Introduction

POWDER METALLURGY PARTS are formed by several methods that range from high-pressure die compaction to pressureless shaping methods, such as slip casting. Die compaction at high pressures where densification and shaping occur simultaneously is the dominant approach. However, shaping of P/M products is also accomplished by various low-pressure methods using binders to maintain part shape for further consolidation by sintering. Another alternative is full-density processing, where the application of high pressure at high temperatures leads to P/M components with mechanical properties approaching and sometimes exceeding those of wrought forms. Finally, P/M part technology also includes spray forming of metal powders into high-density parts.

In all of these methods, the basic purpose is to consolidate powders into useful forms. As simple as this sounds, however, shaping and consolidation of powders is a complicated subject. The selection of a shaping/consolidation method involves many decisions, which may include:

• The type of powder to be used (i.e., spherical, sponge, flake)

• The chemistry of the powder (i.e., prealloyed, elemental blend, partially alloyed)

• The use of rigid or flexible tools

• The use of a binder or lubricant

• The use of a directed powder spray to directly consolidate the powder as it is being made

This article briefly introduces and compares powder shaping and consolidation methods, which are described in more detail in subsequent articles of this Section. The emphasis here is to introduce methods for shaping of powder forms and to briefly describe common powder compaction methods, such as those listed in Table 1. The differences between compaction and shaping technologies are determined by many production and application factors, such as part size, desired final density, and shape complexity.

Table 1 Compaction options

Process

Cold isostatic

Cold

Die

Explosive

Roll

Warm

compaction

forging

compaction

compaction

compaction

compaction

Pressure

Moderate, 400

Very high, >800

High, 700

Very high, >1

Low

High, 700

MPa

MPa

MPa

GPa

MPa

Temperature

Ambient

Ambient

Ambient

Very high

Ambient

Warm

Tooling

Soft

Hard

Hard

Soft

Hard

Hard, heated

Deformation rate

Low

High

High

Very high

Low

High

Continuous

No

No

No

No

Yes

No

Pressing

3

1

1

1

1

1

direction

Shape complexity

Moderate to high

Moderate

High

Low

Low

Moderate

Polymer level

None

None

Low, 0.5%

None

Low, 0.1%

Low, 0.6%

Precision

Low

Moderate

High

Low

High

High

Use

Moderate

Low

Extensive

Very low

Moderate

Source: Ref 1

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