Why Are There Black Spots on My Aluminum Welds? Here’s What You Need to Know.

A manufacturer contacted us recently with a problem:  Their welding performance looked good and their machine performing well. But each aluminum weld created had a dark spot that was noticeable. They were concerned about the impact this cosmetic defect was having on the appearance of their product, and the perception that it could be impacting the quality of the welds they are producing.

We see this phenomenon often in machines using a frequency converter transformer operating at the upper electrical limit. As the head lifts after the weld is formed, an electrical arc can happen between the electrode and the part when the head lifts due to residual magnetic fields and electrical current.

The solution is an easy one – installing a Tip Arc Relay. This is a common addition we include when retrofitting an older Sciaky machine with the WeldComputer Waveform Synthesis Control. In this post we will explore what the Tip Arc Relay is and if your machine needs one.

What is a Tip Arc Relay?

Most frequency converter welders have a piece of hardware known as a Tip Arc Relay installed across the transformer primary input terminals. 

The Tip Arc Relay’s purpose is to collapse any residual magnetic field in the transformer during the hold time so there is no remaining circulating current in the machine secondary electrical circuit at the time the electrodes unclamp.

Unfortunately, many older welding machines leverage a tip arc relay that is fraught with service issues and uses an expensive 90A fuse that is susceptible to blowing often.

Do I need a Tip Arc Relay for my machine?

If the materials welded require a relatively low current, you might not need a Tip Arc Relay. An easy way to determine if you need to add one is to take a look at the parts you are already welding. The tell-tale sign of this arc is the appearance of a little black dot on the surface of any of your welded parts. This is most typically seen when welding aluminum at a high current.

WeldComputer offers a Solid State Tip Arc Relay as an optional add-on for retrofitted controls on Sciaky spot welders with a frequency converter transformer. The Solid State Tip Arc Relay eliminates the common service issues that typically occur with other Tip Arc Relays because the WeldComputer system performs the function electronically, without any physical contacts that wear down or fuses that can blow.

We encourage customers to consider adding a Solid State Tip Arc Relay if they want to take advantage of the full electrical capacity of the machine. Even if welding is being performed at lower current, if there’s any possibility welding could be performed at higher currents in the future, adding in the Tip Arc Relay could save maintenance headaches down the road.

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