Page 34 - Australasian Paint & Panel Magazine Mar-Apr 2021

PRODUCT FOCUS
34
PAINT&PANEL MARCH / APRIL 2021
34 WELDING • 37 3M • 46 RIVETING • 48 BONDING
YOU CAN’T MAKE
IT IF YOU DON’T
BREAK IT
S
SO YOU THINK YOU ARE GOOD AT WELDING? I-CAR’S WELDING GURU GEOFF MITCHELL WOULD BEG TO DIFFER IF YOU DON’T UNDERTAKE DESTRUCTIVE TESTING.
O, WE HAVE JUST WELDED A
new structural part in. Pro- cedure states a combination of plug welds and squeeze-
type resistance spot welds (STRSWs). Before we welded the vehicle, did we spend time completing machine set up and destructive tests on offcut steel to check the welder settings are correct? Did we? Are you sure? Or did we think “our machine is fully auto-
matic, she’ll be right”?
We need to remember that today’s
steels have tighter grain structures than the mild steel we used to see in vehicles. These tighter grain struc- tures create stronger steels. Several
OEMs state when welding steels over 580Mpa spot welding machines should be switched to manual opera- tion mode. This will mean completing set up and testing welds for fusion. Another critical setting is clamping pressure. Without correct clamping pressure on the spot welding machine the panel flanges will not compress tight enough and the result will be molten metal blow out between the flanges or even a complete blow out of the weld zone leaving an awkward hole to fix.
So can molten metal blow out also ap- ply if we are completing plugs welds? Certainly, it can.
WIDTH OF THE WELD ZONE
By moving the arc length away from the work, a wider weld bead is produced at a lower heat. On the arc length setting this is achieved by dialling the setting down and pulling the arc back to- wards the contact tip. The negative effect of this when completing plug welds is that the arc may be too wide and bridge the hole be- ing filled. This in turn will avoid penetration
into the base panel. It will leave a very nice appearance to the weld head, but this can be deceiving when considering strength of the weld.
DEPTH OF PENETRATION
Adjusting the arc length control will af- fect the depth of penetration. Turn the arc setting up and the arc is moved clos- er to the work piece creating a narrow hot weld zone which results in deeper penetration of the base panel. This can be a disadvantage when trying to weld thinner steel as excessive penetration weakens the HAZ zone. But for complet- ing plug welds we need the narrower arc to firstly reach the base panel