Safety measures for the operation

Of rolling machines

1 Loose clothing and long hair can easily be

drawn between the rollers.

2 Care should be taken when putting the panel

into the rollers that the operator’s fingers are

kept clear.

5.10 Wheeling machines

These machines (Figures 5.16 and 5.17) can be used

to form flat sheets of metal into double-curvature

shapes such as are found in automobile bodies.

They are also used for removing dents, buckles

and creases from sheets or panels previously

shaped, for reducing the thickness of welds, and

for planishing or smoothing panels which have

been preshaped by hand. The main frame of the

wheeling machine is of large C form. The size of

Figure 5.15Cone rolling machine (Frost Auto

Restoration Techniques Ltd )

Figure 5.16Wheeling machine (Frost Auto Restoration Techniques Ltd )

176Repair of Vehicle Bodies

the gap in this frame usually determines the

machine’s specifications, which are from 0.75 m to

1 m in width and about 0.6 m in depth; the wheel

diameters are approximately 90 mm. The machine

consists simply of an upper wheel which is nearly

flat and a second lower wheel which is curved or

convex in shape; the two wheels meet at a common

centre. The lower wheel runs free on a spindle carried

by a vertical arm, which may be raised or lowered

by screw movement through a hand wheel

which regulates the pressure that can be applied to

the work. Some machines have a quick pressure

release mechanism attached to the spindle. There

are three standard shapes of faces for the bottom

wheel – flat, small radius and full radius – and the

choice of wheel depends on the required shape of

the finished panel. The upper wheel is carried on a

horizontal shaft which is allowed to rotate freely in

bearings. The top wheel and housing can be swivelled

round through 90° to make it more accessible

when wheeling certain shaped panels. This also

applies to the housing for the bottom wheel,

enabling it to move in conjunction with the top

wheel.

Up to three times as much lift or stretch is

obtainable with aluminium than with steel, and

consequently aluminium can be shaped more by

wheeling than steel. When wheeling aluminium,

care must be taken not to apply too much pressure

by the bottom wheel as this could have the effect

of overstretching the material.

This machine is one of the few machines that

has been used in the panel beating trade since its

infancy. The art of wheeling a panel to the correct

shape and contour requires a highly skilled craftsman,

who is known in the trade as a wheeler.

5.11 Swaging machines

These machines (Figure 5.18) can be used on

sheet metal blanks to carry out a large number of

different operations such as swaging, wiring, joggling,

flanging, beading and many other edge-type

treatments. Hence the machine is also called a jennying,

swaging, burring or beading machine,

despite the fact that the same basic machine is

used to perform the different operations. In body

work the machine is used in the stiffening and

strengthening of panels; for decoration in the form

of beading or swaging; for the edge preparation of

panels, such as wiring; and for making joints

between panels as in lap and joggle joints. It can

also be used to give rigidity to large flat panels to

prevent ‘drumming’.

The basic machine consists of a machine frame

carrying two horizontal shafts which are geared

Figure 5.17Range of wheeling machines (Frost Auto Restoration Techniques Ltd )

Metal forming processes and machines 177

together. The shafts are mounted one above the

other, one of them in a fixed housing, and the other

in a housing which has some vertical adjustment

with reference to the fixed shaft. It also has some

horizontal adjustment controlled by a gauging

device known as the stop. In hand machines the

shafts are turned by a handle which is fixed to the

end of one shaft; in power driven machines they

are turned by an electric motor which is connected

through gearing to the shafts. The shafts are usually

arranged so that they have a 1:1 rotation. The

actual swaging is done by attachments fitted on to

the ends of the shafts, and the shape and form of

these attachments can be varied as is shown in

Figure 5.19. Attached to one end of the shafts are

male and female rollers shaped to produce a swage

of the desired form. The top section of the frame

carrying the upper roller and shaft is hinged at the

back and kept in upward tension by a flat spring.

The wheels are brought into position vertically by

the operation of a small handscrew. A small lever

situated near the gear wheel provides horizontal

adjustment so that the wheels can be set to match

exactly. An adjustable guide is provided to ensure

that the swaged impression will be true and parallel

with the edge of the panel.

To set up the swaging machine for operation,

first select a pair of wheels which will give the

Figure 5.18Swaging machine (Selson Machine

Tool Co. Ltd )

Figure 5.19Swaging attachments

178Repair of Vehicle Bodies

required section. Fit these wheels to the shafts and

line them up by slackening the locking screw and

adjusting the small lever at the rear of the frame

until the wheels engage centrally with each other.

Next set the stop to the distance required between

the centre of the moulding and the edge of the

sheet. Adjust the top screw until the wheel forms a

depression in the metal and then run the metal

through the wheels. Give another half turn on the

handscrew and repeat the operation until the

wheel ‘bottoms’, at which stage the swage will be

fully formed. The object of forming the swage in

gradual stages is to avoid strain on the metal

which may result in splitting or distorting the

panel.

