Welding is the partial joining of two or more metals
by deposition; the welding methods used for body
maintenance and repair can be classified into the fol-
lowing methods.

FUSION WELDING

Fusion welding is a method of welding in which the
weld connection is made by forming or supplying the
weld metal at the part where the weld is to be made.

PRESSURE WELDING

Pressure welding is a method of welding in which the
weld connection is made by applying external pres-
sure while the part where the weld is to be made is in
a molten or semi-molten condition.

BRAZING

Brazing is a method of welding in which the weld
connection is made by supplying a filler metal (which
is molten at a temperature lower than the melting
temperature of the base metal) at the place where
the joining is to be made without melting the base
metal itself.

Welding methods

Fusion methods

Shielded arc welding

Gas welding

Electric resistance spot welding

gas arc welding

Pressure methods

[Temperature approximatery 1,500˚C (2,732˚F) or higher at weld area]

Brazing methods

Brazing

Soldering

Temperature: 620

–

950˚C

(1,148

–

1,742˚F)

Temperature: 183

–

310˚C

(361

–

590˚F)

Temperature: 1,130

–

1,550˚C

(2,066

–

2,822˚F)

AB301447AB

WELDING

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BASE OF BODY REPAIR

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ELECTRIC RESISTANCE SPOT WELDING

M4090002000040

Electric resistance spot welding is a method for fus-
ing metal parts together. Two or three metal sheets
are positioned between two copper-alloy electrode
tips, and pressure and a large current are then
applied, thus causing the contacting surfaces to heat
up and fuse together because of the electric contact
resistance.

ADVANTAGES OF ELECTRIC
RESISTANCE SPOT WELDING

• Because the time required for welding at each

point is brief, the work can be done quickly and at
reduced cost.

• Because both metals are fused and pressure

applied to make the weld, the strength and reli-
ability are both high.

• Because the time required to make the welds is

short, there is little occurrence of distortion of the
panel due to heat.

PROCEDURE

There are three basic stages in electric resistance spot weld-
ing.
1. Initial pressure application stage

This stage precedes the current application. Applying
pressure to the steel panels through the electrode tips
ensures a uniform contact resistance and a smoother
current flow.

2. Current application stage

While an ample amount of pressure is being applied, the
current is sent through the electrode tips. The contact
resistance causes the contact surfaces of the steel panels to
heat up and fuse together.

3. Holding stage

When the current application is finished and a nugget (a
solidified piece of molten metal) forms at the weld, the
pressure application is continued in order to strengthen the
weld. This is the most important stage of electric resistance
spot welding in ensuring the strength of the weld.

AB200026

AB200027

AB200028

WELDING

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NUGGET FORMATION

Generally speaking, the size of the nugget will
increase as the welding current increases, and as
the size of the nugget increases, the strength of the
weld will also increase.
Nugget formation will not begin until the current level
reaches a certain point; however, once this welding
current level is passed, the strength will increase rap-
idly (between points A and B).

As the current level increases further, the weld
strength for thick panels [more than 1.6 mm (0.063
inch)] continues to increase proportionately (between
points B and C); however, for thin panels [1.6 mm
(0.063 inch) or less], the weld strength reaches a
peak very quickly and will increase only slightly, even
if the current level increases (between points B' and
C').
Then, for both thick panels and thin panels, the mol-
ten metal will scatter if the current level increases
past a certain point.

AB301468

Small

← Welding current → Large

eak

←

Shear strength per point

→

Strong

Cooling water

Elect-
rode

Nugget

Steel
panel

Water
temperature

540

(1,000)

1,095

(2,000)

1,650˚C

(3,000)˚F

Max. Heating temperature

Melting point

1.6 mm (0.063 in)
or less

More than
1.6 mm
(0.063 in)

C Is The Scatter Point

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