5.1 Introduction

The compaction of metal powders has the following major functions:

1. to consolidate the powder into desired shape

2. to impart, to as high a degree as possible, the desired final dimensions with due consideration to any dimensional changes resulting from sintering.

3. to impart the desired level and type of porosity.

4. to impart adequate strength for subsequent handling.

Several approaches exist for achieving these goals. In general the techniques can be categorised as (a) continuous vs discontinuous process, (b) pressures - high vs low, (c) compaction velocity - high vs low (d) temperature - room to elevated temperature; (e) uniaxial vs hydrostatic pressures.

In the present chapter only cold compaction methods shall be described.

5.2 Die Compaction

Die compaction represents the most widely used method and is considered as the conventional technique. This involves rigid dies and special mechanical or hydraulic presses. Densities of up to 90 % of full density can be achieved following the compaction cycle, the duration of which may be of the order of just a few seconds for very small parts.

Powders do not respond to pressing in the same way as fluids and do not assume the same density throughout the compact. The friction between the powder and die wall and between individual powder particles hinders the transmission of pressure. A high uniformity in green parts can be achieved depending on:

• the kind of compacting technique

• the type of tools

• the materials to be pressed and the lubricant.

The compacting techniques used may be...