What is the welding principle of resistance spot welding machine

What is the welding principle of resistance spot welding machine
Spot welding is to melt metal through resistance heat under the action of electrode pressure, and crystallize under the action of electrode pressure to form a joint after the power is cut off. At the same time, a plastic ring is formed around the joint
The spot welding cycle includes four phases that are pre-compressed, energized heating, forging and rest.
1. In the pre-compression stage, the weldment is in close contact to obtain stable contact resistance
2. During the electrification and heating stage, ensure that the contact surface of the two weldments begins to melt at the electrode holder to form a nugget
3. Forging stage When the nugget reaches the appropriate shape and size, the welding current is cut off, and the nugget is cooled and crystallized under the action of the electrode pressure
Spot welding joint form: overlapping, folding
Composed of two or more weldments of equal or unequal thickness

Design principles of spot welding machine joints and structure

The margin should not be too small//The amount of overlap is sufficient//The pitch is appropriate//The assembly gap should be as small as possible//The electrode can be reached
Right pitch
In order to limit the shunt, there should be a suitable point pitch, the minimum value is related to the thickness of the weldment, the conductivity of the metal, the surface cleanliness and the diameter of the nugget. The table shows the recommended minimum dot pitch
It is usually classified according to the number of solder joints that can be formed in a spot welding cycle in the direction of electrode feeding, mainly including:
Double-sided single spot welding
Single-sided double spot welding
Single-sided single spot welding
Double-sided double spot welding
Multi-spot welding

Spot welding method:
a) Double-sided single spot welding
b) Single-sided double spot welding
c) Single-sided single spot welding

Spot welding process:
Clean up before welding and strictly stipulate the storage time
Spot welding current is large, impedance is small, and secondary voltage is low
Oxide film on the surface of the weldment, oil stains, etc. directly affect heat precipitation, nugget formation and electrode life, and cause defects and reduce strength
Cleaning the surface of the weldment before welding is a very critical and important process
Common methods: mechanical cleaning, chemical cleaning

Spot welding process parameters mainly include
Welding current
Power-on time
Electrode pressure
Shape and size of electrode working end face
The selection of process parameters mainly depends on the nature of the metal material, plate thickness, structural form, etc.

The most important parameters of spot welding
Segment AB: Steep shape. Due to the small welding current, the nugget cannot be formed or the size of the nugget is too small, so the shear load of the welding joint is low and very unstable
BC segment: steady rise. As the current increases, the nugget increases steadily and the shear load continues to increase
The shear load near point C does not change much (the warping between the plates limits the expansion of the nugget diameter)
The thicker the weldment, the steeper the BC section, that is, the more sensitive the current change is to the shear load
After point C: due to excessive current, overheating, splashing, deep indentation, etc., performance degradation

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