Orbital Welding 4x4i1l

ORBITAL WELDING

Introduction Orbital welding first found use in the 1960s when the aerospace industry recognized the need for a superior ing technique for aircraft hydraulic lines. The solution: a mechanism to rotate a welding arc from a tungsten electrode around a tube-weld t. Regulating weld current with a control system automated the entire process.  The result was a more precise, reliable method than manual welding.

Orbital welding became practical for many industries in the early 1980s with the development of portable combination power supply/control systems that operated from 110-V AC. Modern orbital-welding systems offer computer controls that store welding schedules in memory. The skills of a certified welder are thus built into the system, enabling the production of enormous numbers of

Orbital welding uses the gas-tungsten-arcwelding (GTAW) process as the source of the electric are that melts the base material and forms the weld.  During GTAW an electric arc forms between a tungsten electrode and the workpiece. To initiate the archigh-voltage signal will ionize the shielding gas to generate a path for the weld current.  A capacitor dumps current into the arc to reduce are voltage to a point where the power supply can regulate. The power supply responds to the demand and provides current

ORBITAL WELDING MACHINE

Material weldability •In general, the commonly used 300-series stainless steels offer a high degree of weldability using orbital equipment, except for Types 303/303SE,which contain additives for ease of machining. •The 400-series stainless steels, while generally weldable, may require post-weld heat treatment. •Fabricators should be prepared to adjust the orbital-welding setup to accommodate for potential differences among material heats.

Weld-t fitup •Fitup is dependent on the weld-specification requirements on tube straightness, weld concavity, reinforcement, and drop through. • If no specification exists, the laws of physics require that the molten material flow and compensate for tube mismatch and any gap in the weld t. •The use of tube and pipe end-prep facing equipment helps to ensure end squareness and flatness. The i.d. and o.d. should be burrfree with no chamfer.

Shielding-gas basics •During welding, an inert gas directed to the tube o.d. and i.d. prevents the molten material from combining with oxygen in the ambient atmosphere. With sufficient shielding-gas coverage, welds can have zero tint at the weld-zone i.d. •Argon is the most commonly used shielding gas, for the o.d. and as the i.d. purge gas. •Argon/hydrogen gas mixtures or helium gas may be used as the shielding gas for benefits to specific applications.

Electrode choice: The right tool for the job The tungsten electrode, the source of the welding arc, is singularly the most important element of the welding system. While no one would refute the importance of the ignition device on an automobile airbag, the rip cord for a parachute, or quality tires for our automobiles, the importance of the tungsten electrode is often overlooked.

The welding procedure Many welding equipment suppliers offer a series of pre-engineered weld schedules for a variety of tube diameters, wall thicknesses, and base materials. Welders should always follow these suggested procedures first. However, there will always exist a trade-off in maximum possible weld speed and weld quality and repeatability. Where weld-parameter specifications do not exist or the engineer would like to change those settings, follow these guidelines:

•Arc Length Arc-gap setting depends on weld current, are stability, and tube concentricity or ovality. The welding engineer must keep the electrode at a constant distance from the tube surface with sufficient gap to avoid stubbingout. •Weld Speed Weld speed depends on flow rate of material to be welded and wall thickness. The objective: to weld as fast as possible while still producing a high-quality weld.

As a starting point, set welding speed at 4 to 10 in./min, running faster on thinner-wall materials and slower on heavy-wall tube. Welding current depends on the base material, wall thickness, weld speed, and shielding gas. The objective: to achieve full-penetration defect-free welds. As a starting point, for welding of stainless steel use 1 A of weld current for every 0.001 in. of wall thickness. Thus, for 0.030 in.-wall tubing, set average weld current to 30 A.

Weld Current Levels Orbital welding typically calls for multiple levels of weld current to compensate for heat buildup in the tube during welding.  If the current used to initially penetrate the tubing was held at the same level for the complete weld, penetration would increase as the weld progressed around the tube, resulting in excessive penetration. Typically, orbital-welding procedures employ a minimum of four levels of weld time, with amperage decreasing from level 1 to level 4.

Industries and Applications for Orbital Welding Aerospace: The aerospace industry was the first to recognize the advantages of automated orbital welding. The high-pressure systems of a single aircraft can contain more than 1,500 welded ts, all automatically created with orbital equipment.  Boiler tube: Boiler-tube installation and repair offer perfect applications for orbital welding. Compact orbital weld heads can be clamped in place between rows of heatexchanger tubing.

 Food, dairy and beverage industries: These industries require consistent full-penetration welds on all weld ts. For maximum pipingsystem efficiency, the tubing and tube welds must be as smooth as possible. Any pit, crevice, crack, or incomplete weld t can trap the fluid flowing inside the tubing, becoming a harbor for bacteria.  Nuclear piping: The nuclear industry, with its severe operating environment and associated specifications for high-quality welds, has long been an advocate of orbital welding.

 Offshore applications: Sub-sea hydraulic lines use materials whose properties can be altered during the thermal changes that accompany a typical weld cycle. Hydraulic ts welded with orbital equipment offer superior corrosion resistance and mechanical properties.  Pharmaceutical industry: Pharmaceutical process lines and piping systems deliver highquality water to their processes. This requires high-quality welds to ensure a source of water from the tubes uncontaminated by bacteria, rust, or other contaminant. Orbital welding ensures full-penetration welds with no

 Semiconductor industry: The semiconductor industry requires piping systems with extremely smooth internal surface finish to prevent contaminant buildup on the tubing wall or weld ts. Once large enough, a buildup of particulate, moisture, or contaminant could release and ruin the batch process.  Tube/pipe fittings, valves, and regulators: Hydraulic lines, liquid- and gas-delivery systems, and medical systems all require tubing with termination fittings. Orbital systems provide a means to ensure high productivity of welding and optimum weld quality.

• Orbital Welding is now used in the Aerospace Industry on many systems and components such as : Titanium Fuel Lines • Hydraulic Lines and Components • Aluminum Ducting • Key advantages of Orbital Welding Systems Extremely repeatable welds • Smooth and even tube bore • Smaller heat affected zone (HAZ) • Elimination of defects including porosity and cracking Industries and Applications for Orbital Welding