5.12 Brake presses

Brake presses (Figure 5.20) are devices for bending

sheet metal quickly and accurately, and their rapid

development in the past twenty years has resulted

in a very wide capacity range of up to 1500 tonnes.

The bulk of the machines for bending thin gauge

metal are of 3 m or less, with capacities starting at

20 tonnes and going up to about 200 tonnes. Brake

press capacities are usually given either in tonnage

terms or in maximum bending of a certain metal

thickness, and are based on V-bending pressures.

The tonnage specifications are usually determined

by using a V-die opening of eight times the stock

thickness, with a corner radius to the bend not less

than the metal thickness. There are two important

dimensions in brake press specifications: one is

the maximum bending length over the bed, and

the other is the distance between the housing.

The width between the housing must permit the

work to pass through the machine, and the brake

press length is the overall bending length of the

machine.

Brake presses comprise a frame, a ram or bending

beam, and means for moving the beam. The

frames are always of all-steel construction with

parts welded or bolted together. Obviously these

frames should be as rigid as possible to resist

deflection – a fact of the highest importance.

There are usually three main parts to the frame – a

bed and two side frames. The top of the bed has a

location slot into which the bending tools slide.

The bending beam is usually a steel plate which

works by simply sliding in the main frame. The

load on the beam acts as near to the centre of the

beam as possible to avoid side strain. The bottom

of the beam face is made to receive the top bending

tool or die, generally by means of a side plate

to hold a tongue formed on the tool or die. The

general methods of operating the beam are

mechanical or hydraulic. The mechanical means

comprise a crankshaft rotating in a phosphor

bronze bush in the main frame. The working

strokes are usually between 50 mm and 150 mm

long, and this length can be adjusted to suit varying

conditions. The motor drives a flywheel

through a multiplate friction clutch and single or

double gearing. A brake is fitted to work in conjunction

with the clutch and is of the drum-brake

shoe-operated type. Its function is mainly to hold

the weight of the moving parts when the clutch is

disengaged.

The V-type blade and interchangeable die is used

extensively for forming light mild steel sheet components,

from simple bends to complex multibends

in panels or sheet metals (Figure 5.21). Not only

can it produce straight, sharp bends, but the tools

can be interchanged to give curves or radius bends.

Curved sections, ribbing or stiffening sections,

notching plates, corrugating sheets, and punching

holes in plates can also be formed. The machine is

mostly used in sheet metal industries, but it does

find a use in the manufacturing side of commercial

body work where large and complicated panels are

Figure 5.20Brake press (Edwards Pearson Ltd ) to be formed.

Metal forming processes and machines 179

Figure 5.21Brake press dies and applications

180Repair of Vehicle Bodies

5.13 Forming and drawing

During forming, one area of a sheet metal blank is

held stationary on a die while a punch forces the

other area to assume a new contour or shape. The

force applied is sufficient to stress the metal beyond

its elastic limit so that the change in shape is permanent.

Forming has the distinct characteristic of

stressing the metal at localized areas only; in the

case of bending, for instance, this localized stress

occurs only at the bend radius, resulting in a reduction

of the thickness of the metal at the bend. It is

only in these localized areas that any structured

change occurs within the metal itself. This type of

change in shape of the metal, with little structural

change, is known as metal movement (Figure 5.22).

In drawing, however, total stretching of the metal

occurs, with a correspondingly large amount of

structural change within the metal itself. This structural

change within the metal as a result of applied

forces is known as metal flow (Figure 5.23). Many

irregularly shaped panels are formed by drawing,

but the simplest drawing operation, that of cupping,

more easily illustrates the theory of drawing.

During cupping, metal flows through an opening

provided by a clearance between a punch and a die

which is in a cup shape. The punch exerts a force

on the bottom of the cup so that metal flows away

from the bottom. Owing to the compressive forces

on the outer edge of the blank, metal tends to flow

into this region. These compressive stresses could

cause wrinkles at the edge of the blank and cup,

and to prevent this a blank holder is added around

the punch. Pressure is applied to the blank holder

by springs, air, or an outer ram of a press. If the

blank holder pressure is too high, metal flow will

be restricted and excessive stretching will cause the

cup side walls to break. If the pressure is too low at

the start of the drawing, wrinkles will occur before

the pressure can build up. Thus the blank holder

pressure must be low enough to allow the metal to

move or flow underneath it and high enough to prevent

wrinkling from occurring. This pressure cannot

be reduced or wrinkles will occur, and therefore

a lubricant must be applied to reduce the friction.

Nearly all drawing operations require some lubricant

for this reason.