MOTO
MAN
3-1 Spot Welding Manual for Medar
SECTION 3
THEORY OF OPERATION
In resistance (spot) welding, current is generated by a transformer, and is fired
through electrodes, which hold the metal pieces in place. These electrodes also
apply force to the metal pieces, usually before, during, and after the firing of the
electric current. This method is called resistance welding because it is the
resistance between the contact surfaces of the metals being welded that generates
the heat to fuse them together.
Resistance is the opposition that a substance offers to the flow of electric current.
The less resistance a metal has, the less heat is generated when current passes
through it. Conversely, the higher the resistance of a metal, the more heat is
generated when that same current passes through it. This behavior can be
paraphrased as follows: the heat is where the highest resistance is.
Obtaining the best results in resistance welding requires a thorough understanding
of the materials used in the welding process, careful control of the heat and
pressure at the weld point, and consideration of numerous other factors.
This section discusses the basics of resistance welding, the variables involved, and
why they're so important to the welding process.
3.1 Resistance Welding Variables
The many variables involved in welding can be broadly categorized into two basic
sections: process variables and material variables.
Process variables include:
• Weld current
• Squeeze time
• Electrode force
• Weld time
• Hold time
• Design of the electrode
Material variables include:
• Workpiece material and thicknesses
• Surface condition and cleanliness of materials
• Coating thickness and type
• Part fit-up
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