Role of materials, porosity, structure and shape at the IN MANUFACTURING.
Quality systems for PM must take into account some unique technical aspects connected to the fact that the raw material is in powder form and the powders intrinsic residual porosity.
The following are some of the technical aspects that should be addressed:
1.Role of materials
- Raw materials are offered in standard grades.
- The
supplier, in the specification certifies the range and the capability
of the material in the customer's process.
In spite of that, some of the ranges may prove to be insufficiently tight, especially at the pressing stage, and may compel the supplier to manage the variability accordingly.
2.Role of porosity and structure
In the case of rigid die forming, the density distribution within the components, especially those having an intricate shape, represents an important source of variability for the local properties and the dimensional tolerances of the parts.
In order to achieve the homogeneity in the local properties and dimensional tolerances of the parts the following aspects must be considered:
- Uniformity of powder distribution in the die cavity during filling
- The way in which the press drives and controls the movements of the press tool set
- The Mechanical efficiency of both the press and the tooling
Residual porosity, which can be managed by the aspects outlined above, may have several implications:
- Penetration of agents is strongly promoted by the interconnection of the pores
- Decrease to the precision level - this can be compensated by using softer powders
- Control of the evolution of the structure during thermal treatments; but only in relation to its kinetics.
- The use of secondary operations
3.Role of shapes
The dimensional tolerances of the product will depend largely on the following aspects:
- The structural requirements of the tool sets
- The Elastic deformation of the press and the punches
Intricate and asymmetric shapes are possible with PM (see below), however it is important to note that they involve an increased variability during sintering as well as during subsequent thermal treatment, if specified.
