Vehicle repair weld testing quality

control BS EN ISO 9001–2000

Those vehicle body repair companies wishing to

obtain British Standards will have to conduct weld

test procedures. These procedures will have to

become an integral part of the company’s policy on

quality in the repair of vehicles while maintaining

safe working practices. In addition regular testing

will demonstrate the skill and ability of body technicians

to maintain a high quality of weld standard

in all types of crash repair work carried out by

their company.

12.16 Equipment maintenance and safety

For the best results the gas and contact nozzle of

the welding torch must be cleaned of welding spatter

at regular intervals. Unless this is done, there is

a risk of the welding current arcing between the

contact nozzle and the gas nozzle to the workpiece,

which could cause severe damage to the welding

torch. When cleaning the gun of spatter and

deposits the condition of the gas distributer should

also be checked, and if it appears to be burnt and

worn by spatter then it should be replaced. This is

because in addition to distributing the gas it also

acts as an insulator, and is of vital importance to

the service life of the swan neck of the torch. It is

recommended that the machine should be cleaned

with compressed air once yearly, or more frequently

if it is used in dusty conditions. The feed

mechanism and rollers require more frequent

cleaning. Regular maintenance to the following

parts is important: gas nozzle, gas distributor, contact

nozzle and wire guide rollers. It is never advisable

to weld with a worn-out contact nozzle and

deformed gas nozzle.

Any exposure to a naked welding arc, even for a

fraction of a second, is sufficient to damage the

cornea of the eye (welding flash). Consequently a

welding screen should always be used, preferably

Gas shielded arc welding 341

of the helmet and visor type. By using this type

both hands are free for control over the welding

equipment. The hand-held type of welding screen

is of course fully adequate from a safety point of

view but only leaves one hand free. This could

result in a shakier movement of the gun and a loss

of precision in following the joint.

Wear welding gloves and suitably fitting protective

clothing, especially when welding overhead so

that the welding spatter does not run down the

neck or sleeves of the overall worn.

Another hazard is the build-up of fumes given

off by the welding process, which could be dangerous

to health when welding in a confined space.

When welding in a normal workshop there is no

problem, but if welding in a tightly enclosed area,

such as inside the boot of a car, make sure that the

area is well ventilated.

Precaution must be taken when welding vehicle

panels in case there are flammable materials

attached to the other side of the panel which could

ignite and burst into flames. Therefore always have

adequate fire-fighting appliances available.

Questions

1 Explain the term ‘MIG/MAG welding’.

2 Explain the term ‘TIG welding’.

3 What is an inert gas? Explain its function in

welding.

4 What are the advantages of gas shielded arc

welding?

5 Name three types of gases that could be used in

MIG/MAG welding.

6 What is the difference between water-cooled and

air-cooled torches in TIG welding?

7 What determines the size of the ceramic nozzle

to be used for TIG welding?

8 Which material are the electrodes made from in

the TIG welding process?

9 State the advantages of MIG/MAG welding when

compared with oxy-acetylene welding, for the

repair of vehicle panels.

10 When MIG welding aluminium and its alloys,

which type of gas would be most suitable for use?

11 Describe the difference between plug welding

and spot welding.

12 Explain the mode of metal transfer used for

welding thin-gauge materials.

13 Describe the three functions that most MIG/MAG

welding equipment is capable of performing.

14 Explain the term ‘spray transfer’.

15 Describe the purpose of a contact tip in a

MIG/MAG welding torch.

16 Show, with the aid of a sketch, a repair situation

where resistance spot welding can be substituted

by a MIG/MAG spot weld.

17 With the aid of diagrams, describe the following

defects made by MIG/MAG welding: (a) porosity

(b) incomplete fusion (c) spatter on workpiece (d)

poor penetration.

18 What colours are used to identify argon and

argon-mix cylinders?

19 Why is it important to disconnect a battery on a

vehicle before commencing any MIG/MAG

welding operation?

20 List the safety precautions to be observed before

and during welding.

21 Explain the form in which the electrode is

manufactured for MIG/MAG welding.

22 With the aid of a sketch, show a repair application

which involves MIG/MAG spot welding.

23 Describe the major features of a TIG welding torch.

24 Which mode of metal transfer uses the short-arc

process in MIG/MAG welding?

