Twice as Nice

Using tandem welding to produce parts for the yellow goods industry is the best choice

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Huge excavator buckets, big front-end loaders, large cranes – joining heavy components in the yellow goods industry presents particular welding challenges. Enormous sizes and extremely thick materials are an everyday occurrence. Take, for example, a 5-ft.-long, heavy-duty axle made from steel up to 2 in. thick.

“Welding heavy axles up to 2 in. thick presents challenges in managing distortion during production,” says Matthew Clark, welding application engineer, Fronius USA. “That’s where tandem arc welding makes a difference. With our system, we can decrease the number of welding passes and overall heat input, which enables an increase in productivity and reduces rework for our customers.”

In tandem welding, two wires share the same arc and are melted at the same time, forming a single molten pool. The “lead” wire generates much of the deep penetration on the base plate at high travel speeds, and the “trail” wire adds to the overall deposition.

Tandem welding offers the deposition rates often required to join thick materials. Increased deposition translates to increased travel speeds and decreased cycle times compared to single wire. The process is highly versatile and offers a high degree of flexibility.

Tandem welding is based on two independent welding power sources that are synchronized, along with two wire drives and two contact tips. The electrically isolated contact tips with the wire electrodes are contained within one torch body surrounded by a single gas nozzle. The two arcs are synchronized and form a single molten pool.

The wires are positioned one behind the other. The “lead” wire generates much of the deep penetration on the base plate at high travel speeds, and the “trail” wire adds to the overall deposition.

The weld arcs can be controlled independently and precisely coordinated and either wire can be the lead wire. This allows the programmer to take full advantage of the robot’s capabilities. Shutting off one of the wires during welding allows for more control in an area where torch access might be restricted, for example. The welding process can be controlled through the robot controller from twin to single wire, and back, during a continuous weld bead.

This tandem welding setup forms the basis of the Fronius TPS/i Twin Push welding process. When it comes to tandem welding, the main challenge is successfully controlling both arcs. The Twin Push system requires a Twin controller that synchronizes the welding process and acts as a robot interface. Both wires can be synchronized accordingly using the Twin controller. Ignition of the trail arc is synchronized with a slight delay following the lead arc: This prevents the two arcs deflecting one another, commonly referred to as arc blow, ensuring an optimum weld start. The process also offers the ability to offset the wires, allowing for diverse material fit-up conditions.

“The synchronized start enables a smoother arc-start, reducing spatter,” Clark says. “The two power sources work together, synchronizing everything in the background right down to droplet detachment. This increases process efficiency, simplifying the operator’s job.

Touching on tandem

With tandem welding, pulsed arc welding helps reduce spatter and achieve better arc characteristics. Pulse Multi Control (PMC) is a further development of the pulsed arc from Fronius. PMC features a short, focused pulsed arc that enables improved penetration and higher travel speeds, which fits well with the tandem welding process. At the same time, with Penetration Stabilizer and Arc Length Stabilizer, PMC generates a powerful and stable arc for control of the weld pool. The welding results are reproducible and stable.

The Fronius TPS/i Twin welding system is based on two independent welding power sources, along with two wire drives and two contact tips. The electrically isolated contact tips are contained within one torch body.

“The Arc Length and Penetration Stabilizers are two separate parameters that when used together work together to compensate for slight deviations in material fit-up caused by several factors such as variations in contact tip to work distance, improper material preparation or fixturing, and so on,” Clark says.

The benefits of tandem welding are high deposition rates produced at high speeds.

“With a deposition rate of up to 55 lbs./hour and a speed of up to 157 ipm, the TPS/i Twin systems are quite effective,” Clark notes. “This is made possible with wire speeds of up to 1,180 ipm for each wire. Despite this speed, a quality finish with reliable penetration and no weld seam porosity is achieved. This reduces cycle time per part.”

With the TPS/i Twin welding process, the two power sources work together, synchronizing everything in the background right down to droplet detachment.

The TPS/i Twin Push system is effective on carbon and stainless steel. For aluminum applications, the Twin Push-Pull system is available. The CMT Twin system uses the Cold Metal Transfer process, thereby enabling welding of aluminum, nickel-base alloys and high-strength steels. The controlled heat input provided by CMT is also well-suited for thin sheet applications. With CMT Twin, different processes can be used on each electrode, for example PMC on the lead electrode and CMT on the trail electrode. This allows for further optimization of the weldment.

Smart assistance

For even better tandem welding, intelligent welding process parameters for the TPS/i Twin systems automatically adjust the arc in the background. This provides maximum control – supported by robot assistance systems. In combination with robot control, together they all help make the production process as efficient as possible.

This not only saves time and minimizes errors, but it also means that welds can be reproduced at the desired quality without the need for manual fine-tuning. The welds can meet higher demands thanks to their outstanding design.

Watch the video to see a closer view of the TPS/i Twin systems for tandem welding.

  • SeamTracking automatically compensates for clamping and component tolerances during welding, thus preventing errors and unnecessary rejects.
  • TouchSense was developed for fillet welds and groove welds; the wire or gas nozzle precisely contacts the component and offsets the start and end position to the robot, which calculates the exact weld seam path.
  • With WireSense, the wire electrode measures component deviations, such as joint location and any gaps through a height difference, and transmits the values to the robot.
  • With Teachmode, there is a voltage on the wire to sense a short. Once a short is detected, the wire is pulled back before it bends, thus preventing teaching of the weld path. The set stickout always remains the same.
  • With short-circuit detection, the welding system detects accumulations of spatter inside the gas nozzle. Cleaning routines can be optimized and process reliability can be increased.
  • With Slaghammer, slag that has formed during previous welding on the electrode is knocked off ensuring smoother arc starts.
  • Spatter-free ignition enables safe and clean ignition.

Tandem welding has become a well-proven process used worldwide, especially in the production of yellow goods. It allows welding production to increase without sacrificing weld quality. The TPS/i TWIN Push welding system integrates additional enhancements to the process. For users, this means even higher deposition rates, higher welding speeds and overall higher production.

Fronius USA LLC

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