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CHAPTER 5: OPERATING INSTRUCTIONS
875DP/500DP/500HV DUAL PULSE
RESISTANCE WELDING POWER SUPPLIES
990-290
5-7
Electrode Force and %ENERGY
The heat of resistance welding is produced, in part, by the resistance of the interface between the work
pieces to the flow of electricity (the contact resistance).
Sufficient electrode force is required to contain the molten material produced during the weld.
However, as the force is increased, the contact resistance decreases.
Lower contact resistance requires additional energy to produce the heat required to form a weld.
The higher the electrode force, the greater the energy (current and/or time) required to produce a given
weld. Low force usually results in lower bond strength. Increased force requires higher energy but
usually results in a stronger bond. Energy is proportional to time and the square of the welding current.
Polarity
Users of stored energy equipment have found that the direction of current flow can have a marked effect
on the weld characteristics of some material combinations. This effect occurs when welding:
x
Materials with large differences in resistivity, such as copper and nickel.
x
Identical materials with thickness ratios greater than 4 to 1.
Since polarity can be an important consideration in resistance welding of some material combinations,
be sure to check the weld schedule results using both positive and negative polarity. Polarity can be
changed in the PROGRAM state. The general rule is that the more resistive material, or the thinner
material, should be placed against the negative (-) electrode.
CAUTION:
If weld schedules are chained together, do NOT change polarity. All schedules in the
chain must have the same polarity or the relay contacts may be damaged.