25 With the aid of a sketch, illustrate one method of

metal transfer used in MIG/MAG welding.

26 With the aid of a sketch, explain how plug

welding is carried out in repair work.

27 Describe the differences between the processes

of TIG welding and MIG/MAG welding.

28 By using a sketch, illustrate a typical weld fault in

MIG/MAG welding.

29 State the function of the controls of standard

MIG/MAG welding equipment.

30 Explain the setting to be used when welding a

large gap with MIG/MAG welding.

Craft techniques

and minor

accident damage

13.1 Panel beating: forming panels

by hand

Essentially, panel beating is a hand method of

producing hollow or double-curvature shapes by

means of hammering. Nevertheless, the panel

beater’s craft still retains its place in body work and

as yet is irreplaceable by more modern methods;

in spite of the tremendous developments in recent

years of mechanical methods of forming, panel

beating remains an essential means of fabrication of

special parts. Some metal shapes cannot be

produced at all by mechanical methods and others

only with great difficulty, and in such cases panel

beating is used to finish the shape that has been

roughed out by power processes. Often, too, the prototype

of a component ultimately to be made

in quantity by stamping or pressing is hand made to

allow minor modifications to be studied before

mechanical production begins; the part produced by

panel beating is used as the pattern for press or

stamp tools. Panel beating may also be used where a

small number of components only are required and

where the cost of press or stamp tools would be

uneconomic. In body repair work, panel beating is

used to advantage where sections which are either

unobtainable or uneconomical to replace completely

can be fabricated by hand either in part or as a

whole. In many cases corroded areas can be repaired

by fabricating new sections for replacement purposes.

In the body building trade, panel beating is

still used to a large extent where new vehicles are

being built either in aluminium or mild steel. Many

of the components for these vehicles are still made

using the traditional hand shaping methods. Also a

lot of the aluminium moulds used in fibreglass construction,

where highly developed double-curvature

shapes are needed, are made by hand, welded and

dressed and planished or wheeled to a final finish.

Panel beating is essentially a hammering process,

involving different kinds of blows that can be

struck on sheet metal. It should be borne in mind

that most metals used in body work possess high

malleability and may be overstretched even with

a wood tool. The types of blow that can be struck

on sheet metal are three:

Solid blow, where the work is struck solidly over

a steel stake.

Elastic blow, where either the head or the tool or

both is made of a resilient material such as wood.

Floating blow, where the stake is not directly

under the hammer.

Each type of blow has its uses for particular

purposes. A solid blow will stretch the sheet, and

may be necessary when forming a panel, bending

a curved strip or angle, removing a loose or tight

place in a sheet, or throwing an edge over when

thickness is not a consideration. An elastic blow will

form metal without undue stretching; indeed, metal

can be thickened if desired, as in working out a tuck

or pucker. The floating blow is given to the metal

when it is held over a suitable head and hit ‘off the

solid’, so forming ‘dents’ at the points of impact.

13.2 Shaping metal by hand

Thin-gauge mild steel and light aluminium sheet

material up to 1.2 mm, and in some cases even

1.6 mm, can be satisfactorily hand beaten by wood

Another method is that of raising the metal by

means of floating blows over steel stakes or wood

formers. This raising process can be speeded up

considerably by ‘taking in’ or making tucks at the

edges of the metal. This method is generally called

puckering, and after being made each pucker must

be eliminated by careful blows to drive the metal

into itself, so thickening the work at the edges.

Much greater advantage may be taken of puckering

in aluminium alloy sheet than in most metals

because of its malleability and ductility. The exact

degree of shaping of the metal which is permissible

depends upon the particular alloy being worked, its

malleability and the ability of the craftsman.

Another method of shaping metal which can be

used in conjunction with hollowing and raising is

that of wheeling. A panel can either be wheeled

from a flat sheet to the desired double-curvature

shape, or it can be preshaped using either hollowing

or raising techniques and its final shaping and

smoothing completed by wheeling. The technique

of wheeling is not entirely done by hand, as a

wheeling machine is used. The finished result

depends on the skill of the craftsman as he manipulates

the sheet by hand in the wheeling machine.

