Aircraft are designed to meet certain standards in terms of flight hours and service life. Each aircraft contains millions of parts and miles of wire and tubing, all housed in a high-strength aluminum frame that undergoes the daily stresses of flight. Maintenance — both routine and unscheduled — is critical throughout the service life of an aircraft, and welding plays a major role in the process.
Welding keeps aircraft in service as a cost-effective method for increasing the service life of many aircraft components. Replacement parts can be extremely expensive and not readily available, with some having lead times of more than a year. Welding helps control the cost of aircraft maintenance and avoid long periods of downtime. The gas tungsten arc welding (GTAW, or TIG) process was developed specifically for aircraft welding.
In the 1970s, welding manufacturers pioneered squarewave TIG welding technology and incorporated it into the transformer-based power sources of the time: large, bulky welding machines that weighed hundreds of pounds and became a permanent fixture in the shop. As welding technologies become more advanced, and the alloys being built into planes become more varied, it may finally be time to investigate new welding power sources that substantially improve the quality, productivity, and efficiency of your work. This article gives an overview of modern TIG welding technology and how it advances aircraft maintenance and repair.
Why TIG welding?
Materials used in aircraft design are anything but ordinary, ranging from stainless steel and aluminum to nickel, magnesium, titanium, cobalt, and niobium. Critical tolerances, dimensional requirements, and metallurgical considerations all combine to create extreme welding challenges and potential mistakes that may result in defects such as cracking, distortion, and irreversible changes in microstructure that mandate the scrapping of parts.
TIG welding is the perfect process for such an application. Pinpoint control of the arc allows for accurate and precise weld placement and superior control over heat input. High current density provides a concentrated arc while an inert atmospheric gas protects the molten weld puddle from oxidation, porosity, and harmful inclusions.
Welding is used in all types of aircraft repair applications, from air-handling ducts to engine parts and components. Typical TIG welding applications in aircraft repair include dimensional restoration (buildup), crack repair, patch welding, and component replacement.
Advances in technology
New TIG welding technologies offer a number of efficiencies: reduced heat input, a narrowed weld bead and heat affected zone, improved directional control, and output ranges and capabilities extended beyond traditional transformer products. Three specific elements achieve these efficiencies: arc starts, pulsed DC output and advanced AC waveshape controls.
Arc starting is the critical first step of every TIG weld. Conventional machines often generate a burst of current during starts that helps initiate the arc but could severely damage the part, especially in very thin applications such as blade and vane repair. Inverters have brought the ability to regulate the output down to a microsecond for the exact amount of starting amperage to light the arc but for such a short duration that any effect to the base material is eliminated. This reduces the need for copper start blocks and allows for direct starting on thin sections while protecting the base metal from burn-through and distortion.
Pulsed TIG welding
DC electrode negative puts most of the welding heat into the puddle, which provides good penetration and helps to keep the tungsten sharp. It’s the preferred method for welding such metals as steel, stainless steel, nickel alloys, and titanium. The cone-shaped arc forms off the end of the tungsten. As amperage is increased, so is the diameter of the welding cone. This is somewhat dependent on the diameter of the tungsten and electrode preparation, as the arc is emitted from the electrode at 90 degrees to the grind angle.
Miller FABTECH Presentation Highlights Advanced GTAW Technology for Welding Repair on Alloys Used in Aircraft Engines, Components
Brent Williams will present "Inverter Technology Improves Aircraft Engine and Component Repair" on Wednesday, Nov. 3 at 4:05 p.m. at the FABTECH show in Atlanta.