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1. The
principles of Resistance Welding
On the surface of the metal material, Contact electrode,
pressing and making a flow of high current for a settled
time, and it uses the
electronic resistance existing in the contact surface in order to generate a
high level of heat
and it puts together the materials by making Nuggets, which
is Melting Joining.
Q = 0.24 * I 2 * R
* T
Q : Caloric Value (Cal). I : Current (A).
R : The contact resistance between Materials (Ω).
T : The time of applying an electric current (sec).
The Caloric Value generated here will be calculated
by Joule.
( The amount of Caloric Value to heat 1
Liter of Water to 1 Degree in Celsius. ; 1J = 0.24cal, 1cal = 4.2 J )
2. Important factors of Resistance Welding.
1) The welding current.
- The caloric value is proportionate
to the square value of current, it has the most huge impact on welding.
- Nugget is generated by the current density in the
contact surface, it is needed to heighten the current density.
- In case
generated too excessive current density, it will cause a overheating and a
deformation in the part of
melting.
- The damage of surface caused by excessive current,
creates sloppy and blowholes so that it lessens the depreciation of its degree of strength.
2) Applying Pressure.
- It is the physical force which is applied through
cylinder, it has some effect on the formation for the resistance in contact surface.
- The value of Applied Pressure is
in inverse proportion to the contact resistance.
- It prevents the Welding parts
from sectional heating, and leads to the same result of Welding.
- In case Applied Pressure is high,
the contact resistance is relatively low.
Consequently, Due to the lack of the generation of
heat, It will cause the depreciation of its degree of strength
and too many of excessive welding tracks.
3) The welding time.
- It is the time of the welding
time. It is proportionate to the Caloric Value.
- Excessive welding
time will cause the overheating around the contact surface which is caused
by thermal
Conduction, and the basic material
will be inflated and transformed.
- In case the welding
time is shorter than normal, Due to the fact that selectional part will be
melted, the
degree of strength will be poor.
4) Electrode.
- The quality and shape of the electrode has a tremendous effect on the result
of welding.
- It is required to have a high level of thermal conductivity and electrical
conductivity.
- It is important to keep the degree of hardness in a high temperature.
- Due to the fact that it will be transformed, it will cause the change of the
current density and the applying
pressure.
- It is advisable to decide the time of replace and maintenance in order to
keep the good welding quality.
5) The surface condition of
the material.
- Once the material is decided, there will be change
of contact resistance due to the oxidized clinker or the tiny
unevenness in the surface of the metal.
- Due to the oxidized clinker, the tiny unevenness
and a foreign substance, the resistance will be high and be
the cause of sectional overheating.
- In order to heighten the productivity in the same
condition of Welding, it is important to manage the
consistency of the welding material and the surface of the material.
6) The wave form of Welding
current.
- It is the factor which decides the temperature distribution(the heatingprocedure and cooling procedure)
during Welding.
- It is required to have a wide range of waveforms
according to the quality and shape of the material.
- The inappropriate waveform will cause the deformation and scattering, it
will be difficult to get the high
quality of the welding results.
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