Controle da temperatura de um componente metálico por resfriamento ativo por quase-imersão

Abstract

The additive manufacturing of metallic components allows the production of parts with different geometries with reduced unit cost and faster speed when used for low scale production, when compared to traditional manufacturing methods. Among the different techniques to perform additive manufacturing of metallic components, WAAM (Wire + Arc Additive Manufacturing) stands out due to its low implementation cost, high deposition rates, and good part integrity. As a disadvantage, there is a build-up of heat on the part resulting from the deposition of the material, which can cause non-conformities of diferente types. To reduce heat buildup, near-immersion active cooling (NIAC) has been proposed in the literature. The fundamental idea of NIAC is to deposit the material in a tank in which the level of a cooling liquid (usually water) is kept at a fixed distance from the top of the preform. This significantly reduces heat buildup. The closer the liquid is to the deposition layer, the greater the cooling. One possibility to increase the versatility of the NIAC is to adopt a closed loop control structure to control the interpass temperature, that is, hte layer temperature in between the deposition passes. As a result, it would be possible to make this temperature follow reference values provided by an operator. As an initial step in the project of such a control system, the present work involved the construction of a prototype with the main characteristics of a WAAM machine with NIAC. In this development, the deposition vat was replaced by a tank. Moreover, an electrical resistance and an aluminum plate set represented the energy source and the preform, and the computer and the pumping system of the real process were replaced by an Arduino UNO and a set of tanks and DC pump, respectively. With the prototype built, a controller was implemented to track temperature references for the aluminum sheet. In particular, a proportional-integral controller was adopted. The controller parameters were adjusted based on the Ziegler and Nichols step response method and refined experimentally. To improve the performance of the controller, conditional integration was adopted for windup elimination. Furthermore, a heuristic technique was implemented to decrease the convergence time. This technique consisted in modifying the control action for a short time interval when the tracking error was larger than a tolerance. The results showed that it was possible to guide the plate temperature around reference values. To do this, the control system changes the water level in the tank in which the resistor is placed. This result indicates that it is also possible to control the interpass temperature in the real process.