粉末高速压制成形件密度影响因素分析

Analysis of Influence Factors for Density of Compressed Powder Products during High Velocity Compaction

成形坯件的密度大小及其均匀性是影响粉末高速压制成品力学性能的重要参数。利用Drucker-Prager Cap模型和瞬态显式动力学有限元方法,得到了压制过程中粉末的密度变化和分布规律;量化分析了边壁摩擦因数、高径比、单位质量能量、初始松装密度对密度大小和均匀性的影响,采用正交试验方法研究了这些因素的敏感性。得到的主要结论包括:密度分布不均主要集中于压坯上下端面边缘处,且其密度差随着压制过程的进行不断增大,压坯越靠近边壁的部分,其密度不均匀性越明显;单位质量能量是影响密度的主要因素,改善边壁润滑条件、高径比和初始松装密度并不能有效提高压坯密度;边壁摩擦因数和单位质量能量对密度均匀性影响最大;密度随着单位质量能量的增大而不断提高,当单位质量能量达到临界值后平均密度不再上升,但是密度均匀性不断改善。

The density and its uniformity were crucial parameters which affected the mechanics properties of high velocity compacted powder products. The distribution and variation of densities in powder compaction processes were obtained by using Drucker-Prager Cap model and transient explicit dynamics finite element method. Four parameters, i.e., sidewall friction coefficient, height-to-diameter ratio, energy per unit mass and initial relative density were analyzed quantitatively to study their effects on the density and its uniformity. The sensitivity of these factors were studied by orthogonal tests. The main conclusions are drawn as following： the non-uniformity of the density mainly concentrates on the top and bottom surfaces, and the density difference increases with the compact processes. The non-uniformity of density is more obvious along the sidewall locations. The major factor that has the greatest impact on density is the energy per unit mass, while the improvement of lubrication conditions of sidewall, height-to-diameter ratio, initial relative density do not affect the density obviously. The major factors that have the greater impact on density non-uniformity are sidewall friction coefficient and energy per unit mass. The density increases with the energy per unit mass. Once the energy per unit mass reaches its critical value, the average density does not increase any more, but the density uniformity keeps improved.