Page 36 - Australasian Paint & Panel Mar-Apr 2019

Tech Talk • I Car
36
PAINT&PANEL MARCH / APRIL 2019
WWW.PAINTANDPANEL.COM.AU
Light weighting the vehicle struc- ture with aluminium and compos-
ites is becoming a common trend. With this in mind how many techni- cians are trained in aluminium repairs or welding methods?
Firstly, take into account the hazards that go with aluminium repairs and welding. The aluminium dust is flam- mable, and the MIG welding process produces ozone. Are you ready for these issues?
The equipment levels required for welding aluminium are specific to each OEM, but the common trend is they all call for welding machines which have dual pulse settings. The single pulse setting on these machines can be used for silicon bronze and some types of al- uminium, but the dual pulse settings will be required to lower the heat input into the aluminium structures. With dual pulse there are so many more set- tings required in the background pro- gram to adjust to get just the right flow. Without the correct training on these welders technicians will struggle to comprehend the process. The points
Aluminiumweldinghas very little room for
error. The weld can look really nice but have no strength because of weld bead just sitting on top.”
technicians must take into account when welding aluminium are:
At the start of the weld, due to the thermal expansion and thermal heat transfer of aluminium, the filler wire will not fuse to the base material un- til the puddle is formed. The welding machine has a built-in hot start fea- ture which increases the starting amps to create the puddle much quicker and then slopes the amps down to the welding settings required for the thickness being welded. With- out a puddle being formed the entire weld will sit on top of the joint with no fusion.
The middle of the weld zone requires care not to overheat the base substitute, the heat will accumulate and the panel will get hotter as the weld progresses. To overcome this technicians require hand speed changes along the weld length. They can also program a slope down setting in the machine which will gradually reduce the welding amps as the weld gets longer to overcome the heat issues.
The end of an aluminium weld will form a crater, this crater is a weak area due to the undercut it leaves. The pulse welding machines have a crater fill set- ting where at the end of the weld, when the trigger is activated, it will reduce the welding amps down to a percentage set by the operator. This must be com- pleted at the end of every aluminium weld performed. If crater fill is not used correctly, the weld will have a shear point in future accidents.
The issue with a dual pulse welding machine is wire input to the weld zone. Due to having a high and low pulse in the process, the filler wire cannot be the same on both pulses. Dual pulse welding machines have a background setting which is called DELTA. This is the adjustment for dif- ferent meterage of filler wire for each pulse. If this is set at zero then on the high pulse the weld will starve for wire and on the low pulse there will be a lot of splatter.
Aluminium welding has very little room for error. The weld can look really nice but have no strength because of weld bead just sitting on top. Or it could be a case of being completed too hot and the weld bead boiled causing po- rosity, a weld full of porosity will have no strength.
Is your workshop ready for the tech- nology changes being seen, do you have technicians who are trained in the latest skills required or will it be a case of holding up a job while you explore the options or losing the job to another shop who has completed the skills training?
Background setting map for dual pulse welding machine.
If crater fill is not used correctly the weld will have a shear point in future accidents. The weld can look really nice but have
no strength because of weld bead just sitting on top.