small and multi-functional products of all kinds continue to emerge, the corresponding micro-plastic-forming process of the research of great importance to all countries, the paper introduced a micro - plastic forming process of the basic concepts, and from the perspective of technology to achieve detailed information on the key issues in the field and the latest progress and future development of the technology direction of the idea of his own.
Micro-plastic parts forming means forming at least two-dimensional size in millimeters of plastic processing [1], with the electronics, biotechnology, medical devices, as well as the development of micro-electro-mechanical systems, light, thin, short, small and multi-function of the products continue to emerge, the relevant parts of the metal is also a growing trend inevitably small, and micro-forging, stamping and other metal micro-forming micro-plastic forming the current direction of development of new technology.
At present, micro-plastic-forming process of the study is currently carried out in the following areas: micro-plastic-forming process of the development, micro-forming die design, manufacturing, micro-forming device, micro-forming die and the measurement and test parts. When the blank is reduced to micro-scale size, the blank, including the performance of flow stress, anisotropy, such as plastic and forming limit compared with the macro-scale, great changes have taken place; forming process itself, the size effect will also appear: forming force, friction , the size of the volume will be rebound with blank size-related; the corresponding micro-forming mold equipment design requirements and also with the traditional plastic forming equipment is quite different. This is related to the researchers made a series of new research.
Forming properties of a material size effect
Microscale under some mechanical characteristics of materials and a macro scale to show different characteristics, at the macro-scale has nothing to do with the sample size of some mechanical parameters of the micro-scale is associated with the sample size.
Miyazaki, Kals, Kocanda, Geiger, etc. [2-6] on different materials found in a one-way tensile test specimens with reduced size, the material flow stress also decreased, such as the size effect The first scale effect. Geiger surface layer model proposed to explain this phenomenon: the sample size decreases, the surface layer of grain size of the percentage share of increase in grain suffered as a result of the surface layer and the inner bound to be small compared to grain, so the overall material flow stress is reduced.
When the sample size and the material reduced to the same intrinsic size an order of magnitude, the material with the first category showed the opposite phenomenon of size effect: Fleck [7] and other experiments in micro-reverse turn found in non-dimensional hardening rate than the macro-scale by 3 times larger; Stolken [8], such as thin-beam bending in the experiment found that the bending non-dimensional hardening rate decreases as the beam thickness and a significant increase in scale effect of this second category, known as scale effect. Geiger and others, as the plastic method through experiments carried out to explain the phenomenon: in the polycrystalline material, when the sample size and characteristics forming machine of grain size in the same order of magnitude, the sample cross-section of each grain plastic deformation occurs without because of the favorable orientation of the grain free but with a negative selective plastic deformation occurred, so that will lead to the largest relative sheet bending and yield stress increased.
In addition to the above size effect, the fine grain size and shape in the direction of grain also led to differences in the deformation of different grains and the non-uniform size and performance parts of the dispersion, thus affecting the stability of quality parts. Heating conditions in favor of grain would increase the deformation of the position may improve the scale effect and the inhomogeneity of deformation, Engel forming a temperature (20-300 experiment [9] and found that the process of billet deformation hardening occurs However, recrystallization does not occur, you can improve the flow stress, so that after the blank deformation hardness distribution and reduce the dispersion process of forming. Balendra [10] and others also studied the amorphous material forming the heat-assisted micro-through laser heating, local heating of the billet in order to reduce the forming force and improve the forming limit of materials.
The use of superplastic materials can also improve the material properties of micro-forming, superplastic forming in the material melting point temperature range of 0.5-0.7 times, in the temperature range of billets available in low-stress deformation, superplastic materials with conventional micro-forming Compared with the micro-forming micro-formability better [11]. Superplastic forming micro-current, but also the need for further study pressure, temperature and time on the impact of micro-forming properties.