Page 19 - MetalForming September 2009

and distortion in the finished weld. The traditional “stacked-dime” cosmetic appearance of a GTAW weld conveys a sense of visual quality to the process.
Procedure Qualification and Certification
The American Welding Society and The American Society of Mechanical Engineers provide widely accepted international standards for GTAW-pro- cedure qualification, written specifical- ly for a variety of materials. GTAW per- formed to a specific code requires a Welding Procedure Specification (WPS), a formal document that describes welding procedures to ensure repeatability when the process is per- formed by properly trained welders. A Procedure Qualification Record (PQR) is a record of the welding variables used to produce an acceptable test weldment, as well as the results of tests conducted on the weldment to qualify the WPS.
With procedures established for a given welding process and joint design, they then must be strictly followed dur- ing subsequent production welding. This requirement encourages the addi- tion of automation to a GTAW opera- tion, to ensure repeatability and trace- ability, and the ability to establish limits and restrict the adjustment of any vari- able to stay within qualified procedures.
Where Robots Make Sense
Robotic GTAW provides a number of quality-control advantages, including automated, repeatable, uniform and consistent welds, with increased produc- tivity—particularly when considering the speed of torch repositioning between welds. Using a robotic arm provides repeatable access to welds that might otherwise be difficult to reach manual- ly or that might require torch rotation.
Key benefits of robotic GTAW weld- ing include:
• Repeatable, precise heat control and exact penetration to meet chal- lenging quality standards;
• On-the-fly procedure adjustment, for automatic switching of procedures between thick and thin applications;
• Torch movement and automated
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