Calculation of t8/5 by response surface methodology for electric arc welding applications

Abstract

One of the greatest difficulties traditionally found in stainless steel constructions has been the execution of welding parts in them. At the present time, the available technology allows us to use arc welding processes for that application without any disadvantage. Response surface methodology is used to optimise a process in which the variables that take part in it are not related to each other by a mathematical law. Therefore, an empiric model must be formulated. With this methodology the optimisation of one selected variable may be done. In this work, the cooling time that takes place from 800 to 500ºC, t 8/5, after TIG welding operation, is modelled by the response surface method. The arc power, the welding velocity and the thermal efficiency factor are considered as the variables that have influence on the t 8/5 value. Different cooling times,t 8/5 , for different combinations of values for the variables are previously determined by a numerical method. The input values for the variables have been experimentally established. The results indicate that response surface methodology may be considered as a valid technique for these purposes.

New method for determining cooling time and preheating temperature in arc welding

“…The value b is a function of the applied steel for welding and its geometry which can be confirmed in [25][26][27][28]. Figure 1 shows the diagram for cooling temperatures in this example as a function of time, t. It can be seen that function T 1 (t) has a slower decreasing rate and its cooling time is equal to t 8/5 = 50 seconds.…”

“…However, the results obtained in this work [31] are not presented, since this work proves that there is no quoted formula. In the work [28], results are included for cooling time t 8/5 . These results have a larger error.…”

“…If there is only one example of welding, it can be concluded that the curve T 1 (t) for higher values of time, t, can have larger deviations regarding the curve T 2 (t). Therefore, it is concluded that the 2-D Rosenthal model of the equation for calculating t 8/5 [25,28] develops large deviations. A confirmation of this lies in a series of papers [26,27] which have emphasized that this equation demands large values for cooling time, t 8/5 , which can be considered as a paradox.…”

Experimental Validation of a Numerical Method that Predicts the Size of the Heat Affected Zone. Optimization of the Welding Parameters by the Taguchi’s Method

“…(1) with the appropriate boundary conditions. The temporal evolution is performed by a Crank-Nicolson scheme [20,32]. For the spatial derivatives terms, a second-order finite differences scheme has been used with a discretization of the 2D geometry of the plates to be welded with squared elements of side Dx.…”

“…The current work carries out an experimental validation of a numerical method [20] in order to determine its accuracy in the prediction of the HAZ. To do that, experiments have been carried out using the robotic arm GMAW welding technique [21] which allows to control the size of the HAZ proportionally to the welding parameters defined in the process.…”