Study on Seam Tracking System for Laser Welding using 6-axis Articulated Robot

Abstract

High power laser welding has an advantage of remarkable improvement of productivity. However, now the application of laser welding to large structures is limited due to severe control of joint gap, lack of available in-process control and small spot size as compared with arc welding.
In the present paper, the fundamental performance of seam tracking system has been investigated in order to apply laser welding to large welded structures using 6kW fiber laser and a 6-axis robot.
Seam tracking is a method of mainly detecting a weld line by a light cutting method. In other words, the weld line is irradiated with light for weld line detection from the outside. The reflection form of the light and the intensity distribution of the reflected light are acquired by the camera. A unique algorithm or image processing is executed for detection of the weld line. It is one of methods to perform seam tracking⁶⁾⁷⁾⁸⁾.
If there are a lot of tack welds in the weld line, laser welding must be performed while seam tracking system detects the tack welds in real time during welding. In order to recognize the outline of a tack weld, data of four monitoring parameters were extracted in image processing so that it was possible to judge accurately whether a weld line or tack welds.
As a result, the average tracking accuracy of the seam tracking system for linear laser welding using a 6-axis articulated robot was plus 0.072mm. The precision of laser positioning for sound welding was able to be kept within the tolerance range of ±0.15mm.