Page 160 - Welding Robots Technology, System Issues, and Applications

148 Welding Robots
wire diameter and the plate thickness or eventually the leg length in the case of
fillet welds. The output data is usually the welding parameters: current, voltage,
welding speed and number of weld beads/layers. With databases of this type in the
computer the selection of the welding parameters may be done automatically. Even
the selection of the wire diameter may be carried out automatically as a function of
the thickness of the components or stay for free selection being an input parameter.
It would be expectable that, with this information in the computer having a CAD
model of the component to be welded, the system could be able to select the
welding data for each weld and send it to the robotic welding system. Although it
seems easy to achieve this goal in the case of single welds, some data is missing in
the available databases for the case of welds with multiple layers. In fact, in this
case the position of the torch for each layer needs to be indicated to the robot.

Since that for the majority of the companies that produce multi-layer welds there is
only a small number of distinct welds, then it is not hard to fill up the database for
their particular case. Consequently, using this method it is easy to carry out the off-
line programming of the components to be welded, being only necessary to adjust
the coordinates of the process points in the first specimen to be welded.

Furthermore, when robots are used to weld, the programming problem arises
immediately. In this chapter a robotic welding example having CAD programming
capabilities will be introduced, giving special attention to the implementation
details. The subject will be addressed by extending the concepts presented in
Section 4.5 along with a simple CAD interface that enable simpler and faster
programming. A few test cases will be presented, explained and discussed with the
objective of demonstrating that the basic features are available and can be used to
build powerful robotic welding solutions.

5.2 A Robotic Welding System

Robots manipulators are essentially position-controlled devices that can receive a
trajectory and run it continuously. With welding applications it is necessary to start
from a trajectory, given for example from a CAD model of the work-piece, and to
have the means to correct it in real time, as function of the observed results of the
welding process.

5.2.1 Overview of the System

To achieve the above-mentioned goal, systems for guidance and inspection are
needed (see Chapter 3), but also the possibility to correct in real time the position
of the robot and the welding parameters, and a computational platform suitable for
developing the software necessary to handle the monitoring and control tasks.
Unfortunately these features aren’t usually available for the following reasons: