Powder Metallurgy uses various processes to make sintered components. Conventional Powder Metallurgy process involves four steps:
An iron-based powder mix is the initial material for manufacturing of sintered components. Properties of the final component are achieved by adding different alloying elements and other additives. The powder mix must also contain a solid lubricant, which is there to reduce friction between the powder mass and surfaces of the compaction tool.
It is normal to use steel or carbide tools, with the load applied axially. The powder to be compacted is delivered under gravity, to the tool in a predetermined amount. A filling shoe delivers the powder to the die cavity. After the initial compaction, usually under pressures of 400-800 MPa the green component has a density of around 85-90%. It is possible to press parts with complicated shapes in a single operation and with a relatively high production rate of up to 25 parts per minute. The part has its predetermined shape after compaction, but not its final dimensions. Allowance is made for shrinkage during the sintering process.
After Compaction the green components must be Sintered (baked) to achieve their required mechanical properties. Sintering is a heat treatment process, usually performed in a belt conveyor furnace in a controlled atmosphere. The parts are heated in a controlled atmosphere to a temperature that is below the melting point of the main metal for between 15 and 60 minutes, depending on the application. During this process the powder grains in the green component grow together through a diffusion process.
There are three furnace zones; pre-heating, where the lubricant is burned off, sintering and cooling. Minor shrinkage takes place, which gives the component its final dimensions. Properties of the component can be adjusted by changing the cooling rate.
Various optional post-sintering process steps are available for sintered components. Heat Treatment operations, for example, are carried out in the same way as for conventional steel. In principle the surface treatments applied to solid metal can be applied to sintered components, with the understanding that the porosity of the sintered component may affect the treatment. In some cases it may be necessary to close the porosity using for example steam treatment. It must be emphasised however that due to its larger surface area, due to the porosity, the corrosion resistance of sintered components will not be as effective as those achieved for solid material.
Typical applications for components produced by this route include the production of complex components such as Pressure plates, gears, cams, sprockets, levers, ratchets and bushing etc for use in the following industries, Automobile, Hydraulic & Agriculture
Component size is limited by press tonnage at compaction stage.
Residual Porosity lowers the final component Mechanical & Physical properties and is not conducive to solution based surface treatment due to the potential for the leaching back of the plating fluids.
|Profile Dimension to lerances|
|Size mm||Fe & SS||Brass & Bronze*|
|0 - 12.5||+/- 0.025||+/- 0.10|
|12.5 - 25.4||+/- 0.05||+/- 0.150|
|25.4 - 38.0||+/- 0.1||+/- 0.2|
|38.0 - 75.0||+/- 0.150||+/- 0.3|
|75.0-150.0||+/- 0.20||+/- 0.4|
|150.0 - 200.0||+/- 0.25||+/- 0.5|
|* It is recommended that these materials be sized ( re-struck) for close tolerance control.|