Commonly called, by abuse of language, 3D printing, additive manufacturing (AM) is a real revolution, because it makes it possible to overcome the limits of traditional manufacturing (plastic injection, machining, forming, assembly). Indeed, it gives full latitude to manufacture parts of great complexity, which cannot be produced using other techniques, thus opening up prospects for innovation. However, the mainstream press tends to portray AM as push-button technology, accessible to everyone. The reality is quite different.
In AM, the material and the part are manufactured simultaneously, layer following layer, from a digital model. But making a part isn’t just regarding transferring a digital design to the machine, pressing a button, and waiting for the part to be made. There are many steps upstream and downstream. The complete process includes designing the part, preparing the machine, setting it up, then manufacturing the part, and finally post-processing it. The design of the part is divided into several stages: the selection of the material and the structure (solid or lattice); the design of the digital model describing the geometry of the part with or without topological optimization; the discretization of the surface of the part; the positioning and orientation of the part, or even parts, on the manufacturing plate; placing the part on supports and cutting the digital model into strata representing the layers to be produced. The preparation of the machine includes, according to the processes: the cleaning of the machine, the loading of the raw material, possibly its homogenization and its leveling on the bed of the manufacturing chamber and the adjustment of the height of the leveler.
The configuration of the machine consists in configuring it; for example, for the powder bed fusion by laser category, to choose the scanning speed of the laser, its power, the size of the beam, the scanning strategy, the number of passes of the leveler. Do not forget to record the input data for the traceability of the manufacturing process. At the end of the process, the part must be extracted from the unprocessed raw material and cleaned. Then, it is necessary to proceed to the thermal post-treatment of the part. This consists, depending on the process, of annealing to eliminate residual stresses or to perfect the process of bonding the raw material or even to debind the part. Finally, the part is detached from the machine’s build plate, its supports are cut, its surface condition improved and it is cleaned. Besides the fact that these many steps demonstrate the need to review the design procedures, they highlight the complexity of the process.
Consequently, before AM can be adopted by manufacturers, mainly those concerned with the production of small series (aeronautics, aerospace and medical), it is essential to qualify the machines and to demonstrate that the parts produced in AM meet the same quality requirements as those achieved by traditional techniques. For this, it is necessary to carry out checks not only on the machines, but also at all stages of the manufacturing process, namely on the raw material, on the material and on the finished part.
This article discusses all of these controls. Some are common to traditional techniques, but others are specific to AM. Different control methods are also suggested. In the first part, the principle of AM, the different categories of processes and the advantages of the technology are recalled.
The reader will find a glossary and a table of acronyms used at the end of the article.
