Learn the nuances of using single- and dual-wire filler metals
By TRE HEFLIN-KING, Applications Engineering Manager at Hobart, Troy, Ohio
Reprinted with permission: AWS Welding Journal
Automation has undoubtedly been a welcome addition to the welding industry. It has helped address the persistent gap in skilled labor and delivered precise, repeatable welds that ensure the uniformity needed for high-volume part production. While welding automation has the capability to improve part throughput significantly, it’s essential to consider whether an operation is using single- or dual-wire filler metals to achieve the desired weld sizes.
Dual-Wire Filler Metals
Dual-wire welding uses two wire electrodes that simultaneously feed into the welding arc. This process increases the deposition rate, thereby enhancing productivity. Operators can approach dual-wire welding in one of two ways: twin-wire welding or tandem-wire welding.
In twin-wire welding, both filler metal wires are fed into a single welding arc, and everything is powered by a single power source. In this approach, the two wires share the welding current, enhancing arc stability and control over the entire welding process. Tandem welding uses two wire electrodes that are fed into separate welding arcs but positioned closely together to achieve a combined welding effect. The independent control of each wire’s parameters (e.g., feed speed, current, and voltage) allows greater flexibility and precision over the bead shape. Both options promote faster travel speeds and increase the deposition rate, achieving a larger weld size.
Using a dual-wire robotic system yields higher productivity, improved weld quality, and better adherence to desired weld sizes, but it can present some operational challenges.
Troubleshooting two wires: Managing a single-wire system can be challenging when troubleshooting common welding issues, such as bird nesting, tip failure, poor wire feeding, and clogs. A two-wire setup doubles the likelihood of those occurrences. Diagnosing and resolving the issue can increase downtime, which negatively affects productivity. In this case, a proper setup is crucial in helping to mitigate the likelihood of the wire-feed difficulties.
Synchronization: Achieving proper synchronization between the two wires and their respective arcs can be challenging. Improper alignment or timing issues can lead to interference, inconsistent-sized welds, or welds of varying quality. Programmable logic controllers (PLCs) can help manage and control welding process parameters, assisting automated welding systems in maintaining the correct settings.
Torch angles and positions: Setting the correct torch angles and positions for both wires is critical for optimal arc stability and bead formation. Depending on the workpiece, operators may face access issues with the robot. Misalignment and lack of access can result in defects and uneven weld sizes. Proper tooling and double checking that the tool center point for the torches is set correctly will help ensure correct positioning.
Equipment calibration: Ensuring that the robot, power source, and feeding system are accurately calibrated for dual-wire welding and that all necessary parameters for the workpiece are set is essential. Any discrepancies can result in inconsistent weld sizes, poor weld placement, and reduced quality.
Single-Wire Filler Metals
The single-wire welding process uses only one filler metal to create a weld. With this process, moderating the travel speed of the robot is extremely important. If the robot moves too quickly, the outcome may be small, underfilled, ropey welds that run the risk of undercut.
With the power that welding automation provides, there’s a natural inclination to set the automation at maximum travel speed to produce as many parts as possible. When using single wires, you can become limited by the achievable deposition; therefore, it’s best to program the robot to move fast enough to achieve the desired cycle times while maintaining the appropriate weld size. A travel speed that is either too fast or too slow will compromise quality, ultimately reducing productivity and throughput. Another factor in achieving quality single-wire welds is using a welding wire that is appropriate for the application. If you are welding in the flat and horizontal position, flux cored wires of that classification are a great option. Metal cored products should also be considered for these applications if you want to reduce postweld cleanup and don’t want to deal with the slag that flux cored wires produce.
Because dual-wire welding inherently tends to create larger welds, single-wire operations need to pay special attention to several common challenges to avoid undersized, defective welds.
Welding position: Achieving the desired weld size in various welding positions can be a challenge with a single wire. For example, 1F, or flat fillet, is an easy and ideal position because gravity helps keep the metal in place. However, the workpiece may need to be oriented to weld in the 2F position, which involves a vertically positioned workpiece with a horizontal weld joint. This requires careful control of the filler metal’s deposition to prevent weld belly (the sagging that occurs due to gravity). Positioning the parts correctly and with the appropriate access is vital in robotic welding.
Parameter control: It is important to consider the materials you are welding and their various conditions. A weld joint made with clean base material in a T-joint configuration may require different parameters than a weld joint made with coated base material in a lap joint configuration. Using a filler material with a robust parameter window and synergic welding processes can help mitigate weld quality issues that may arise from complicated part designs.
Part consistency: There’s little room for error in robotic welding. A robot will go where it’s programmed to go, making it imperative that the parts are consistent (e.g., the joint is always in the same place). If there are any nuances to the workpiece or the location of the joint, they may be reflected in how the weld is laid. Add-ons, such as through-the-arc seam tracking or integrated visual seam tracking systems, can help mitigate part-to-part consistency issues.
Extra Considerations for Success
Regardless of the process, additional setup work can help ensure that the automatic weld meets the proper specifications. Before initiating production of the part, scrap material can be used to test the robot’s weld settings to make sure the welds produced meet expectations. Troubleshooting on the front end will save time on the back end and ensure that the welds are consistently sized correctly.
Additionally, fixturing, tooling, and clamping should be considered. Accounting for all components required in the welding process improves the robot’s access to the joint. When possible, parts should be programmed in position to ensure better weld quality while achieving fast cycle times.
Despite the advent of welding automation, where precision and repeatability are hallmarks, a perfectly laid and sized weld is not guaranteed. The factors of single- or dual-wire filler metals present more elements to monitor and consider. Understanding the nuances of both processes will help ensure the right-sized weld is laid every time — regardless of whether the robot is wielding one wire or two.