North America's largest metal forming, fabricating, welding and finishing event heads to Orange County Convention Center in October 2024. FABTECH provides a convenient "one stop shop" venue where you can meet with world-class suppliers, see the latest industry products and developments, and find the tools to improve productivity, increase profits and discover new solutions to all of your metal forming, fabricating, welding and finishing needs.
North America's Largest Metal Forming, Fabricating, Welding and Finishing Event
A plasma system can save time during automotive restoration
Reprinted with permission: The AWS Welding Journal
Whether a professional or a home enthusiast, many people enjoy restoring old vehicles. But the one aspect of automotive restoration that many agree isn’t so enjoyable is removing the spot welds when replacing sheet metal panels. Most of the tasks involved with panel replacement move along rather quickly, like welding. However, to properly remove the old panel and get the area ready for the new one, the seams along the mounting surfaces must be clean and undamaged. That means removing the spot welds. This task is usually accomplished by drilling, cutting, or grinding.
Spot Weld Removal Methods
Drilling uses an actual drill to cut through the spot weld itself and often goes through both layers of metal. Cutting involves a spot weld cutting tool to cut a circle around the spot weld. Drilling or cutting a spot weld takes about 3 min per weld. Both of these methods often damage the lower layer of metal, which needs to be intact as the new panel will mount to these surfaces.
Grinding is another traditional method of spot weld removal. The idea is to grind through the spot weld but only remove the top layer of metal. When correctly done, this technique does less damage to the bottom layer of metal than drilling. Also, it takes less time, averaging 2 min per weld.
While the average automotive panel can have more than 100 spot welds, some panels have many more. For example, the floor pan of a 1968 Pontiac Firebird has 178 spot welds. If it takes as little as 90 s to grind a weld, that’s almost 5 h to remove the spot welds in that floor pan. What if there was a faster way to accomplish this?
Plasma gouging has been around for a long time, but until recently, it was not considered an effective way to remove spot welds. In the past, plasma piercing has been used to remove spot welds, but like drilling, this method went through the spot weld itself and both layers of metal.
Modern technology has vastly widened the range of tasks that can be accomplished using a plasma system. And plasma gouging can now effectively be used to remove spot welds with no or minimal impact on the bottom layer of metal. This method is also three to four times faster than the traditional techniques, averaging 30 s or less per weld.
The Spot Weld Plasma Gouging Technique How it Works
Rather than gouging through the spot weld, the plasma gouging technique gouges around the spot weld, only going through the top layer of metal. Once that top layer around the spot weld is removed, it easily comes off. In fact, many times you can hear the pop of the layers as they separate. All that’s left to do is grind off what’s left of the spot weld, clean up the mounting surface, and install the replacement panel.
The trick to this technique is to hold the torch at a flat angle and never let the top layer of metal get hot enough to affect the bottom layer. This is accomplished by either flicking up the torch or releasing the trigger as soon as the metal of the top layer starts to melt. The pressure from the arc “washes” away the molten metal, but is cool enough so that it doesn’t stick to anything or get caught between the layers.
Learning the Technique
Any plasma system with a gouge setting can be used with this technique. To begin, set the amperage as low as it will go. The system used in this project goes down to 10 A. If the system being used has an air pressure adjustment, set it at the lowest setting.
Mark the spot welds, then place the plasma torch at a flat angle just beyond the spot weld. Press the trigger and start the arc. The metal of the top layer around the spot weld will start to melt or burn away. As soon as the metal begins to glow or melt, the torch is flicked up or the trigger is released. That moment allows the metal to cool slightly. Then the torch is flicked back down or retriggered to continue melting the top layer. As soon as the bottom layer is revealed, flick the torch up or release the trigger. Then start the process over.
The constant movement of the torch or intermittent triggering allows the operator to control the melting rate of the top layer, manipulating it so that the arc does not affect the bottom layer. Remove the metal around one half of the spot weld, then repeat the process on the other half.
By holding the torch at an angle, you can deflect the path of the arc to connect with the top layer of metal, leaving the bottom layer untouched. For the thinner sheet metal of older, classic vehicles, try holding the torch at an even flatter angle and bouncing the arc off the metal. Use a very light touch with older, thinner metal. Older, worn, rusted metal will quickly melt; watch closely, and move the torch as needed. Change the angle of the torch as you work. Each situation will be different, depending on the thickness of the metal. Remember, you can always go back and gouge more, rather than keeping the heat applied too long and melting through the bottom layer.
Once the welds are gouged, the top layer usually comes right off. If needed, insert a seambuster or chisel in between the layers and pop any bits of metal that are still attached. Then grind what’s left of the spot weld.
It’s an easy technique to learn. Find some old parts with spot welds to practice on or create practice parts. Run several lines of spot welds on two pieces of automotive gauge sheet metal and try the gouging technique on them. Be patient with it, as it saves hours when replacing multiple panels. Experiment by holding the torch and gouging at various angles and perfect the technique that works for you and your plasma system.
Plasma Gouging Spot Welds vs. Grinding Spot Welds
We decided to make a comparison by removing 20 spot welds using the grinding technique and another 20 using the plasma gouging method on the firewall of a 1969 Chevy Camaro. One operator used a Kobalt 4½-in. angle grinder and a DeWalt aluminum oxide grinding wheel. These are the tools and method he regularly uses to remove spot welds in his work. For the plasma system, we used a Hypertherm Powermax45® XP. The operator of the plasma system uses this system and the spot weld gouging technique in her daily job.
The grinding method took 30 min for 20 welds — 90 s per weld.
The plasma gouging method took 10 min for 20 welds — 30 s per weld.
The plasma system did the job three times faster than the grinding method on this project. One big advantage of the plasma gouging method was seeing the progress of the work. There was no need to stop working and check. The minutes saved start to add up when the entire number of spot welds in a panel is considered.
The Advantages of Using a Plasma System in Automotive Restoration
The smart automotive restoration professional takes advantage of all the tools and methods that help in getting the job done. Restorers need to have several techniques in their wheelhouse and quickly adapt to whatever technique the spot weld situation requires.
Plasma systems are normally associated with cutting, but plasma gouging has been used for years to remove fillet and butt joint welds effectively. New technology plasma systems are all about precision. The plasma torch can be used as a scalpel, cleanly slicing or gouging away tenths of an inch.
By utilizing the spot weld plasma gouging technique, the time it takes to remove a panel can be reduced. When used on a restoration project involving multiple replacement panels, those saved minutes add up to hours; and when properly used, there is no effect on the bottom layer.
LEAD PICTURE: Plasma gouging allows the fabricator to remove spot welds in a manner that is more efficient than any other method. Properly done, this process has no impact on the bottom layer. Look closely at the spot welds in this photo, the rusty surface of the bottom layer is easily visible through the gouged areas of the top layer, untouched by the gouging arc.
FABTECH 2024
About the Expo
North America's largest metal forming, fabricating, welding and finishing event heads to Orange County Convention Center in October 2024. FABTECH provides a convenient "one stop shop" venue where you can meet with world-class suppliers, see the latest industry products and developments, and find the tools to improve productivity, increase profits and discover new solutions to all of your metal forming, fabricating, welding and finishing needs.
