Advanced Welding Processes: Technologies and Process Control

Welding automation and robotics 233
Work flow
A smooth flow of components to and from the robot system is essential if the
full capabilities of the unit are to be realized; this will at the least mean
careful scheduling of parts and may involve some investment in automatic
delivery and discharge systems.
Component tolerances
The positional repeatability of most fusion welding robots is of the order of
0.1 mm. The standard welding robot will expect the weld seam to be in
exactly the same place and in the same condition with respect to gaps and
misalignment as the original part which was used for programming. Deviation
from these conditions may result in a defective weld and damage to the
jigging. It is, therefore, important to establish the tolerance on fit-up and
maintain the component dimensions within specified limits. In some cases,
this will involve improving control of component variability and may entail
investment in pressing, cutting or machining equipment.
Joint design
Careful joint design can be used to reduce the sensitivity to component
tolerances, for example unsupported square butt joints and fillet welds in
thin sheet may be replaced with lap joints to eliminate problems with gaps
and give more tolerance to lateral movement. The fact that a robot can follow
relatively complex three-dimensional paths should not be used as an incentive
for using complex joint profiles; these not only make it more difficult to
achieve the required quality, they often increase the cycle time. Simple joint
profiles are usually the best. Accessibility must also be considered when
designing for robot welding; it may be impossible to weld a component
completely without removing it from the jig and repositioning it. This can
often be avoided by repositioning the welds to suit the robot. Some of these
considerations are illustrated in Fig. 11.7.
11.5.7 Applications
Resistance spot welding
Resistance spot welding robots form the largest single group of welding
applications. Most of these are in the automotive industry, where a group of
robots can work simultaneously on a single body shell. Articulated arm
robots are most commonly used, but there are examples of gantry systems
being used for larger components, such as railway wagon side panels. [272]
The robotic automation approach is appropriate in those applications where