Page 42 - Australasian Paint & Panel magazine

Spot welding
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PAINT&PANEL MARCH / APRIL 2023
construction. Next is to adjust your hot start percentage, your crater fill percent- age, your slopes and your delta percent- ages. Depending on your panel thick- ness there are also pulse frequencies that can be sped up or slowed down. Re- member most aluminium welds are fin- ished off the gun, grinding them will weaken the area.
BRONZING
Has anyone else heard a panel technician casually saying: “Oh yes we have inverter welders because the insurance company insisted but I just bronze everything”?
“Silicon bronze was introduced to our market as the be all and end all of not overheating high strength steel,” says
Mitchell. “But there was little training or understanding of how it works and when it’s appropriate to use it. We don’t include it with our welding course any- more, we have a specific course for those who want to learn to do it correctly.
“Silicon bronze is an adhesive, not a fusion type of joint. If applied incorrectly and the base metal is melted like we do with fusion welds, then the weld puddle will reject the new alloy being added and the surrounding steel will crack. So again gas selection is critical, 100% Argon – the coolest shielding gas — is used to avoid the base steel from being overheated.
Some manufacturer’s procedures do state the use of silicon bronzing “In general though you shouldn’t be trained after a procedure comes into your workshop. You train for when the procedure does pop up so you know how to do it. If you have a silicon bronze machine and OEM method states you should use it and you haven’t been trained – don’t think you can just give it a go,” Mitchell says
D D O O W W N N T T O O T T H H E E W W I IR R E E
“A lot of people we train don’t under- stand the importance of the tensile strength of a welding wire. The wire most commonly used is ER70s.6, This wire has a tensile strength of 80,000 psi and a yield strength of 68,000 psi. Con- vert this into the Megapascals that our steel strength is listed as in OEM proce- dures and we find it has a strength of 545 MPa. If we put a butt joint with 545 MPa wire into a major structural part like a B pillar which can be 1400 MPa, then we’ve got a problem.”
In Mitchell’s experience younger technicians tend to embrace training and achieve good results. Many older ones are resistant – they won’t admit they’ve got an eyesight problem and won’t believe that they are welding in- correctly on HSS and UHSS. “It's not normally a case that they can't weld but they were taught to weld on mild steel. The metallurgical structure of today's steels are far more complex and require all new welding tech- niques,” Mitchell says.
Visit i-car.com.au where you will find a host of tailored welding courses for your body repair technicians.