Mitsubishi Evolution X. Manual - part 3

WELDING

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BASE OF BODY REPAIR

9-9

MIG SPOT WELDING

This welding method is used in areas where regular
spot welding cannot be done. The two panels are
stacked together, the tip of the torch (one designed
for use in MIG spot welding) is positioned on one
side, an arc is generated for a short time, and a par-
tial melting is done to obtain a spot weld.

Procedure

CAUTION

• Make sure that the area to be welded is per-

fectly clean; remove oxidation film, scales,
rust, dirt, etc.

• The two panels to be welded must be in per-

fect contact with each other.

• The number and pitch of the weld points

should be approximately the same as for the
factory welds.

1. Position the tip of the nozzle at a right angle to the

surface to be welded.

2. Being sure that the two prongs are not leaning to

either side, set them in direct contact with the
panel to the welded.

3. Welding will begin when the torch trigger is

squeezed, and will stop automatically when the
weld is complete.

FEATURES OF MIG SPOT WELDING

In comparison to resistance spot welding, MIG spot
welding has the following advantages and disadvan-
tages.

AB200036

Gas cup

Gas outlet

Wire

Item

Mig spot welding

Electric resistance spot welding

Working
characteristics

• Light weight

• Welding possible at various

positions (no limit upon welding
positions)

• Although the torch with separate

transformer is lightweight, the torch
combined with transformer type is heavy.

• The arm must be exchanged to conform

to the weld location.

Weld time/point

Slow (0.5 second or more)

Fast (0.5 second or less)

Treatment after
welding

Necessary (grinding by grinder,
etc.)

Unnecessary

Power

High voltage, low current
(15

− 30 V, 50 − 200 A)

Low voltage, high current
(2

− 4 V, 4 − 10 kA)

Flux material

• CO

(carbonic acid gas)

• Weld wire

Unnecessary

Weld points/10
minutes
(rate of use)

• 25 points or less

• Arc instability and contact tip

burn if rate of use is exceeded.

• 50 − 60 points

• Welding rod deformation and transformer

overheating if rate of use is exceeded.

Distortion caused by
welding

Occurs easily

Rare

WELDING

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BASE OF BODY REPAIR

9-10

The MIG welding done around the doors, wheelhouse arches,
etc., to prevent the flanges from coming undone after hemming
work is also called MIG spot welding.

PLUG WELDING

CAUTION

In order to prevent the formation of blowholes, fill in each
hole completely in one pass.Be sure that the two panels
are in perfect contact.Be sure that the penetration goes all
the way to the bottom panel.
Plug welding is done by making holes 5

− 6 mm (0.2−0.24 inch)

in diameter in one of the panels to be welded together, position-
ing the torch at a right angle to the holes and then filling in the
holes one at a time.

Welding strength

Depends on strength of welding
wire itself.

• Same as base material

• Little oxidation

• Uniform welding quality

Weld traces

Button head (slightly convex)

Slight concave
(Almost no indentation if swivel tip
used.)

Re-repairability
(cutting away welded
area)

Difficult
(Much welding trace High hardness
of weld points)

Easy
(Can be separated by spot cutter.)

Item

Mig spot welding

Electric resistance spot welding

AB200037AD

Swivel tip

AB200038 AB

AB301460 AD

Torch

Perfect
contact

5 – 6 mm
(0.2 – 0.24 in)
Diameter
hole

WELDING

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BASE OF BODY REPAIR

9-11

CONTINUOUS WELDING

There are several types of continuous welding: fillet (lap joint)
welding, butt welding, T joint welding, gap welding, etc.; these
are called short-circuit arc welding, and provide a stable arc at
a relatively low current.

Torch angle and welding technique

There are two welding techniques: forehand welding and back-
hand welding.
Forehand welding: Penetration is shallow and the bead is flat.
Backhand welding: Penetration is deep and the bead has a

convex shape.

The angle of the torch should be 15

− 30 degree angle for

either technique, and the tip should be maintained at a distance
of 6

− 10 mm (0.24 − 0.39 inch) from the surface being welded.

Preventing warping

1. Backhand technique

Because the direction for each weld pass and that for the
fusion progression are opposite, the residual stress is
evenly distributed.

2. Symmetrical technique

Because the welds are made in symmetrical positions in
relation to the center of the joint, the residual stress is also
symmetrical.

3. "Stepping stone" technique

Because the welds are made at random positions, the
residual stress is the most evenly distributed; however, the
possibility of flaws at the starting and stopping points is rela-
tively high.

AB200041

AB301457

15 – 30˚

Forehand
technique

Backhand
technique

AB200043AD

Anti-Warp Welding Techniques

Backhand technique

Symmetrical technique

"Stepping stone" technique

WELDING

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BASE OF BODY REPAIR

9-12

NOTES REGARDING MIG WELDING

Note the following notes regarding MIG welding.

1. The surface to be welded must be perfectly

clean; be sure to remove any non-conductive
paint.

2. If the end of the wire forms into a ball, it will

adversely affect the formation of the arc; cut the
end off with a pair of wire snips or a similar tool.

3. Select a welding current to match the thickness of

the panels being welded.

4. For continuous welding, maintain a constant weld

speed and keep both the height and the width of
the bead constant.
In addition, the tack welding pitch and the welding
bead should be shorter as the thickness of the
panels being welded decreases.

OTHER TYPES OF WELDING

M4090004000046

BRAZING

In brazing, a filler metal is melted into the joint of the
panels to be welded at a comparatively low tempera-
ture to fuse them together without melting the panels
themselves. In other words, through the aid of a flux
and because of the capillarity phenomenon, the mol-
ten filler metal will flow into the joint between the two
panels which are in contact with each other and
spread along the metal surfaces. When this molten
filler metal cools and solidifies, it will from a strong
joint of the two panels. Note that, if two panels of dif-
ferent kinds of metal are brazed, the electrolysis gen-
erated between the two metals will cause moisture to
from, which will result in corrosion.
Panels should not be connected together by brazing
at any place except those places indicated. The fol-
lowing materials (filler metals) are usually used for
brazing.

1. Brass filler metal (brass solder)

Brass filler metal is an alloy consisting of 60%
copper and 40% zinc with a melting temperature
of approximately 850

− 1,050°C (1,562 −

1,922

°F), and it is the most commonly used braz-

ing filler metal used for body repair.
The filler metal itself is coated with flux to facili-
tate penetration between the panels to be joined.

2. Silver alloy filler metal (silver solder)

Silver alloy filler metal consists of silver, copper,
zinc or cadmium, nickel, and tin, or other metals.
This filler metal is most applicable for the brazing
of steel and non-ferrous alloy other than alumi-
num, magnesium, and others with low melting
points.

Notes with regard to brazing work

• Use a wire brush, sandpaper, file etc., to remove

any oxide film grease, dirt, etc., from the surfaces
of the panels to be brazed.

• When doing brass brazing, if the panels and the

filler metal are heated excessively, a weak
iron-copper alloy will form, which could crack
easily. Be careful not to apply excessive heat.

• The joint of the panels must overlap as indicated

in the illustration.

AB200044

Examples of brazed joints

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