Robotic TIG Welding – Does It Make Sense for Your Company?
by Geoff Lipnevicius
, Manager - Product Development
Lincoln Electric, Automation Division Posted 09/08/2009
You’ve probably heard the allegory of the tortoise and the hare. The turtle was slow and steady, where as the hare would go fast and then stop for breaks. Many people live by the saying "slow and steady wins the race."
The Gas Tungsten Arc Welding (GTAW) Process is a slow and precise business. Quality of the weld, not time, is most often the major factor when GTAW is used. Skilled Tungsten Inert Gas (TIG) welders earn some of the industry’s highest wages due to the precision and skill this manual technique demands.
However, as manufacturing continues to be challenged by a shortage of skilled welders, and companies look to increase productivity without compromising quality, they more frequently have turned to automated solutions.
“Robotic” and “TIG welding” provide the analogy to the hare and the tortoise, and today’s technology combines the best features of the two processes, and has also contributed to a number of significant breakthroughs. Here’s a look at those, as well as the pertinent factors your company should examine when considering robotic TIG welding.
Benefits of GTAW
The primary benefit of the TIG process is the high quality welds it is capable of making in almost all metals and alloys. While carbon steel, stainless steel, and aluminum applications are commonplace, examples of some of the more exotic materials include titanium, zirconium, columbium, tantalum, and austenitic nickel-chromium-based superalloys.
These materials are found in a wide range of industries, including aerospace, military, motorsports, nuclear, pipe, power generation, nuclear, as well as maintenance and repair.
The common thread among these industries is that they frequently utilize thin gauge, high performance materials that exhibit some combination of superior mechanical properties, electrical properties, and thermal properties, all of which require consistency, exact penetration, repeatable control of many factors, including travel speeds, gas coverage, temperature control, and precise heat control to avoid shrinkage and distortion.
The TIG process produces a narrow Heat Affected Zone (HAZ), which in turn, reduces solidification stress, cracking, and distortion in the finished weld. The traditional ‘stacked-dime’ cosmetic appearance of a TIG weld conveys a sense of visual quality to the process.
Procedure Qualification & Certification
The American Welding Society (AWS) and The American Society of Mechanical Engineers (ASME) both provide widely accepted international standards for TIG procedure qualification, and are written specific to many materials.
TIG Welding to a specific code requires a Welding Procedure Specification (WPS), a formal document describing welding procedures to assure repeatability by properly trained welders. A Procedure Qualification Record (PQR) is a record of welding variables used to produce an acceptable test weldment and the results of tests conducted on the weldment to qualify a Welding Procedure Specification.
Once procedures are established for a welding process and joint design, they must be strictly followed in subsequent production welding. This requirement encourages the combination of TIG Welding and Automation for repeatability, traceability, and the ability to establish limits and restrict the adjustment of any variable to stay within qualified procedures.
Benefits & Applications of Robotic GTAW
Robotic TIG provides a number of quality control advantages, including automated, repeatable, uniform, consistent welds, with increased productivity – especially when considering the speed of torch repositioning between welds. Using a robotic arm provides repeatable access to welds that might be difficult to reach or require torch rotation that would be impossible by the human counterpart.
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% and as much as 300% in some cases.
- Reduced operator training time, reduced inspection costs, and improved weld quality.
- Ability to save multiple weld schedules and several hundred welding programs for easy retrieval.
Robotic TIG welding is already used in a wide range of successful applications, including:
- Thin plate material: filament end rounding of sharp corners, fusing basing of coil ends, joining corner edges of thin materials and pipe welding involving exotic materials
- Thick plate and overlay applications: heavy wall aluminum, overlay and hard surfacing and narrow groove, thick wall sections.
- Instrument diaphragms and other delicate expansion bellows.
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 conduct 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 insure 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 insures 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.
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.
TIG welding thick to thin materials has not always been easy for an automated system. The introduction of Micro-Start technology allows for a low amperage starting (2 amps) on thin materials that automatically transitions to a high amperage for thicker materials. New digital communication technology on a robotic system can automatically adjust procedures based on the torch location as it weaves from thick materials (high amperage) to thin materials (low amperage) for automated, consistent penetration control.
Torch design has evolved dramatically. Smaller profile torches and improvement in the design of the gas diffusers and lenses which smooth out the shielding gas flow and allow for greater tungsten stickout can provide better access to tight joint configurations.
Production Monitoring software can aid in weld data collection and is designed to allow fabricators to analyze and improve their welding operations and processes. It also aids in meeting ISO, Six Sigma, statistical process control (SPC), quality cost delivery (QCD), overall equipment effectiveness (OEE) and lean manufacturing efforts.
Is Robotic TIG Right for My Company?
There are a number of questions to ask when considering a move to robotic TIG welding. They include:
- Is TIG welding an integral part of your manufacturing process? Are you looking to improve productivity and implement high levels of repeatable quality welding mild steel, stainless steel, aluminum, copper, titanium or other exotic alloys?
- Are you experiencing quality problems or competitive cost pressures from your customers? Do you have difficulty in hiring qualified TIG welders? Is your turnover of trained TIG welders excessive? Are your labor costs increasing?
- Do you have stringent quality requirements that could be improved by automating your welding operations? Do you need improved process control for travel speed, heat input and gas coverage that an automated solution might provide?
- Are you talking to a Robotic TIG Welding integrator that is knowledgeable in the welding process and can provide ongoing future support for the robot system as your needs change?
The best way to determine if your company can benefit from robotic TIG welding is to ask a manufacturer, such as The Lincoln Electric Company, to review your prints or apply a robot to your own actual parts for a no-charge productivity improvement analysis. Application Engineers analyze your current welding processes and procedures and then propose improvements to provide the best return on investment and increase productivity and quality control for your shop floor.