Question

Does the force of compaction in powder metallurgy affect final part properties? How?

 

Answer 1

The forming of a sintered component begins with the densification of the metal powder in a rigid die having a cavity of more or less complicated contour. In this operation, high pressures (usually 650 N/mm2 ) are exerted upon the powder in the die cavity, simultaneously from top and bottom, via two or more vertically moving compacting punches. Under the influence of such high compacting pressures, the powder particles are being squeezed together so closely that their surface irregularities interlock and a certain amount of cold welding takes place between their surfaces. After ejection from the die, if the compacting operation was successful, the compact owns sufficient strength (so-called green-strength) to withstand further handling without damage. In order to facilitate the compacting operation and reduce tool-wear to a minimum, a lubricant is admixed to the powder before compacting. In order to fully comprehend the possibilities and limitations of powder compacting, it is required not only to study the empirical phenomena of this process, but also to reveal the basic mechanisms behind them.

Following symbols are used

Density - Porosity - Compacting Pressure At first, some definitions are required:

• Specific Weight: ? = m/Vt (measured in g/cm3);

m = mass of the material; Vt = true volume of the material. •

DENSITY v/s pressure relation

Axial Stress Distribution

Formulation of stress is provided in the diagram its a exponential relation.