LIBRARY ı6ıul 0) - Cranfield University

8. Discussion
8.1 Introduction
The aim of this work was to develop an integration concept between robot
off-line programming, welded component design, welding procedure generation,
process monitoring and adaptive control to ensure weld quality in robotic gas metal
arc welding of thin sheet steel. Based on this concept, a self-adjusting system capable
of adapting the of line generated robot program to changes in the welding cell
environment as well as performing position and process monitoring and control was
implemented.
Robot off-line programming has received increased attention due to its
obvious potential in increasing robot productivity by not stopping the production for
robot programming. However, this technique has not been widely adopted by the
industry due to positional and process related errors (see Chapter 3) which makes the
off-line generated program inaccurate and, therefore, requires further calibration
before satisfactory welds can be produced.
Generally, most of the errors that occur are due to changes in the robot
environment but sometimes improper selection of power source set-up welding
parameters and/or differences between the welding wire or shielding gas batches may
cause an inadequate weld quality to be produced. This could, however, be
compensated for by on-line fine tuning of the welding parameters.
Although several off-line programming systems are reported in the literature,
very few are specifically designed for welding. Most of the available systems do not
incorporate any welding knowledge or expertise; generally the task of setting the
welding procedure is left to the user. Only one published work [ref 85] was found
that reports a fully automated system that was able to generate the robot program
from the part geometrical data contained in CAD drawings and select the welding
procedure which satisfies the appropriate welding code from a previously stored
procedure database. This system was designed, however, for a very specific task,
which was welding bridge panels normally consisting of heavy gauge fillet joints. No
process monitoring and control was reported to be used apart from a spin-arc system
used for seam tracking.
The analysis of the current state-of-the-art of off-line programming for arc
welding applications clearly showed the need for an integrated system that allows off-
line programming to be used without the need for calibration and incorporating a
means of monitoring and controlling the quality of the weld.
Based on this analysis, the following objectives were defined in order to
produce the integrated system:
" to identify the sources of error and propose corrective measures;
. to incorporate welding models into a CAD system, that is integrating the
weld design and the welding procedure generation;
" to generate positional data for off-line programming based on the CAD
model of the part and on the geometry of the welding cell;
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