[0001] This invention relates to rivetting apparatus and to a method of rivetting. The invention
is particularly but not exclusively concerned with a rivetting system for rivetting
sheets in which a rivet with a preformed head is used and in which on the opposite
side of the workpiece from the head the rivet is substantially flush with the surface
of the workpiece.
[0002] According to a first aspect of the invention there is provided a method of rivetting
comprising the steps of holding a flat anvil against a workpiece, driving the shank
of a hollow shanked rivet into the workpiece from one side by means of a punch, causing
the rivet to deform the workpiece by producing a projection of workpiece material
on the other side of the workpiece and thus displacing the anvil, and subsequently
deforming the rivet radially outward by further compression of the workpiece between
the punch and the anvil so as to cause the projection and with it part of the rivet
to flow radially outward as the projection is compressed axially.
[0003] According to a second aspect of the invention there is provided rivetting apparatus
for carrying out the method detailed above comprising: a flat anvil for holding against
a workpiece and a punch arranged to drive a hollow shanked rivet into the workpiece
from one side thereof, the anvil being displacable to permit the rivet to deform the
workpiece by producing a projection of workpiece material on the other side of the
workpiece, and the anvil and punch being arranged to compress the workpiece subsequently
to cause the projection and with it part of the rivet to flow radially outward.
[0004] Preferred features of the invention will be apparent from the subordinate claims
of the specification.
[0005] An embodiment of the invention will now be described, merely by way of example, with
reference to the accompanying drawings, in which:-
Figure 1 is a diagrammatic representation of rivetting apparatus, a rivet and a workpiece
at the commencement of a rivetting operation; and
Figures 2 and 3 correspond to Figure 1 but show an intermediate position during the
rivetting operation and the final position with a completed rivetted joint.
[0006] Referring to Figure 1, the apparatus comprises a base 11 on which is supported an
anvil 12 with a flat upper surface. The anvil has a substantial mass to provide it
with inertia and is supported in such a way that it is movable along the rivetting
axis, in this case vertically, with respect to base 11. In this example, a belville
spring 13 is provided between the base 11 and the anvil 12 both to provide some resistance
to movement of the anvil towards the base and to allow the anvil to recover its original
position as shown in Figure 1 after a rivetting operation. The belville spring 13
is shown merely as a diagrammatic representation of a means for controlling movement
of the anvil 12. As an alternative, which may be preferable, the movement of the anvil
12 with respect to the base 11 may be controlled hydraulically. The required movement
of the anvil 12 may also be provided by the resilience of the base 11 or anvil 12
or the structures on which they are mounted.
[0007] The apparatus also incorporates a movable punch 14 which is powered to be moved towards
the base 11 by means not shown in order to effect a rivetting operation.
[0008] The anvil 12 is provided with a flat upper surface so that precise alignment between
the punch 14 and the anvil 12 is not required. If there is a slight misalignment between
these components a rivetting operation can still be carried out as long as at least
a part of the flat surface of the anvil is aligned with the punch 14.
[0009] The apparatus is shown in Figure 1 with a workpiece consisting of two sheets 15 and
16 which are to be rivetted together. A rivet 17 is also shown supported against the
punch 14. Figure 1 shows the punch 14 in a position where it has just begun to drive
the rivet 17 into the first sheet 15 but prior to rivetting the punch would be retracted
from the position shown to allow a clearance for insertion of sheets 15 and 16. The
rivet 17 should be of a material which is harder than the sheets 15 and 16. For example,
sheets 15 and 16 may be of unhardened metal such as mild steel and rivet 17 could
be made of a harder material but with sufficient ductility to enable the rivet to
be set. Alternatively the sheets 15 and 16 could be fibre-board panels intended as
interior trim for a motor vehicle while rivet 17 is of a ductile metal.
