Overview

Mechanisation of arc welding can be applied in a number of levels, from the very simplest to the highly sophisticated. Welding equipment was originally divided into manual (e.g. when using coated electrodes), semi-automatic (for MIG/MAG welding, with the filler wire feed being mechanised) and automated (e.g. for submerged arc welding, with both the filler wire feed and movement of the welding head being mechanised.

The introduction of the welding robot provided a further level in that, in addition to starting and stopping, the program-controlled movements of the robot could also include moving between welding positions. Fully automatic welding arrived with pallet-controlled loading and unloading of workpieces, as used in Flexible Manufacturing Systems (FMS). These systems are generally used for smaller and medium-sized items, with the welds being made under shielding gas.

Mechanised welding can improve productivity, the quality of the welds and working conditions. In many situations, mechanisation can be used to perform welding that is not possible with manual processes: an example of this is narrow-gap welding.

12.1 Narrow-Gap welding

Narrow-gap welding has the following advantages:

• lower energy requirements

• reduced consumption of filler materials

• reduced end-to-end working time

• reduced distortion of the workpiece.

Narrow-gap welding is suitable for joining sheet and plate in the 25 300 mm range. Joints to be welded are prepared with parallel sides or slightly U-shaped, as shown in Figure 12.1. Joints with parallel sides are cheap to prepare, although difficulties can arise as a result of contraction during welding, which has the effect of...