The process of manufacturing parts in powder metallurgy
High quality and accuracy of details
The basic production process of a sintered part
RAW MATERIAL
The raw material of the sintered component is always metal powder. The characteristics of the material to be achieved determine the chemical composition of the powder. Metal powders can be both pure metal (iron, copper) and alloyed powders (bronze, brass, steel, etc.). There are powders of different nature (spongy, irregular, spherical, laminar) that give certain properties to the component.
MIX
The base powder is mixed with various alloying elements, depending on the composition of the final material (such as graphite, nickel, copper, etc.), with an organic solid lubricant (necessary for compacting the powder), and sometimes with special additives. The result is a powder mixture with a homogeneous distribution of additives. The chemical composition of the material is ensured by strict dosing and control processes and is critical to achieving the mechanical, physical or chemical characteristics of the material.
STRUCTURE DESIGN
Discussion with the customer of the characteristics of strength, size, shape. Creation of documentation and forms for the production of parts.
CONSOLIDATION
In the pressing process, the powder is pressed into raw parts under high pressure. The powder mixture is filled into the cavity of the mixer mold by gravity and uniaxial pressure is applied to it in the range of 200 to 1500 MPa depending on the final density to be achieved.
At this stage, the finished pressed part has an almost final shape, but not the required strength. Very little waste is produced during the pressing process because the exact amount of powder needed to form the part is used. This means cost savings compared to other molding technologies. The compacted part is removed from the mold, and the result is a "green part" that has a certain mechanical strength.
SINTERING
Sintering is a thermal cycle consisting of heating the compacted part for a certain time at a temperature below the melting point of the base metal. The high temperature leads to the welding of particles between them, as well as to alloying elements using the solid-state diffusion mechanism. Sintering is carried out in continuous furnaces, at a controlled rate and in an atmosphere with a controlled chemical composition. Sintering usually takes place at temperatures between 750 and 1300 °C, depending on the material and the characteristics to be achieved. The result of these basic operations is a metal part with certain microporosity, high dimensional accuracy and perfectly functional when the resulting characteristics meet the specifications of the component.
CALIBRATION
Our agglomerated parts ensure high dimensional accuracy. A calibration or sizing process is required to ensure dimensional accuracy.
Dimensional accuracy as well as density is improved by calibration, and the surface roughness of the part can be improved. In this way, expensive additional procedures, which are often necessary in other molding technologies, are minimized.
MECHANICAL TREATMENT
We are equipped with various turning, milling and grinding machines for mechanical treatment.
With these machines, we can mold the parts into their final shape by removing excess material.
Additional operations
Applying additional operations to a sintered component allows one or more characteristics to be improved that cannot be obtained directly in the main process
Calibration (Re-calibration)
This process consists of re-compacting the part inside a rigid mold that has a symmetrical opposite shape to the part.
Size can have several purposes:
● Increased dimensional accuracy in diameter, reaching IT 5. Degree of compaction below 4%.
● Creation of relief geometric details that cannot be realized in a compacted part, or improvement of roughness.
● Sealing. The degree of compaction used is 7-10% and it is also known as minting. Density up to 7.6 g/cm3 is possible.Porosity seepage
Impregnation consists in filling the pores with a chemical product:
● Oil impregnation. The oil contained in the pores can act as a lubricant for the bearing-shaft contact, thus providing self-lubrication.
● Impregnation with plastic or resin ensures sealing. This operation is quite common as part preparation before coating.
● Copper impregnation, called Infiltration. It consists of sintering the part together with a copper plate pressed onto it. Copper melts during sintering and seeps into the pores with the help of capillaries. Infiltration is used to increase the mechanical strength and toughness of low-alloy sintered steels.Mechanical treatment (additional mechanical treatment)
Sintered components can sometimes be machined when a shape or tolerance is required that cannot be acquired by stamping. Sintered parts support all common machining operations, i.e. turning, milling, drilling, tapping, grinding, lapping, reaming, polishing, etc.
Removal of burrs
Burrs are removed either in groups (hammering, shot blasting, etc.) or individually (brushing, polishing, electrolytic removal of burrs, etc.). Mass deburring is sometimes used to ensure a uniform surface or very low roughness.
Cleaning
Cleaning operations are used to reduce or eliminate the amount of solid or liquid contaminants, that a part may contain. There are many methods, depending on the material, the type of contaminant and the required specifications.
Steam treatment
This is a thermal cycle of controlled oxidation of steel, carried out in continuous steam furnaces. A layer of magnetite forms on the surface of the part and porosity. Its application to the component increases compressive strength, seals porosity and improves corrosion resistance in the environment.
Heat treatment
Heat treatment is a thermal cycle that changes the properties of the material. They are usually used to increase the hardness and strength of the component. The main heat treatments of the surface or core are: hardening, cementation and carbonitriding. Induction hardening is used to increase the hardness in the local area of the part. Other possible treatment methods are ion nitriding, oxynitrocementing or annealing.
A special case is hardened components made from a special type of steel that is hardened in a sintering furnace during cooling.Coating
This is the deposition of material on the surface of the component, which changes the properties of the surface without changing the chemical composition of the base metal. Coatings are applied to protect against wear, friction or corrosion.
Sintered parts accept almost all common coatings, such as zinc plating, chrome plating, nickel plating, phosphating, metallization, non-stick coating (polytetrafluoroethylene - PTFE) and other special coatings.Connection with other parts
Sintered parts can be connected to other sintered parts or components made by other technologies. Typical joining methods are welding, brazing, sintering, fitting, gluing, riveting, lapping, etc.