[0010] The rivet 17 has a countersunk circular head 18 and a hollow tubular shank 19. Shank
19 has in this example an upper portion 20 with a relatively thick wall and a lower
portion 25 with a relatively narrow wall thickness to form a deformable portion which
can be set as the rivet is loaded axially. At its lower end, the rivet terminates
in an annular piercing edge 21 which is tapered to a knife edge to facilitate entry
of the rivet the sheets 15 or 16. For some applications the stepped wall thickness
and the knife edge may not be necessary. The length the rivet shank 19 is preferably
selected in relation to the workpiece thickness such that the shank 19 does not penetrate
completely through the workpiece. Sealed joints can thus be formed.
[0011] The nature of the rivetting operation can be seen by comparing Figures 2 and 3 with
Figure 1. As the punch 14 pushes the rivet 17 towards the base 11 and the anvil 12,
the piercing edge of the rivet 17 cuts into the sheets 15 and 16. During this operation,
the inertia associated with the mass of the anvil 12 and the force of the spring 13
hold the anvil clear of the base 11 until after the rivet 17 has passed completely
through the first sheet 15 and penetrated substantially into the second sheet 16 as
shown in Figure 2. At this stage the rivet head 18 comes into contact with the first
sheet 15. During this part of the rivetting operation a disc 22 is cut or punched
out from the first sheet 15 by the rivet 17. This disc is held captive within hollow
shank 19 of the rivet and is forced up into the narrower part 20 of the shank so that
it becomes firmly retained. The rivet 17 also causes the surface of the workpiece
opposite to the punch to be displaced axially to form a protuding portion 23. During
further movement of the punch 14 the anvil is driven towards the base 11 until the
anvil reaches the position shown in Figure 3 in which it is supported directly and
positively against further movement by the base 11. This is illustrated in Figure
3 by a complete flattening of the belville spring 13 but other forms of positive stop
may be provided. Further movement of the punch 14 against the positively fixed anvil
12 causes the protuding portion 19 of the rivet to be deformed outward as illustrated
in Figure 3. During this deformation, the rivet is expanded outward by the outward
flow of the workpiece as the protuding portion is flattened. Further movement of the
punch 14 causes the rivet head 18 to be at least partially embedded in the first sheet
15 as illustated in Figure 3. This completes the rivetting operation apart from retraction
of the punch 14 and removal of the rivetted workpiece. In the completed rivetted joint,
a substantially flush surface results at the side of the joint where the rivet has
been set. Also, depending on the materials employed and the impact applied to the
punch, a substantially flush surface can be provided on the head side of the rivet.
[0012] The rivetting apparatus described above can be fixed or portable. The anvil 11 and
the punch 14 can, for example, be mounted on robotically controlled arms which move
them into desired operating positions.
1. A method of rivetting comprising the steps of holding a flat anvil against a workpiece,
driving the shank of a hollow shanked rivet into the workpiece from one side by means
of a punch, causing the rivet to deform the workpiece by producing a projection of
workpiece material on the other side of the workpiece and thus displacing the anvil,
and subsequently deforming the rivet radially outward by further compression of the
workpiece between the punch and the anvil so as to cause the projection and with it
part of the rivet to flow radially outward as the projection is compressed axially.
2. A method as claimed in claim 1 wherein the length of the rivet shank is selected
in relation to the workpiece thickness such that the shank does not penetrate completely
through the workpiece.
3. Rivetting apparatus for carrying out the method of claim 1 comprising: a flat anvil
for holding against a workpiece and a punch arranged to drive a hollow shanked rivet
into the workpiece from one side thereof, the anvil being displacable to permit the
rivet to deform the workpiece by producing a projection of workpiece material on the
other side of the workpiece, and the anvil and punch being arranged to compress the
workpiece subsequently to cause the projection and with it part of the rivet to flow
radially outward.
4. Rivetting apparatus as claimed in claim 3 in which the anvil is supported with
respect to a base and is movable towards and away from the base, the arrangement being
such that, in use, the anvil is displaced towards the base as the said projection
of workpiece material is produced and is positively supported by the anvil as the
workpiece is subsequently compressed.
5. Rivetting apparatus as claimed in claim 3 or 4 in which the anvil and the punch
are carried by robot arms for moving them into desired operating positions.