Aerospace Technic and Technology

In recent years, the actual production of metal products directly from electronic data according to a three-dimensional model based on layer-by-layer manufacturing has evolved from rapid prototyping to additive manufacturing. As the quality of additively manufactured metal products continues to increase and their manufacturing processes improve and develop, the demand for additive manufacturing is increasing. Additive manufacturing technology, also known as 3D printing, has become increasingly popular recently. Using additive manufacturing, almost any complex geometry can be manufactured with high degree of precision. After the production of parts using the SLM technology from metal powder, post-processing is applied, in particular electrochemical polishing, the main purpose of which is to reduce surface roughness, increase the gloss of surface elements, and remove metal powder that has partially melted onto the outer surface of the product at the point of contact between the molten metal and the border of the part and the powder, which is located next to the melt. This is especially important for inclined surfaces, internal channels and cellular structures with developed outer surface. For research, samples were made using SLM technology from AISI 316L austenitic steel powder. The samples have a cube shape with a base of 10 mm, a height of 10 mm, and a thickness of 10 mm, with cell widths of 4 mm and 2 mm. The main body of both samples was printed using the same modes at a laser power of 220 W, a scanning speed of 1000 mm/s and a distance between laser passes of 0.14 mm. Samples were printed on Alfa-280 3D printer manufactured by ALT Ukraine LLC. Electropolishing was carried out in a solution of orthophosphoric acid (H₃PO₄) with glycerol (C₃H₈O₃) by immersing the test samples in the electrolytic solution at a voltage of 17 V and a current density of 3 A/cm2. The control of weight and geometric parameters was carried out with the help of ADV-2000 analytical balances and MKC-25 micrometer. The electropolishing of the experimental samples took place in four stages: 1) visual - optical inspection with fixation, weight control before the start of the process; 2) electropolishing for 3 minutes, visual - optical inspection with photo fixation; weight control after 3 min. polishing process; 3) electropolishing of the same samples for another 3 minutes, visual – optical inspection with photo fixation, weight control after 6 minutes. polishing; 4) electropolishing of the same samples for another 3 minutes, visual - optical inspection with photo fixation; weight control after 9 min. electropolishing process. At each stage, a real current-voltage curve was recorded using an oscilloscope. As a result of weight control before and after the test, it was established that the samples lost approximately the same weight in the range of 6.9...7.1 % relative to the initial one. Based on the analysis of the obtained results, it was established that at a current density of 3 A/cm2 and at a voltage of 17 V, effective active uniform polishing of the surface of samples with a cellular structure of scaffold type with a variable cell size from 4 to 2 mm is realized.

SLM technology; AISI 316L; electrochemical polishing; relative mass loss

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