Effect of powder particle size on green properties and stress wave

Abstract

In the powder metallurgy (PM) industry, high velocity compaction (HVC) technique is a new way to obtain higher density parts. In this study, three reduced pure iron powders with different particle sizes were pressed by HYP35-2 High Velocity Compaction Machine. A computer controlled universal testing machine was used to measure the bending strength of the green body. The relationships among the particle size, the impact velocity, the green density, the stress wave, the bending strength and the radial springback were discussed. The results show that the powder of -200 mesh is the best option among the three powders for the HVC process. At the identical impact velocity, the green density for the powder of -200 mesh is higher than the other two types of powders, while the bending strength and the radial springback for the powder of -300 mesh is the highest. In addition, the stress waves exhibit similar, pulsed waveforms. As the impact velocity rises up, the duration of the first peak decreases gradually, while that of the stress wave increases slowly. The response time for the powder of -200 mesh is shorter than the other two types of powders.

Numerical investigation into the densification of ferrous powder in high velocity compaction

“…Unbalanced force shows this trend and promotes the evolution of porosity. This phenomenon may be the internal characterization of stress wave [10][11][12], and the relation will be studied in the future.…”

“…In addition, the peaks of stress wave increase with increasing impact height, and high density can be related to high impact height. Wang et al [11] also found that the HVC of iron powder of different sizes may have similar pulsed waveforms. The duration of the first peak decreases gradually, and the density of the powder increases with increasing impact height.…”

“…However, the dynamic change in the density or distribution of density has not been reported yet. Other researchers have attempted to illustrate densification from stress waves in HVC [10][11][12]. For example, Wang et al [10] indicated that stress wave, which is transmitted and reflected in walls within the powder body, may be related to the densification of ferrous powder in HVC.…”