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 operators 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 5.15 Cone rolling machine (Frost Auto
Restoration Techniques Ltd)
Figure 5.16 Wheeling machine (Frost Auto Restoration Techniques Ltd)
176 Repair of Vehicle Bodies
the gap in this frame usually determines the
machines 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
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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 5.17 Range 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 5.18 Swaging machine (Selson Machine
Tool Co. Ltd)
Figure 5.19 Swaging attachments
178 Repair 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
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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 5.20 Brake press (Edwards Pearson Ltd) to be formed.
Metal forming processes and machines 179
Figure 5.21 Brake press dies and applications
180 Repair 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.
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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.
