A STUDY ON PARAMETER OPTIMIZATION FOR CIRCUMFERENTIAL GAS TUNGSTEN ARE (GTA) WELDING OF SMALL PIPES CONSIDERING BACKING GAS-PRESSURE .1. ANALYSIS OF WELD POOL SURFACE PROFILE
Sj. Na et Tj. Lho, A STUDY ON PARAMETER OPTIMIZATION FOR CIRCUMFERENTIAL GAS TUNGSTEN ARE (GTA) WELDING OF SMALL PIPES CONSIDERING BACKING GAS-PRESSURE .1. ANALYSIS OF WELD POOL SURFACE PROFILE, Proceedings of the Institution of Mechanical Engineers. Part B, Journal of engineering manufacture, 210(1), 1996, pp. 77-85
It is well known that the weld bead becomes wider and the weld pool ha
ngs down as the circumferential welding of small-diameter pipes progre
sses, if constant welding conditions are maintained over the entire jo
int length and/or no appropriate backing gas is supplied into the pipe
. In order to obtain a weld bead which is uniform in width and does no
t hang down over the whole circumference of the pipe, the welding para
meters such as welding current, welding velocity and backing gas press
ure should be optimized as the welding progresses. In order to optimiz
e the welding parameters, a mathematical model for determining the tem
perature distribution in the pipe workpiece and the surface profile of
the resultant weld pool is indispensable. An efficient finite differe
nce model was adopted for calculating the three-dimensional transient
temperature distribution in circumferential gas tungsten are (GTA) wel
ding of pipes. Its solution was obtained by employing the alternating
direction implicit (ADI)finite difference method, in which a periodic
boundary condition and a periodic cubic spline function were used. For
calculating the weld pool surface profiles in full penetration circum
ferential welding of pipes, a governing equation was derived in the cy
lindrical coordinate and solved using a simple finite difference model
with the ADI scheme. In Part 2 of this paper, an efficient parameter
optimization method is used to evaluate the optimal welding current fo
r a required bead width when the welding velocity is given.