An experienced panel beater uses the beating

method suitable to the job in hand, complex shapes

often being beaten up by using both hollowing

and raising or wheeling methods. For light-gauge

material too much hollowing or blocking is not

to be recommended, as it tends unduly to thin the

metal. The skilled panel beater is a craftsman who,

to a great extent, relies on a good eye for line and

form; this can only be cultivated by years of experience

which, combined with dexterity in the use of

hand tools, is the secret of his craftsmanship. Wood

formers or jigs, upon which the beaten shape can

be tried in order to obtain uniformity of shape for

each workpiece, are used for many jobs. The shape

of the job is retained in the vision of the panel

beater, who can, by beating on the sandbag and

raising over a suitable stake, obtain a very good

approximation to the desired form. This only needs

hammering lightly on the wood former to obtain

the finished shape. Until the metal fits the former it

is often necessary to check repeatedly to find any

high or low areas which may prevent the workpiece

from fitting the former correctly. Instead

of using formers or jigs many panel beaters use

templates only, which are cut to the shape of the

various cross-sections of the workpiece. These

templates are used towards the end of the beating

process to check the finished shape of the job.

After shaping, the surface of the finished panel

has to be smoothed by the technique of planishing,

using a steel bench stake, or by wheeling.

Hollowing

One of the methods of shaping metal by hand is that

of hollowing (Figure 13.2). In this method the metals

used for the purpose of shaping panels for body

work applications are usually aluminium and its

alloys and mild steel; aluminium is by far the easier

of the two to shape owing to its higher ductility and

malleability properties. This is a process of shaping a

sheet metal blank into a double-curvature shape by

beating the blank into a sandbag or hard wood block

with the aid of a pear-shaped boxwood mallet, or for

thin metal a rubber mallet, or for steel a hollowing

hammer with a steel head.

First the blank which is going to be shaped is cut

to size and the edges trimmed for any rag by filing.

If this rag is not removed as the blank is shaped, it

may tend to split from the edge of the rag. The next

step is to place the metal blank, which should be

held tilted, on to a sandbag, and to give it a series

Craft techniques and minor accident damage 343

Figure 13.1Shaping metal by hand

mallets into double curvature forms (Figure 13.1).

The usual practice is to beat the metal in a suitable

recess in a wood block or upon a sandbag in what

is known as the hollowing or blocking process.

Alternatively, the metal can be hammered into a

wood block hollowed out to the shape of the job.

344Repair of Vehicle Bodies

of blows around its outside edge, working towards

the centre by means of a pear-shaped mallet. This

hammering has the effect of sinking the metal into

the sandbag, which is of course resilient to the

blows. After each blow the disc is turned and the

next blow struck near the first one, and so on until

a series of overlapping blows is made round the

circumference of the blank. The tendency will be

for creases or wrinkles to appear on the edges of

the metal and these must be gently malleted flat to

avoid overlapping of the metal and eventual cracking.

The hammering of each course has to be done

with steady and even blows to bring up a regular

curved shape. On completion of the first course of

blows, a second course is begun further in from the

edge of the metal than the first set. This process of

hammering in courses and rotating the blank is

continued until eventually the centre of the blank

is reached; by this time it will have taken on a

double-curvature shape, but should greater depth

be required the whole operation must be started

again, working gradually from the edge towards

the centre of the work until it is completely to the

desired shape and size (Figure 13.3).

At this stage templates cut to the correct size

and shape can be used to check that the panel

being shaped is the correct size and curvature.

Alternatively it is possible to use a jig constructed

to the correct size and shape, usually in wood. It

may be necessary during the beating-up process to

anneal the work-piece to restore its malleability,

because the hammering tends to harden the metal

by work hardening. In some cases, instead of using

a sandbag for the shaping to be carried out on, a

hollowed-out recess in a wood block can be used.

When the panel has reached the desired shape by

hollowing it can then be smothed to a final finish

by hand planishing using a hand dolly or over a

stake, or wheeling to obtain the final smoothness.

Raising

Raising is another method of shaping metal by

hand into a double-curvature shape (Figure 13.4).

The method of raising is carried out by drawing

the metal in courses over a suitably shaped steel

stake or wood block, using floating blows which

are struck slightly off the stake with a boxwood

pear-shaped mallet. A series of blows is made in

the metal starting at the centre, the blows being

struck slightly off the stake. This has the effect

of shrinking or reducing the circumference of the

blank, thus forcing it down and around the stake.

