Costs of PBF technologies
In this section, the authors assume that the reader is acquainted with PBF technologies and the respective terminology. In case pf any doubt, the reader may consult the PBF technologies section of D4AM Wiki or the recommended reference material in the section.
The production costs of manufacturing of plastic products (SLS and MJF) are presented in details and the production costs of manufacturing of metal products are listed, while the long process of calculation of its costs will be completed in future. The authors of D4 Wiki hope that the interested specialists in other AM technologies may provide their contributions to this section.
"Collective" production
A very important features of PBF technologies is that they actually represent simultaneous manufacturing of a set of products, called batch, during a single production process, using a single production machine. The PBF technologies, as all additive manufacturing technologies in principle, represent a kind of “collective” production. For that reason, there are no production costs of an individual product of the batch, and, in principle, only production costs of a batch may be calculated.
Activity-based value-chain model of PBF technologies
The calculation of costs of a batch of products may be performed by analysis of the production process of the batch. The activity-based value chain of PBF technologies comprises the following activities:
Modelling, which comprises developing of the models of products which are going to be manufactured. The raw models of the products are usually developed by mechanical designers, but these models have to be checked for their consistency, and sometimes corrected, to be able to be manufactured in an optimal way using the PBF technology. The development of process-ready models requires a computer, 3D modelling software and a skilled designer (usually a mechanical engineer), who knows 3D modelling, understands well both the product and the possibilities and requirements of AM and PBF technologies.
Assembly, when the process-ready models of all the products that are going to be produced in a single manufacturing process are assembled in the batch model. This activity is performed by another skilled professional, assembly designer, who is defining the spatial distribution of the products within the production chamber, thus preparing them to be produced in an optimal way from the aspects of accuracy of product dimensions and consumption of the space of a production bin. For these purposes the assembly designer needs a specialized software for assembly and a computer.
Setup, which comprises loading of the batch model in the memory of PBF machine, as well as the other processes of preparation of the production chamber by heating and atmosphere conditioning. This activity is performed by a trained machine operator.
Building, when the PBF machine manufactures products from the batch simultaneously on a layer-by-layer principle using the powder and energy. The process is completely automated and does not need human supervision or participation.
Removal is performed after the completion of the building, and starts with removing of the products from the production chamber. At this moment arises difference between the activity-based models of PBF technologies for polymers and metal materials. After removal from process chamber, the polymer products should be removed from the product bin, while metal products need to be detached from the baseplate. While removal of the polymer products from the product bin is performed by the machine operator, the detachment of the metal products from the baseplate requires specialized equipment, electric energy and a trained operator.
The final activity of the production process is also different in processes of production of polymer and metal products:
Blasting is the last activity in production of the polymer products by PBF. During that activity is removed powder attached to each of the individual products. The blasting is performed in the blasting cabinet and requires abrasive, electric energy and a trained operator.
Post-processing represents a necessary phase in production of metal products by PBF for at least two reasons:
the process of detachment from the baseplate strongly affects the surface quality of the parts of the product where the supports were attached, and, in vast majority of cases, such surface quality is not acceptable.
the residual stresses after the PBF production of metal products are high, and the appropriate heat treatment is necessary to prevent deformation of the products after detachment; the heat-treatment is also used to induce transformations of the microstructure of the material, thus improving mechanical properties of material to a satisfactory level.
In principle, the steps presented above lead to raw products that are described by the ram 3D models at the beginning of the process. The raw products may be subjected to further processing, mostly for aesthetic reasons, but, being that it goes beyond the requests of the input 3D model, such activities do not belong to activity chain model of PBF technology.