Advanced Welding Processes: Technologies and Process Control

228
Advanced welding processes
Welding packages for arc welding
For arc welding applications a power source with facilities for remote control
and output stabilization is required. The use of the electronic regulation
systems and computer control discussed in Chapter 3 simplifies the control
interface between the robot controller and the welding system as well as
ensuring that repeatable performance can be achieved. In the GTAW system,
the robot simply needs to carry a fairly lightweight torch and cables, whereas
in GMAW and FCAW applications, the filler wire must be fed to the welding
head. Trouble-free wire feeding is essential to avoid system failure and it is
desirable to mount the wire feeder at the rear of the robot arm with a fairly
short conduit to conduct the wire from this feeder to the torch. Some systems
employ an auxiliary feeder immediately adjacent to the torch to ensure positive
wire feeding and it is common to use large-capacity pay-off packs of lowcurvature
wire to improve feedability. Wire cutting and torch cleaning facilities
must also be provided and in some cases interchangeable torch heads are
also used; these are stored in a carousel and may be automatically replaced
during the robot cycle.
Welding packages for laser welding
In laser welding applications the laser beam may be conducted along the
robot arm to the workstation by a series of mirrors in the case of a CO 2 laser
or by means of flexible fibre optic cables in the case of Nd:YAG diode and
fibre lasers.
11.5.3 Robot control systems
The robot control system is required to:
∑ control the position of the welding head;
∑ control the welding package;
∑ interface with auxiliary systems;
∑ interface with the operator;
∑ provide program storage.
Control of position
By driving three or more actuators simultaneously the end of the robot arm
may be made to trace any path within its three-dimensional operating envelope.
However, to enable the position and velocity of the end effector to be controlled,
information concerning the position and rate of change of position of each
actuator or axis must be obtained and processed. The position of the individual
actuators is usually obtained from a shaft encoder which is attached to the