The disc or blank is rotated after each blow as in

hollowing, but working from the centre in courses

outwards towards the edges of the blank. The same

process is repeated with frequent annealing of the

metal until the final degree of raising is reached

Figure 13.2The technique of hollowing

Figure 13.3A panel being shaped by hollowing

(Frost Auto Restoration Techniques Ltd )

Craft techniques and minor accident damage 345

and the desired shape obtained (Figure 13.5). In

the course of the raising, the edges of the metal

around the circumference will be continually subjected

to creasing, and care and skill is needed to

avoid allowing these creases to become too sharp.

If they are not worked out the edge will crack or

fracture as the shape proceeds.

tuck is lightly malleted to stiffen the metal and

hold the tuck in position. This is done in three or

four places on the circumference of the blank, thus

decreasing its diameter. Then working from the

base or point of the tuck, this surplus metal is

malleted out over a stake towards the edge of the

disc. This has to be done very carefully with the

minimum of blows, and overlapping must not take

place. As each tuck is formed and worked out,

the blank deepens towards its final shape.

The processes of hollowing and raising in sheet

metal are often applied together in the making of

articles in the form of double-curvature shapes,

bowl-like shapes, etc. When the work is only

slightly domed, the process of hollowing alone

may be sufficient to complete the work. There are

limitations to the depth which can be obtained by

hollowing. This is governed by the diameter of the

finished article and access for hand tools. Where

the diameter is going to be small and the article

deep, the raising method will have to be used to

shape the work. Again as in the hollowing process,

the final finish can be obtained by planishing the

preshaped article to a smooth surface finish.

Wheeling

The craft of wheeling has been used for many

years in the production of curved panel assemblies

that are used to make up the modern vehicle body.

Wheeling was a very skilled art when vehicles were

coach built and hand methods were employed to

make the component panels (Figure 13.7). With the

advent of mass production and the development

of the motor car, speed of production became an

essential factor. Consequently hand-made panels,

Figure 13.4Raising

Figure 13.5A panel being shaped by raising (Frost

Auto Restoration Techniques Ltd )

Figure 13.6A pucker or tuck made at the edge of

the panel to quicken the raising process

When the article is partly beaten up over the

stake, a series of tucks can be made in the outer

edges of the work in order to quicken up the beating

or raising process by taking in or shrinking

surplus metal. This method is to make a pucker

or tuck at any point on the edge of the blank by

bending the metal on a stake into an ear-shaped

form (Figure 13.6). After the tuck is formed, the

disc is placed on a steel stake and each side of the

346Repair of Vehicle Bodies

which were usually made by wheeling, were

replaced by pressed panels made on power presses

with mating dies, which very speedily produced

accurate panels having a good surface finish.

Today wheeling is still used to produce panels for

prototype vehicles; one-off assemblies which are

specially built to order, and small-volume production,

where the panels are prepressed to somewhere

near the finished shape and then finished

off by wheeling (Figures 13.8 and 13.9). The vehicle

building industry still uses wheeling in producing

panels for commercial and private coaches,

road transport vehicles and any assembly requiring

a double-curvature shape in its production.

The art of wheeling lies in the operator’s ability

to handle the panel successfully in the wheeling

machine (Figure 13.10). Wheeling is simply the

stretching of metal between two steel rolls known

as wheels. The upper wheel has a flat face and

revolves freely on its own bearings. The lower

wheel also revolves but has a convex curved face

and is made interchangeable so that different shaped

lower wheels, from nearly flat to full curved, can

be used. The two wheels meet at a common centre

at which the stretching takes place when the wheels

are tensioned by applying pressure through the

bottom wheel against the panel which is pressed

on to the top wheel. As the metal panel is pushed

through the wheels a stretched area, the length of

Figure 13.7Wheeling a panel to restore a vintage

vehicle (Frost Auto Restoration Techniques Ltd )

Figure 13.8Sports car panel being shaped by

wheeling (Autokraft Ltd )

Figure 13.9Sports car panel being shaped by

wheeling (Autokraft Ltd )

Craft techniques and minor accident damage 347

the panel, is produced, and is known as the wheel

track. By carefully allowing these wheel tracks to

overlap on the entire surface of the flat panel being

wheeled, a curve in one direction only develops.

