CHAPTER 6: ADVANCED WELD FUNCTIONS
MODEL HF2 2 kHz HIGH FREQUENCY RESISTANCE WELDING POWER SUPPLY
6-6
990-057
Weld Periods not required can be set to zero. Properly used, Pre/Postheat can significantly reduce weld
splash and electrode sticking.
In the normal application of Pre/Postheat, the Preheat Period provides sufficient heat to displace the
plating or oxides, seat the electrodes against the base metals, and force the parts into intimate contact.
The Preheat Period should be two or three times longer than the Weld Period, which completes the
structural weld. The Weld Period weld current should be greater than the Preheat Period weld current
by a factor of two or three since the first bond significantly reduces the resistance of the interface
between the parts. The Postheat Period immediately follows to provide grain refinement in the parts.
Pre/Postheat can be used with Unitek Peco Force Fired Manual or Air Actuated Weld Heads. For
Manually Actuated Weld Heads, weld current begins when the Force Firing Switch closes. For Force
Fired Air Actuated Weld Heads, weld current begins when both levels of a two-level Foot Switch are
closed and the Force Firing Switch in the Air Actuated Weld Head closes.
When Pre/Postheat is used with a Non-Force Fired Air Actuated Weld Head, the Squeeze (SQZ) Period
must be used to allow sufficient time for the electrodes to close and apply the required weld force to the
parts before the Weld Period begins. Weld current begins when the Squeeze Period ends and both levels
of a two-level Foot Switch are closed.
When Pre/Postheat is used with any type of Air Actuated Weld Head, the Hold Period can be used to
automatically keep the electrodes closed on the parts after weld current has terminated for the purpose of
providing additional heat sinking or parts cooling. Squeeze and Hold Periods have no meaning with
Manually Actuated Weld Heads and do not appear on either the weld schedule Program or Run screens.
Pre/Postheat - Weld Graph Run Screen
(Figure 6-11)
Weld schedule 004 is pre-programmed at the
factory for Pre/Postheat operation. The HF2
Weld Control automatically recognizes the
presence of a Manually or Air Actuated Weld
Head before the first weld is made.
Figure 11. Pre/Postheat
Weld Graph Screen
Pre/Postheat - Alphanumeric Run Screen
(Figure 6-12)
To simultaneously view all pre-programmed
time periods and energy settings, press [CHNG]
to select the Alphanumeric Run screen. The 7
digit Weld Counter is displayed in the upper
right corner.
Figure 12. Pre/Postheat
Alphanumeric Screen
