QMT Features: May 2011
Laser seam tracking raises quality and productivity in robotic welding of vehicle exhausts
Laser seam tracking sensors are increasing the efficiency of automated welding cells producing exhaust treatment products for heavy vehicles

British-manufactured laser seam tracking sensors from Meta Vision Systems are increasing the efficiency of automated welding cells producing exhaust treatment products for heavy vehicles at the Nyköping factory of Swenox AB, Sweden.

European legislation on exhaust emissions is becoming increasingly stringent, which has prompted advanced on-vehicle treatment solutions to be developed by companies like Swenox to meet the requirements of lorry and bus manufacturers.

The products catalytically convert carbon monoxide, unburnt hydrocarbons and oxides of nitrogen to their harmless gaseous constituents and water vapour, and include filters to trap particulates. They are integrated into complete exhaust systems that Swenox also fabricates to customer requirements.

Design and manufacture of such system are extremely demanding, requiring gas tight joints on convoluted shapes. There are often conflicting criteria, such as a requirement to minimise weight while maintaining durability and operational reliability.

A considerable amount of arc welding is needed to join the individual components. The nature of the constituent materials results in spring back and heat distortion, making automatic welding difficult to achieve and so calling for the use of seam tracking. However, due to the large variation in reflectivity of the materials, most ordinary laser sensors struggle to detect the seams.

Oxford-based Meta Vision Systems' new SLS sensor, which forms part of its SmartLaserPilot system, has overcome the problem through its singular ability to remain unaffected by varying surface conditions and reflections from the metals being welded. It does this using real-time, automatic intensity control of the laser stripe, allowing the vision analysis software to deliver a high quality image at all times.

The Meta sensors are used in two twin-robot welding cells at Swenox, a single robot controller driving both ABB robots in each cell. The sensor head contains a megapixel camera and more computing power than a powerful laptop computer. With its weaving, seam search and reframing functions, it collects information on the position of the joint being welded and communicates it to the robot controller via an Ethernet link and switches.

Based on this data, robot motions are continuously adjusted when effecting multi-layer lap joints with tacks as well as circumferential and other welds. The welding equipment was supplied by Fronius CMT.

Glyn Powell, the engineer responsible for the robotic cells at Nyköping, commented, "Installation of the Meta SLS vision system has been a major success for Swenox.
To be able to assemble and tack-weld components off-line and then move them into our robotic cells and weld them with consistent quality without any modification to the programs is a massive achievement.

Our aim is to manufacture a top quality product that is the very best of its type available on the market today and without doubt the Meta laser tracking system is playing a major part in our achieving this goal."


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