September 16, 2008
Robotic GTAW is a little-known process that has made significant advancements recently, thanks in part to the advancements made to manual GTAW that have made it more user-friendly and compatible with the environment. Applications that were once nearly impossible to accomplish can be handled with relative ease with modern GTAW systems. Even today robotic GTAW continues to improve and advance into new fields to create a better future for the welding industry.
Many welding applications require precise control, exact penetration, or minimal heat input regardless of bead appearance, while others are focused solely on the surface of the weld. This is where the advantages of gas tungsten arc welding (GTAW) are most prominent, and in most situations require a high level of welder skill, focus, and control. In the past robotic GTAW has been largely avoided because of the complexity involved with both GTAW and robotic equipment. However, significant improvements in GTAW technologies have increased simplicity in overcoming many of the problems of the past and have led to new technologies.
Recent advancements have made it more user-friendly and compatible with the surrounding environment. Combining a GTAW system with a robotic arm effectively amplifies consistency and weld appearance. Applications that were once nearly impossible to accomplish can be handled with relative ease with the modern GTAW systems. Even today robotic GTAW continues to improve and venture into new fields to create a better future for the welding industry.
Many manufactures have avoided robotic GTAW because of the continuous high-frequency noise transmitted that can interfere with robots, computers, and other sensitive equipment. This noise can cause inconsistencies in robotic programming or even damage internal components. To avoid this situation, manufacturers of robots and welding equipment attempt to protect the robotic equipment by shielding most of the internal cables. This can be time-consuming, costly, and require extensive knowledge in both GTAW and robotics.
Other concerns are related to the process itself. In manual GTAW, the welder controls the wire feed rate and heat input through hand feeding and a remote foot pedal. This allows the welder to make quick adjustments when there is a defect or inconsistency in the part being welded. This poses a particular problem for robotic welding systems because robots follow a path and set of commands with little to no variation. If problems occur during the welding, the robot typically cannot adjust without the use of expensive sensor equipment to detect abnormalities.
Furthermore, a manual welder can see how the tungsten electrode is wearing and can change the process to compensate or reshape the tip. A robotic system does not have the means to do this except for parameter feedback to tell when the tungsten needs to be changed.
A number of advancements in GTAW have reduced the complexity of the process and given welders a wider range of control. Figure 1shows a typical waveform for GTAW in which welders can manipulate almost every variable. This allows the operator to fine-tune the weld to the last detail, which increases the range of applications. This also gives robotic systems more versatility to cover areas that may need special attention. For example, in a typical robotic welding program, the parameters can change almost indefinitely depending on how the programmer wants to set the system. Using these controls also allows the welder to create nice-looking welds consistently.
To compensate for the high-frequency noise produced by GTAW systems, some manufacturers have started building their robotic arms with case-hardened frames, special shielded cables, and noise filters that eliminate the effects of high frequency. In addition, wire feeder control units have become more precise and can even allow the wire feed rate to vary based on pulse parameters or locations in welding patterns, such as weaves. Thus, a robotic system can simulate how a manual welder would respond to known changes in the workpiece.
With recent developments in GTAW, a number of other technologies have appeared. For example, a robotic system can use alternating current (AC) and direct current (DC) within the same weld without extinguishing the arc. This is used to effectively extend the tungsten life and add additional heat or penetration control. Other examples of new technology include synchroTIG; hot-wire GTAW, hybrid GTAW, and the increasingly popular plasma welding, which uses a GTAW system in a different orientation to provide better control of the arc and keyhole formation.
Generally speaking, robotic welding can lead to increased productivity, efficiency, and a safer environment. Robotic GTAW can be used in repetitively difficult applications such as thin plate or thick-plate overlay work, which require a high amount of control to successfully weld the joint. A robotic system provides control and consistent output, whereas a manual welder may tire from the repetitiveness, especially in fine-detail applications. Robotic welding also can reduce the overall heat input with faster speeds and fewer midweld corrections.
GTAW is a slow process—it's one-third to one-quarter the welding speed of a typical gas metal arc welding process. Long weld passes can become particularly difficult for manual welders to keep consistent. However, with a robotic system, the movement and speed remain regulated for the duration of the weld.
Robotic GTAW also can improve the aesthetics of a weld and reduce the amount of grinding, repair, or rework. Bicycle and motorcycle manufacturing is an example of an industry that has long been concerned about the appearance of welds (seeFigure 2).
As previously mentioned, manual GTAW requires a high level of skill and dexterity—a welder must balance a torch in one hand, a filler rod in the other, and use his foot to control the current. With a robotic system, the filler rate, welding angle, weld location, and parameters can be preset and maintained constantly throughout the weld. Meanwhile the operator can focus on other tasks as the part is being welded, thereby increasing the efficiency of the process dramatically.
Frank Armao "Preparing for Aluminum Welding," Practical Welding Today (April 2001).
"Gas tungsten arc welding," Wikimedia Foundation Inc., http://en.wikipedia.org/wiki/gas_tungsten_arc_welding.
Howard B. Cary and Scott C. Helzer, Modern Welding Technology, 6th ed., Upper Saddle River, NJ: Prentice Hall pp., 69-77.
Daihen Co., Welding Handbook, Gas Tungsten Arc Version, Osaka, Japan, 2000
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