Industrial and Power Electronics
DEPARTMENT OF ELECTRONICS
Dr.K.DHANAKODI
Assistant of Processor
Department of Electronics & Communication Systems
S.R.M.V College of Arts and Science
Coimbatore – 641 020
, UNIT-II
Welding and Heating
Definition
Resistance welding is the process of fusing two or more metal pieces
together by passing heavy current through the areas of contact to be
welded. The duration of the current may vary from a few milliseconds
to several seconds depending upon the job requirement.
Resistance Welding
This process is based on the resistance to a current flow between the two
metal pieces where weld heat is produced. The welding heat is given
by
H= twʃ0 i2 r dt
Where r is the resistance between the pieces to be welded and t w, time
during which weld current flows. Either alternating current or short
pulses of uni-directional current may be used.
,Basic Circuit A.C resistance welding
The basic circuit for resistance welding using A.C power is
shown in fig.15. It consists of a welding transformer and a
line contactor. The line contactor may be a magnetically
controlled contactor or ignitron contactor. The function of
ignitron contactor is to connect the primary of the welding
transformer across a.c. supply during welding interval only.
The secondary of the welding transformer has relatively small
number of turns and is rated for hundreds or thousands of
amperes for heavy welds. It is connected to the electrodes
through which the current passes into the job to be welded.
When the metal pieces are forced together by the
electrodes with high pressure, the resistance between the
metal pieces decreases to make a weld. The welding current is
made to flow for only fraction of a second with the help of the
, Contactor which must close many times to make a number of
welds respectively.
The metallic pieces are forced together by passing
large current (1000 to 100000 A) through these pieces. The
welding current is supplied by two electrodes which held the
two pieces. In a typical system, a.c. supply is applied to the
welding transformer via power transformer, a circuit breaker
and a contactor. The welding transformer steps down the
voltage at the electrode tips and steps up the current to
provide large welding current. The electrode tips are water
cooled so as to avoid their getting welded to the workpiece.
The resistance of the workpiece depends on the metal
to be welded. Steel for example has high resistance so that
the welding heat is easily produced. While aluminium has
low resistance and there welding heat is harder to obtain.
DEPARTMENT OF ELECTRONICS
Dr.K.DHANAKODI
Assistant of Processor
Department of Electronics & Communication Systems
S.R.M.V College of Arts and Science
Coimbatore – 641 020
, UNIT-II
Welding and Heating
Definition
Resistance welding is the process of fusing two or more metal pieces
together by passing heavy current through the areas of contact to be
welded. The duration of the current may vary from a few milliseconds
to several seconds depending upon the job requirement.
Resistance Welding
This process is based on the resistance to a current flow between the two
metal pieces where weld heat is produced. The welding heat is given
by
H= twʃ0 i2 r dt
Where r is the resistance between the pieces to be welded and t w, time
during which weld current flows. Either alternating current or short
pulses of uni-directional current may be used.
,Basic Circuit A.C resistance welding
The basic circuit for resistance welding using A.C power is
shown in fig.15. It consists of a welding transformer and a
line contactor. The line contactor may be a magnetically
controlled contactor or ignitron contactor. The function of
ignitron contactor is to connect the primary of the welding
transformer across a.c. supply during welding interval only.
The secondary of the welding transformer has relatively small
number of turns and is rated for hundreds or thousands of
amperes for heavy welds. It is connected to the electrodes
through which the current passes into the job to be welded.
When the metal pieces are forced together by the
electrodes with high pressure, the resistance between the
metal pieces decreases to make a weld. The welding current is
made to flow for only fraction of a second with the help of the
, Contactor which must close many times to make a number of
welds respectively.
The metallic pieces are forced together by passing
large current (1000 to 100000 A) through these pieces. The
welding current is supplied by two electrodes which held the
two pieces. In a typical system, a.c. supply is applied to the
welding transformer via power transformer, a circuit breaker
and a contactor. The welding transformer steps down the
voltage at the electrode tips and steps up the current to
provide large welding current. The electrode tips are water
cooled so as to avoid their getting welded to the workpiece.
The resistance of the workpiece depends on the metal
to be welded. Steel for example has high resistance so that
the welding heat is easily produced. While aluminium has
low resistance and there welding heat is harder to obtain.
