Page 41 - Australasian Paint & Panel magazine

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43 • SPOT WELDING 46 MIG WELDING • 48 WELDING SAFETY
PAINT&PANEL MARCH / APRIL 2023 WWW.PAINTANDPANEL.COM.AU
IT’S WHAT YOU DO WITH IT
HOW WELL DO YOU REALLY KNOW YOUR WELDING EQUIPMENT? I-CAR WELDING GURU GEOFF MITCHELL TALKS ABOUT WHY THE MACHINE, HOWEVER STATE-OF- THE-ART, CAN’T NECESSARILY MAKE THE RIGHT CHOICES.
WELDING SKILLS
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BIG SIGH FOR THE GOOD OLD
days where a transformer type welder was the go and mild steel was king. On the oth- er hand, as occupants of today’s cars we can certainly appreciate the im- proved levels of crash protection that the
latest construction materials afford. I-CAR’s Mitchell says that it’s only rel- atively recently that welding machines have been developed more specifically for car repair – before that we piggy-
backed off the heavy industrial sector. Now we have amazing whizz-bang, ‘foolproof’ welding machines that a trained monkey could operate – right? Just select a program tell it how thick the metal is and away you go, you just can’t
go wrong. Errr wrong, very very wrong. Without having a proper understanding of how each grade of high strength steel (HSS) and ultra high strength steel (UHSS) reacts under different heat conditions, and the importance of using the right wire and achieving the correct arc length, you can’t truly understand which is the right pro- gram to set the machine to without a full
tutorial of the machines menu page. “When your inverter synergic mig/ mag welding machine is delivered, that machine was probably set at the factory for an industrial purpose, not an automotive purpose. So you need to check a few things before you are ready to weld. Your liner size is criti- cal – if that’s oversized it’s going to cause you problems with inconsistent wire feed to the weld zone. Most ma- chines, when new, will have a 1mm liner which is too wide for working with 0.6 mm or 0.8 mm wire. Liners are the forgotten, out of sight issue on
welding machines,” Mitchell says. “You need to really study and under- stand the menu of that machine. If you put the wrong gas mix in, the wrong
wire diameter, or the wrong wire spec, the machine will try to weld on an incor- rect synergic curve. These machines all have synergic curves built into the back- ground by the engineers who made them. So if you don’t have the right syn- ergic curves set in the background you’ve got problems.”
It’s not uncommon for technicians to use the wrong gas mix or select the wrong gas mix in the menu list. “You’ve got to take into account we’re welding 0.6 mm, 0.7 mm steel, so you need a gas that is for that thickness steel. So you go to Argoshield Light, which is a mixture of CO2 and argon with small amount of oxygen. The CO2 percentage is the part that puts the heat into the weld zone. You start getting higher percentages of CO2 and oxygen that are greater than what we use in our industry. Every time you pull the trigger on a low setting you’re going to blow a hole, all because the shielding gas is allowing the steel to melt quicker. So you’ve got to make sure you’ve got the right shielding gas and the right wire. Some shops use 0.8 mm wire, some shops use 0.6 mm wire. It’s their preference; they’ll both do the job
but 0.6 is much more controllable on a thinner steel and minimises the heat af- fect zone (HAZ) considerably.
“Everything we do is about the heat af- fect zone. We have to minimise the heat we’re putting into these joints and we don’t do that by turning the machine down. All that does is sit a cold weld on top of the joint, It’s about having the right gas and turning the machine up. So you’re welding hotter, faster,” Mitchell says.
ALUMINIUM WELDING
“You need to go through a massive learning curve when you start welding aluminium. You have to start selecting your types of wire, because there’s so many different aluminium wires and that sets the synergic curve in the back- ground, then you need to select if single pulse or dual pulse is best for the joint