Additive manufacturing and hybrid printing according to Eplus3D “
While additive and subtractive manufacturing processes appear to be on quite opposite ground, in fact, as these technologies develop, the benefits of hybrid manufacturing are becoming increasingly evident. Hybrid manufacturing systems, simultaneously equipped with additive and subtractive technologies, could represent a great technological advance for the industry. These two technologies can be seen as complementary and able to take advantage of the advantages of each.
The joint use of additive and subtractive technologies is not a new concept. For example, the post-processing of metal parts produced by 3D printing often involves CNC machining to provide them with mechanical precision and better surface finish. However, there is another way to combine these two processes, which we call hybrid manufacturing.
Hybrid manufacturing consists of bringing together additive technology and subtractive technology in the same machine in order to benefit from the advantages of each of these technologies: the geometric complexity of additive processes with the high precision of subtractive processes. In this way, it is possible to obtain an additive and machined part in one step, thus speeding up the entire production process. Naturally, the design of a hybrid part must take into account the requirements of each of these technologies.
The applications of hybrid systems can be varied such as the manufacturing of small series of metal parts or the repair of damaged or worn parts.
Directed energy deposit
Directed energy deposition (DED) is one of the additive processes that can be used in hybrid technologies. This process involves fusing the material with a laser or electron beam as it is deposited through a nozzle on the build platform. The deposited material can then be machined to obtain a better surface finish and greater mechanical precision. Alternatively, it is also possible to add material to a machined part to increase the geometric complexity of the part.
Another of the advantages of the DED additive process must be the fact that it is possible to use a 5 axis system in the printhead, allowing the printing of geometrically complex areas without the need to place support structures.
DED is suitable for producing large parts and repairing mechanical components, and both of these features are quite advantageous when comparing this process with laser melting of metal powder. On the other hand, the fusion of metallic powder makes it possible to obtain parts with a better finish and dimensional precision.
It is with the objective of making a hybrid part that we started this project, using a CNC machined part to which we added a castle by the process of laser melting of metal powder. We cannot speak of hybrid manufacturing, but of hybrid printing, since we used two different equipment, a CNC milling machine and the Eplus3D EP-M150 3D printer, to produce this part.
Another aspect that we wanted to study with this experiment was the bonding capacity between two steels of different chemical compositions. We used 1.1730 steel construction for the CNC machined part and the hybrid castle was printed with 1.4404 (316L) stainless steel metal powder.
The project started with the 3D modeling of the part and the study of its fixation on the construction plate of the 3D printer. We opted for a simple parallelepiped geometry with an inner box, to which an additive castle was added, that is to say a part that would have to be produced in 3D printing. Inside, this castle is made up of a series of thin slats 1mm thick which, despite a simple geometry, would be very difficult to perform otherwise.
Another important aspect of this study was how to clamp the hybrid parts to the build pad. On the one hand, the printer does not have a part straightening system, as happens in CNC machines and, on the other hand, it would be difficult to add a clamping system that would not disturb the dynamics. printer operation. In addition, the build plate is attached to the printer by four screws, which does not guarantee its performance.
It was decided to make several holes in the plate while thinking of the different fixing possibilities in future hybrid prints.
The build plate (and all of its holes) is symmetrical about its central axis. In order to avoid positioning errors when clamping it on the printer, an arrow indicating its position in relation to the coater has been added, this one, in relation to the mobile mechanism which transports the metal powder from the feed cylinder on the build plate.
Once the printing is finished, the metallic powder which has not been poured must be removed. It is only after removing this powder that we can remove the build plate from the printer. Unmelted powder is sieved and reused for future printing. After removing all the metal powder, the build plate is removed from the machine.
The first hybrid printing project was successful. We can say that the project had about 70% preparation and 30% execution, being the study phase of fixing the parts to the printing plate that gave us the most work to define.
Although the laser metal powder melting process is not as versatile as the DED process, we can prove that it is possible to successfully combine CNC milling and laser metal powder melting.
However, it is important to note that here we have some limitations to be aware of. Hybrid hoods should grow from a perfectly horizontal, ground plane to ensure the hoods are welded to their base. It would not be possible to perform this experiment if the printing plane was a surface with a certain three-dimensional profile.
It is also essential to ensure that no parts are above the print surface so that they do not interfere with the movement of the coater. In other words, if you want to hybrid print a part with more complex geometry, you have to think about how to ensure the connection between the parts without interfering with the dynamics of the printer.
It has also been possible to demonstrate that it is possible to make a hybrid impression using similar metals, but with different chemical compositions.