To create double curvature on the same panel,

stretching must take place in two opposing directions;

therefore a second set of wheel tracks must

cross the first set transversely, and this is achieved

by turning the panel through approximately 90°

before making the second tracks. As the panel is

pushed through the wheels the pressure can be

increased gradually until the desired curvature is

obtained. Therefore the skill of wheeling lies in

the use of correct wheel pressures and careful

manipulation of the panel through the wheels; this

can only be learnt by experience. An alternative

method of achieving double curvature on a flat

panel is to form the first curve by using a rolling

machine, and then to wheel it in one direction only,

allowing the tracks to cover the panel in the opposite

direction to the first curve, thus stretching the

metal in such a way to form the double curvature

shape. Wheeling can therefore be used, first, for

shaping a flat metal blank to a finished doublecurved

panel; second, to finish a preshaped panel

which has been hollowed or raised to its final

shape; and third, to smooth or planish a preshaped

panel to its final finish.

The materials best suited for wheeling are

aluminium, some of the aluminium alloys and mild

steel, all of which possess the properties of

malleability and ductility to a certain degree.

When using the wheeling machine for wheeling

aluminium and its alloys, care should be taken not

to put too much pressure on the work of raising

the bottom wheel. Up to three times as much

lift or stretch is obtainable with aluminium than

with steel, and much more shaping by wheeling is

possible in the case of aluminium than with harder

metals like mild steel. Thus too much pressure

could have the effect of overstretching the particular

panel or workpiece. The wheeling machine

may be used simply to planish, producing a smooth

surface by the friction and rolling action derived

from passing the sheet backwards and forwards

between the wheels when these have just the right

amount of pressure.

Where components of moderate curvature are to

be produced by wheeling alone, the sheet or blank

is placed between the two wheels at one edge or in

the case of a round blank in the centre; pressure of

the exact amount suitable for both the thickness

and the type of material is applied and the sheet is

wheeled. In the case of aluminium the wheeling

lines are difficult to see, but by smearing the surface

of the panel or sheet with mineral turpentine

or very light oil these tracks become more easily

seen and are therefore more easily lapped. Care

should be taken at this stage when passing the

metal through the wheels not to twist or jerk the

panel, as this could result in ridged sections and an

uneven surface. Movement of the sheet is varied

until the desired shape is obtained, those parts of

the panel which require to be only slightly curved

receiving less wheeling than other parts which must

be more curved.

To wheel a panel that has been preshaped by

blocking in a sandbag, it is necessary to smooth

its surface without altering its shape, and for this

reason the panel should be pulled right through

the wheels at every stroke. This edge-to-edge

wheeling will result in an evenly stretched panel

surface. When carrying out this smoothing work,

or planishing as it could be termed, the pressure

exerted on the work by the wheels should be very

slight. Another common task that can be successfully

carried out with the wheeling machine is to

tighten up the loose wavy edges which sometimes

Figure 13.10The technique of wheeling

(Autokraft Ltd )

348Repair of Vehicle Bodies

occur when shaping a panel by hand. The method

of overcoming this trouble is to wheel directly

adjacent to the stretched edge. This stretches the

area being wheeled and so tightens up the loose

edge. The reverse sort of problem, that of a panel

with a fullness or stretched area just in from the

edge of the sheet, can also be overcome by

wheeling. The method is to start wheeling from

the centre of the fullness on a track parallel to the

edge and to work right out to the edge of the panel.

With most machines three standard wheels are

supplied which are generally referred to as flat,

medium and full curved. The widths of the wheel

tracks are flat 25 mm (1 in), medium 10 mm ( in),

and full curve 5 mm ( in). The best rule to follow

when selecting a wheel is to use the flattest wheel

possible for the job you are doing. This not only

speeds up the wheeling but prevents to a large

extent marking the surface of the panel with wheel

tracks, which are really the evidence of an overstretched

panel (Figure 13.11).

4 When wheeling, the panel should be held without

tension, allowing it to move freely without

twisting or jerking it.

5 The wheel tracks must be carefully overlapped

to achieve a smooth curved surface.