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Powder metallurgy technology (metal powder press molding, metal powder injection molding) as a widely used precision forming technology, with fewer non-cutting machining, material utilization, clean and efficient manufacturing process, the advantages of low-cost production, and manufacturing complex shape and difficult to process product. Powder metallurgy technology through flexible material formulation to achieve the unique properties of the parts, especially for the preparation of the composite material in. Practice shows that, by precise control of the production process, powder metallurgy products can achieve both high accuracy and good dimensional consistency. After finishing after precision parts up to IT6-IT7 level by resintering precision parts after finishing up IT5-IT6 level. Precision powder metallurgy gear up to the same precision hobbing machining. Surface roughness can be achieved Powder Metallurgy Parts Ra1.0-6.3. Because of powder metallurgy with these unique advantages, powder metallurgy research new technology and new technologies by domestic and foreign industrial and academic attention. In order to further improve the quality and performance of powder parts, powder forming prediction law under different conditions, abroad in the early eighties, some analysts reports powder metallurgy sintering material deformation finite element method, after three years of development, We made a series of achievements in the powder pressing process modeling, material yield criterion and so on. Physical modeling and numerical simulation of powder compaction process, have important theoretical and practical significance. On the one hand, the theoretical analysis and a lot of experiments to establish accurate mathematical model that can more accurately understand the mechanism of powder compaction densification process, the more accurate the prediction elastically deformable material pressed metal powder metallurgy parts, in order to improve the precision parts for the pressing process development and mold design, improvement and creation of new technology for higher density and a uniform powder compacts have important theoretical guidance. On the other hand, since the material performance requirements of diversity leads to a powder composition, diversity and complexity of the preparation process, the simulation can respond to market needs quickly develop new powder metallurgy products provide strong technical support, greatly reducing the workload of test and shorten the new materials, new product development cycle. National Natural Science Foundation project "high densification of metal powder precision forming technology infrastructure and application systems" (Project Release No. 50135020), the National High Technology Research and Development Program (863 Program) project "high-performance powder metallurgy materials precision temperature and pressure forming technology" (Project Release No. 2001AA337010), Guangdong Province, five major special research project "High-performance precision powder metallurgy parts of advanced manufacturing technology and key equipment" (Project Release No. A1040203), Ministry of Education, Research Science and Technology major projects, "PM Wen molding technology "(Education Technology Division [2002] No. 78) and other research funding.
Metal powder pressing process involves many nonlinear factors, the special mechanical properties of the powder material plastic flow is the most basic. Because these materials are very different and often dense metal, usually fluid and organic materials, and therefore there is currently no proven mechanical models are available, the international community on this issue is still in the exploratory stage.
First, the mechanical properties of the powder material is very complicated. In the loose state, between each other discrete powder particles, powder body in slight external force will be able to flow, not maintain a fixed shape. But the mechanical properties of powders and body fluids and is essentially different from the ordinary. For example, according to Pascal's law by the static pressure of the fluid pressure load is uniform in all directions, while the powder body is completely incompatible with the law, as for the flow and volume changes of the law, and general fluid powder body more different. With the pressing process is carried out, the powder bulk density increased, collusion and adsorption between particles to each other, thus getting the whole exhibit mechanical properties of the dense metal. Thus, plastic flow and mechanical properties of the powder material is different from the fluid, and is different from the dense metal. Because of these characteristics of metal powder materials, the mechanics modeling work quite difficult. Mechanical model capable of accurately and reliably reflect the mechanical properties of the metal powder has not been widely recognized.
Secondly, there is a strong pressing process geometric nonlinearity. Initial relative density of the powder body is usually about from 0.4 to 0.5, the final relative density is usually 0.8 to close to 1. The density of such a large change in the material means that there is a large displacement and strain, which used a small displacement, small strain assumption can not be used to solve such problems, geometric nonlinearity factors must be considered in the solution process. In addition, in the mold of sharp corners and recessed portion, mechanical properties and flow conditions change dramatically powder, is an important factor numerical singularity and grid distortion.
Finally, the powder pressing problem boundary conditions can be quite complex. As the repression carried out, the contact area of the mold powder body is constantly changing, dynamic simulation process requires judgment and separation of the contact between them. At the same time, the friction between the powder and the mold is used in accordance with the law of Coulomb friction process, one of the issues related to the relationship of friction coefficient and how the powder density is simulation work.