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II. Repair of Body Outer Plate

1. Types Of Outer Plate Damage

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1 Break or crackle

The body always vibrates as the vehicle runs; and it bears an alternating load. When the vehicle suddenly

accelerates, sharply turns and emergently brakes, the body will be affected by inertia force. When the

vehicle runs on a rough road, the body will get bent and deformed by torsion.

If the vehicle experiences this kind of outside force in a long term, the outer plate of the body will get

broken and cracked on the parts that stress concentrates and the structure is weak.

It is easy for the stress to concentrate at the turning, edging and narrow places of the body outer plate, for

example, it is easy for the 4 corners of the slide door sash to get broken and cracked.

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2  Corrosion

The corrosion of the body outer plate is mostly caused by mud accumulated on the surface of the metal,

which results in rust. Only in some special situations, it is caused by contacting chemical materials, which

belongs to chemical corrosion. When the metal outer plate corrodes, the rust is generated on the outer

plate, and then peels off layer by layer, so that holes appear and become bigger and bigger. Rust is easily

generated on the outer plate of the skirt, drip channel, and at the joints of doors and sashes, and at the

interlayer formed by outer plate and frame jointing places.

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3 Recess

Recess is a kind of structural damage, caused by crash or squeezing on the outer plate of the body. As to

slight recess, the metal dose not extend. It belongs to plastic deformation. When it is seriously impacted

and squeezed, the metal outer plate will be torn. For the vehicles running on city, side wall outter plates

being crashed and scratched is common.

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4 Bending and torsion

Beading and torsion deformation belongs to mechanic damage. Many causes result in this kind of situation,

such as body being crashed or squeezed, an alternating load in vibrating as the vehicle runs, sudden

acceleration, emergent brake, sharp turn and running through a bad pavement, etc. Those can all result in

bending and torsion deformation on body outer plate.

Slight deformation should be confirmed by inspection. For serious bending and torsion deformation, they

can be easily found by appearance. The deformation information can be usually defined according to the

clearance between door frame and their relative position changes.

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5 Breakup Welding

Outer plate being breakup welding is caused by bad welding between metal plates.

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2. Repair Of Outer Plate

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Repair of crackle

The crackle on the metal outer plate can be repaired by CO2 gas Protecting welding. When welded, the

two sides of the metal plate should be aligned, and then spot-weld on the outside of the outer plate. If the

crackle length is less than 50mm, it should be welded from the crackle end, and along the run of the

crackle and the outside edge. If the crackle length is very long, it should be spot-welded in some intervals,

and then weld the crackle in several sections. So, it can prevent the crackle metal from being over-burnt

and warping because of an extremely high temperature.

If the crackle appears on the place that is greatly loaded and it is very convenient to weld, 2-step welding

can be adopted, that is, After spot-welding on the outside, then you can first weld on the inside of the

crackle. After that, a welding seam is then applied on the outside in the same run.

After the welding finishes, put a backing block under the crackle, and then use a hammer to gently knock

on the outside of the crackle to remove the remaining welding stress. Finally, trim the appearance of the

crackle to make it smooth and convenient to apply paint.

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Repair of partial damage of the outer plate

When the outer plate has partial rust or serious damage and even cannot be repaired, it can be mended by

cutting off the damage or pasting a new one on it.

How to cut off the damage:

a. Confirm the area that needs cutting;

b. Cut a paper example;

c. Cut the metal plate according to the paper example;

d. Paste the metal piece cut onto the surface of the area that needs cutting off;

e. Use a draw needle tip to make an outline along the sides of the metal piece. And cut off the

damaged or rusted area along the outline;

f. Use a wooden hammer or a backing block to smooth the cut, and use a file to file the burr, to assure

that the cut is parallel with both sides of the substitute piece and the clearance should be no more

than 1mm;

g. Substitute the damaged area with the piece. Use pliers to hold it and spot-weld the joint in an

interval of 50mm for fixation;

h. Weld in sections. First weld the central part and then the left and right in turn, to avoid deformation;

i. Use a hammer or block to knock on the seam to remove the remaining stress. And use a file or

hand grindstone to grind the seam to make it smooth to the plates around. Finally, paint the substitute

piece.

