Traditionally, semi-automated welding using a column and boom welding manipulator has been done by fixing a welding torch at a set distance from a workpiece, then manually adjusting this relationship during welding to account for any variances in part geometry. This method of welding torch control works great for short duration welds or when the parts being welded have a high degree of geometric similarity. There are, however, many instances where adjusting the welding torch manually is either not physically possible (ID welding pipe) or it becomes a tedious task for the operator (which can affect weld quality).
Now, many manufacturers are looking to Weld Seam Tracking systems to precisely control the torch to workpiece relationship during welding; limiting the need for operator input and increasing both weld quality and production rate.
A basic seam tracking system, as shown in Figure 1, consists of: A sensor (or sensors) to detect changes in welding torch position, A controller that interprets the sensor’s signal and outputs a command for movement, and a set of linear actuation slides which support the welding torch and make vertical and horizontal corrections to maintain the ideal welding position.
There are three main types of seam tracking systems: Tactile, Through Arc Seam Tracking, Laser Vision. The difference between these systems lies in the way they sense the geometry of the weld seam or path.
Tactile Seam Tracking
As the name suggests, tactile sensors physically contact the weld seam using a contact probe. As the torch position changes relative to the workpiece, the probe deflects in the opposite direction and the controller makes adjustments to return the torch to its original position. Tactile seam tracking systems are best suited for weld seams with large, distinct geometry. If the weld seam is too small, the probe can lose contact with the seam and run the welding torch off track.
Through Arc Seam Tacking
Trough Arc Seam tracking systems use feedback from Voltage, Amperage, and Wire Feed Speed sensors to identify changes in torch position. For example, if we were welding down the center of a fillet joint and began to drift to one side, the torch to work distance would decrease causing an increase in arc Amperage (CV welding). For this method of tacking to work, the welding torch must oscillate back and forth perpendicular to the weld seam. In doing so, the system is continually making a comparison of welding amperage on the left and right side of the weld seam; between the two amperage peaks must lie the center. Through Arc tracking systems are best suited for weld seams with large, distinct geometry such as large bevel and fillet welds.
Laser Vision Seam Tracking
Laser Vision Seam tracking systems use a laser ribbon which is projecting onto the surface of the part creating a distinct laser line across the weld seam. The laser line is then viewed at a slight angle using a camera. The result is a line profile that exactly matches the geometry of the weld seam. A reference point is then created on the line profile and the controller will make any necessary movements to keep this reference point in the same position relative to the welding torch. Laser Vision systems have a very high resolution allowing them to reliably track both large and small weld seams.
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