Pressing: an essential stage in powder sintering
In the pressing stage, the powder mix, with the addition of polymeric binders and lubricants, is placed into the mould.
This is an essential phase of the powder sintering process because it is at this stage that mechanical parts take shape.
In fact, during the compression phase, the powder mixture, previously prepared in the mixing phase, is placed into the mould which was designed in the co-design phase with the customer. The mould generally consists of a matrix, two punches and a pin and is located inside the press, the machinery in which the powders will undergo the pressing process. This compression can take place either unilaterally or bilaterally.
How the pressing process takes place
At first, the powder thickens and is evenly distributed in the mould, resulting in a reduction in volume. Subsequently, the powder grains undergo a mechanical shock that causes them to deform, allowing the density of the part to increase until it reaches the specific density of the base material.
The pressure with which the powders are compressed is strictly linked to the density to be reached and depends on the type of materials used for the powder mix and the particle size of the powders.
Extraction of the mechanical part
Once the pressing phase is complete and the desired density has been reached, the mould is opened and the compacted mechanical part, commonly referred to at this stage as the ‘green part’, is extracted.
Extraction is carried out by means of matrix extractors which allow the mechanical part to be gently removed from the mould, thus avoiding any risk of breaking the part.
The mechanical part has therefore reached the specific density to move on to the actual powder sintering phase.