Additive manufacturing gives designers “free complexity” or maximum freedom to generate complex geometries, but this “free complexity” can be very expensive if the entire process is not taken into account and the limitations of 3D printing are not well understood.
Regardless of the technology, the entire process of any part manufactured by additive manufacturing will follow eight basic steps, although the options at each step may vary.
The first five stages to achieve a physical object from a 3D model are critical to securing the final product, and involve a succession of conversions of the information made by different software. Below, we tell you in detail each stage of the process:
1. Creating the 3D model
We must start from a CAD model, 3D model, that meets the requirements of the piece and in whose design all those design rules or conditions applicable to the technology that is intended to be used have been applied. The fulfillment of the requirements will have been previously validated and the model will not be the same, even if it is the same material, if it is going to be manufactured by FDM or by laser sintering. Later we will review the different ways to obtain this 3D model.
This model is then transformed to the . STL, standard until now in additive manufacturing, by which the surfaces of the solid are approached by triangles. The parameters used by the software to perform this conversion will influence the final result of the piece, and a greater or lesser degree of detail can be achieved. We are facing the first process that can become a source of deviation or modification in the information of the piece.
Even though the . STL is the best known and used in 3D printing, there are other more elaborate formats that are spreading and that provide much more accurate information about the pieces, their requirements and the process to follow. These formats are .AMF and .3MF.
2. Define construction process
The 3D model is divided into layers (slicing), the orientation of the construction is defined, the support structures that may be necessary for the deposition of layers in orientations close to the horizontal are defined and the path or sequence of manufacture is defined. These actions are carried out with a specific software, adapted to the technology and sometimes defined by the particular printer brand, and is the second potential source of deviation or modification on the initial information. The result of a piece with different orientation, structure of supports or manufacturing sequence may be different.
When it comes to applications with high added value, and in technologies where the thermal input is high (e.g. L-PBF, DED, WAAM, FDM in high melting point materials), it may be required or highly recommended to perform the simulation of the manufacturing process prior to manufacture, with the aim of analyzing the possibility of appearance of deformations or defects (microcracks, micro-vacuums,…) and determine the best combination of parameters, orientation, support structures, or even evaluate convenient changes in the design. This simulation is performed using specific finite element calculation (FEM) software.
At this stage, the chamber or manufacturing platform is also prepared for the grouping or stacking of parts that will be manufactured at the same time, which is known as nesting, and of the witness specimens that must be manufactured at the same time as the pieces, according to the applicable standard or procedure, to validate the result of the manufacture once executed.
3. Preparation of raw material
The correct preparation of the raw material for manufacturing begins with the reception of the material. Depending on the application and nature of the raw material, it may be required to be accompanied by a certificate attesting to the key characteristics, such as composition, diameter (thread), size, morphology and distribution of the particles (dust), etc. These key characteristics will be defined in the applicable standard or technical specification of purchase. Additionally, a reception inspection can be performed.
In the case of dust technologies that allow the reuse of unconsolidated dust in previous constructions, the established procedures must be followed to, firstly, guarantee the correct state of the powder for reuse, and, secondly, proceed to the percentage of mixture (used powder + virgin powder) that the applicable standard or procedure allows.
The last step will be the loading of the raw material into the printer, which may be by loading the cartridge load of material, powder feeding, external unit coupling or other methods.
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