Estimação do aporte de calor em processo de soldagem por descarga capacitiva usando técnica de problema inverso

Abstract

This work presents an experimental and numerical procedure for estimating the thermal input in the capacitive discharge welding process of K-type thermocouples wire. The ob jective of the work is to promote improvements in a device at the important temperature, the thermocouple. The work of proposed improvement in the solution of this in metals and also of possible energy solution of risk solution. The thermal model used is based on the equation of transient three-dimensional heat diffusion with phase change, modeled as a function of enthalpy. The thermal properties of chromel and alumel, materials that make up the two wires of k-type thermocouples, were considered temperature-dependent. The model was solved using the program COMSOL Multiphysics. The equation of the power curve in relation to time was defined from theoretical concepts of capacitor discharge. The nonlinear inverse problem technique used to solve the heat conduction problem was the iterative Function Specification Method. This technique estimates the heat rate that minimizes an objective function, defined as the square of the experimental and numerical temperature difference for each time interval. A numerical code was used in MATLAB together with software COMSOL Multiphysics to applied the inverse problem technique. The experimental method was used to obtain temperatures close to the welding region, which were used to apply the inverse problem technique. To calculate the efficiency of the process, the integral of the power estimated by time was used, and the energy stored in the capacitors bank of the equipment, defined by concepts of electricity. The proposed methodology was able for estimating the thermal input and efficiency for the capacitive discharge welding process.The heat rate was estimated from experimental temperature data, the temperatures calculated computationally, from the estimated heat rate, showed low divergence in relation to the experimental data. In addition, the development of a ca pacitive discharge welding equipment is presented. The equipment consists of a capacitors bank that stores the energy supplied by a switched source. The amount of energy stored in capacitors bank is controlled by an Arduino microcontroller. The equipment interface has a liquid crystal display and a button, which allow the operator to select the type of thermocouple he wants to weld. This equipment was able to weld thermocouples wire thicker than 24 AWG.