Unidad de Posgrado Civil y Mecánica

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    Evaluación de costos de mecanizado por arranque de viruta para aceros inoxidables ASTM a743 grado CA6-NM y soldadura ER312 y ER410 para el CIRT-CELEC EP
    (Universidad Técnica de Ambato. Facultad de Ingeniería Civil y Mecánica. Maestría en Mecánica Mención Manufactura, 2021) Salazar Freire, Mayra Isamar; Cabrera Anda, Santiago Paúl
    The research project focuses on the analysis of milling and turning costs in hydraulic turbine impellers. This is important because the machining parameters were evaluated and how they affected the useful life of the inserts used for roughing stainless steel ASTM A743 grade CA6-NM, base material, and ER 312 and ER 410 welding. For this purpose, the machining costs were experimentally compared with different cutting tools to establish variables and their relationship with the final machining cost. The present study had a qualitative and quantitative approach in which variables, which intervened in the machining process by chip removal, were handled. The parameters used for each of the cutting tools were the following based on those recommended by the manufacturer of each one as shown below: TD1 Vc=225 (m/min), TD2 gives 270 (m/min), TD3 gives 100 m/min and TD4 = 250 m/min, for the turning process. Giving from this group the Taylor slope 0.79, while the data offered by stainless steel A743 with ER 410 welding gives n=0.8 and stainless steel A743 with ER 312 welding gives = 0.87. For the milling process, the following parameters were also considered: FD1 Vc=120 (m/min), FD2 Vc=120 (m/min), FD3 Vc=235 (m/min) and FD4 Vc=400 (m/min). On the other hand, the costs of using machinery and consumables in the order of the inserts detailed above were 16.67, 19.38, 16.12 and 10.11dollars, respectively. Finally, the hypothesis was validated, defining as optimum parameters the type of insert, cutting speed and recommended feed rate, concluding with the experimental comparison of the different inserts and fulfilling the proposed objectives.
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    Estudio del tratamiento térmico post soldadura del acero inoxidable martensítico ASTM A743 grado CA6-NM y su incidencia en las propiedades mecánicas del material aplicado a la recuperación de rodetes hidráulicos
    (Universidad Técnica de Ambato, Facultad de Ingeniería Civil y Mecánica. Maestría en Diseño Mecánico, 2017) Auz Mogrovejo, Juan José; Vaca Ortega, Wilson Henry
    ASTM A743 grade CA6-NM Martensitic Stainless Steel is used in the manufacture of runners and other components of hydraulic turbines to provide a good combination between mechanical properties and resistance to cavitation and corrosion. Due to its low carbon content it has good weldability; however, it is necessary to perform post-weld heat treatment to alleviate stress and to fine tune the microstructure and mechanical properties in order to recover characteristics similar to those of the original material. Through the present work the effect of the heat treatment of ASTM A743 grade CA6-NM steel was studied after applying deposits of multi-step welding of accumulation type or restoration the thickness of the base metal using a GMAW robotized process with ER410NiMo electrodes on slotted coupons which reproduce part of the worn surface of a hydraulic runner. The welded coupons were subjected to different heat treatments in order to compare the mechanical properties of the weld material without heat treatment and with post-weld tempering at a temperature of 600 °C during two different holding times, one and two hours; in addition, this process was performed for one, two and three cycles of recovery by welding plus heat treatment. Eight cases of study were considered, including the original base material, the weld without heat treatment and six cases of post-welding tempering, which were subjected to tests of tension, impact, hardness and metallography to characterize and establish the variation of the mechanical properties. From this analysis it was determined that the post-weld heat treatment applied allows to improve the properties that are affected by the welding process. The best combination of mechanical properties was obtained for tempering at 600 °C during two hours in the first recovery. It was verified that even in the third recovery the properties of the material are within the parameters required by the standard ASTM A743. Finally, a procedure is proposed for the recovery of Francis hydraulic runners as an alternative for the maintenance of turbines at a lower cost.