Key benefits of robotic TIG welding include:
• Repeatable, precise heat control and exact penetration to meet challenging quality standards
• On-the-fly procedure adjustment, for automatic switching of procedures between thick and thin applications
• Torch movement and automated control of the welding variables such as preflow, starting amperage, upslope time, welding amperage, pulse frequency, downslope, crater-fill, and postflow. Arc length can be automatically maintained with automatic voltage control (AVC) and bead width, penetration, and surface appearance can be tightly controlled.
• Improved welding productivity by a minimum of 100 percent and as much as 300 percent in some cases
• Reduced operator training time, reduced inspection costs, and improved weld quality
• Ability to save multiple welding schedules and several hundred welding programs for easy retrieval
Automated TIG welding is already used in a wide range of successful applications, including:
• Primary exhaust casing and ventilation duct
• Thrust reverser, cowlings, jet pipes and heat shield applications
• Cargo loading and landing gear applications
• Instrument diaphragms and other delicate expansion bellows
• Repairing turbine blades, crank shaft/torque tube weld buildup
While the FAA strictly regulates which materials can be used for specific components, weight savings drives the innovative materials that are sourced for these applications. This translates into better economics and justification for materials that range in price from hundreds to thousands of dollars per pound. Materials including stainless steel, titanium, 4130 Cr-MO, inconel, aluminum and special alloy steels are commonly used in these applications.
The robotic TIG process provides advantages for each of these materials. For example, aluminum is traditionally more difficult to weld because it tends to expand quickly and conducts heat well. Robotic TIG helps control heat input and ensures a strong, reliable weld.
Titanium has a wide continuous service temperature range, and the highest strength-to-weight ratio of any metal. However, titanium, has a high melting point and isn’t very resistant to corrosion during the welding process. Robotic TIG welding can provide precise repeatable procedures to reduce the risk of contamination.
Stainless has a high chromium content, which when TIG welded by hand, can easily become overheated. Robotic TIG welding can be introduced to qualify procedures to ensure that an undesirable dark color, negatively affecting the appearance, does not occur.
For heat-resistant alloys, such as nickel, used in aerospace and nuclear, it’s more difficult to achieve 100 percent penetration by hand. Robotic TIG welding ensures amperage to travel speed to control to a precise penetration profile.
Intelligent robotic TIG welding systems
The advancement of robotic TIG welding technology has spurred the development of sophisticated, yet cost-effective, vision systems that have substantially improved quality-control, assisting with joint location tracking and error-proofing.
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’s 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 robot then calculates any offsets and adjusts the entire weld path accordingly. This technology advancement is particularly suitable on thin materials where arc placement is critical.
When it comes to repairing turbine blades, dynamic laser-based vision scanning and welding is required. Turbine blades are often subject to severe field conditions that cause the material to vary significantly from their original tolerances. The blades may be skewed or eroded, so a laser-based vision camera can be applied to adapt the weld schedule to a custom shape.
After welding, the same laser-based technology can be applied to provide objective, consistent measurements that are far superior to human visual inspection. This provides more information such as weld geometry and part geometry. It can also be used to detect defects such as surface porosity, undercut, entry angle, and toe radius which are critical for fatigue life assessment. This technology can be used in conjunction with ultrasonic testing (UT) devices used for internal defect sensing. The ability to print or archive these quality-related statistics serves as adequate documentation and validation.
TIG welding waveforms have been created to produce a pulsed output for faster travel speeds and others that include higher amperage peaks that result in a more forceful welding arc for anodized applications.
The center at Davis Applied Technology College was completely revamped and outfitted with the latest Lincoln Electric welding equipment and technology.
ASME Turbo Expo 2011 will be held June 6-10 in Vancouver, British Columbia, Canada.