Powder metallurgy technology

Powder metallurgy technology through a flexible formula achieving part of the unique properties of materials, especially suitable for preparation of composite materials. Practice has shown that, through a precise control of the production process, allows the powder metallurgy product reached a very high level of accuracy and also has a good size consistency. Metal powder pressing process involves more numerous nonlinear factors, special for powder material plastic flow and mechanical properties is the most basic. Because such materials and common dense metal, generally fluid and organic materials are very different, so there is currently no proven mechanical models are available, on this issue at the international level is still in the exploration phase. First, the mechanical properties of powder materials is very complicated. In loose condition, the powder particles between discrete, powder in small forces can flow under, does not maintain a fixed shape. Mechanical properties of powder and common fluid is essentially different from. For example, according to Pascal's law, subjected to pressure loading static fluid pressure is uniform in all directions, while the powder is completely incompatible with the laws, as to the variation of flow pattern and volume, powder more and very different from ordinary fluids. As the compacting process, powder density gradually increasing, goulian and adsorption between particles, thus gradually as a whole showed tight mechanical properties of metals. Therefore, plastic flow and mechanical properties of powder materials are different from the fluid, and different from dense metals. Due to the above characteristics of the metal powder material and its mechanical modeling work has considerable difficulty. Accurately and reliably reflect a mechanical model of metal powder and mechanical properties have not yet been widely accepted by metal powder suppliers. Secondly, there is a strong geometric non-linear factors in the compacting process. Initial relative density of powder usually 0.4 to 0.5 per cent, relative density is typically 0.8 to eventually close to 1. Such a large density change means that exist within a larger displacement and strain in materials and thus commonly used small small displacement, contingency assumptions cannot be used for this type of problem solving, geometric nonlinear factors must be taken into account in the solution process. In addition, in the mold of a sharp corner and part of the Groove, and mechanical properties of powder flow changes are severe, singularity and numerical grid distortion is an important factor. Finally, powder pressing the boundary conditions of the problem are complex. As repression, powder and contact areas of the mould changing, analog process requires dynamic contact and separation of judging between them. Meanwhile, friction between the powder and die according to Coulomb friction law of common processing, how their relationship between friction coefficient and density of powders, is also one simulation involved.Source:

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