利用直接挤压和径向压实技术制造多孔坯料薄壁衬套的工艺模型

A. Mikhailov, Ye. Shtefan, O. Mikhailov
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摘要

通过计算机建模研究了粉末材料薄壁衬套制造的变形过程。采用连续体方法创建了建模方法。该方法基于多孔体塑性变形流变学模型和有限元法。公认的材料流变模型可以描述粉末和多孔坯料的变形。它考虑到了这些材料在拉伸和压缩时的不同阻力。采用连续加载法,分阶段对变形过程进行建模。确定弹性应力,计算塑性势能,并在必要时在每个加载步骤对模型的应力和材料参数进行修正。孔隙率值在无负载的坯料和区域达到最大,累积变形在直接挤压时达到最小。背压的作用使这些参数的分布更加均匀,孔隙率降低,固相的累积变形增加。在薄壁衬套的径向压制过程中,材料会发生局部变形。产品部分的孔隙率随半径增大而增加。随着成型工具直径的逐渐增大,技术过渡次数的增加可减少残余孔隙率的不均匀分布及其数值。但是,半径范围内气孔分布的不均匀性依然存在。在径向压制过程中,产品两端会形成毛刺。可以通过改变坯料的初始形状来减少毛刺。直接挤压工艺可以使残留孔隙分布更均匀,并使产品材料产生累积塑性变形。不过,这种工艺需要施加较大的载荷,导致工具的稳定性较差。径向压实法(其特点是局部变形)要求的载荷不高,使用的设备功率也不大。然而,残余孔隙率在衬套半径上的分布是不均匀的。关键词:塑性理论、粉末材料、计算机建模、有限元法、应力应变状态、气孔分布。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
Modeling of manufacturing processes of thin-walled bushings from porous blanks using direct extrusion and radial compaction
The deformation process of powder materials thin-walled bushings manufacture was investigated by computer modeling. Two shape formation bushings schemeswere considered (direct extrusion and radial compaction).A continuum approach was used to create a modeling method. The method is based on rheological models of porous body plastic deformation and the finite element method. The accepted material rheological model allows describing the deformation of both powder and porous blanks. It takes into account the different resistance of these materials in tension and compression. Modeling of the deformation process was carried out in stages, using the method of successive loads. The elastic stresses were determined, the plastic potential was calculated and, if it was necessary, the stresses and material parameters of the model were corrected at each load step. The porosity value is reach maximum in blank and area, that is free from the loads, and the accumulated deformation is reachminimum in direct extrusion. The effect of back pressure leads to a more uniform distribution of these parameters, a decrease in porosity and an increase in the accumulated deformation of the solid phase. During radial compaction of thin-walled bushings, deformation of the material occurs locally. Porosity in the product section increases with increasing radius. Increasing the number of technological transitions with a gradual increase in the forming tool diameter reduces the uneven distribution of residual porosity and its value. However, the unevenness of the porosity distribution over the radius remains. In the process of radial compaction, a burr is formed on the ends of the product. The burr can be reduced by changing the initial shape of the blank. The process of direct extrusion allows obtaining more uniform distribution of residual porosity and accumulated plastic deformation of product material. However, this technological process requires the higher loads application, which leads to less stability of the tool. The radial compaction method (which characterized by local deformation) requires not high loads and allows not powerful equipment using. However, the distribution of residual porosity over the radius of the bushing is uneven. Keywords: plasticity theory, powder materials, computer modeling, finite element method, stress-strain state, porosity distribution.
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