Aerospace Technic and Technology

Additive manufacturing technology, also known as 3D printing, has become an increasing amount of popular lately, and the number of materials and methods that can be used is expanding. As manufacturing processes continue to improve and evolve, the demand for faster, less expensive manufacturing processes has enabled a range of Rapid Prototyping (RP) processes to be developed. Since production processes continue to evolve and grow, the demand for faster and less expensive production processes has allowed the development of a series of processes of rapid prototyping (RP). With additive manufacturing, virtually any geometry with variations in size and complexity can be produced with a high degree of accuracy. The typical microstructure of the metal after the completion of the construction process is the dispersed dendritic and cellular structures of the γ-phase within the melt baths of single tracks, because of the overlap of which a part is created layer by layer. The main problems of ensuring high-quality products using SLM technology are porosity, hot cracking, anisotropy, surface roughness, and ensuring the necessary microstructure of the synthesized material. Improvement of surface roughness, the brilliance of stainless steel surface elements after electrochemical polishing (EP) is one of the most important characteristics of the process. Samples were made using the SLM technology from austenitic steel powder AISI 316L with a controlled defect in the form of local overheating, because of which an orange variability is formed, which is formed during 3-D printing. The samples are inversely symmetrical, have an equilateral trapezoid shape with bases of 20 and 5 mm, a height of 10 mm, and a thickness of 5 mm. The main body of both samples was printed in the same modes at a power of 220 W, a speed of 1000 mm / s, and a track spacing of 0,14 mm. To form a controlled defect when printing the boundaries of the samples, the following modes were used: power 120 W, speed 1050 mm / s, and distance between tracks 0,02 mm. The samples were printed in an Alfa-280 3D printer manufactured by ALT Ukraine. Etching to reveal the microstructure of the samples was conducted using an HCl + HNO3 solution. Electropolishing was conducted in a solution of orthophosphoric acid (H3PO4) with glycerol (C3H8O3) at a current density of 3 A / cm2. Metallographic studies have shown that the configuration of the tracks in the area of increasing the cross-section of the samples is more uniform. Based on this study, schemes for distributing zones with varying degrees of track equiaxiality and structure uniformity were constructed. A more intense interaction of the reagent with the microstructure near the surface with greater roughness was found. The electropolishing of isosceles trapezoids occurred in three stages: 1) visual - optical examination with fixation, control of roughness, weight, and geometry before starting the process; 2) control of roughness and geometry after 3 min. process; 3) visual - optical examination with fixation, control of roughness, weight, and geometry after 6 min electropolishing. From the analysis of the obtained roughness data and the real volt-ampere curve, it was found that zone 2 with the largest area had an insignificant change in roughness, zone 1 and zone 3 with a decrease in the area had a more significant loss on average by 33%. Controlling the weight before and after the test showed that the samples lost approximately the same weight of about 1,5%. Based on the ratio of the results obtained, it was found that when a fixed current strength and constant power are applied, electropolishing is not effective for active uniform anodization of the surface of a simple figure with a change in the area in the section. It was found that electropolishing most intensively occurs in an area with a smaller cross-sectional area.

SLM technology; AISI 316L; microstructure; electropolishing; weight loss; roughness

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