The Powder Metallurgy Process

The conventional P/M process (Powder Metallurgy 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 20 compaction presses ranging from 4 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/cm^3.
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.

In-House value-added 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
•    Tumbling

 

 

Heat Treating
Sintered powdered metal parts can undergo heat treating operations to optimize properties such as strength and hardness.
We offer the full spectrum of heat treating services to suit any application:
Neutral Hardening
Neutral hardening involves heating parts in a carbon neutral atmosphere and then quenching to increase the strength and hardness of the part. This process is used on medium to high carbon containing ferrous parts.
Carburizing
We use gas carburizing to increase the carbon content of the part's surface, thus increasing strength and hardness of the surface of the PM part. This process uses low carbon containing ferrous parts. The porosity of the PM component affects the depth of carbon penetration: the lower the density, the greater the carbon penetration. Defined carburized case depths are difficult to achieve until the part density is lover than 7.1 g/cm3.
Carbonitriding
Carbonitriding is similar to carburizing but relies on both carbon and nitrogen to alloy with the ferrous parts to increase the surface hardness. Defined carbonitrided layers are generally not obtained until the density of the component exceeds 7.1 g/cc, due to the porosity of the PM component.
Steam Treating
During the steam treating process, the components are heated to about 550C temperature and then exposed to steam. The steam reacts with the ferrous parts to form an oxide layer on the surface and in the pores. The oxide is predominately Fe3O4 (magnetite). The typical steam treat layer is 2 to 5 µm in thickness. By this treatment, surface hardness and corrosion resistance are improved.
Tempering
Tempering is performed on all heat treated components. Components in the as-heat treated state tend to be brittle. Tempering increases the toughness without sacrificing the wear resistance of the component.