The Powder Metallurgy Process
The conventional P/M process involves following steps:
Powder blending: enables a uniform mixture, provides the appropriate material properties and ensures minimum friction between the tool and powder particles. Plain iron powder and a combination of other elements and additives are blended together into a fully homogeneous mixture. Each blend is tailored to meet the exact physical requirements of the finished component.
Mixing can be performed by the powder supplier or the P/M parts manufacturer.
Mixing Equipment Available at NAPOSINT is a 1 tone conical blender.
Powder compaction: densification of the metal powder in a rigid die having a cavity of more or less complicated contour. In this operation, high pressures (usually 600 N/mm2) are exerted upon the powder in the die cavity, simultaneously from top and bottom, via two or more vertically moving compacting punches.
NAPOSINT has over 10 compaction presses ranging from 6 to 200 tones capacity.
NAPOSINT has Warm compaction capability allowing increased density for improved physical properties. Green densities are increased with warm compaction compared to conventional pressing process. The higher density levels achieved (lower porosity levels), are closer to the maximum pore-free density of the green compact.
NAPOSINT uses sintering materials in accordance with DIN 30910 in the density range up to 7.3 g/cm3.
Sintering: process by which metal powder compacts (green parts) are transformed into coherent solids at temperatures below their melting point. In the furnace both temperature and atmosphere are strictly controlled. During sintering, the powder particles are bonded together by diffusion and other atomic transport mechanisms, and the resulting somewhat porous body acquires a certain mechanical strength.
Our furnaces are mesh belt furnaces with three operating zones; a pre-heat or de-lube zone, a sintering zone and a cooling zone. The furnaces usually operate between 1100 to 1120 C for ferrous parts and 790 to 845 C for bronze materials.
NAPOSINT has a potential sintering capacity of over 570 tones/year from 2 furnaces.
Sizing, Coining and Repressing (sometimes referred to as calibration) increases both precision and density and reduces the P/M part's roughness.
Secondary Operations
Outside of P/M's core manufacturing process, there are many options available to tailor a powder metal part for its intended application. They include:
- Steam treating
- Heat treatment
- Oil impregnation
- Machining
- Plating
- Tumbling