What defects often appear in the process of powder metallurgy compact?

What defects often appear in the process of powder metallurgy compact?

In the process of powder metallurgy compaction, there will be defects in the compact due to various reasons, leading to the scrapping of powder metallurgy parts. So, what defects often appear in the process of powder metallurgy compact?

1. The compact density does not meet the design requirements

In the production of powder metallurgy parts, the higher the density of materials, the higher their physical and mechanical properties. In other words, the compacts density and distribution of powder metallurgy parts will determine the properties of products. Therefore, in the process of powder metallurgy mold debugging and pressing, the density of the compact must be tested. During density detection, it should be noted that the compacts with different structures and requirements should be treated differently.

2. The size of the compact does not meet the requirements

2.1 The radial dimension is unqualified or the hole spacing is unqualified

There may be a problem with mold design or manufacturing. If the error can be eliminated by adjusting the process (that is, by adjusting the powder composition, compact density, sintering process, etc.). It can also be remedied, otherwise only scrap the mold.

2.2 The axial dimension is unqualified

For the non stepped cylindrical compacts, the axial dimensions can be adjusted and stabilized by adjusting the powder loading, changing the pressing pressure or extending the holding time. For step blank, the step height can be changed by adjusting the forming position of the combined die punch, the powder loading ratio of each set, and the running speed of the floating die punch.

3. Geometric tolerance out of tolerance

3.1 Straightness

The reasons for out of tolerance straightness are: out of tolerance straightness of die, uneven density distribution of compact, uneven wall thickness of compact, etc.

3.2 Parallelism

The causes of out of tolerance parallelism are: out of tolerance parallelism of die, uneven powder loading, etc.

3.3 Coaxiality

The reasons for coaxiality out of tolerance include: out of tolerance of mold precision, low precision of pressing tooling and equipment, unqualified mold installation, uneven dress, etc.

When the powder flow rate is appropriate, the mold accuracy meets the design requirements, and the pressing tooling and equipment accuracy meet the installation requirements, the form and position tolerance is mainly related to the density distribution of the compact. When the pressing method is determined, the density distribution of the compact is directly related to the powder filling effect.

4. Unqualified appearance

High roughness, excessive burr, edge and corner loss, galling and crack are common appearance defects of compacts.

The above is an introduction to the defects produced in the process of powder metallurgy compact. There are many defects in powder metallurgy compact, but the defects that can make the product scrapped and are not easy to find are: uneven density and compact cracks, so we should pay special attention to them.