LIBRARY ı6ıul 0) - Cranfield University

3. Proposed Strategy for Off-line Programming and Control of
Robotic Arc Welding Operations
The primary aim of using off-line programming in robotic welding is to
improve productivity by not stopping the production line during the programming of
the welding tasks. However, from the literature review in the previous chapter it is
clear that the application of off-line programming in robotic welding is not that
straightforward. Further to the common production problems normally found in on-
line programmed operations, the robot absolute accuracy appears to be an important
factor.
It is generally accepted that for quality welds to be produced, two main
requirements must be fulfilled:
a) the wire-tip must be positioned relative to the joint centre-line within the
allowable GMAW process tolerances;
b) the welding parameters must be adequate, producing the required quality
with an overall stable process.
These requirements can be achieved by off-line process optimisation and on-
line monitoring and control of the welding parameters and the wire-tip position
relative to the joint. Also, the off-line generated robot program should consider, in
addition to the setting of adequate welding parameters, the communication issues with
the external equipment normally used for implementing the monitoring and control
functions.
This chapter presents the overall concept of the proposed strategy for off-line
programming and control of robotic gas metal arc welding and the assumptions made
to achieve this.
3.1 Identification of sources of error
For a control strategy to be effective, it is necessary that the sources of error
are identified and preventive and/or corrective measures are applied. The errors that
normally occur in robotic gas metal arc welding using off-line programming (see
sections 2.4 and 2.5) can be classified according to their type into two main groups- a)
Positioning related errors; b) Process related errors.
3.1.1 Positioning errors
The positioning errors are related to the torch and wire tip positioning relative
to the joint centre-line. They can be further classified, according to their source, into
three main groups, namely: a) Robot errors; b) Programming errors; and c)
Component errors. This classification is proposed in order to make it easier to
understand the nature of the discrepancies and deal with them separately.
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