| Abstract Scope |
Wire Arc Additive Manufacturing by GMA-DED is especially important for the manufacture of parts in carbon steel, since the use of powders of this material is extremely difficult due to the high reactivity with oxygen in the atmosphere. Additionally, the good deposition rate that electric arc processes have is noteworthy. On the other hand, laser processing provides better dimensional resolution. Thus, although the laser process, using powder, is more expensive, it delivers a final surface with better quality and dimensional tolerance. Also, with regard to laser processing, there is the possibility of using wires, which would be a competitor with the use of arc processing, but the laser has a lower deposition rate, but better dimensional resolution. Thus, a question arises: what would be the best possible resolution to be achieved by arc processes? Therefore, in this work, 0.6 mm diameter carbon steel wire was used, depositing material by Wire Arc Additive Manufacturing (WAAM) with the GMA-DED process. The objective is to demonstrate that the arc process with ultrafine wires could achieve resolutions close to those obtained by laser processing. For the parametric study and deposition of parts, a multi-process welding source was used, operating in conventional mode (constant voltage) and MAG process. It is noteworthy that the terminology "welding" must be used with attention, considering that two or more pieces were not joined, but "depositions" were performed. In addition to the source, a table with three degrees of freedom was used to move the refrigerated torch and a container for continuous cooling of the substrate. It is important to highlight that the torch must be as small as possible and kept as straight as possible to reduce feed problems of the ultrafine wire used. Regarding the wire, commercial wire AWS A5.18 / ASME SFA-5.18 carbon steel with 0.6 mm diameter was used. It is noteworthy that although it is a commercial wire, the 0.6 mm gauge is not easily found. As a shielding gas, two mixtures were used: Ar+8%CO2 and Ar+25%CO2, respectively for the free-flight and short-circuit metal transfer modes. The flow rate used was 10 L/min. As the welding source was used in conventional mode, the voltage and the wire feed speed parameters were initially varied to establish the parameters, together with the distance from the contact tip to the workpiece distance (CTWD). The methodological approach used followed the line of initially parameterizing beads on plate, followed by layer over layer, building a wall. The objective was to try to use the MAG process with the highest possible productivity. Thus, we tried to work with high deposition speeds (TS), close to 1.0 m/min. For this, it was necessary to use wire feed speeds (WFS) which were also high, but which were limited by the feedability of the thin wire. The results obtained indicate that there are two main challenges to be overcome. The first concerns the low feedability of the 0.6 mm wire, i.e., the electrode wire cannot pass through the entire torch conduit, even if it is as aligned as possible. Another challenge is related to the humping effect, i.e., due to the small energy used, it was not possible in some tests to promote adequate fusion along the length of the deposit. From the depositions of the layers that were properly deposited, the parts/walls were deposited, which, in the case of the use of free-flight metal transfer, it was not possible to obtain an adequate part (wall), because of such feedability and/or humping problem. On the other hand, while using of short-circuit metal transfer, appropriate part (wall) was achieved with experimental set of 19.0 V (voltage); 5.0 m/min (WFS); 12 mm (CTWD); 500 mm/min (TS); 0.95 mm of layer height. The cross section of the piece presented constancy of the width (average of 2.95 mm) and low lateral undulation. From the results presented it is possible to conclude that the two main challenges to be overcome in Wire Arc Additive Manufacturing by GMA-DED using 0.6 mm thin wire are low feedability and the humping effect. It is also possible to assert that by using free-flight metal transfer it was not possible to obtain an adequate part (wall) and, on the other hand, by using short-circuit metal transfer the appropriate piece (wall) was obtained, showing the quality of the deposit, which obtained an average width of 2.95 mm. Therefore, it was possible to deposit parts with small thicknesses, but it was not yet possible to obtain resolutions in the order of millimeters. Keywords: GMA-DED; WAAM; Short-circuit Transfer; Free-flight transfer; Carbon Steel. |