APPENDIX D: DEFINING THE OPTIMUM PROCESS
UB25 LINEAR DC RESISTANCE WELDING CONTROL
990-665
D-5
R1 & R7
The electrode resistances affect the conduction of energy and weld heat to the parts and
also the rate of heat sinking from the parts at the end of the weld.
R2, R4 & R 6
The electrode to part and part to part
“Contact Resistances”
determine the amount of
heat generation in these areas. The contact resistances decline over time as the parts
achieve better fit up.
R3 & R5
The metal
“Bulk Resistances”
become higher during the weld as the parts are heated.
If a weld is initiated when the contact resistances are still high, the heat generated is in relation to the level
and location of the contact resistances, as the materials have not had a chance to fit up correctly. It is
common for the heat generated at the electrode to part and part to part resistances to cause multiple welding
problems when welding resistive materials (see below). Conductive materials can be welded by using
high contact resistance and fast heating as their bulk resistance is not high and cannot be relied upon for
heat generation.
•
Part marking and surface heating
•
Weld splash or expulsion
•
Electrode sticking
•
Weak welds
If a weld is initiated when both parts and
electrodes are fitted up correctly as show on
the right, the contact resistance is lower and
bulk resistance now controls the heat
generation. This type of weld is achieved with
a slower heating rate and normally longer time
is preferred for welding resistive materials
which can generate heat through their bulk
resistance.
The contact resistance present at the weld when the power supply is fired has a great impact on the heat
balance of a weld and therefore also the heat affected zone.
High Contact
Resistance
Electrode
Electrode
Better Part to part and
electrode to part fit up.
Electrode
Electrode
