Problems for Robots in Arc Welding

Because of the hazards for human workers in continuous arc welding, it is logical to consider industrial robots for the process. However, there are significant technical and economic problems encountered in applying robots to arc welding.

Continuous arc welding is commonly used in the fabrication industries where products consisting of many components are made in low quantities.

It is difficult to justify automation of any form in these circumstances.

A related problem is that arc welding is often performed in confined areas that are difficult to access, such as the insides of tanks, pressure vessels, and ship hulls.

Humans can position themselves into these areas more readily than robots.

One of the most difficult technical problems for welding robots is the presence of variations in the components that are to be welded.

These variations are manifested in two forms. One is the variation in the dimensions of the parts in a batch production job.

This type of dimensional variation means that the arc-welding path to be followed will change slightly from part to part.

The second variation is in the edges and surfaces to be welded together. Instead of being straight and regular, the edges are typically irregular.

This causes variations in the gap between the parts and other problems in the way the pieces mate together prior to the welding process.

Human welders are able to compensate for both of these variations by changing certain parameters in the welding process (e.g., adjusting the welding path, changing the speed at which the joint is traversed, depositing more filler metal where the gap is large, etc.).

Industrial robots do not possess the sensing capabilities, skills, and judgment of human welders to make these compensations.

There are two approaches to compensate for these variations and irregularities in robot welding applications:

  1. Correct the stream production operations so that the variations are reduced to the point where they do not create a problem in the robot welding process.
  2. Provide the robot with sensors to monitor the variations in the welding process and the control logic to compensate for part variations and weld gap irregularities.

Correction of the production operations that deliver parts to the arc-welding process is an attractive alternative because it tends to contribute to the overall quality of the product, and because it simplifies the welding robot project.

The potential disadvantage of this approach is that it is likely to increase the cost of manufacturing the individual components because their dimensions must be held to closer tolerances.

The second approach represents an area of intensive research and development activity in robotics.

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Santhakumar Raja

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