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Repair of uneven damage of the outer plate caused by crash

When the outer plate is crashed, a concave pit appears on it. The repair should be taken from the point C

(Figure 5-17). Put the block on the top of the protrusion area, use a hammer to knock it and correspondingly

change the position of the block. After the protrusion area is knocked down to the level, most of concave

in B area will spring back. It is already very much like the former outline of the plate. As to some little

remaining depressions, use a block with a same radian with the plate and use a hand to press the block

upwards. Knock the top point of the concave with a hammer (Figure 5-19).

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At the beginning of knocking it, make your force slightly greater. In the finishing period of repair, make

your force softer and try your best to reduce the beating times. Make sure not to knock one point for too

many times to avoid extending on partial area of the metal plate, which may make the repair complex.

As to the concave with a comparatively big radian, a backing plate whose area should be comparatively

big can be put under the center of the concave. Directly push up the depressed plate by a propping-up

tool. Sometimes, the concave place can be heated to dark red to reduce the pushing force. A slight rise is

recommended when pushing up. (Figure 5-20)

Heat-shrinkable method:

After the concave area is pushed up, if the plate is greatly stretched and its area is too big to repair, the

heat-shrinkable method can be adopted.

Use oxygen-acetylene flame to heat to cherry red. The area of heating depends to its extension degree.

The heating area should be bigger (Diameter approx. 20-30mm), when it is seriously extended or the area

is big. If it is slightly extended or the area is small, the heating area should be smaller (Diameter approx.

10-15mm). Quickly knock the heated points with a wooden hammer while they are hot. A backing block

is recommended to push it up. After it cools down, use an iron hammer to gently knock for smoothness.

The shrinkage order is from the highest point gradually to the center and then to the edge. Heat and then

flatten the extended area repeatedly, till the plate is completely flat. If the protrusion is very high, first

compress the whole protrusion to its half. After it cools down, heat the former heating point to remove the

rest half of the protrusion.

When the method is applied, it must be specially noted that you'd better not use the heat-shrinkage

method to avoid side effects. Especially for thin plates, prevent them from being melted through hole..

When the outer plate is lightly crashed and the depressed area belongs to elastic deformation, you may

press its inside to recover to its former shape.

Some depressed area can be repair by prying which is a repair method without disassembling parts. You

Illustration 5-18 Panel Flattening (A)

A Concave Point   B Protrusion Point   C Knocking Point

Illustration 5-19 Panel Flattening (B)

 1 Hammer 2 Panel Parts 3 Backing Block

Figure 5-20 Heat and flatten the protrusion    

  1 heating point

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can make a reshaping repair according to lever principle by making use of different clearances. To repair

by prying without disassembling parts can maintain the original assembling quality and improve the working

efficiency.

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Repair of outer plate breakup welding

Outer plate being breakup welding is caused by bad welding between welding wire and metal plates. For

the general breakup welding of the welding seam, a new welding can be applied after removing the

welding wire accumulated at the joint. For the breakup welding of spot-welding, you can use a one-side

spot welder to spot-weld nearby the breakup welding points. The new points are 10-15mm away from

the original points. Before spot-welding, you should clean up the greasy dirt and rusty spot at the welding

points and also make sure that the plates are well aligned.

For the breakup welding that occurs at the flanging edges, an intermittent gas welding can be applied at

the edge of the plate to make the plate edge melted after the 2 plates are well aligned. The every seam

length of the intermittent weld is about 30mm, and the interval of welding seam can refer to the former

welding interval.

Another repair method for outer plate breakup welding is plug welding. It is better to apply CO2 gas

protecting welding. Drill a hole of diameter   6mm on the outer plate, and then press and well paste the

2 plates. Fill the hole with welding wire by CO2 gas protecting welding. When welding, the welding wire

moves in circular way directing to the inner plate to have the inner and outer plates merged together.

After welding, polish and trim the surface, and then paint.