What are Submerged Arc Welding?
Submerged arc welding (SAW) will handle the welding, but controlling where and how you weld can be as important as what’s melting the wire.
Buying a SAW system without auxiliary equipment like a manipulator or gantry is like buying an engine without the rest of the car. You can turn it on and it’ll make some smoke, but it’s not going to get you where you need to go.
Knowing your applications will help you determine what auxiliary equipment you need to manipulate the welding head and get the productivity you want.
Describe the Joint:
One of the first things to determine when selecting SAW auxiliary equipment is the type and variety of joints you will weld. Will there be:
- Large V-groove joints with plenty of space for a large welding torch?
- Narrow, deep grooves to minimize the amount of weld material to be deposited?
- Multipass welds, and if so, how many passes?
- Fillet welds?
- Cladding applications where multiple passes need to be laid in succession?
- Straight and consistent or wavy and inconsistent welds?
Define a Typical Project:
The workpiece to be welded will also help identify the requirements of your auxiliary equipment. The following are good questions to ask:
- Are the joints in long and straight or round materials?
- Are they vertical?
- How large is the workpiece, and does it need to be positioned or rotated to access all welding locations?
When welding a large workpiece, the time required to position it can significantly affect productivity. Flipping a large workpiece over to reach a weld takes time and can be dangerous for the operators.
A boom-and-column manipulator is probably the most cost-effective and versatile method of holding a weld head above a workpiece. If the joint is long and straight, a boom-and-column manipulator on rails with a powered travel car can be effective. It is important to ensure that the car’s speed can accommodate rapid-traverse as well as typical welding speeds.
If the workpiece is round, like a wind tower or a pressure vessel, it will need to be rotated under the torch. Turning rolls and welding positioners are commonly used for this. Rolls rotate long and often very heavy cylindrical workpieces that have a center of mass that is roughly on the workpiece centerline. Positioners rotate workpieces with a center of mass that does not lie on or near the axis of rotation.
The amount of weld wire being deposited and the thickness of the base metal determine other equipment requirements. For example, conventional flame or induction heating equipment may be needed to preheat thick material.
The answers to two process questions can determine what kind of ancillary equipment is necessary:
- How much current is needed?
- How long do I need to weld?
If you will be welding with a lot of current for extended periods of time it is imperative that the welding circuit be sized properly. If your cables aren’t big enough on either side of the arc, you run the risk of melting something besides the electrode.
Another important consideration is heat transfer. As current travels through welding cables, they heat up and could melt. There must be enough air around the cables to keep them cool.
Find Your Automation ROI:
In some instances, the cost of automating SAW has long payback times. In others, the cost is quickly justified.
On one hand, multipass welds are often difficult to automate because the placement of successive beads can be very important. A well-trained SAW operator can be hard to beat.
On the other hand, cladding, structural sections, heavy-wall pressure vessels, and other processes that require high deposition rates are prime candidates for automation. Relying on a human operator to accurately deposit hundreds of pounds of weld metal in successive beads for hours at a time is usually not economical, practical, or even possible.
For applications such as these, a typical single-wire submerged arc process can easily deposit 15 or 20 lbs. per hour, and a twin or tandem two-wire submerged arc process can deposit upwards of 40 lbs. per hour, offering up to 10 times or 1,000 percent higher deposition rate than a typical manual shielded metal arc welding or gas metal arc welding process.
Choose Seam Tracking:
Seam tracking can make welding an irregular path on wavy joints easier. A sensor or feedback from the weld is used to adjust the position of the weld head so it stays over a predetermined location on the joint. It can improve productivity for many applications and help less experienced operators execute good welds.
The most common tracking methods are tactile, laser, and through-arc.
Tactile seam tracking is economical. A mechanical probe rides along the joint and sends signals to powered cross slides to follow the line of motion. It requires a well-defined joint, and therefore is not well-suited for butt welds or very shallow joint profiles.
Laser seam tracking projects a laser beam onto the workpiece and uses image processing algorithms to recognize a weld joint profile. The profile is used to precisely position the welding head. Since there is no physical contact between the sensor and the workpiece, laser seam tracking sensors aren’t susceptible to jamming or breaking. They can be used to automate multipass welds; however, the increased functionality comes with a higher price.
Through-arc seam tracking requires oscillation of the weld head and uses real time voltage and current readings to locate the edges of the joint. This is typically used with GMAW systems, but can be used with SAW systems as well. A combination of your technical requirements, budget allowance, and the supplier or system integrator will help determine the right system to track your welds.
Recover Unused Flux:
Large V-grooves and multipass welds typically require large spools or drums of welding wire and properly-sized flux delivery and recovery systems. As a rule of thumb, 2 lbs. of flux are needed for every pound of wire consumed. Flux capacity can be extended by using a flux recovery system: basically a vacuum that sucks up the flux that has not turned to slag so it can be reused. Using a flux recovery system can reduce the flux to wire ratio. The savings in recovered flux alone can offset the cost of a properly sized system.
Flux capacity can come with hidden costs of its own. A gravity-fed hopper needs to be located above the welding head, which means that the weight of the hopper plus the welding head and wire spool need to be supported. Generally speaking, the heavier the weld head, the more costly the equipment required to support it over your workpiece.
Monitor Weld Quality:
Monitoring and watching the weld in progress is also important. There are a few approaches to position an operator to observe the weld on large workpieces: put an operator seat next to the weld head; add scaffolding or a ladder so the operator can stand next to the weld head; or place a camera at the weld head.
Adding an operator seat effectively turns a manipulator or gantry into an elevator, and the additional requirements can significantly increase the system cost. Ladders and scaffolding can be cumbersome and contribute to repetitive stress-strain injuries if the operator maintains a less-than-comfortable position for extended periods of time. A weld camera can keep the operator in a safe position while providing a clear view of the weld in progress.
Look at the Whole Picture:
Submerged arc welding relies heavily on auxiliary equipment like manipulators or gantries, seam tracking systems, cameras, and flux management systems to create sound welds. It’s important to understand your applications and communicate your requirements to your integrator or vendor.
Asking the right questions will help you specify a system that provides the functionality and safety you need and maximize your return on investment.