Manufacturing
Processes

Outline
Introduction
Powder Manufacturing
Powder Metallurgy Process
Sintering
Other Powder Metal Processes
Powder Metal Products
Powder Metallurgy Design

Powder Metallurgy

Powder Metallurgy
Metal
Powder
Metal Product

Examples of Powder
Metal Products
Gears
Cams
Cranks
Bearings
Roller bearing cages
Housings
Light bulb filaments
Sprinkler mechanisms

Powder Metal Materials
Elemental
A pure metal, most commonly iron, aluminum or copper
Prealloyed
An alloy of the required composition, most commonly copper alloys, stainless steel or high-speed steel

Powder Manufacturing
Conversion of molten metal to powder
Atomization

Powder Manufacturing
Other methods of producing powder:
- Chemical reduction of particulate compounds
- Electrolytic deposition
- Pulverization or grinding of brittle materials
- Thermal decomposition
- Precipitation from solutions
- Condensation of metal vapors

Particle Shape

Particle Size
The process of separating particles by size is called classification

Particle Size
Micrograph of screened powder particles, showing that particles may be longer than the mesh is wide

Particle Size
Mixing particles of different sizes allows decreased porosity and a higher packing ratio void smaller, more numerous voids voids filled by smaller particles, small voids remain

Powder Metallurgy
Process

Blending and Mixing
Blending
Combining powders of the same material but possibly different particle sizes
Mixing
Combining powders of different materials

Compaction
High pressure is applied to squeeze the powder into the desired shape

Example of a Powder
Press

Sintering
Heats the powder below the melting point to allow solid-state diffusion and bond the particles together

Sintering
Diagram of particles in sintering, showing the possible movements of atoms

Sintering

Sintering

Sintering Production
Lines

Examples of Sintering
Production Lines

Sintering
Strength of sintered structures as related to density, showing that the strength is higher when the density is higher (less residual porosity)

Other Powder Metal
Processes
Cold Isostatic Pressing
Hot Isostatic Pressing
Injection Molding
Powder Rolling
Powder Extrusion
Plasma Spraying

Isostatic Pressing
Uses pressurized fluid to compress the powder equally in all directions
Cold Isostatic Pressing
Compaction performed at room temperature
Hot Isostatic Pressing
Performed at high temperatures and pressures

Example of an Isostatic
Press

Injection Molding
The powder is mixed with a binder and molded, and the binder is removed before sintering

Powder Rolling
Powder is compressed in a rolling mill to form a strip

Powder Extrusion
The powder can be extruded within a container or after being formed into billets

Plasma Spraying
Uses a plasma arc to propel molten droplets at a surface at a high velocity, forming a high-density structure

Plasma Spraying

Powder Metal Products
1. Porous or permeable products
2. Products of complex shapes
3. Products made of materials that are difficult to machine or have high melting points
4. Products which require the combined properties of multiple materials
5. Products in which powder metallurgy produces superior properties

Powder Metallurgy
Design
1. The shape must permit removal from the die
2. The shape should not have thin walls or sharp corners
3. The shape should permit the construction of strong tooling
4. The shape of the part should be within the thickness range for which the powder can be properly compacted
5. The part should have as few changes in section thickness as possible

Powder Metallurgy
Design
6. Parts can be designed to take advantage of the capabilities of the powder metallurgy process
7. The design should be consistent with available equipment
8. Consideration should be given for product tolerances
9. Design should consider the dimensional changes that occur after pressing, such as shrinkage during sintering

Powder Metallurgy
Design

Powder Metallurgy
Design

Powder Metallurgy
Advantages
1. Elimination/reduction of machining
2. High production rates
3. Complex shapes can be produced
4. Wide composition variations are possible
5. Wide property variations are possible
6. Scrap is eliminated or reduced

Powder Metallurgy
Disadvantages
1. Inferior strength properties
2. Relatively high die cost
3. High material cost

Summary
Powder metallurgy can create parts that would otherwise be difficult to form, including those with complex shapes or porosity
Sintering bonds particles together by allowing atoms to move, forming necks and grain boundaries between the particles