Page 20 - MetalForming September 2009

Robotic Gas Tungsten Arc Welding
control of the welding variables such as shielding-gas preflow, starting weld current, current upslope time, weld- ing current, pulse frequency, current downslope time, crater-fill time, and gas post flow. Arc length can be auto- matically maintained with automatic voltage control, and bead width, pene- tration, and surface appearance can be tightly controlled.
• Improved welding productivity, by as much as 300 percent;
• Reduced operator training time and inspection costs, and improved weld quality; and
• The ability to save multiple weld schedules and several hundred weld- ing programs, for easy retrieval.
Robotic GTAW is used in a range of successful applications, including:
• Thin plate: Fusing coil ends, joining corner edges of thin materials and pipe welding of exotic materials;
• Thick plate and overlay applica-
tions: heavy-wall aluminum, overlay
R
and hardsurfacing, and narrow-groove,
thick-wall sections.
• Instrument diaphragms and deli-
cate expansion bellows.
Stainless steel, titanium, 4130 Cr-
Mo, Inconel, aluminum and special- alloy steels commonly are used in these applications. The robotic GTAW process provides advantages for each of these materials. For example, aluminum is traditionally difficult to weld using the GTAW process because it tends to expand quickly and conduct heat well. Robotic GTAW helps control heat input and ensures strong, reliable welds.
Titanium has a wide continuous- service temperature range, and the high- est strength-to-weight ratio of any metal. However, titanium has a high melting point and is not very resistant to corrosion during the welding process. Robotic GTAW welding can provide precise, repeatable procedures to reduce the risk of contamination.
Stainless steels have a high chromi- um content, which when GTA-welded manually can easily become overheated.
Robotic GTAW can be introduced to avoid the appearance of an undesirable dark color on the surface of the weldment.
With heat-resistant alloys used in aerospace and nuclear applications, it’s more difficult to achieve 100-percent penetration when welding by hand. Robotic GTAW ensures the proper ratio of amperage to travel speed, resulting in a precise weld-penetration profile.
Intelligent, Robotic GTAW
The advancement of robotic GTAW technology has spurred the develop- ment of sophisticated yet cost-effective vision systems that have substantially improved quality control, assisting with joint-location tracking and error-proof- ing. During procedure qualification, the operator calibrates the camera and teaches the weld path on an ideal part. This reference image is stored in the robot controller memory. On each part thereafter, the camera takes a picture before an arc is established, and the robot performs a pattern match between the reference image and the new image. The controller then calcu- lates any required robot offsets and adjusts the entire weld path according- ly. This technology advancement is par- ticularly suitable on thin materials where arc placement is critical.
GTAW waveforms have been created to produce a pulsed output for faster travel speeds, as well as higher amperage peaks that result in a more forceful welding arc, ideal for anodized appli- cations. Also, GTAW of thick-to-thin materials has not always been easy for an automated system to perform. The introduction of Micro-Start technolo- gy allows for a low-amperage (2 A) starting current on thin materials that automatically transitions to a high amperage for thicker materials. New digital communication technology with a robotic system can automatically adjust the welding procedure based on torch location as it weaves from the thick material (high amperage) to thin material (low amperage), for consis- tent penetration control.
Torch design also has evolved dra- matically. Smaller-profile torches and
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